Finally I finished the amp and put in cabinet. I also made a passive preamp (a pot in a box🙂 ). I haven't had a chance to listen to it properly yet, to many other jobs around the house😡.
Hi,
congratulations chrisb03, your setup seems to be fairly complex, but looks outstanding audiophil. Maybe, you did the right thing intuitively, putting the pot into an external box.
Today I did some trials with the 2-channel UcD180 and the 3-way speaker's fabric. And in fact, I could hear the interference of the switching residuals in all 3 drivers, "best" in the tweeter.
The tweeter (or the mid range alternatively) and the bass were driven separately by one UcD each. The modules are screwed on a aluminum plate, 45mm from each other (see the links, I already posted earlier). The supply secondary side is still very simple, a schottky bridge plus 10000µF per rail, driving both modules together, this will be changed in the future. The input wiring was coming from the two XLRs, going together through a 4-wire screened cable to two symmetrical double pots (balanced) and from there through separate screened cables to the UcDs.
The whistling was to be heard over the full potentiometer range, quietest at the left and right ends. It was interesting to modulate the frequency of the whistling by pushing the woofer a bit. It's easy to explain now: pushing the woofer generates some voltage, acting as a disturbance variable in the control loop. This is to be cancelled by the control, therefore changing the switching frequency as a side effect of the modulator's working principle. BTW, the switching residual at my modules are 400kHz sine with 340mV rms.
Disconncting the power from one of the modules let the whistling disappear completely. Coupling both outputs through a 47nF cap does the same by synchronising the UcDs. Disconnecting the inputs lowered the wistling noise a lot, but it was still existent. Connecting a 10nF cap across the inputs, changes the sound a bit but does not eliminate the interference. The whistling with inputs connected was audible up to about one meter distance from the tweeter anyway (Monacor DT254, sensivity 92dB/1W@1m). This mixing product of the interference is only possible by passing the two frequencies through a nonlinear stage. The amplitudes would be linearly added otherwise, no other frequencies would be audible. I concluded, this could be an effect at a pn-junction of the input stage. So I had to minimise any coupling from one module to the input of the other. I changed the wiring and its connections to the pots. Each channel got its own cable, consequently from the XLRs to the pots and back to the modules, with the shield connected to the XLRs grounding.
And - WOW!
Any remaining hum has gone, independent of the pot position. 🙂 And the whistling is much less audible, the maximum distance from the tweeter is now about 25cm, to hear that. It is not completely independent of the potentiometer position, there is a very narrow range near zero, where it is somewhat audible, at the other pot positions the whistling is not disturbing anymore (hearing distance below 15cm).
Hmm, one could believe, a synchronised version of the UcD would give more flexibility in mounting and wiring of the UcDs. As I believe, the frequency variation is not an necessary behaviour of the self oscillating principle, it is a side effect. An edge modulating principle (similar to PEDEC) should cancel this problem, because the modules could be synchronised without degrading the control performance.
JohnW, wouldn't you like to cooperate with Bruno and Jan-Peter to get the best out of your two worlds? 😀
My conclusion: monoblocks in separate cases are the easiest way to avoid such interferences, if UcD or ZAPPulse modules are used. Otherwise one should take care to avoid any coupling possibilities between the modules (separate wiring, distances, shielding e.t.c.). Although the interferences are hardly audible with a correct setup and a normal hearing position, I'm bothered a bit by the knowledge of the existence of this marginal imperfection.
Good luck for your ClassD projects!
Best regards, Timo.
congratulations chrisb03, your setup seems to be fairly complex, but looks outstanding audiophil. Maybe, you did the right thing intuitively, putting the pot into an external box.
Today I did some trials with the 2-channel UcD180 and the 3-way speaker's fabric. And in fact, I could hear the interference of the switching residuals in all 3 drivers, "best" in the tweeter.
The tweeter (or the mid range alternatively) and the bass were driven separately by one UcD each. The modules are screwed on a aluminum plate, 45mm from each other (see the links, I already posted earlier). The supply secondary side is still very simple, a schottky bridge plus 10000µF per rail, driving both modules together, this will be changed in the future. The input wiring was coming from the two XLRs, going together through a 4-wire screened cable to two symmetrical double pots (balanced) and from there through separate screened cables to the UcDs.
The whistling was to be heard over the full potentiometer range, quietest at the left and right ends. It was interesting to modulate the frequency of the whistling by pushing the woofer a bit. It's easy to explain now: pushing the woofer generates some voltage, acting as a disturbance variable in the control loop. This is to be cancelled by the control, therefore changing the switching frequency as a side effect of the modulator's working principle. BTW, the switching residual at my modules are 400kHz sine with 340mV rms.
Disconncting the power from one of the modules let the whistling disappear completely. Coupling both outputs through a 47nF cap does the same by synchronising the UcDs. Disconnecting the inputs lowered the wistling noise a lot, but it was still existent. Connecting a 10nF cap across the inputs, changes the sound a bit but does not eliminate the interference. The whistling with inputs connected was audible up to about one meter distance from the tweeter anyway (Monacor DT254, sensivity 92dB/1W@1m). This mixing product of the interference is only possible by passing the two frequencies through a nonlinear stage. The amplitudes would be linearly added otherwise, no other frequencies would be audible. I concluded, this could be an effect at a pn-junction of the input stage. So I had to minimise any coupling from one module to the input of the other. I changed the wiring and its connections to the pots. Each channel got its own cable, consequently from the XLRs to the pots and back to the modules, with the shield connected to the XLRs grounding.
And - WOW!
Any remaining hum has gone, independent of the pot position. 🙂 And the whistling is much less audible, the maximum distance from the tweeter is now about 25cm, to hear that. It is not completely independent of the potentiometer position, there is a very narrow range near zero, where it is somewhat audible, at the other pot positions the whistling is not disturbing anymore (hearing distance below 15cm).
Hmm, one could believe, a synchronised version of the UcD would give more flexibility in mounting and wiring of the UcDs. As I believe, the frequency variation is not an necessary behaviour of the self oscillating principle, it is a side effect. An edge modulating principle (similar to PEDEC) should cancel this problem, because the modules could be synchronised without degrading the control performance.
JohnW, wouldn't you like to cooperate with Bruno and Jan-Peter to get the best out of your two worlds? 😀
My conclusion: monoblocks in separate cases are the easiest way to avoid such interferences, if UcD or ZAPPulse modules are used. Otherwise one should take care to avoid any coupling possibilities between the modules (separate wiring, distances, shielding e.t.c.). Although the interferences are hardly audible with a correct setup and a normal hearing position, I'm bothered a bit by the knowledge of the existence of this marginal imperfection.
Good luck for your ClassD projects!
Best regards, Timo.
Hi,
Wouldn't PWM always have a level of frequency modulation? Some worse than others, it's not exactly a bad thing and should be fairly minimal with this scheme anyway.
According to previous discussions, I dont' believe using a cap to couple the modules is effectively synchronising them, if it were, they'd both output the exact same signals.
I think what is actually occuring here (to try and make sense of this benefit we're hearing about) might be that the induced noise is being coupled in a common mode fashion and therefore cancelling out. So maybe with some experimentation we could find a value that works better, ie, little to no coupling of audio signals, and enough coupling at switching frequencies to just sufficiently attenuate the heterodyning. Of course a simple cap may not be the best way of achieving this.. but if it can be made to work in such a simple way without any risk of suffering the obvious down side of it.. job well done. I think I have to add the following disclaimer, still not the preferred method, just a last resort kind of thing.
Regards
Chris
Wouldn't PWM always have a level of frequency modulation? Some worse than others, it's not exactly a bad thing and should be fairly minimal with this scheme anyway.
According to previous discussions, I dont' believe using a cap to couple the modules is effectively synchronising them, if it were, they'd both output the exact same signals.
I think what is actually occuring here (to try and make sense of this benefit we're hearing about) might be that the induced noise is being coupled in a common mode fashion and therefore cancelling out. So maybe with some experimentation we could find a value that works better, ie, little to no coupling of audio signals, and enough coupling at switching frequencies to just sufficiently attenuate the heterodyning. Of course a simple cap may not be the best way of achieving this.. but if it can be made to work in such a simple way without any risk of suffering the obvious down side of it.. job well done. I think I have to add the following disclaimer, still not the preferred method, just a last resort kind of thing.
Regards
Chris
Hi Chris,
don't know, if I understand you right. I do not believe, that a pure PWM is a frequency varying modulation. Even symmetrical and asymmetrical PWM do change the ratio of the pos/neg pulse with, if you want, a frequency change inside of one cycle, but not more.
As I believe to understand the self oscillating principle, if you use a pure hysteretic controller with constant control voltage amplitude, you won't get a constant frequency. But there are principles to synchronise the switching frequency by modifying the modulating scheme. The simplest way is to add a synchronising pulse train to the comparators input. This will work over a restricted modulation index range only. Another way is to shift rising and/or falling edges of each cycle according to the control deviation, without changing the frequency itself. I believe, JohnW used a similar way in his design.
Therefore synchronising the UcDs will not necessarily make their outputs identical. They are no more completely independet, so they will exhibit lower linearity (and THD?) performance at least. It would be interesting to know, if this is tolerable in a active speaker system, because the amps may not need so much channel separation.
Could be a question to Jan-Peter: Did you do such measurements with synchronised modules already?
Of course, I fully agree with you, it will not be easy to find a setup for cancelling out the interference. Seriously, the current amount of whistling is a thing, I can live with. And my ears grow older with every day...
Regards
Timo
don't know, if I understand you right. I do not believe, that a pure PWM is a frequency varying modulation. Even symmetrical and asymmetrical PWM do change the ratio of the pos/neg pulse with, if you want, a frequency change inside of one cycle, but not more.
As I believe to understand the self oscillating principle, if you use a pure hysteretic controller with constant control voltage amplitude, you won't get a constant frequency. But there are principles to synchronise the switching frequency by modifying the modulating scheme. The simplest way is to add a synchronising pulse train to the comparators input. This will work over a restricted modulation index range only. Another way is to shift rising and/or falling edges of each cycle according to the control deviation, without changing the frequency itself. I believe, JohnW used a similar way in his design.
Therefore synchronising the UcDs will not necessarily make their outputs identical. They are no more completely independet, so they will exhibit lower linearity (and THD?) performance at least. It would be interesting to know, if this is tolerable in a active speaker system, because the amps may not need so much channel separation.
Could be a question to Jan-Peter: Did you do such measurements with synchronised modules already?
Of course, I fully agree with you, it will not be easy to find a setup for cancelling out the interference. Seriously, the current amount of whistling is a thing, I can live with. And my ears grow older with every day...
Regards
Timo
Hi Timo, thanks for the "audiophile" compliment. I put the pot in a separate box for two reasons.
1. The pot wires would have gone past the transformers, the capacitors, and the IEC, I didn't feel comfortable doing that.
2. Keeping the amp as a pure power amp was more versatile for future preamp.
At this stage I think a preamp is a waste of money. My DAC and Amp's sensitivities are match well. As I'm writing this, I'm listening to my setup and wow!......or should I say WOW!! As I'm currently running bookshelves, I was planning on buy a high quality sub to complete the setup. I don't think I need it now, geez this amp as brought out the best in these Sonus Fabers. I can't wait to try the amp on my cousins full range (floor standers). I will try and compare to some other amps as well.
I've got it cranked up and my ears haven't fatigued yet, that's a good indicator for quality for all components involved in this setup. I'm happy with the setup as I got the DAC and speakers secondhand and saved over 50%.
By the way, I don't get the whistling you are/have experienced, maybe I can't hear it, having said that I wont go looking for it just in case I do hear it. Then it will annoy the sh!t out of me. Ignorance is bliss.
Chris
1. The pot wires would have gone past the transformers, the capacitors, and the IEC, I didn't feel comfortable doing that.
2. Keeping the amp as a pure power amp was more versatile for future preamp.
At this stage I think a preamp is a waste of money. My DAC and Amp's sensitivities are match well. As I'm writing this, I'm listening to my setup and wow!......or should I say WOW!! As I'm currently running bookshelves, I was planning on buy a high quality sub to complete the setup. I don't think I need it now, geez this amp as brought out the best in these Sonus Fabers. I can't wait to try the amp on my cousins full range (floor standers). I will try and compare to some other amps as well.
I've got it cranked up and my ears haven't fatigued yet, that's a good indicator for quality for all components involved in this setup. I'm happy with the setup as I got the DAC and speakers secondhand and saved over 50%.
By the way, I don't get the whistling you are/have experienced, maybe I can't hear it, having said that I wont go looking for it just in case I do hear it. Then it will annoy the sh!t out of me. Ignorance is bliss.
Chris
Hi Timo,
I think what I was trying to say is that PWM isn't a solide clock signal per se, there must be some minor (very minor, so minor I shouldnt' have mentioned it minor because I've been thinking of nothing but self oscillation schemes for so long minor lol) frequency shift in clock controlled schemes as you traverse the modulation index. I might need to rethink that after some sleep however 🙂 UcD would be worse than that as far as frequency modulation, and a pure hysteresis modulator with no form of .. compensation.. would be worse yet.
In a pure hysteresis modulator I think the best way of stabalizing the frequency spread is by modulating the hysteresis band with the audio reference. This would probably make it more like UcD's spread, than a clocked one.
If I understand what you're saying about shifting the rising/falling edges of the wave, this is more of an error correction technique than frequency correction, as you basically said, "without changing frequency". I've never heard of it being implemented in a self oscillation scheme? If I'm not entirely mistaken JohnW used clocked/digital means, I've been meaning to read up on what he did for awhile now. I know it's exactly what class T does, in a seemingly highly complex way. Doesn't self oscillation do away with the need for this sort of thing entirely, and hence one of its major benefits?
In my mind, synchronised means in unison, operating as one, meaning they'd be switching identically, and therefore would have to have the exact same output signals, as they'd have the exact same switching signals/times/modulation.
If you're saying the coupling via the cap is only skewing the wave over one way or the other, without changing it's frequency (very much).. which I believe it is (but not the reason for it cancelling the heterodyning), then we've only added distortion, and have synchronised nothing. So then how do we see any benefit from it? For now I have to stubbornly stick with my common mode coupling of the noise theory.
I still agree with you as well, certainly the best measure is avoidance, second best shielding/ Faraday cage if it can be done without hurting convection cooling of it, but I'd like to understand more of why this mysterious coupling cap thing works.
Regards
I think what I was trying to say is that PWM isn't a solide clock signal per se, there must be some minor (very minor, so minor I shouldnt' have mentioned it minor because I've been thinking of nothing but self oscillation schemes for so long minor lol) frequency shift in clock controlled schemes as you traverse the modulation index. I might need to rethink that after some sleep however 🙂 UcD would be worse than that as far as frequency modulation, and a pure hysteresis modulator with no form of .. compensation.. would be worse yet.
In a pure hysteresis modulator I think the best way of stabalizing the frequency spread is by modulating the hysteresis band with the audio reference. This would probably make it more like UcD's spread, than a clocked one.
If I understand what you're saying about shifting the rising/falling edges of the wave, this is more of an error correction technique than frequency correction, as you basically said, "without changing frequency". I've never heard of it being implemented in a self oscillation scheme? If I'm not entirely mistaken JohnW used clocked/digital means, I've been meaning to read up on what he did for awhile now. I know it's exactly what class T does, in a seemingly highly complex way. Doesn't self oscillation do away with the need for this sort of thing entirely, and hence one of its major benefits?
In my mind, synchronised means in unison, operating as one, meaning they'd be switching identically, and therefore would have to have the exact same output signals, as they'd have the exact same switching signals/times/modulation.
If you're saying the coupling via the cap is only skewing the wave over one way or the other, without changing it's frequency (very much).. which I believe it is (but not the reason for it cancelling the heterodyning), then we've only added distortion, and have synchronised nothing. So then how do we see any benefit from it? For now I have to stubbornly stick with my common mode coupling of the noise theory.
I still agree with you as well, certainly the best measure is avoidance, second best shielding/ Faraday cage if it can be done without hurting convection cooling of it, but I'd like to understand more of why this mysterious coupling cap thing works.
Regards
Hello Tiki,
I have built a test amplifier with (at the moment) three UcD180 channels built inside a 19"/2HE case. With one 160VA transformer and symmetrical input. All UcD180 modules has a star wiring from the powersupply and the /ON line goes together to one switch. The other side of the switch goes to the central gnd point of the powersupply. The amplifiers are only grounded thrue the XLR chassie connectors. In this setup I have;
- no hum.
- noise is very low, and quit pleasant pure white.
- and no sign of any form of whistling.
Channel one has a Fsw-408kHz / Channel two has a Fsw-406kHz.
Today I have done a FFT with our AP, please check this link: www.hypex.nl/classd/FFT-3CH-UcD180.wmf
Yellow line is measured on CH2, and CH1 has an outputsignal of 26dBV in 8 ohm. So the channel seperation is something about 108dB by 1kHz.
The red line, is whereby CH1 is switched of, so you only measure the outputnoise of the UcD180 (and channel 3 is still switched on).
I can't see any form of mixing the two switching frequency in this FFT measurement.
Thereby I have also connect a loudspeaker and tried with my 40 years old ears to hear anything. I do not hear any whistling tones.....
Ofcourse you can use a synchronize module, but correct hooked up you don't need this. And I have told this earlier but a synchromodule does degreed the loopgain and increase automatically the distortion.
Ok, I agree with you it would be easier if you can make the wires the way you like, so a synchro module makes it easier. But on the other hand one of the most imported aspect of a good audio setup if the correct wiring.
And now the funny part......if you make your wires correct for the best audio performance, you have automatically very little or none problems with whistling.
Regards,
Jan-Peter
I have built a test amplifier with (at the moment) three UcD180 channels built inside a 19"/2HE case. With one 160VA transformer and symmetrical input. All UcD180 modules has a star wiring from the powersupply and the /ON line goes together to one switch. The other side of the switch goes to the central gnd point of the powersupply. The amplifiers are only grounded thrue the XLR chassie connectors. In this setup I have;
- no hum.
- noise is very low, and quit pleasant pure white.
- and no sign of any form of whistling.
Channel one has a Fsw-408kHz / Channel two has a Fsw-406kHz.
Today I have done a FFT with our AP, please check this link: www.hypex.nl/classd/FFT-3CH-UcD180.wmf
Yellow line is measured on CH2, and CH1 has an outputsignal of 26dBV in 8 ohm. So the channel seperation is something about 108dB by 1kHz.
The red line, is whereby CH1 is switched of, so you only measure the outputnoise of the UcD180 (and channel 3 is still switched on).
I can't see any form of mixing the two switching frequency in this FFT measurement.
Thereby I have also connect a loudspeaker and tried with my 40 years old ears to hear anything. I do not hear any whistling tones.....
Ofcourse you can use a synchronize module, but correct hooked up you don't need this. And I have told this earlier but a synchromodule does degreed the loopgain and increase automatically the distortion.
Ok, I agree with you it would be easier if you can make the wires the way you like, so a synchro module makes it easier. But on the other hand one of the most imported aspect of a good audio setup if the correct wiring.
And now the funny part......if you make your wires correct for the best audio performance, you have automatically very little or none problems with whistling.
Regards,
Jan-Peter
Few questions about one man who is trying to find if UCD400 parts are adequate for him.
-I have 2 400VA/30V transformers, with for each 4 10mF capacities. Are these adequate for A UCD400 amplifier or not. In that case, what power can I expect for them on a 4 Ohms loudspeaker ?
- is a UCD 400 amplifier adequate for a peerlees XLS 10 based subwoofer ?
- why is the order impossible today on hypex website ?
Thanks for all in advance
-I have 2 400VA/30V transformers, with for each 4 10mF capacities. Are these adequate for A UCD400 amplifier or not. In that case, what power can I expect for them on a 4 Ohms loudspeaker ?
- is a UCD 400 amplifier adequate for a peerlees XLS 10 based subwoofer ?
- why is the order impossible today on hypex website ?
Thanks for all in advance
Your transformers are more suitable for the UcD180, for maximum power for the 400 you would need 60 VDC...
The UcD400 will be great for a XLS 10" Sub...
They (Hypex) are out of modules at the moment. Jan Peter can tell you when they will be in stock again...
/Stefan
The UcD400 will be great for a XLS 10" Sub...
They (Hypex) are out of modules at the moment. Jan Peter can tell you when they will be in stock again...
/Stefan
peranders said:
I think it's absolutely gorgeous
Is this bloke running a batch of those amps ?
If so, I now understand why Hypex ran out of stock !
Thmartin...
It's my amps...
and no I did not buy all of the stock😀 😀
I'm just building 4 amps for now, 1 UcD400 and 3 UcD180...
Quad-amping my front speaker system.
But I think that I'm going to try the upgraded UcD400 when it's back in stock...
I really like the sound of them!
Stefan
It's my amps...
and no I did not buy all of the stock😀 😀
I'm just building 4 amps for now, 1 UcD400 and 3 UcD180...
Quad-amping my front speaker system.
But I think that I'm going to try the upgraded UcD400 when it's back in stock...
I really like the sound of them!
Stefan
My box, which is supposed to receive the UCD is here
http://perso.wanadoo.fr/b.hecart/images/Ampli/Construction/Taille%20r%E9elle/DSCN1906.JPG
EDIT: For the second time, make this image smaller or let it be linked. /peranders, moderator and don't remove my remark!
http://perso.wanadoo.fr/b.hecart/images/Ampli/Construction/Taille%20r%E9elle/DSCN1906.JPG
EDIT: For the second time, make this image smaller or let it be linked. /peranders, moderator and don't remove my remark!
Nice case.
However, the picture is very big and I'm sure the dial-up users would prefer something slightly smaller than 1.2 MB...
However, the picture is very big and I'm sure the dial-up users would prefer something slightly smaller than 1.2 MB...
I apologize, wanted to make a link and made a mistake
Shorter one
Hopping it will not be too big
Photos of the fabrication of the case and of the subwoofer are on
http://perso.wanadoo.fr/b.hecart/DIY
Shorter one
An externally hosted image should be here but it was not working when we last tested it.
Hopping it will not be too big
Photos of the fabrication of the case and of the subwoofer are on
http://perso.wanadoo.fr/b.hecart/DIY
OA51 said:
Hi Stefan
Congratulations !
You've done a magnificient job designing and buildind those babies. I absolutely love the wood cases and your highly skilled handcraft
This is a credit to you.I intend to build a pair of monoblocks with UCD400s to feed the lower section of my active 3 ways system. Upper and midrange drivers are fed with these little things :
http://thierry-martin.9online.fr/freres.jpg
http://thierry-martin.9online.fr/face.jpg
As you can see I lacked imagination 🙄
The UCD400 monoblocks will take place into a third "ARC look-alike" box that I'm building.
Thierry
Good evening,
(in Germany at least). Thanks to Chris and Jan-Peter for their explanations and helpful hints.
Chris, two different things were done with the 10nF cap: first connecting the outputs together by this cap. As I understood, this should synchronise the modules. Maybe for low output signals only, this would keep the distortion inside the low power level, where our listening also has restricted dynamics (don't know, if this opinion is correct).
Second was only a small test to short any switching frequency at the inputs directly, which did not function, of course.
Jan-Peter, what I did not say in my last post, above a certain level of pushing the woofer (thus introducing a voltage to the output), the whistling was completely gone. I would like to interprete that as a interference frequency of 0Hz, that means synchronised switching frequencies. This was not a serious measurement. But it could explain the absolute absence of interference in your measurements. If you drive one channel, its switching frequency will be spread because of the modulation index dependence. So you would "see" the mixing product of 2kHz only, while the input signal of the driven channel crosses the zero level. Anyway, the more then 100dB at 2kHz is a very good level, I think. If you have some time to waste, it would be nice to see a similar measurement of the crosstalk with both inputs open or "shorted" with an appropriate resistor (10k...100k). Is it possible to see a photo of your setup?
Nevertheless I should learn some more about wise audio wiring.
BTW, because my ears are additional 4 years older, maybe I'm hunting for a tinnitus?
Thanks again!
Stefan, your amps exhibit a very high WAF (womens acceptance factor), I should show your pictures to my wife.
Best regards,
Timo
(in Germany at least). Thanks to Chris and Jan-Peter for their explanations and helpful hints.
Chris, two different things were done with the 10nF cap: first connecting the outputs together by this cap. As I understood, this should synchronise the modules. Maybe for low output signals only, this would keep the distortion inside the low power level, where our listening also has restricted dynamics (don't know, if this opinion is correct).
Second was only a small test to short any switching frequency at the inputs directly, which did not function, of course.
Jan-Peter, what I did not say in my last post, above a certain level of pushing the woofer (thus introducing a voltage to the output), the whistling was completely gone. I would like to interprete that as a interference frequency of 0Hz, that means synchronised switching frequencies. This was not a serious measurement. But it could explain the absolute absence of interference in your measurements. If you drive one channel, its switching frequency will be spread because of the modulation index dependence. So you would "see" the mixing product of 2kHz only, while the input signal of the driven channel crosses the zero level. Anyway, the more then 100dB at 2kHz is a very good level, I think. If you have some time to waste, it would be nice to see a similar measurement of the crosstalk with both inputs open or "shorted" with an appropriate resistor (10k...100k). Is it possible to see a photo of your setup?
Nevertheless I should learn some more about wise audio wiring.
BTW, because my ears are additional 4 years older, maybe I'm hunting for a tinnitus?
Thanks again!
Stefan, your amps exhibit a very high WAF (womens acceptance factor), I should show your pictures to my wife.
Best regards,
Timo