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#1
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V72 electrolytics and brightness
I have read some posts about the V72 being a dark preamp, but it seems
to me that any V72 which sounds dark simply has bad power supply electrolytics, if the tubes are new and the broadcast filter variable cap (15khz) has not deteriorated or been tampered with. In a class A design such as the V72 the power supply capacitors are part of the audio circuit. This is primarily the case for the 8 uF cap that feeds the inductor for the output stage. The V72 has a fair amount of neg. feedback that will compensate for the aged components and tubes, and will correct the deficiencies of the amp more or less depending on the signal that it amplifies, but there are inherent distortions that will never be eliminated without replacing the 8 uF caps for the P.S. Aged electrolytics will lose their ESR and act like an inductor on high frequencies. This means that on sharp transients and high frequencies the filter cap becomes 'open' and will not supply current to the circuit. All electrolytics age with time, and NOS electrolytics will age in some instances faster than regularly used electrolytics. Any capacitor manufacturer will provide a usable shelf life at a certain temperature and this life is less than a decade. 40 year old electrolytics will not sound the same as they were 10, 20 or 30 years ago, just like old tubes. Many internet stores sell V72 amps which are racked for high prices but with old tubes and caps, and then the buyer may find him or herself asking why the preamps sound dull and distorted. The amps themselves are very clean sounding once they have been restored to spec. |
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#2
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#3
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#5
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(Mark) wrote in message . com...
(maxdm) wrote in message om... Aged electrolytics will lose their ESR and act like an inductor on high frequencies. This means that on sharp transients and high frequencies the filter cap becomes 'open' and will not supply current to the circuit. Actually aged electrolytics will have a reduced capacitance and an increased ESR. ESR = Effective series resistance Aged electrolytics will act like a reduced value cap with a resistor in series. Usually this introduces a 120 Hz or 60 Hz hum or degrades the bass response. Mark Old electrolytics lose capacitance and therefore the bass frequencies will modulate the power supply voltage, this also applies to ripple which is a low frequency. ES Resistance increases (resistance in series with cap) on the top end as well, electrolytics are notably less of a perfect capacitor on the high end and become inductive etc. My point is that This said, I replaced an electrolytic coupling cap on a U67 that still measured above it's rated capacitance and bass impact and high frequencies etc. all improved dramatically. Old electrolytics sound fuzzy and distorted. |
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#6
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(maxdm) wrote in message . com...
(Mark) wrote in message . com... (maxdm) wrote in message om... Aged electrolytics will lose their ESR and act like an inductor on high frequencies. This means that on sharp transients and high frequencies the filter cap becomes 'open' and will not supply current to the circuit. Actually aged electrolytics will have a reduced capacitance and an increased ESR. ESR = Effective series resistance Aged electrolytics will act like a reduced value cap with a resistor in series. Usually this introduces a 120 Hz or 60 Hz hum or degrades the bass response. Mark Old electrolytics lose capacitance and therefore the bass frequencies will modulate the power supply voltage, this also applies to ripple which is a low frequency. ES Resistance increases (resistance in series with cap) on the top end as well, electrolytics are notably less of a perfect capacitor on the high end and become inductive etc. My point is that This said, I replaced an electrolytic coupling cap on a U67 that still measured above it's rated capacitance and bass impact and high frequencies etc. all improved dramatically. Old electrolytics sound fuzzy and distorted. OK so you heard this dramatic improvment or measured it? Surley if it was dramatic, it could be measured as well. I doubt that the inducatance of an electrolytic cap is significant at anything below 1 MHz compared to the ESR. but if you hear it I guess it must be true. Mark |
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#7
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(maxdm) wrote in message . com...
(Mark) wrote in message . com... (maxdm) wrote in message om... Aged electrolytics will lose their ESR and act like an inductor on high frequencies. This means that on sharp transients and high frequencies the filter cap becomes 'open' and will not supply current to the circuit. Actually aged electrolytics will have a reduced capacitance and an increased ESR. ESR = Effective series resistance Aged electrolytics will act like a reduced value cap with a resistor in series. Usually this introduces a 120 Hz or 60 Hz hum or degrades the bass response. Mark Old electrolytics lose capacitance and therefore the bass frequencies will modulate the power supply voltage, this also applies to ripple which is a low frequency. ES Resistance increases (resistance in series with cap) on the top end as well, electrolytics are notably less of a perfect capacitor on the high end and become inductive etc. My point is that This said, I replaced an electrolytic coupling cap on a U67 that still measured above it's rated capacitance and bass impact and high frequencies etc. all improved dramatically. Old electrolytics sound fuzzy and distorted. OK so you heard this dramatic improvment or measured it? Surley if it was dramatic, it could be measured as well. I doubt that the inducatance of an electrolytic cap is significant at anything below 1 MHz compared to the ESR. but if you hear it I guess it must be true. Mark |
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#8
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Mark wrote:
Old electrolytics sound fuzzy and distorted. OK so you heard this dramatic improvment or measured it? Surley if it was dramatic, it could be measured as well. When caps get old, we can measure decreased capacitance, higher ESR, and all kinds of nonlinear effects. All of these are symptoms of the same problem. I doubt that the inducatance of an electrolytic cap is significant at anything below 1 MHz compared to the ESR. The existing series inductance is probably more significant when the parallel capacitance starts going away. Especially at very high frequencies. But ALL of these things are symptoms, and not the inherent problem. The inherent problem is mechanical and chemical failure of the capacitor. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#9
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Mark wrote:
Old electrolytics sound fuzzy and distorted. OK so you heard this dramatic improvment or measured it? Surley if it was dramatic, it could be measured as well. When caps get old, we can measure decreased capacitance, higher ESR, and all kinds of nonlinear effects. All of these are symptoms of the same problem. I doubt that the inducatance of an electrolytic cap is significant at anything below 1 MHz compared to the ESR. The existing series inductance is probably more significant when the parallel capacitance starts going away. Especially at very high frequencies. But ALL of these things are symptoms, and not the inherent problem. The inherent problem is mechanical and chemical failure of the capacitor. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#11
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#12
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"Mark" wrote in message
m... OK so you heard this dramatic improvment or measured it? Surley if it was dramatic, it could be measured as well. I doubt that the inducatance of an electrolytic cap is significant at anything below 1 MHz compared to the ESR. Mmmm...naah. At least for new electrolytics. An example: a 1000uF 50V FC series electrolytic has a resonant frequency of 9.3kHz, and an ESR of about 0.18 ohms. So from 9.3kHz on up, it's essentially an inductor with a small resistance in series. In general, bigger caps (more uF, that is) have lower resonance points; 3300uF caps seem to cluster around 7kHz. I don't know what the resonance point of the caps in the V72 might be, but I'm confident it's way, way less thank 1MHz. And like I said, above the resonance point, the cap is for all intents and purposes an inductor. Peace, Paul |
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#13
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"Paul Stamler" wrote in message ...
"Mark" wrote in message m... OK so you heard this dramatic improvment or measured it? Surley if it was dramatic, it could be measured as well. I doubt that the inducatance of an electrolytic cap is significant at anything below 1 MHz compared to the ESR. Mmmm...naah. At least for new electrolytics. An example: a 1000uF 50V FC series electrolytic has a resonant frequency of 9.3kHz, and an ESR of about 0.18 ohms. So from 9.3kHz on up, it's essentially an inductor with a small resistance in series. In general, bigger caps (more uF, that is) have lower resonance points; 3300uF caps seem to cluster around 7kHz. I don't know what the resonance point of the caps in the V72 might be, but I'm confident it's way, way less thank 1MHz. And like I said, above the resonance point, the cap is for all intents and purposes an inductor. Peace, Paul And how much effect will an inductive reactance of 0.18 Ohms or even 0.5 Ohms have in a tube audio circuit? Your taking about the inductance of a few inches of wire. I'm sure you can come up with an unusual case where it might have a small effect, but..... I stand by my original statement, the most likely effect of a worn out cap in a tube circuit is on the bass response and the hum. Lets get a schematic of a V72 and plug it into PSPICE and increase the ESR and decrease the capacitance of the 8 uF cap and see what happens to the frequency response and power supply rejection. Mark |
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#14
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"Paul Stamler" wrote in message ...
"Mark" wrote in message m... OK so you heard this dramatic improvment or measured it? Surley if it was dramatic, it could be measured as well. I doubt that the inducatance of an electrolytic cap is significant at anything below 1 MHz compared to the ESR. Mmmm...naah. At least for new electrolytics. An example: a 1000uF 50V FC series electrolytic has a resonant frequency of 9.3kHz, and an ESR of about 0.18 ohms. So from 9.3kHz on up, it's essentially an inductor with a small resistance in series. In general, bigger caps (more uF, that is) have lower resonance points; 3300uF caps seem to cluster around 7kHz. I don't know what the resonance point of the caps in the V72 might be, but I'm confident it's way, way less thank 1MHz. And like I said, above the resonance point, the cap is for all intents and purposes an inductor. Peace, Paul And how much effect will an inductive reactance of 0.18 Ohms or even 0.5 Ohms have in a tube audio circuit? Your taking about the inductance of a few inches of wire. I'm sure you can come up with an unusual case where it might have a small effect, but..... I stand by my original statement, the most likely effect of a worn out cap in a tube circuit is on the bass response and the hum. Lets get a schematic of a V72 and plug it into PSPICE and increase the ESR and decrease the capacitance of the 8 uF cap and see what happens to the frequency response and power supply rejection. Mark |
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#15
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A schematic of the V72 is on the web he
http://members.ozemail.com.au/~gwagner/v72.htm Adjustment of the 40pF variable in the feedback path (near the top) will "dramaticaly" effect the high frequency response. The capacitance and ESR of the 8uF caps will primarly impact power supply hum. The "sound coloration" of this circuit is primarily a function of the quality of the input and output transformers which are outside the feedback loop and which probably roll off the bass and may have some roll off or peaking in the high frequencies depending on the source. Mark |
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#16
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"Paul Stamler" Mark I doubt that the inducatance of an electrolytic cap is significant at anything below 1 MHz compared to the ESR. Mmmm...naah. At least for new electrolytics. An example: a 1000uF 50V FC series electrolytic has a resonant frequency of 9.3kHz, and an ESR of about 0.18 ohms. So from 9.3kHz on up, it's essentially an inductor with a small resistance in series. ** That is *completely false* - electro caps are ***NOT*** inductive. The 1000uF, 50 volt Panasonic FC series cap you quoted is speced at *0.034* ohms impedance at *100 kHz* - which even at that frequency consists mostly of resistance ( ie its ESR). The frequency where the component becomes effectively an inductor ( due ONLY to the existence of its connecting leads) is above 500kHz. See: http://www.panasonic.com/industrial/...BA0000CE22.pdf In general, bigger caps (more uF, that is) have lower resonance points; 3300uF caps seem to cluster around 7kHz. ** A Panasonic 3,300 uF, 35 volt, FC cap has a speced impedance of * 0.015 * ohms at *100kHz.* See: http://www.panasonic.com/industrial/...BA0000CE22.pdf I don't know what the resonance point of the caps in the V72 might be, but I'm confident it's way, way less thank 1MHz. And like I said, above the resonance point, the cap is for all intents and purposes an inductor. ** Strange indeed then how SMPS manage to work so well using only electros to filter and suppress harmonics up to several MHz from the output !!! The TRUTH is that the effective inductance of any cap, including electros, is due to the length and spacing of its connecting wires. A few inches of PCB track or hand wiring will have so much inductance as to TOTALLY swamp that due to the cap itself. ................ Phil |
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#17
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The TRUTH is that the effective inductance of any cap, including electros,
is due to the length and spacing of its connecting wires. A few inches of PCB track or hand wiring will have so much inductance as to TOTALLY swamp that due to the cap itself. Aged E. capacitors will act like an inductor. New E. capacitors will not exhibit this problem nearly as much. Aged E. capacitors will induce distortion even when implemented in the power supply. Negative feedback in the amp reduces the distortion due to ageing of components, the v72 has a moderate amount of neg feedback. if you temporarily eliminate negative feedback from the circuit and listen to the preamp or analize technically it you *will* hear just how much the amplifier's characteristics change depending on the power supply's impedance/current capability/stability (new or old caps in P.S.). In Class A discrete circuits the power supply is a key element to the sound. it is in the signal path indirectly. Electrolytics are used because they are cheap and small, not because they are ideal. for critical applications those amps used paper caps. 8 uF 450v paper capacitors (or film) are huge and cannot be placed in 'miniature' tube equipment such as V72 etc. try recapping the electrolytics in anything that is over 10 years of age.. tube or solid state.. and you will notice a dramatic change in the sound. |
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#18
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"maxdm" try recapping the electrolytics in anything that is over 10 years of age.. tube or solid state.. and you will notice a dramatic change in the sound. ** New age mysticism, pyramids and crystals - ie a load of stinking ****e. ............ Phil |
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#19
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"Phil Allison" wrote in message ...
"maxdm" try recapping the electrolytics in anything that is over 10 years of age.. tube or solid state.. and you will notice a dramatic change in the sound. ** New age mysticism, pyramids and crystals - ie a load of stinking ****e. ........... Phil Yep, but people don't like their beliefs to become confused by the facts. Mark |
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#20
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"Phil Allison" wrote in message ...
"maxdm" try recapping the electrolytics in anything that is over 10 years of age.. tube or solid state.. and you will notice a dramatic change in the sound. ** New age mysticism, pyramids and crystals - ie a load of stinking ****e. ........... Phil You have obviously never recapped an old preamp or amp or compressor etc. I have. and there is a big difference in sound, power supply included. It is common knowledge that electrolytics degrade with age, especially when left uncharged. if you don't notice a difference than chances are that you have not got the ears to be an engineer or be involved in audio. You show no proof to your argument, which leads me to believe you have no significant working experience with audio circuits either. Continue to use old equipment that sounds mushy and distorted, if you like but keep your silly comments regarding pyramids to yourself. |
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#21
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"maxdm"
"Phil Allison" try recapping the electrolytics in anything that is over 10 years of age.. tube or solid state.. and you will notice a dramatic change in the sound. ** New age mysticism, pyramids and crystals - ie a load of stinking ****e. You have obviously never recapped an old preamp or amp or compressor etc. I have. and there is a big difference in sound, power supply included. ** Pure self delusion. It is common knowledge that electrolytics degrade with age, especially when left uncharged. ** Electros have no virtually inductance and which can never increase, only the ESR rises at the ends of a cap's useful life - and this can be 30 years or more. if you don't notice a difference than chances are that you have not got the ears to be an engineer or be involved in audio. ** Typical audiophool ******'s line of smug bull****. You show no proof to your argument, ** I have quoted you the facts - disprove them if you can. OTOH you have produced noting but unsupported drivel. which leads me to believe you have no significant working experience with audio circuits either. ** Oh - only about 40 years worth, first as a hobby then full time work in service and design of audio electronics - both tube and solid state. Continue to use old equipment that sounds mushy and distorted, if you like but keep your silly comments regarding pyramids to yourself. ** Go stick the nearest pyramid up your backside - you posturing dangerous fool. ............. Phil |
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#22
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On 26 Nov 2004 16:31:07 -0800, (maxdm) wrote:
"Phil Allison" wrote in message ... "maxdm" ... { smoe new age crap snipped } ........... Phil You have obviously never recapped an old preamp or amp or compressor You have obviously never gone to http://groups.google.com, clicked on Advanced groups search, and put in Phil Allison for author. If you had, you'd find out that ... My God, Phil is now trolling AAPL-S! God help him, they'll eat him alive and feed his bones to their dogs... NO troll deserves THAT! ... Continue to use old equipment that sounds mushy and distorted, if you like but keep your silly comments regarding pyramids to yourself. ----- http://mindspring.com/~benbradley |
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#23
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"Ben Bradley" "Phil Allison" You have obviously never gone to http://groups.google.com, clicked on Advanced groups search, and put in Phil Allison for author. If you had, you'd find out that ... My God, Phil is now trolling AAPL-S! God help him, they'll eat him alive and feed his bones to their dogs... NO troll deserves THAT! ** Got news for you ****head - I have been posting regularly on AAPLS for several years. That wasteland of a NG is chocked up with scumbag equipment dealers on the make and anencephalic fader jocks posing as technical experts - including a few ape brained ones from Canada. I just rattle their cages now and then with a few unpalatable technical facts and personal assessments. ............... Phil |
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#24
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** Go stick the nearest pyramid up your backside - you posturing dangerous fool. ............ Phil Gee ...40 years of experience and this is the way you deal with technical issues? who is posturing here?? I will give some real-world examples: As you wrote after 30 years or so (v72 have an average age of 45 years??) the capacitor degrades. Esr goes out of spec, capacitance goes down, mechanical problems due to drying up oxidization etc. generally speaking they go out of spec. some caps only have a shelf life of 5 years or so depending on temperature and storage conditions. I was just reading the specs while shopping for capacitors a week ago. Some V72's you buy have been in storage unused for years. I have recapped a class A Single ended parallel power amp that is less than 10 years old which I bought used and was going to sell because of mushy high end poor soundstaging etc. With the new caps the highs came back (no feedback in circuit) and the amp works very nicely. A 40 year old U67 I have lacked punch, definition and smeared transients. soft and mushy (sound familiar?) I selected the best out 15 different EF86/806 tubes and the sound improved..to a point. One of the top experts on Neumanns worldwide advised me not to change the original decoupling cap, since he maintained that with the low current and voltages inside the mic those caps are virtually eternal. I changed the cap (still had more than rated capacitance) with a new one and the mic is now amazing. excellent for lead vocals and even drums, whereas before it made everything mushy and distant--sounding. I still have the old cap for resale of the mic just in case etc. I have a 50's V72 that I re-capped and the depth, hardness, high-end/transient response improved quite a bit. The other V72's I have sound a bit mushy on the high end compared to the recapped one. If someone wants to hear the effect of changing different power supply smoothing caps on a V72 or other class a cicuit try this. Get a 1 uF 400v cap and put it in parallel with the smoothing cap connected to the output stage. You will hear a different high end response depending on the circuit..this is due to the different esr/resonance/hysteresis characteristics of the film cap vs. old worn-out cap. Get a new electrolytic cap and put it in parallel to the old one (as long as the old one is not leaky) temporarily. You will hear a difference in the response of the pre. You will hear less of a difference on circuits that have a higher degree of power-supply rejection (such as op-amps, class ab, high feedback etc.) Class A circuits wil benefit, though. |
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#25
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"maxdm" Gee ...40 years of experience and this is the way you deal with technical issues? ** Electros have no virtually inductance and which can never increase, only the ESR rises at the ends of a cap's useful life - and this can be 30 years or more. if you don't notice a difference than chances are that you have not got the ears to be an engineer or be involved in audio. ** Typical audiophool ******'s line of smug bull****. You show no proof to your argument, ** I have quoted you the facts - disprove them if you can. OTOH you have produced noting but unsupported drivel. which leads me to believe you have no significant working experience with audio circuits either. ** Oh - only about 40 years worth, first as a hobby then full time work in service and design of audio electronics - both tube and solid state. Gee ...40 years of experience and this is the way you deal with technical issues? Continue to use old equipment that sounds mushy and distorted, if you like but keep your silly comments regarding pyramids to yourself. ** Go stick the nearest pyramid up your backside - you posturing dangerous fool. ............. Phil |
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#26
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On Sat, 27 Nov 2004 12:41:53 +0100, Phil Allison wrote:
"maxdm" Gee ...40 years of experience and this is the way you deal with technical issues? ** Electros have no virtually inductance and which can never increase, It has no virtually inductance and can never increase. Hmm. Neat trick. Typical inductances of new electrolytics: 100uF/35-50V: .22-.31uH 100uF/450V: .27-.32uH 330uF/35-100V: .15-.3uH 1000uF/35-50V: .15-.3uH 3300uF/35-50V: .1-.27uH In the latter case, that's enough for the resonant frequency (above which the inductance predominates) to be as low as 5.3-8.6kHz, well within the audio range. Peace, Paul |
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#27
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"Paul Stamler" Phil Allison wrote: ** Electros have no virtually inductance and which can never increase, Typical inductances of new electrolytics: 100uF/35-50V: .22-.31uH 100uF/450V: .27-.32uH 330uF/35-100V: .15-.3uH 1000uF/35-50V: .15-.3uH 3300uF/35-50V: .1-.27uH An example: a 1000uF 50V FC series electrolytic has a resonant frequency of 9.3kHz, and an ESR of about 0.18 ohms. So from 9.3kHz on up, it's essentially an inductor with a small resistance in series. ** That is *completely false* - electro caps are ***NOT*** inductive. The 1000uF, 50 volt Panasonic FC series cap you quoted is speced at *0.034* ohms impedance at *100 kHz* - which even at that frequency consists mostly of resistance ( ie its ESR). The frequency where the component becomes effectively an inductor ( due ONLY to the existence of its connecting leads) is above 500kHz. See: http://www.panasonic.com/industrial/...BA0000CE22.pdf In general, bigger caps (more uF, that is) have lower resonance points; 3300uF caps seem to cluster around 7kHz. ** A Panasonic 3,300 uF, 35 volt, FC cap has a speced impedance of * 0.015 * ohms at *100kHz.* See: http://www.panasonic.com/industrial/...BA0000CE22.pdf I don't know what the resonance point of the caps in the V72 might be, but I'm confident it's way, way less thank 1MHz. And like I said, above the resonance point, the cap is for all intents and purposes an inductor. ** Strange indeed then how SMPS manage to work so well using only electros to filter and suppress harmonics up to several MHz from the output !!! The TRUTH is that the effective inductance of any cap, including electros, is due to the length and spacing of its connecting wires. A few inches of PCB track or hand wiring will have so much inductance as to TOTALLY swamp that due to the cap itself. ** How about you reply to the facts and stop cowering ?????????? Using the data published by Panasonic the inductance of their 3300 uF, 50 volt FC cap is less than 23nH !!!! 23 nH is the inductance of 1 inch of straight wire. YOUR claim - and nobody else's - that electros behave like an inductor above the frequency where the impedance falls to its minimum is FALSE. Go check an ACTUAL impedance curve and see that the Q factor is incredibly low. Go put some electros across the output of signal generator set to 100kHz and see for yourself !!! ................ Phil |
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#28
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#29
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"Chel van Gennip" wrote in message ... On Sun, 28 Nov 2004 02:28:46 +0100, Chel van Gennip wrote: Typical inductances of new electrolytics: 100uF/35-50V: .22-.31uH 100uF/450V: .27-.32uH 330uF/35-100V: .15-.3uH 1000uF/35-50V: .15-.3uH 3300uF/35-50V: .1-.27uH In the latter case, that's enough for the resonant frequency (above which the inductance predominates) to be as low as 5.3-8.6kHz, well within the audio range. Just look at the impedance curve of this LC series circuit, at 20kHz: 0.03Ohm, yes this impedance is inductive, yes at resonance frequency the impedance is lower, and yes we are talking about frequencies in the audio range. Fore those not so used to calculus, the impedance of three mentioned capacitors for different frequencies, the ESR set at 0.01 Ohm, capaciter seen as RLC series circuit. Requency at factor 3.1623 steps. 100uf/.30uH 1000uF/.22uH 3300uF/.18uH R 1.0e-02 1.0e-02 1.0e-02 L 3.0e-07 2.2e-07 1.8e-07 C 1.0e-04 1.0e-03 3.3e-03 Freq. Z Z Z 10 159.155 15.915 4.823 32 50.329 5.033 1.525 100 15.915 1.591 0.482 316 5.032 0.503 0.152 1000 1.590 0.158 0.048 3162 0.497 0.047 0.015 10000 0.141 0.010 0.012 31623 0.014 0.040 0.036 100000 0.173 0.137 0.113 The ESRs I measured were higher, though, on the order of .15-.45 ohms. Caveat: the error factor in measuring the ESR in my setup is a good deal higher than measuring resonant frequency, so take those numbers with a grain of salt. But they accord at least fairly well with the manufacturer's datasheets. Peace, Paul |
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#30
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"Paul Stamler" The ESRs I measured were higher, though, on the order of .15-.45 ohms. Caveat: the error factor in measuring the ESR in my setup is a good deal higher than measuring resonant frequency, so take those numbers with a grain of salt. ** Your worthless numbers need a whole bucket of salt. For Christs sake Paul - just measure the impedance at 100kHz - the result will give you the effective ESR and prove the lack of inductive effects at audio frequencies. Then wake up to yourself and realise that even a 1 inch length of copper wire has more inductive reactance than resistance above a few kHz. .............. Phil |
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