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#1
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Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay.
Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem. Customer took the unit to a tech who carried out the mod as described in an email from the company. Only now the unit is something like 12dB down in level than before. I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct. Original Pultec schematic he http://www.gyraf.dk/gy_pd/pultec/pultech.gif The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary. The pultec schematic shows a 1k resistor in series with a capacitor on the output, the unit is question has a factory fitted 2k2 resistor across the output, but no cap. I am not having much joy from the company on this matter, but it seems to me that putting 100 ohms across the output transformer is going to reduce the output level rather drastically. This transformer is directly connected to pins 2 & 3 of the output XLR, so essentialy there is 100 ohms across pins 2 & 3. Transformer secondary measures 113 ohms DC disconnected. I have been trying to suggest that either this 100 ohms is incorrect, or the 100 ohms in parallel with the 0.1uF capacitor is not intended to be put across the output, but should in fact be installed somewhere else. Maybe on the grounding circuit to prevent the motorboating under certain conditions I can't create on the bench. Any thoughts on this? I'm getting rather frustrated. Cheers. |
#2
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On Tue, 2 Feb 2021 13:42:49 -0800 (PST), gareth magennis
wrote: Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay. Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem. Customer took the unit to a tech who carried out the mod as described in an email from the company. Only now the unit is something like 12dB down in level than before. I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct. Original Pultec schematic he http://www.gyraf.dk/gy_pd/pultec/pultech.gif The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary. The pultec schematic shows a 1k resistor in series with a capacitor on the output, the unit is question has a factory fitted 2k2 resistor across the output, but no cap. I am not having much joy from the company on this matter, but it seems to me that putting 100 ohms across the output transformer is going to reduce the output level rather drastically. This transformer is directly connected to pins 2 & 3 of the output XLR, so essentialy there is 100 ohms across pins 2 & 3. Transformer secondary measures 113 ohms DC disconnected. I have been trying to suggest that either this 100 ohms is incorrect, or the 100 ohms in parallel with the 0.1uF capacitor is not intended to be put across the output, but should in fact be installed somewhere else. Maybe on the grounding circuit to prevent the motorboating under certain conditions I can't create on the bench. Any thoughts on this? I'm getting rather frustrated. Cheers. Motor boating is normally caused by taking negative feedback from the secondary of the output transformer. It is the low frequency phase shift as the transformer runs out of puff that causes it. But this circuit appears to have no feedback of any kind so it is hard to see what could motorboat. They already have a Zobel network on the output to keep things tame at the top end. If you are losing 12dB when you add the 100 ohms, this thing has a seriously high output impedance (caused by the lack of feedback). I think the approach here is to see how high a resistor value you can get away with before motorboating starts. Then perhaps drop that by one value and stick with that. Valves are very variable, so it is very unlikely that every unit will need so drastic a fix as 100 ohms. d -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
#3
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On Tuesday, 2 February 2021 at 22:01:06 UTC, Don Pearce wrote:
On Tue, 2 Feb 2021 13:42:49 -0800 (PST), gareth magennis wrote: Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay. Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem. Customer took the unit to a tech who carried out the mod as described in an email from the company. Only now the unit is something like 12dB down in level than before. I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct. Original Pultec schematic he http://www.gyraf.dk/gy_pd/pultec/pultech.gif The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary. The pultec schematic shows a 1k resistor in series with a capacitor on the output, the unit is question has a factory fitted 2k2 resistor across the output, but no cap. I am not having much joy from the company on this matter, but it seems to me that putting 100 ohms across the output transformer is going to reduce the output level rather drastically. This transformer is directly connected to pins 2 & 3 of the output XLR, so essentialy there is 100 ohms across pins 2 & 3. Transformer secondary measures 113 ohms DC disconnected. I have been trying to suggest that either this 100 ohms is incorrect, or the 100 ohms in parallel with the 0.1uF capacitor is not intended to be put across the output, but should in fact be installed somewhere else. Maybe on the grounding circuit to prevent the motorboating under certain conditions I can't create on the bench. Any thoughts on this? I'm getting rather frustrated. Cheers. Motor boating is normally caused by taking negative feedback from the secondary of the output transformer. It is the low frequency phase shift as the transformer runs out of puff that causes it. But this circuit appears to have no feedback of any kind so it is hard to see what could motorboat. They already have a Zobel network on the output to keep things tame at the top end. If you are losing 12dB when you add the 100 ohms, this thing has a seriously high output impedance (caused by the lack of feedback). I think the approach here is to see how high a resistor value you can get away with before motorboating starts. Then perhaps drop that by one value and stick with that. Valves are very variable, so it is very unlikely that every unit will need so drastic a fix as 100 ohms. d -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus Ok, thanks. I haven't experienced this motorboating because apparently it only happens in certain known production units, and only when connected to a patchbay. Presumably all those long cables and earth loops are a factor. I doubt I will be able to make it motorboat on the bench, it appears to be fine. Also the schematic I posted is of the original Pultec, I don't have the schematic of this clone, which is not exactly the same. They don't have a zobel network on the output, just a 2k2 resistor across the output, no capacitor. And obviously they use different transformers so most componet values are going to be different. I will experiment with different resistor values to see when things start to go bad. The problem is, the customer has a pair of these, only one of which exhibited the motorboating, and thus only one had the mod done. Now he has one unit 12 db lower than the other. Not good. |
#4
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gareth magennis wrote:
=================== Any thoughts on this? I'm getting rather frustrated. ** Motorboating in audio stages that do not use NFB is caused by supply rail coupling of imposed signal from the later stages back to the first stage - usually at a sub sonic frequency. The inter-stage coupling caps are way too large at 270nF - try 22nF instead for each. This shifts the -3dB point up to to 7 Hz. Increasing the PSU filter caps - by paralleling with a 47uF - will also help reduce LF coupling. ...... Phil |
#5
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On Tuesday, 2 February 2021 at 23:13:16 UTC, wrote:
gareth magennis wrote: =================== Any thoughts on this? I'm getting rather frustrated. ** Motorboating in audio stages that do not use NFB is caused by supply rail coupling of imposed signal from the later stages back to the first stage - usually at a sub sonic frequency. The inter-stage coupling caps are way too large at 270nF - try 22nF instead for each. This shifts the -3dB point up to to 7 Hz. Increasing the PSU filter caps - by paralleling with a 47uF - will also help reduce LF coupling. ..... Phil Yes, customer was reporting a "tick" every couple of seconds. |
#6
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On Tuesday, 2 February 2021 at 23:15:30 UTC, gareth magennis wrote:
On Tuesday, 2 February 2021 at 23:13:16 UTC, wrote: gareth magennis wrote: =================== Any thoughts on this? I'm getting rather frustrated. ** Motorboating in audio stages that do not use NFB is caused by supply rail coupling of imposed signal from the later stages back to the first stage - usually at a sub sonic frequency. The inter-stage coupling caps are way too large at 270nF - try 22nF instead for each. This shifts the -3dB point up to to 7 Hz. Increasing the PSU filter caps - by paralleling with a 47uF - will also help reduce LF coupling. ..... Phil Yes, customer was reporting a "tick" every couple of seconds. How can I force this motorboating to happen on my bench, so I can deal with it? I've not seen it yet. |
#7
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On 2/2/2021 6:35 PM, gareth magennis wrote:
How can I force this motorboating to happen on my bench, so I can deal with it? I've not seen it yet. If it only happens when connected to a patchbay, it's likely due to the cable capacitance hanging across the output. You should ask the owner with the problem a couple of questions: 1. How long are the cables between the EQ and the patchbay? If it's going to a normalled jack, add the length of the cable between the normalled jack of the pair to wherever it goes. 2. If it's going to a normalled jack, what's that jack going to? or Does it motorboat if the normalled connection is broken (stick a cable in the "destination" patchbay jack) You could experiment with loading the output with a capacitor. Start with 500 pF and go up in value to about 0.01 uF to see if you can make it take off. I agree than 100 ohms sounds like a pretty hefty load, but you can see what the source impedance really is by putting in a tone and measuring the open circuit voltage at the output. Then hang resistance across it until the voltage drops in half (6 dB if you're using a meter calibrated in dB). The resistance value that gives you the 6 dB drop will be representative of the output impedance of the unit. -- For a good time, call http://mikeriversaudio.wordpress.com |
#8
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gareth magennis is soooo annoying :
============================== Any thoughts on this? I'm getting rather frustrated. ** The feeling is mutual - pal. ** Motorboating in audio stages that do not use NFB is caused by supply rail coupling of imposed signal from the later stages back to the first stage - usually at a sub sonic frequency. Yes, customer was reporting a "tick" every couple of seconds. ** How the hell is a tick = sub sonic oscillation? The term "motor-boating" is kinda obvious. Got any idea what "hiss", "hum" and buzz" actually sound like ? Know why they have those names ? ....... Phil |
#9
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gareth magennis is super annoying :
========================= How can I force this motorboating to happen on my bench, so I can deal with it? I've not seen it yet. ** FFS !!! How will you ever know if you have fixed it ????? Rule one of troubleshooting: " Observe the Fault " ...... Phil |
#10
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On Wednesday, 3 February 2021 at 01:48:00 UTC, wrote:
gareth magennis is super annoying : ========================= How can I force this motorboating to happen on my bench, so I can deal with it? I've not seen it yet. ** FFS !!! How will you ever know if you have fixed it ????? Rule one of troubleshooting: " Observe the Fault " ..... Phil Ok, I think I may have got to the bottom of this. I found this, which I believe is the issue and its solution. https://www.gearslutz.com/board/so-m...fications.html There, it states the mod is a 25pf in series with 100 ohms, which makes much more sense. I fitted it and, of course, it doesn't drop the level by 12dB. I did measure things before finding this, and the output inpedence of the circuit is around 360 ohms, in the method described by Mike. Thanks MIke. I also tried to measure the low frequency rolloff, which was way below 10 Hz. Thanks, Phil. Maybe there never was any "motorboating", this notion came from the customer in his email to the company. I never found any, despite adding caps on the output like Mike suggested. |
#11
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gareth magennis wrote:
=================== Maybe there never was any "motorboating", this notion came from the customer in his email to the company. ** So you OP here was an entire pile of bull crap. I never found any, despite adding caps on the output like Mike suggested. ** So what the **** were you trying to *fix* ????? Dear Mr Magennis, your total lack of insight & professionalism is appalling. If I were your employer, I would hand you broom and tell you sweep the floor. ......... Phil |
#12
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On Wednesday, 3 February 2021 at 12:06:07 UTC, wrote:
gareth magennis wrote: =================== Maybe there never was any "motorboating", this notion came from the customer in his email to the company. ** So you OP here was an entire pile of bull crap. I never found any, despite adding caps on the output like Mike suggested. ** So what the **** were you trying to *fix* ????? Dear Mr Magennis, your total lack of insight & professionalism is appalling. If I were your employer, I would hand you broom and tell you sweep the floor. ........ Phil I think it is obvious I fixed an incorrect modification instruction from the company. I felt strongly enough that this instruction was just not right, that I felt the need to post my concerns here, where I might get some vaulable insight into whether these concerns bore any weight, or perhaps I was missing something. As usual, it turned out worthwhile. Both Don and yourself explained the motorboating phenomenon in a system without negative feedback. Thanks, that is valuable education indeed, and I appreciate that. It doesn't really matter that the alleged motorboating may have turned out to be a red herring, I think we all learned something from that. I said from the outset I was unable to recreate it, it was reported as such by the customer. My only concern now is that I return the unit to the customer with the proper mod in place, to find it really does have a motorboating problem I can't recreate on the bench, as the mod actually seems to be a low pass filter to stop hf oscillations, not to stop a motorboating issue. |
#13
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gareth magennis wrote a pile of self serving drivel:
=========================================== My only concern now is that I return the unit to the customer with the proper mod in place, ** Which does next to nothing. to find it really does have a motorboating problem I can't recreate on the bench, ** There is another way a piece of audio gear can be made to " motor boat " at a low frequency. You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level. Bet your dopey customer has done that by missconnecting the patch bay. Try it and see if what YOU get matches with their story. ...... Phil |
#14
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On Wednesday, 3 February 2021 at 22:36:33 UTC, wrote:
gareth magennis wrote a pile of self serving drivel: =========================================== My only concern now is that I return the unit to the customer with the proper mod in place, ** Which does next to nothing. to find it really does have a motorboating problem I can't recreate on the bench, ** There is another way a piece of audio gear can be made to " motor boat " at a low frequency. You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level. Bet your dopey customer has done that by missconnecting the patch bay. Try it and see if what YOU get matches with their story. ..... Phil Funny, that's what I just said, but in a different language. |
#15
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On Wednesday, 3 February 2021 at 23:09:36 UTC, gareth magennis wrote:
On Wednesday, 3 February 2021 at 22:36:33 UTC, wrote: gareth magennis wrote a pile of self serving drivel: =========================================== My only concern now is that I return the unit to the customer with the proper mod in place, ** Which does next to nothing. to find it really does have a motorboating problem I can't recreate on the bench, ** There is another way a piece of audio gear can be made to " motor boat " at a low frequency. You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level. Bet your dopey customer has done that by missconnecting the patch bay. Try it and see if what YOU get matches with their story. ..... Phil Funny, that's what I just said, but in a different language. I think we are actually on the same page here. |
#16
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gareth magennis is a massive narcissist :
------------------------------------------------------------------------ You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level. Bet your dopey customer has done that by missconnecting the patch bay. Try it and see if what YOU get matches with their story. Funny, that's what I just said, but in a different language. ** You said *nothing of the sort* - you pathetic bull**** artist. Got a broom handy - know how to use it? ....... Phil |
#17
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On Wednesday, 3 February 2021 at 23:20:53 UTC, wrote:
gareth magennis is a massive narcissist : ------------------------------------------------------------------------ You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level. Bet your dopey customer has done that by missconnecting the patch bay. Try it and see if what YOU get matches with their story. Funny, that's what I just said, but in a different language. ** You said *nothing of the sort* - you pathetic bull**** artist. Got a broom handy - know how to use it? ...... Phil Oh well, I tried. |
#18
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gareth magennis wrote:
===================== ------------------------------------------------------------------------ You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level. Bet your dopey customer has done that by missconnecting the patch bay. Try it and see if what YOU get matches with their story. Funny, that's what I just said, but in a different language. ** You said *nothing of the sort* - you pathetic bull**** artist. Got a broom handy - know how to use it? Oh well, I tried. ** ROTFL !!!! The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency. ...... Phil |
#19
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On Thursday, 4 February 2021 at 00:21:30 UTC, wrote:
gareth magennis wrote: ===================== ------------------------------------------------------------------------ You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level. Bet your dopey customer has done that by missconnecting the patch bay. Try it and see if what YOU get matches with their story. Funny, that's what I just said, but in a different language. ** You said *nothing of the sort* - you pathetic bull**** artist. Got a broom handy - know how to use it? Oh well, I tried. ** ROTFL !!!! The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency. ..... Phil OK, briefly, I talked at length to the customer today. His experience of this "motorboating" was an oscillation around 90 Hz. I had an email converation with the company today. They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay. They designed this mod to combat this occasional 90Hz problem, and made circuit revisions thereafter. I was incorrect in assuming this mod was to guard against HF oscillations. If you refer back to the Gearslutz thread I referred to, you will find this problem described thus: 2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables. link to thread again he https://www.gearslutz.com/board/so-m...fications.html |
#20
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On Thursday, 4 February 2021 at 23:17:09 UTC, gareth magennis wrote:
On Thursday, 4 February 2021 at 00:21:30 UTC, wrote: gareth magennis wrote: ===================== ------------------------------------------------------------------------ You mentioned there is a "patch bay" the unit plugs into. If somehow enough output signal gets back to the input, positive feedback results in low frequency oscillation - typically a sub sonic square wave at high level. Bet your dopey customer has done that by missconnecting the patch bay. Try it and see if what YOU get matches with their story. Funny, that's what I just said, but in a different language. ** You said *nothing of the sort* - you pathetic bull**** artist. Got a broom handy - know how to use it? Oh well, I tried. ** ROTFL !!!! The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency. ..... Phil OK, briefly, I talked at length to the customer today. His experience of this "motorboating" was an oscillation around 90 Hz. I had an email converation with the company today. They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay. They designed this mod to combat this occasional 90Hz problem, and made circuit revisions thereafter. I was incorrect in assuming this mod was to guard against HF oscillations. If you refer back to the Gearslutz thread I referred to, you will find this problem described thus: 2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables. link to thread again he https://www.gearslutz.com/board/so-m...fications.html I haven't been able to experience this problem, but it is starting to look like it is not a full blown oscillation at full volume, but rather some background noise problem, where a 90Hz tone gets added to the audio. Dunno, this is work in progress I guess. |
#21
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gareth magennis is a total IDIOT wrote:
================================== ** You said *nothing of the sort* - you pathetic bull**** artist. Got a broom handy - know how to use it? Oh well, I tried. ** ROTFL !!!! The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency. OK, briefly, I talked at length to the customer today. His experience of this "motorboating" was an oscillation around 90 Hz. ** Jesus ****ing Christ - STOP using the wrong names for things. !! Does a motorboat sound like a 90 Hz tone to you ??? I had an email converation with the company today. They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay. ** Absolute ******** !!! I was incorrect in assuming this mod was to guard against HF oscillations. ** That may be the one thing you got correct. 2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables. ** So it is now a "buzz" - not a motorboat sound. Sounds *hell of a lot* like " parasitic oscillations " which can be discontinuous. If so, despite being in the supersonic range may generate an audible buzz at some rate. FFS leave audio alone, your broom awaits. ....... Phil |
#22
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On Thursday, 4 February 2021 at 23:29:41 UTC, wrote:
gareth magennis is a total IDIOT wrote: ================================== ** You said *nothing of the sort* - you pathetic bull**** artist. Got a broom handy - know how to use it? Oh well, I tried. ** ROTFL !!!! The only thing this tedious prick " tried " was to bull**** his way out of admitting his massive incompetency. OK, briefly, I talked at length to the customer today. His experience of this "motorboating" was an oscillation around 90 Hz. ** Jesus ****ing Christ - STOP using the wrong names for things. !! Does a motorboat sound like a 90 Hz tone to you ??? I had an email converation with the company today. They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay. ** Absolute ******** !!! I was incorrect in assuming this mod was to guard against HF oscillations. ** That may be the one thing you got correct. 2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables. ** So it is now a "buzz" - not a motorboat sound. Sounds *hell of a lot* like " parasitic oscillations " which can be discontinuous. If so, despite being in the supersonic range may generate an audible buzz at some rate. FFS leave audio alone, your broom awaits. ...... Phil Phil, read this carefully, this is what I said. I talked at length to the customer today. His experience of this "motorboating" was an oscillation around 90 Hz. Do you see the quote marks around motorboating? I haven't experienced any such oscillations, all I have done is to quote the customer who has claimed "motorboating". Today I learned that this "motorboating" he experienced was in fact a 90 Hz oscillation. Your reply to this information was: ** Jesus ****ing Christ - STOP using the wrong names for things. !! Does a motorboat sound like a 90 Hz tone to you ??? Arguing semantics here is not very helpful, is it. I know you're better than that. |
#23
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![]() **** off Nut Case TROLL !! ===================== I talked at length to the customer today. His experience of this "motorboating" was an oscillation around 90 Hz. ** Jesus ****ing Christ - STOP using the wrong names for things. !! Does a motorboat sound like a 90 Hz tone to you ??? I had an email converation with the company today. They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay. ** Absolute ******** !!! I was incorrect in assuming this mod was to guard against HF oscillations. ** That may be the one thing you got correct. 2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables. ** So it is now a "buzz" - not a motorboat sound. Sounds *hell of a lot* like " parasitic oscillations " which can be discontinuous. If so, despite being in the supersonic range may generate an audible buzz at some rate. FFS leave audio alone, your broom awaits. il Phil, read this carefully, this is what I said. ** Get ****ed you smug pile of ****. Do you see the quote marks around motorboating? ** Means nothing to me. Cos a customer uses a totally wrong name does not excuse you doing it. So far, YOU have NOT ONCE used the right name !!!!!!!!!!!!!!!!!!!!!!!!!!!!! I haven't experienced any such oscillations, all I have done is to quote the customer who has claimed "motorboating". ** Quoting bull**** on usenet is not a good idea - ****head. Why did you *never* ask them to *explain* what the noise sounded like ??? Because you are an ASD ****ed idiot - that's why. ** Jesus ****ing Christ - STOP using the wrong names for things. !! Does a motorboat sound like a 90 Hz tone to you ??? Arguing semantics here is not very helpful, ** This has not one tiny thing to do with ****ing "semantics" !!!!!!!!! Get a BIG dictionary and shove it you your stupid fat arse !!! ....... Phil |
#24
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On Friday, 5 February 2021 at 00:19:50 UTC, wrote:
**** off Nut Case TROLL !! ===================== I talked at length to the customer today. His experience of this "motorboating" was an oscillation around 90 Hz. ** Jesus ****ing Christ - STOP using the wrong names for things. !! Does a motorboat sound like a 90 Hz tone to you ??? I had an email converation with the company today. They say they had problems with the first batch of units that would oscillate around 90 Hz when connected to a remote patchbay. ** Absolute ******** !!! I was incorrect in assuming this mod was to guard against HF oscillations. ** That may be the one thing you got correct. 2. The thing with the added capacitors and resistors is to properly load the output stages, which would solve a buzz you might hear if you run long output cables. ** So it is now a "buzz" - not a motorboat sound. Sounds *hell of a lot* like " parasitic oscillations " which can be discontinuous. If so, despite being in the supersonic range may generate an audible buzz at some rate. FFS leave audio alone, your broom awaits. il Phil, read this carefully, this is what I said. ** Get ****ed you smug pile of ****. Do you see the quote marks around motorboating? ** Means nothing to me. Cos a customer uses a totally wrong name does not excuse you doing it. So far, YOU have NOT ONCE used the right name !!!!!!!!!!!!!!!!!!!!!!!!!!!!! I haven't experienced any such oscillations, all I have done is to quote the customer who has claimed "motorboating". ** Quoting bull**** on usenet is not a good idea - ****head. Why did you *never* ask them to *explain* what the noise sounded like ??? Because you are an ASD ****ed idiot - that's why. ** Jesus ****ing Christ - STOP using the wrong names for things. !! Does a motorboat sound like a 90 Hz tone to you ??? Arguing semantics here is not very helpful, ** This has not one tiny thing to do with ****ing "semantics" !!!!!!!!! Get a BIG dictionary and shove it you your stupid fat arse !!! ...... Phil Here's a thought. 90Hz equates to 5400 rpm. That sounds like a small outboard motor to me. Night. |
#25
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gareth magennis ned shooting :
------------------------------------------ ** This has not one tiny thing to do with ****ing "semantics" !!!!!!!!! Get a BIG dictionary and shove it you your stupid fat arse !!! ...... Phil Here's a thought. ** You do not have any cos you' re a mental retard. 90Hz equates to 5400 rpm. That sounds like a small outboard motor to me. ** But the sound is ****ing BUZZ not a tone of any kind !!!!! FOAD moron. ..... Phil |
#26
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On Friday, 5 February 2021 at 01:30:29 UTC, wrote:
gareth magennis ned shooting : ------------------------------------------ ** This has not one tiny thing to do with ****ing "semantics" !!!!!!!!! Get a BIG dictionary and shove it you your stupid fat arse !!! ...... Phil Here's a thought. ** You do not have any cos you' re a mental retard. 90Hz equates to 5400 rpm. That sounds like a small outboard motor to me. ** But the sound is ****ing BUZZ not a tone of any kind !!!!! FOAD moron. ..... Phil Phil, the original problem was putting a 100 ohm resistor across the output transformer and dropping the output level by 12 db. Remember that? I don't remember any input from you to indicate this might actually be something of concern. |
#27
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gareth magennis total **** wrote:
========================== ** You have a very punchable face. What out what I can do to you on SED. ....... Phil |
#28
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On Saturday, 6 February 2021 at 00:23:40 UTC, wrote:
gareth magennis total **** wrote: ========================== ** You have a very punchable face. What out what I can do to you on SED. ...... Phil Is that a threat? |
#29
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gareth magennis wrote:
Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay. Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem. Customer took the unit to a tech who carried out the mod as described in an email from the company. Only now the unit is something like 12dB down in level than before. I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct. Original Pultec schematic he http://www.gyraf.dk/gy_pd/pultec/pultech.gif The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary. You sure they aren't in series? If they were in series, that would sound like a normal zobel network designed to keep the transformer from ringing or to add a stabilization pole for something else. In parallel they would just swamp the transformer which is designed for a 600 ohm load. I bet, given the description, that the thing works perfectly fine with a 600 ohm load, and only motorboats when connected to modern high-z transformerless inputs. I bet the transformer sounds better with the 600 ohm load too. The Pultec design is intended for a 600 ohm load. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#30
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On Thursday, 11 February 2021 at 12:53:54 UTC, Scott Dorsey wrote:
gareth magennis wrote: Right, I have this Pultec EQP-1A clone that apparently was motorboating, but only when attached to a patchbay. Turns out the manufacturer knew certain serial numbered units were prone to this and offered a mod to fix the problem. Customer took the unit to a tech who carried out the mod as described in an email from the company. Only now the unit is something like 12dB down in level than before. I have removed the mod, and there is in fact about 12dB drop in level with it fitted, the customer is correct. Original Pultec schematic he http://www.gyraf.dk/gy_pd/pultec/pultech.gif The mod is to wire a 100 ohm resistor in parallel with a 0.1uF capacitor directly accross the output transformer secondary. You sure they aren't in series? If they were in series, that would sound like a normal zobel network designed to keep the transformer from ringing or to add a stabilization pole for something else. In parallel they would just swamp the transformer which is designed for a 600 ohm load. I bet, given the description, that the thing works perfectly fine with a 600 ohm load, and only motorboats when connected to modern high-z transformerless inputs. I bet the transformer sounds better with the 600 ohm load too. The Pultec design is intended for a 600 ohm load. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." One of the first things I did was to try them in series, in case this was the error. This produced a significant rolloff at 10 KHz, so I guessed that wasn't the error. The Gearslutz post says 100 Ohms in series with 25pf, which I thought made a lot more sense. I'm reluctant to accept that without comfirmation from the company, though, which I still haven't received. Is that a typo? should it be 22pF, or even 22nF? I struggled to find a 25pF cap. Hence my reluctance. |
#31
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gareth magennis wrote:
The Gearslutz post says 100 Ohms in series with 25pf, which I thought made a lot more sense. I'm reluctant to accept that without comfirmation from the company, though, which I still haven't received. Is that a typo? should it be 22pF, or even 22nF? I struggled to find a 25pF cap. Hence my reluctance. Put a 1 KHz square wave through. Does it look nice and square at the output or does it ring? Mild ringing: http://www.panix.com/~kludge/xformers/DSC00263.JPG Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG If you add a 600 ohm termination resistor (which everybody should be using running a Pultec into a modern output anyway) does it get better or worse? If the square wave looks good, things are good. You can use the calibration output from a Tek scope as a 1kc square wave generator. It's convenient and comes free with the scope. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#32
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On 25/02/2021 7:01 pm, Scott Dorsey wrote:
gareth magennis wrote: The Gearslutz post says 100 Ohms in series with 25pf, which I thought made a lot more sense. I'm reluctant to accept that without comfirmation from the company, though, which I still haven't received. Is that a typo? should it be 22pF, or even 22nF? I struggled to find a 25pF cap. Hence my reluctance. Put a 1 KHz square wave through. Does it look nice and square at the output or does it ring? Mild ringing: http://www.panix.com/~kludge/xformers/DSC00263.JPG Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG If you add a 600 ohm termination resistor (which everybody should be using running a Pultec into a modern output anyway) does it get better or worse? If the square wave looks good, things are good. You can use the calibration output from a Tek scope as a 1kc square wave generator. It's convenient and comes free with the scope. --scott Any idea what the catastrophic ringing harmonics would look like on a spectrum analyzer. |
#33
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On Fri, 26 Feb 2021 02:29:37 -0600, gray_wolf
wrote: On 25/02/2021 7:01 pm, Scott Dorsey wrote: gareth magennis wrote: The Gearslutz post says 100 Ohms in series with 25pf, which I thought made a lot more sense. I'm reluctant to accept that without comfirmation from the company, though, which I still haven't received. Is that a typo? should it be 22pF, or even 22nF? I struggled to find a 25pF cap. Hence my reluctance. Put a 1 KHz square wave through. Does it look nice and square at the output or does it ring? Mild ringing: http://www.panix.com/~kludge/xformers/DSC00263.JPG Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG If you add a 600 ohm termination resistor (which everybody should be using running a Pultec into a modern output anyway) does it get better or worse? If the square wave looks good, things are good. You can use the calibration output from a Tek scope as a 1kc square wave generator. It's convenient and comes free with the scope. --scott Any idea what the catastrophic ringing harmonics would look like on a spectrum analyzer. The same is non-catastrophic but bigger. That is just a judgement call. The way you judge it to be actual ringing is that one harmonic is much bigger than any other. That is the ringing frequency. d -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
#34
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Don Pearce wrote:
----------------------------- gray_wolf Any idea what the catastrophic ringing harmonics would look like on a spectrum analyzer. The same is non-catastrophic but bigger. That is just a judgement call. The way you judge it to be actual ringing is that one harmonic is much bigger than any other. That is the ringing frequency. ** You sure about "any" ? Square waves have cascading, odd numbered harmonics. The ringing one would merely be out of step with the others. FYI: I like to test 31 band graphics using just a few square wave frequencies. 40, 300 and 3000Hz for example. Then move each slider through its full travel and watch the result on my scope. Malfunction or wiper noise is VERY obvious. ....... Phil |
#35
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On Fri, 26 Feb 2021 01:57:59 -0800 (PST), "
wrote: ** You sure about "any" ? Square waves have cascading, odd numbered harmonics. The ringing one would merely be out of step with the others. Ringing and how it works was brought home to me when I had to set up a CNC mill. Part of the setup was automatic, and was for the movement servos to characterize themselves. When they come to a fast stop, the heavy stuff attached rings (wobbles), and that has to be prevented. So the servos use feedback to find the frequency of that ring. Then they use a convolution algorithm to notch that frequency out of the transient edge. Result - fast stops and no ringing or oscillation. In linear systems frequencies can't be created out of nothing. All frequencies are present in a fast edge, and this is where the energy for the ring comes from. Remove that frequency from the edge and you will not see any ringing. Note - this is not the same as harmonics of the square wave. It is a continuous sinc curve of energy associated with each edge. This is super non-intuitive but provided there is no non-linearity, it works. d -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
#36
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On Friday, 26 February 2021 at 13:23:46 UTC, Don Pearce wrote:
On Fri, 26 Feb 2021 01:57:59 -0800 (PST), " wrote: ** You sure about "any" ? Square waves have cascading, odd numbered harmonics. The ringing one would merely be out of step with the others. Ringing and how it works was brought home to me when I had to set up a CNC mill. Part of the setup was automatic, and was for the movement servos to characterize themselves. When they come to a fast stop, the heavy stuff attached rings (wobbles), and that has to be prevented. So the servos use feedback to find the frequency of that ring. Then they use a convolution algorithm to notch that frequency out of the transient edge. Result - fast stops and no ringing or oscillation. In linear systems frequencies can't be created out of nothing. All frequencies are present in a fast edge, and this is where the energy for the ring comes from. Remove that frequency from the edge and you will not see any ringing. Note - this is not the same as harmonics of the square wave. It is a continuous sinc curve of energy associated with each edge. This is super non-intuitive but provided there is no non-linearity, it works. d -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus This Pultech clone has "catastophic ringing" with a 1kHz square wave, almost identical to the example posted. A 600 ohm resistor alone reduces level by almost half, but the ringing remains at the same proportion of the square wave amplitude. A 100ohm resistor in series with 10nF reduces the catastophing ringing initial spikes hugely, but nowhere near to "mild ringing", and has a slight rolloff on a sine wave at 10 and 20 kHz but not 1kHz. A 100ohm resistor with 68 nF has way too much hf rolloff, but the ringing is eliminated entirely with a sloping squarewave wavefront showing the hf cut. A 100 ohm resistor with 4.4nF to 1nF causes full amplitude oscillation, very bad. The 10nF seems to be the most useful. Anything higher does eventually elliminate the ringing, but with unacceptable rolloff. Thanks, Gareth. |
#37
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gray_wolf wrote:
kludge wrote: Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG Any idea what the catastrophic ringing harmonics would look like on a spectrum analyzer. They aren't harmonics! They are the result of parasitic LC networks caused by the series inductance of the transformer winding and the capacitance between turns. In the case of simply-wound transformers (like the one in that picture), the result is one big narrowband resonance somewhere. Any signal anywhere near that resonance excites it, even the harmonics of the 1kc. And once it gets excited, it will continue bouncing back and forth at its resonant frequency until the energy is gone and that capacitor is discharged. So on a spectrum analyzer that would likely be one single narrow spike. Now... there are better ways to wind transformers in order to distribute that across a wider area, so that you get more smaller resonances instead of one big one. Those can result in multiple smaller spikes. If the transformer is designed well, the spike is well above the audible region where it can be eaten by a zobel network. That severely ringing transformer was designed for communications applications where having a very high ratio was more important than bandwidth or low distortion, so that resonance is much more extreme and much lower than anyone would tolerate for a pro audio transformer. But, this is a 200:80k ohm transformer.... the fact that it works at all is a miracle. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#38
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On Friday, 26 February 2021 at 15:45:36 UTC, Scott Dorsey wrote:
gray_wolf wrote: kludge wrote: Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG Any idea what the catastrophic ringing harmonics would look like on a spectrum analyzer. They aren't harmonics! They are the result of parasitic LC networks caused by the series inductance of the transformer winding and the capacitance between turns. In the case of simply-wound transformers (like the one in that picture), the result is one big narrowband resonance somewhere. Any signal anywhere near that resonance excites it, even the harmonics of the 1kc. And once it gets excited, it will continue bouncing back and forth at its resonant frequency until the energy is gone and that capacitor is discharged. So on a spectrum analyzer that would likely be one single narrow spike. Now... there are better ways to wind transformers in order to distribute that across a wider area, so that you get more smaller resonances instead of one big one. Those can result in multiple smaller spikes. If the transformer is designed well, the spike is well above the audible region where it can be eaten by a zobel network. That severely ringing transformer was designed for communications applications where having a very high ratio was more important than bandwidth or low distortion, so that resonance is much more extreme and much lower than anyone would tolerate for a pro audio transformer. But, this is a 200:80k ohm transformer.... the fact that it works at all is a miracle. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." So it might be possible that the company's mod advice of 100 ohms in parallel with 0.1uF should really be 100 ohms in series with 0.01uF? Gareth. |
#39
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Scott Dorsey wrote:
--------------------------------- Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG Any idea what the catastrophic ringing harmonics would look like on a spectrum analyzer. They aren't harmonics! ** The ringing frequency is excited by *one* of the harmonics in the square wave. Can be the fundamental too. So on a spectrum analyzer that would likely be one single narrow spike. ** Now, the input is a square wave with odd numbered harmonics. Plus resonances *cannot * create any new frequencies !!! So the effect on an analyser display is that *one* harmonics is boosted. ....... Phil |
#40
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On Fri, 26 Feb 2021 01:57:59 -0800 (PST), "
wrote: ** You sure about "any" ? Square waves have cascading, odd numbered harmonics. The ringing one would merely be out of step with the others. Nothing to do with the frequency of the wave or its harmonics. Each ringing event is separate and is triggered by the broadband energy of the rising or falling edge. The frequency of the ring is determined by the LC circuit that is being struck by that edge. The ringing will be restarted at twice the frequency of the square wave, but that is not the same thing as the ringing frequency. d -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
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