Home |
Search |
Today's Posts |
#41
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Iain Churches wrote:
"Tynan AgviŠr" wrote in message . 70... is 80 dB enough for this? Regards, John Byrns With the mics I am currently using, 80dB is good.My current mic pres have 66, and that is *barely* enough. OK. So that's me back to the drawing board:-) Except that my mic pre is to be plugged into the line input of a console so 60dB is more than sufficient. Line in of a console - sorry can you explain what that is?? Cheers Ian |
#42
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Ian Thompson-Bell" wrote in message ... John Byrns wrote: I have also started thinking about packaging issues, which may lead to some changes in the mixer section. I can't remember if the OP said anything about his size and weight requirements? This is important not only from an aethestics point of view but also from an electronic performance one too. Wasn't it Graham who mentioned the possibility of a 3U 19 inch rack mounted construction with plug in, modular channels? This might be a very good format. The psu could then be in its own chassis. A mixer does not necessarily have to have a horizontal operational surface, particularly if rotary faders are chosen. Iain |
#43
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Iain Churches wrote:
"Ian Thompson-Bell" wrote in message ... John Byrns wrote: I have also started thinking about packaging issues, which may lead to some changes in the mixer section. I can't remember if the OP said anything about his size and weight requirements? This is important not only from an aethestics point of view but also from an electronic performance one too. Wasn't it Graham who mentioned the possibility of a 3U 19 inch rack mounted construction with plug in, modular channels? This might be a very good format. The psu could then be in its own chassis. A mixer does not necessarily have to have a horizontal operational surface, particularly if rotary faders are chosen. How are you going to get the channel faders to fit in this space or were you thinking of rotary controls? Cheers Ian |
#44
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Ian Thompson-Bell" wrote in message ... Iain Churches wrote: "Ian Thompson-Bell" wrote in message ... John Byrns wrote: I have also started thinking about packaging issues, which may lead to some changes in the mixer section. I can't remember if the OP said anything about his size and weight requirements? This is important not only from an aethestics point of view but also from an electronic performance one too. Wasn't it Graham who mentioned the possibility of a 3U 19 inch rack mounted construction with plug in, modular channels? This might be a very good format. The psu could then be in its own chassis. A mixer does not necessarily have to have a horizontal operational surface, particularly if rotary faders are chosen. How are you going to get the channel faders to fit in this space or were you thinking of rotary controls? Some early mixers were made like this for OB and location recording use. The ones I have seen invariably had rotary faders. Short throw linear faders tend to be cheap and cheerful, not at all suitable for this prestigious project:-) Iain |
#45
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Iain Churches wrote:
"Ian Thompson-Bell" wrote in message ... Iain Churches wrote: "Ian Thompson-Bell" wrote in message ... John Byrns wrote: I have also started thinking about packaging issues, which may lead to some changes in the mixer section. I can't remember if the OP said anything about his size and weight requirements? This is important not only from an aethestics point of view but also from an electronic performance one too. Wasn't it Graham who mentioned the possibility of a 3U 19 inch rack mounted construction with plug in, modular channels? This might be a very good format. The psu could then be in its own chassis. A mixer does not necessarily have to have a horizontal operational surface, particularly if rotary faders are chosen. How are you going to get the channel faders to fit in this space or were you thinking of rotary controls? Some early mixers were made like this for OB and location recording use. The ones I have seen invariably had rotary faders. Short throw linear faders tend to be cheap and cheerful, not at all suitable for this prestigious project:-) Iain I wasn't thinking of short throw faders, but proper P&G types. Ian |
#46
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Tynan AgviŠr" wrote: is 80 dB enough for this? 80dB is what I'd recommend. Certainly no less than 70dB. With the mics I am currently using, 80dB is good.My current mic pres have 66, and that is *barely* enough. With ribbon mics I expect that's especially so. Graham |
#47
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
robert casey wrote: Are you claiming that you need to *design* a cathode follower for example ? Or *design* a volume control ? Well, you'd need to know if the OP user wants slide pots or twist knobs. and other such ergonomic considerations. And select such accordingly. But that would not change anything in the schematic design. Indeed. Graham |
#48
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Ian Thompson-Bell wrote: Eeyore wrote: John Byrns wrote: I concentrated on the design of the mixer section Yes, that'll require a triode with AC coupled nfb from anode to grid to form the virtual earth, the remainder being routine mix Rs, level controls etc. That's hardly a DESIGN. It's a stock circuit. Hmmm, that assumes virtual earth mixing is the way to go for tubes. A typical triode will have a stage gain of 20 maybe 30dB so the virtual earth will not be that good (Rfb/30 maybe) and there's not really enough gain to make up for mix losses. Gain at the mix amp is invariably noisy. Placing 'gain in hand' would be best after the fader and that's also best for low THD. Also Rfb needs to be large enough not to significantly load the anode, so we are talking 300K or so here which means the mix resistors will be 100K for for 10dB gain make up. Ahh... well my design with a buffered anode wouldn't have that restriction. If you want to stick with VE mixing then a tubed long tailed pair and another triode will make a simple op amp like circuit where Rfb can be much smaller and the open loop gain is much higher making a better VE. Or simpler still just stick a CF on the end of the triode and feed its cathode back to the grid via a lowish Rfb. That would be another way. Graham |
#49
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Ian Thompson-Bell wrote: Eeyore wrote: The pad is *inline* with the signal path, NOT the phantom power. Actually Graham I was referring to a pad external to the mixer, added in-line with the mic cable so the pad *is* in-line with the phantom power. This pad is additional to the 20dB pad inside the mixer which as you rightly say in only in the signal path. Oh I see. I imagined this mixer would have an internal pad. It would be essential IMHO. An external 20dB pad would add about 1k in each leg which wouldn't be a disaster. Graham |
#50
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Ian Thompson-Bell wrote: Iain Churches wrote: "Ian Thompson-Bell" wrote John Byrns wrote: I have also started thinking about packaging issues, which may lead to some changes in the mixer section. I can't remember if the OP said anything about his size and weight requirements? This is important not only from an aethestics point of view but also from an electronic performance one too. Wasn't it Graham who mentioned the possibility of a 3U 19 inch rack mounted construction with plug in, modular channels? This might be a very good format. The psu could then be in its own chassis. A mixer does not necessarily have to have a horizontal operational surface, particularly if rotary faders are chosen. How are you going to get the channel faders to fit in this space or were you thinking of rotary controls? My idea was to have rotary controls on the rack mount unit itself so it's self contained and compact and these could be bypassed with external slide faders that could be mounted in an ancillary 'pod'. Just a thought. Graham |
#51
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Ian Thompson-Bell wrote: I wasn't thinking of short throw faders, but proper P&G types. I shudder to think of the cost of those now ! ALPS also make some decent 'studio faders'. Yes, genuine ones with guide rails and minimal friction etc. Graham |
#52
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Eeyore" wrote in message ... Ian Thompson-Bell wrote: I wasn't thinking of short throw faders, but proper P&G types. I shudder to think of the cost of those now ! Indeed very expensive. Some old-style "quadrant" faders would be appropriate if they could be found. Iain |
#53
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Iain Churches wrote: "Eeyore" wrote Ian Thompson-Bell wrote: I wasn't thinking of short throw faders, but proper P&G types. I shudder to think of the cost of those now ! Indeed very expensive. Some old-style "quadrant" faders would be appropriate if they could be found. I'm not sure what you think they could offer other than an antique look. I'd certainly not like to mix in 3dB steps or whatever it is they provide. Plus aren't they mostly 600 ohm and therefore need further buffering ? Graham |
#54
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
In article ,
Eeyore wrote: John Byrns wrote: Eeyore wrote: John Byrns wrote: Eeyore wrote: No, a pad isn't a problem. The phantom power resistors still go direct to the XLR pins 2 and 3. You obviously missed the "in-line pad" part, an in-line pad definitely has the potential to cause a problem if the wrong type of pad is used. The pad is *inline* with the signal path, NOT the phantom power. Can you explain how an inline pad is going to be able to avoid being in series with the phantom power? HOLY ****. You're dumb as they come for sure. The phantom power NEVER flows through the pad (or it shouldn't at least). See if you can't draw yourself a circuit with the 6k8 phnatom power Rs going to pins 2 and 3 of the XLT input connector for the mic and try and work it out for yourself will you ? I already did exactly that, and the phantom power definitely flows through the pad as a common mode signal. Can you explain how the phantom power might get to the microphone if not through the pad, there is no other route it can take? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#55
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
robert casey wrote in
: Are you claiming that you need to *design* a cathode follower for example ? Or *design* a volume control ? Well, you'd need to know if the OP user wants slide pots or twist knobs. and other such ergonomic considerations. And select such accordingly. But that would not change anything in the schematic design. Well, i prefer sliders by a huge margin, but aint above using twist pots if there is any benefit to it, sonically. |
#56
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
In article ,
Ian Thompson-Bell wrote: John Byrns wrote: In article , Ian Thompson-Bell wrote: John Byrns wrote: I have completed a preliminary design for a 6-in 2-out microphone mixer similar to the one requested by ³Tynan². Excellent. Care to post a schematic? There are a couple of problems with doing that right now. First my scanner has been broken for some time and I either need to repair it, or buy a new one. The repair should be simple if I can locate the required material. The problem is that I left a stack of books piled on top of the scanner for too long a time period, and this caused the thin double sided tape that was used to attach the glass to loose its grip. To fix it I would need to find some suitable thin double sided tape. I should probably just bin it and buy a new one because it only interfaces with my old computer anyway. Hope you get it fixed soon. It is more likely headed for the trash bin, to be replaced by a new one thereby eliminating the hassle of getting out my old computer to run it. I would love to see what you have come up with. I notice your web page is mainly radio related - is that you main tube interst? Yes, early in my life I worked for a while in broadcasting, so I have a fondness for radio related stuff. Regards, John Byrns The second problem is that I took this design as a two-part problem, the design of a microphone amplifier and the design of a mixer. I concentrated on the design of the mixer section, only laying out a concept for my own microphone amplifier design. From previous discussions I had assumed that the idea was to paste in the schematic of the end users favorite vintage tube microphone amplifier. I have had a tube microphone amplifier module sitting on my desk next to my computer for the last 8 years, so yesterday I decided to try interfacing that with my mixer design. I immediately ran into a major problem using this existing microphone amplifier design, and I realized that several other existing microphone amplifier designs would also have similar problems. Welcome to the world of mixer design. As a result I am left without a suitable design for the microphone amplifier section until I can complete my own design. I am left agonizing over how to accomplish all my goals for the microphone amplifier without having to make compromises that I would rather avoid. Welcome to the world of mixer design. I have also started thinking about packaging issues, which may lead to some changes in the mixer section. I can't remember if the OP said anything about his size and weight requirements? This is important not only from an aethestics point of view but also from an electronic performance one too. Good Luck Ian -- Surf my web pages at, http://fmamradios.com/ |
#57
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Iain Churches" wrote in news:hZijj.281635$sV4.19102
@reader1.news.saunalahti.fi: I was just thinking ahead. He may not want them now, but experience tells me that it will not be long before he wants to patch some extermal EQ or processor (even a simple limiter) into a single channel or across the output mix buss. A simple mixer, if it is to be of any practical use, is not actually terribly simple. Iain I never use these things, and dont ever see myself using them. Perhaps if I were working in the studio realm in "secular" music, but I work with acoustic based(Chamber Jazz, String/Woodwind quartets, Appalachian Folk, Bluegrass, acapella vocal stuff, choral) music exclusively and my studio is the concert venue. I like things to be as simple as humanly possible for myriad reasons, the largest of which being that it always sounds better.. |
#58
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
As far as layout goes, and features, the Wendt X4/x5 is nearly perfect.
Unfortunately, it sounds like hot ass. I of course know that the actual layout on the requested mixer could not be anything like that, but the features are spot-on. (I dont need the ENG port though) http://www.wendtinc.net/x4specs.pdf http://www.wendtinc.net/x4specs.htm |
#59
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
In article ,
Eeyore wrote: Ian Thompson-Bell wrote: Eeyore wrote: The pad is *inline* with the signal path, NOT the phantom power. Actually Graham I was referring to a pad external to the mixer, added in-line with the mic cable so the pad *is* in-line with the phantom power. This pad is additional to the 20dB pad inside the mixer which as you rightly say in only in the signal path. Oh I see. I imagined this mixer would have an internal pad. It would be essential IMHO. An external 20dB pad would add about 1k in each leg which wouldn't be a disaster. Graham, you have a worse reading comprehension problem than I do! Not only was Ian referring to an "in-line" pad as I pointed out to you in an earlier post, but the proposed mixer does include a built in switchable 20 dB pad as Ian mentioned above. My impression was that Ian was proposing the possibility of using an additional pad when input levels are above what can be handled by a microphone amplifier with limited gain adjustment capability even with the internal 20 dB pad. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#60
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Eeyore wrote:
Gain at the mix amp is invariably noisy. Placing 'gain in hand' would be best after the fader and that's also best for low THD. Quite right. Missed that one. Cheers Ian |
#61
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Eeyore wrote:
Ian Thompson-Bell wrote: Eeyore wrote: The pad is *inline* with the signal path, NOT the phantom power. Actually Graham I was referring to a pad external to the mixer, added in-line with the mic cable so the pad *is* in-line with the phantom power. This pad is additional to the 20dB pad inside the mixer which as you rightly say in only in the signal path. Oh I see. I imagined this mixer would have an internal pad. It would be essential IMHO. I imagined it would too. However, if a minimum gain of 0db was required, this could present problems with the first stage valve input level i.e. -20dB in the *internal pad*, +20dB in the input transformer = 0dBu at the first valve grid. As the first valve is typically biased at about -1V a 0dB input signal could cause significant grid rectification distortion. Hence my suggestion for a minimum 20dB gain and -20dBu max input (=-20dBu max on first stage grid). If the OP really did have a 0dBu input then I suggested an *additional* external 20dB pad would do the trick. Cheers Ian |
#62
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Tynan AgviŠr wrote:
As far as layout goes, and features, the Wendt X4/x5 is nearly perfect. Unfortunately, it sounds like hot ass. I of course know that the actual layout on the requested mixer could not be anything like that, but the features are spot-on. (I dont need the ENG port though) http://www.wendtinc.net/x4specs.pdf http://www.wendtinc.net/x4specs.htm Doesn't seem to mention the gain provided. Cheers Ian |
#63
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
John Byrns wrote:
In article , Eeyore wrote: Ian Thompson-Bell wrote: Eeyore wrote: The pad is *inline* with the signal path, NOT the phantom power. Actually Graham I was referring to a pad external to the mixer, added in-line with the mic cable so the pad *is* in-line with the phantom power. This pad is additional to the 20dB pad inside the mixer which as you rightly say in only in the signal path. Oh I see. I imagined this mixer would have an internal pad. It would be essential IMHO. An external 20dB pad would add about 1k in each leg which wouldn't be a disaster. Graham, you have a worse reading comprehension problem than I do! Not only was Ian referring to an "in-line" pad as I pointed out to you in an earlier post, but the proposed mixer does include a built in switchable 20 dB pad as Ian mentioned above. My impression was that Ian was proposing the possibility of using an additional pad when input levels are above what can be handled by a microphone amplifier with limited gain adjustment capability even with the internal 20 dB pad. Spot on. Cheers Ian |
#64
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
In article ,
"Tynan AgviŠr" wrote: As far as layout goes, and features, the Wendt X4/x5 is nearly perfect. Unfortunately, it sounds like hot ass. I of course know that the actual layout on the requested mixer could not be anything like that, but the features are spot-on. (I dont need the ENG port though) http://www.wendtinc.net/x4specs.pdf http://www.wendtinc.net/x4specs.htm How can the layout of the Wendt X4/x5 be nearly perfect, it looks like it uses rotary faders? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#65
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Tynan AgviŠr" wrote in message . 3.70... "Iain Churches" wrote in news:hZijj.281635$sV4.19102 @reader1.news.saunalahti.fi: I was just thinking ahead. He may not want them now, but experience tells me that it will not be long before he wants to patch some extermal EQ or processor (even a simple limiter) into a single channel or across the output mix buss. A simple mixer, if it is to be of any practical use, is not actually terribly simple. I never use these things, and dont ever see myself using them. Perhaps if I were working in the studio realm in "secular" music, but I work with acoustic based(Chamber Jazz, String/Woodwind quartets, Appalachian Folk, Bluegrass, acapella vocal stuff, choral) music exclusively and my studio is the concert venue. You have an interesting range of recording repertoire. Mine is restricted to only two of these, classical (mainly baroque) ensembles and jazz. For the latter, I would not even consider a console without good EQ and a gentle compressor or two. For Bluegrass, I think I would want the full Neve and all the bells and whistles it can offer:-) It may well be that something you consider inessential now, will prove to be of vital importance just a little way down the road. If you are going to the time and expense of having a mixer custom built, plan it very very carefully. I like things to be as simple as humanly possible for myriad reasons, the largest of which being that it always sounds better.. That's why I suggested pre and post insert point. You then have simple straight path when no outboard units are connected. Iain |
#66
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Tynan AgviŠr" wrote in message . 3.70... "Iain Churches" wrote in news:hZijj.281635$sV4.19102 @reader1.news.saunalahti.fi: I was just thinking ahead. He may not want them now, but experience tells me that it will not be long before he wants to patch some extermal EQ or processor (even a simple limiter) into a single channel or across the output mix buss. A simple mixer, if it is to be of any practical use, is not actually terribly simple. I never use these things, and dont ever see myself using them. Perhaps if I were working in the studio realm in "secular" music, but I work with acoustic based(Chamber Jazz, String/Woodwind quartets, Appalachian Folk, Bluegrass, acapella vocal stuff, choral) music exclusively and my studio is the concert venue. You have an interesting range of recording repertoi-) Mine is restricted to only two of these, classical (mainly baroque) ensembles and jazz. For the latter, I would not even consider a console without good EQ and a gentle compressor or two. For Bluegrass, I think I would want the full Neve and all the bells and whistles it can offer:-) It may well be that something you consider inessential now, will prove to be of vital importance just a little way down the road. If you are going to the time and expense of having a mixer custom built, plan it very very carefully. I like things to be as simple as humanly possible for myriad reasons, the largest of which being that it always sounds better.. That's why I suggested pre and post insert point. You then have simple straight path when no outboard units are connected. Iain |
#67
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Tynan AgviŠr" wrote in message . 3.70... "Iain Churches" wrote in news:hZijj.281635$sV4.19102 @reader1.news.saunalahti.fi: I was just thinking ahead. He may not want them now, but experience tells me that it will not be long before he wants to patch some extermal EQ or processor (even a simple limiter) into a single channel or across the output mix buss. A simple mixer, if it is to be of any practical use, is not actually terribly simple. I never use these things, and dont ever see myself using them. Perhaps if I were working in the studio realm in "secular" music, but I work with acoustic based(Chamber Jazz, String/Woodwind quartets, Appalachian Folk, Bluegrass, acapella vocal stuff, choral) music exclusively and my studio is the concert venue. You have an interesting range of recording repertoi-) Mine is restricted to only two of these, classical (mainly baroque) ensembles and jazz. For the latter, I would not even consider a console without good EQ and a gentle compressor or two. For Bluegrass, I think I would want the full Neve and all the bells and whistles it can offer:-) It may well be that something you consider inessential now, will prove to be of vital importance just a little way down the road. If you are going to the time and expense of having a mixer custom built, plan it very very carefully. I like things to be as simple as humanly possible for myriad reasons, the largest of which being that it always sounds better.. That's why I suggested pre and post insert point. You then have simple straight path when no outboard units are connected. Iain |
#68
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
In article ,
Ian Thompson-Bell wrote: John Byrns wrote: In article , Ian Thompson-Bell wrote: The one thing John did not mention in his spec was the mic pre gain (or overall gain for that matter). What's yours? The current iteration of my design has a gain of 80 dB from microphone input to line output, 10 dB of this is in the output amplifier, excluding makeup gain. I used this number because it was repeatedly mentioned in the original thread, however I am not a "pro audio" designer and don't know exactly how much gain might actually be required. I would like enough gain to be able to use RCA ribbon mics, or similar, for that vintage sound, is 80 dB enough for this? I know of no pro mixer with more than 80dB gain so from that point of view it should be enough. It will be hard to get better than 50dB S/N with 80dB of gain so more would be rather pointless and I don't think even the most insenstive ribbon would need more gain than that. The big question is what method have you used to vary the gain? In the current iteration of my design, the overall gain of 80 dB is allocated as follows, input transformer 20 dB, microphone amplifier 50 dB, and output amplifier 10 dB exclusive of makeup gain. There is a switchable 20 dB pad at the input, and the gain of the microphone amplifier proper can be varied between 50 dB and zero dB in steps of perhaps 10 dB. The amplifier consists of two stages each with a gain of 34 dB. 18 dB of negative feedback is applied by a feedback loop around the two stages. This feedback should improve the overload margin at the input by 18 dB. The gain is varied by an attenuator between the two stages with attenuation variable between 0 dB and 50 dB, the same switch also adjusts the feedback loop so that the overall feedback remains 18 dB at all attenuation settings. That is my current thinking on the matter, but it is subject to change at any time. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#69
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
In article ,
Ian Thompson-Bell wrote: Eeyore wrote: John Byrns wrote: I concentrated on the design of the mixer section Yes, that'll require a triode with AC coupled nfb from anode to grid to form the virtual earth, the remainder being routine mix Rs, level controls etc. That's hardly a DESIGN. It's a stock circuit. Graham Hmmm, that assumes virtual earth mixing is the way to go for tubes. A typical triode will have a stage gain of 20 maybe 30dB so the virtual earth will not be that good (Rfb/30 maybe) and there's not really enough gain to make up for mix losses. Also Rfb needs to be large enough not to significantly load the anode, so we are talking 300K or so here which means the mix resistors will be 100K for for 10dB gain make up. I have at least for the moment dropped the idea of virtual earth mixing from my design, however my original virtual earth design used a feedback resistor around the tube providing the virtual earth function, equal in value to the resistors used for each channels connection to the virtual earth mix bus. Driving this relatively low value feedback resistor was done by using the same buffer circuit, perhaps a CF, used in the channel modules which have the same problem driving the mixing resistors. With this scheme of equal value resistors the mixer circuit proper has a gain of unity. If you want to stick with VE mixing then a tubed long tailed pair and another triode will make a simple op amp like circuit where Rfb can be much smaller and the open loop gain is much higher making a better VE. Or simpler still just stick a CF on the end of the triode and feed its cathode back to the grid via a lowish Rfb. That was essentially my original scheme, noting that the problem of driving the feedback resistor is no worse than that of the individual channels driving their mixing resistors. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#71
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Ian Thompson-Bell wrote in news:fmlb25$tuc$1
@energise.enta.net: Tynan AgviŠr wrote: As far as layout goes, and features, the Wendt X4/x5 is nearly perfect. Unfortunately, it sounds like hot ass. I of course know that the actual layout on the requested mixer could not be anything like that, but the features are spot-on. (I dont need the ENG port though) http://www.wendtinc.net/x4specs.pdf http://www.wendtinc.net/x4specs.htm Doesn't seem to mention the gain provided. Cheers Ian Ian, i meant features, Sir. The Features are pretty much what I would want. |
#72
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
John Byrns wrote:
In the current iteration of my design, the overall gain of 80 dB is allocated as follows, input transformer 20 dB, microphone amplifier 50 dB, and output amplifier 10 dB exclusive of makeup gain. There is a switchable 20 dB pad at the input, and the gain of the microphone amplifier proper can be varied between 50 dB and zero dB in steps of perhaps 10 dB. The amplifier consists of two stages each with a gain of 34 dB. 18 dB of negative feedback is applied by a feedback loop around the two stages. This feedback should improve the overload margin at the input by 18 dB. The gain is varied by an attenuator between the two stages with attenuation variable between 0 dB and 50 dB, the same switch also adjusts the feedback loop so that the overall feedback remains 18 dB at all attenuation settings. That is my current thinking on the matter, but it is subject to change at any time. A novel scheme. I shall have to think about that topology. Cheers Ian |
#73
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
It is more likely headed for the trash bin, to be replaced by a new one thereby eliminating the hassle of getting out my old computer to run it. Before such things get tossed, I usually take it apart to salvage any usable parts, line cords, circuit boards bearing a few discrete parts like caps, resistors, transistors (heresy in this NG), and the metric screws and nuts (hard to come by in American hardware stores). This is an old tradition in ham radio, the "junk box"... Other bits of it end up in the recycling can, with the beer cans and plastic or glass bottles and packaging. |
#74
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
John wrote:
... Both the line amplifier and the headphone amplifier are push pull circuits. The microphone amplifiers are "SE", as 6 push pull microphone amplifiers seemed a bit much for a portable mixer. ... For what reasons do you perceive PP to be preferable in this application? In particular, why, after converting from balanced to SE, you decided on PP for the output stages? I have been dipping into the thread occasionally hoping to find the bit where voicing is discussed. I wonder by what process an agreement about desired quality of sound can be reached remotely with a prospective end user who wants "something special" Anyway, I'm impressed with your simple approach, and the way you have stuck to the brief without contracting Recalcitrant Engineers' Syndrome. Perhaps your experience of designing valve circuits has made you more wary of added complexity. Ian (wondering in passing what a pad is...but don't worry, I'll look it up) |
#75
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Tynan AgviŠr" wrote: Ian Thompson-Bell wrote Tynan AgviŠr wrote: As far as layout goes, and features, the Wendt X4/x5 is nearly perfect. Unfortunately, it sounds like hot ass. I of course know that the actual layout on the requested mixer could not be anything like that, but the features are spot-on. (I dont need the ENG port though) http://www.wendtinc.net/x4specs.pdf http://www.wendtinc.net/x4specs.htm Doesn't seem to mention the gain provided. Ian, i meant features, Sir. The Features are pretty much what I would want. So really very straighforward. Graham |
#76
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
Ian Iveson wrote: I have been dipping into the thread occasionally hoping to find the bit where voicing is discussed. I wonder by what process an agreement about desired quality of sound can be reached remotely with a prospective end user who wants "something special" Indeed. I'd like to know if Tynan has a particular benchmark tubed mic pre that he likes already. snip Ian (wondering in passing what a pad is...but don't worry, I'll look it up) Attenuator. Graham |
#77
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
In article ,
"Ian Iveson" wrote: John wrote: ... Both the line amplifier and the headphone amplifier are push pull circuits. The microphone amplifiers are "SE", as 6 push pull microphone amplifiers seemed a bit much for a portable mixer. ... For what reasons do you perceive PP to be preferable in this application? In particular, why, after converting from balanced to SE, you decided on PP for the output stages? Two main reasons. First to eliminate DC from the output transformer so that it can be smaller and have better performance. Second to achieve the output power level I desired with a small tube that is used at other locations in the mixer, reducing the number of required tube types to two. I have been dipping into the thread occasionally hoping to find the bit where voicing is discussed. I wonder by what process an agreement about desired quality of sound can be reached remotely with a prospective end user who wants "something special" Anyway, I'm impressed with your simple approach, I have been worrying that my approach is overly complex, there are much simpler approaches, look at a few remote mixers from the 1950s for ideas. and the way you have stuck to the brief without contracting Recalcitrant Engineers' Syndrome. What pray tell is "Recalcitrant Engineers' Syndrome", I have never heard of that before? Perhaps your experience of designing valve circuits has made you more wary of added complexity. A circuit should not be so simple it can't do the job properly, nor should it be more complex than is needed to do the job. A lot of people seem to pursue complexity for complexities sake. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#78
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Ian Iveson" wrote in message .uk... Ian (wondering in passing what a pad is...but don't worry, I'll look it up) It's an attenuator. I can tell you of its origin. In the days of acoustic recording, the recording phonograph was placed in front of the orchestra with the horn pointing forwards. Because of the somewhat limited dynamic of the acoustic recording chain, the loud passages need to be attenuated. The engineer did this by carefully pushing a ball of angora wood (known as "the pad") into the mouth of the horn, and then gradually pulling it out when the loud passage was over. As Sir Michael Caine might say: "Not a lot of people know that!" Iain |
#79
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Eeyore" wrote in
message "Tynan AgviŠr" wrote: Ian Thompson-Bell wrote Tynan AgviŠr wrote: As far as layout goes, and features, the Wendt X4/x5 is nearly perfect. Unfortunately, it sounds like hot ass. I of course know that the actual layout on the requested mixer could not be anything like that, but the features are spot-on. (I dont need the ENG port though) http://www.wendtinc.net/x4specs.pdf http://www.wendtinc.net/x4specs.htm Doesn't seem to mention the gain provided. Ian, i meant features, Sir. The Features are pretty much what I would want. So really very straighforward. Only, imagine what a 1:1 technical implementation in tubes would look like! IOW, replace the IC op amps with comparable tube op amps, but use the same gain staging, equalization, controls, etc. (1) It would a lot larger. (2) It would be a lot heavier. (3) It would use a lot more power. For a moment I thought of an implementation based on the subminiature wire-in tubes that I worked with in the Army back in the 60s. But, that would be way over the head of your average tubie. And, it would still be far larger, gobble power, and literally cook. |
#80
Posted to rec.audio.tubes
|
|||
|
|||
Design for a small tube/valve mixer
"Ian Iveson" wrote in
message .uk John wrote: ... Both the line amplifier and the headphone amplifier are push pull circuits. The microphone amplifiers are "SE", as 6 push pull microphone amplifiers seemed a bit much for a portable mixer. ... For what reasons do you perceive PP to be preferable in this application? Low distortion, redundancy and therefore reliability. In particular, why, after converting from balanced to SE, you decided on PP for the output stages? P-P gives you more dynamic range into real-world low impedance (5k-10k) loads. |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Do the Thiele-Small laws move design quality differences over to the drivers? | Tech | |||
Small room design/treatment | Pro Audio | |||
Small Mixer Issues | Pro Audio | |||
Your help on small system design please | Car Audio | |||
Best small mixer and/or mixer/amp/spkr combo? | Pro Audio |