| Author |
Message |
maxdm
Guest
|
 Posted:
Mon Nov 22, 2004 6:05 pm Post subject:
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.
|
|
| Back to top |
|
 |
Mark
Guest
|
| Posted:
Tue Nov 23, 2004 2:04 am Post subject:
Re: V72 electrolytics and brightness |
|
|
maxdimario@aliceposta.it (maxdm) wrote in message news:<25150933.0411220715.5965772@posting.google.com>...
| Quote: |
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 |
|
| Back to top |
|
|
maxdm
Guest
|
| Posted:
Tue Nov 23, 2004 6:08 pm Post subject:
Re: V72 electrolytics and brightness |
|
|
makolber@yahoo.com (Mark) wrote in message news:<3367f36e.0411221455.65fe8544@posting.google.com>...
| Quote: | maxdimario@aliceposta.it (maxdm) wrote in message news:<25150933.0411220715.5965772@posting.google.com>...
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. |
|
| Back to top |
|
|
Scott Dorsey
Guest
|
| Posted:
Tue Nov 23, 2004 10:04 pm Post subject:
Re: V72 electrolytics and brightness |
|
|
Mark <makolber@yahoo.com> wrote:
| Quote: | 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.
| Quote: | 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." |
|
| Back to top |
|
|
Mark
Guest
|
| Posted:
Tue Nov 23, 2004 10:04 pm Post subject:
Re: V72 electrolytics and brightness |
|
|
maxdimario@aliceposta.it (maxdm) wrote in message news:<25150933.0411230708.502d8846@posting.google.com>...
| Quote: | makolber@yahoo.com (Mark) wrote in message news:<3367f36e.0411221455.65fe8544@posting.google.com>...
maxdimario@aliceposta.it (maxdm) wrote in message news:<25150933.0411220715.5965772@posting.google.com>...
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 |
|
| Back to top |
|
|
Mark
Guest
|
| Posted:
Wed Nov 24, 2004 2:03 am Post subject:
Re: V72 electrolytics and brightness |
|
|
kludge@panix.com (Scott Dorsey) wrote in message news:<co01fr$ebb$1@panix2.panix.com>...
| Quote: | Mark <makolber@yahoo.com> wrote:
Old electrolytics sound fuzzy and distorted.
OK so you heard this dramatic improvment or measured it?
Surley if it was dramatic, it could be measured as well.
When caps get old, we can measure decreased capacitance, higher ESR, and
all kinds of nonlinear effects. All of these are symptoms of the same
problem.
|
Yes you can easily measure the cap. I'm asking if the OP measured the
claimed dramatic change to the audio performance due to the cap to
support the claim that the change was not related to hum and or bass
response as would be expected.
Mark |
|
| Back to top |
|
|
Paul Stamler
Guest
|
| Posted:
Wed Nov 24, 2004 10:05 am Post subject:
Re: V72 electrolytics and brightness |
|
|
"Mark" <makolber@yahoo.com> wrote in message
news:3367f36e.0411231033.735a524@posting.google.com...
| Quote: | OK so you heard this dramatic improvment or measured it?
Surley if it was dramatic, it could be measured as well.
I doubt that the inducatance of an electrolytic cap is significant at
anything below 1 MHz compared to the ESR.
|
Mmmm...naah. At least for new electrolytics. An example: a 1000uF 50V FC
series electrolytic has a resonant frequency of 9.3kHz, and an ESR of about
0.18 ohms. So from 9.3kHz on up, it's essentially an inductor with a small
resistance in series.
In general, bigger caps (more uF, that is) have lower resonance points;
3300uF caps seem to cluster around 7kHz.
I don't know what the resonance point of the caps in the V72 might be, but
I'm confident it's way, way less thank 1MHz. And like I said, above the
resonance point, the cap is for all intents and purposes an inductor.
Peace,
Paul |
|
| Back to top |
|
|
Mark
Guest
|
| Posted:
Wed Nov 24, 2004 6:13 pm Post subject:
Re: V72 electrolytics and brightness |
|
|
"Paul Stamler" <pstamlerhell@pobox.com> wrote in message news:<wYWod.964679$Gx4.140211@bgtnsc04-news.ops.worldnet.att.net>...
| Quote: | "Mark" <makolber@yahoo.com> wrote in message
news:3367f36e.0411231033.735a524@posting.google.com...
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 |
|
| Back to top |
|
|
Mark
Guest
|
| Posted:
Wed Nov 24, 2004 6:13 pm Post subject:
Re: V72 electrolytics and brightness |
|
|
"Paul Stamler" <pstamlerhell@pobox.com> wrote in message news:<wYWod.964679$Gx4.140211@bgtnsc04-news.ops.worldnet.att.net>...
| Quote: | "Mark" <makolber@yahoo.com> wrote in message
news:3367f36e.0411231033.735a524@posting.google.com...
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 |
|
| Back to top |
|
|
Phil Allison
Guest
|
| Posted:
Wed Nov 24, 2004 10:07 pm Post subject:
Re: V72 electrolytics and brightness |
|
|
"Paul Stamler"
Mark
| Quote: |
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/components/pdf/ABA0000CE22.pdf
| Quote: | 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/components/pdf/ABA0000CE22.pdf
| Quote: | 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 |
|
| Back to top |
|
|
Mark
Guest
|
| Posted:
Wed Nov 24, 2004 10:07 pm Post subject:
Re: V72 electrolytics and brightness |
|
|
A schematic of the V72 is on the web here:
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 |
|
| Back to top |
|
|
maxdm
Guest
|
| Posted:
Thu Nov 25, 2004 5:57 pm Post subject:
Re: V72 electrolytics and brightness |
|
|
| Quote: | 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. |
|
| Back to top |
|
|
Phil Allison
Guest
|
| Posted:
Thu Nov 25, 2004 10:13 pm Post subject:
Re: V72 electrolytics and brightness |
|
|
"maxdm"
| Quote: |
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
shite.
............ Phil |
|
| Back to top |
|
|
Mark
Guest
|
| Posted:
Fri Nov 26, 2004 6:11 am Post subject:
Re: V72 electrolytics and brightness |
|
|
"Phil Allison" <philallison@tpg.com.au> wrote in message news:<30mttpF31o60qU1@uni-berlin.de>...
| Quote: | "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
shite.
........... Phil
|
Yep, but people don't like their beliefs to become confused by the facts.
Mark |
|
| Back to top |
|
|
maxdm
Guest
|
| Posted:
Sat Nov 27, 2004 5:31 am Post subject:
Re: V72 electrolytics and brightness |
|
|
"Phil Allison" <philallison@tpg.com.au> wrote in message news:<30mttpF31o60qU1@uni-berlin.de>...
| Quote: | "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
shite.
........... 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. |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in