Hi everybody:
I need help. I have two UCD400ST based monoblocks. My left amp has allways had two "issues": audible "tump" on power on and HF distorion (wich I thought was due to DAC or PS wiring). I have 5 other UCD amps and no one makes a "tump".
Yesterday I make measurements and I got -90mV offset from this amp (at speaker's posts). Wether source is ON or OFF makes no difference on this measured value. His sibling reads +17mV .
Both modules are stock, but DC coupled (signal input cap removed). My DAC is AC coupled (read 0V) and my "pre" is a stepdown tansformer. Reading at amp's input is at the limit of the multimeter capacity: around +/-0.3V, wich may be OV, I guess.
I have double checked the PS (and signal) wiring polarity and it's OK.
What can be wrong?
Please, any tip is welcome.
Another question I have is, what is the function of the trimmer resistor on the module PCB?
I hope it is useful to solve this offset problem 😀
Many thanks in advance.
Mauricio
I need help. I have two UCD400ST based monoblocks. My left amp has allways had two "issues": audible "tump" on power on and HF distorion (wich I thought was due to DAC or PS wiring). I have 5 other UCD amps and no one makes a "tump".
Yesterday I make measurements and I got -90mV offset from this amp (at speaker's posts). Wether source is ON or OFF makes no difference on this measured value. His sibling reads +17mV .
Both modules are stock, but DC coupled (signal input cap removed). My DAC is AC coupled (read 0V) and my "pre" is a stepdown tansformer. Reading at amp's input is at the limit of the multimeter capacity: around +/-0.3V, wich may be OV, I guess.
I have double checked the PS (and signal) wiring polarity and it's OK.
What can be wrong?
Please, any tip is welcome.
Another question I have is, what is the function of the trimmer resistor on the module PCB?
I hope it is useful to solve this offset problem 😀
Many thanks in advance.
Mauricio
maxlorenz, that pot on the main PCB for the dead time adjusting. If you want adjust DC you must do it on the modulator plugin board, which covered by compound! Maybe new versions have DC adj. pot, yet, but it's will on the modulator plugin PCB anyway.Try to ask here -Jan-Peter van Amerongen <info@hypex.nl>.
One of my ucd 180 channels has a dc offset which is not proportional to the dc input also. I think thats just the way it is.
Yeah, but mine has this HF noise and I want to make sure that this is not the cause (or one accompaning symptom) of the noise.
🙁
Thanks
M
🙁
Thanks
M
Hello there
since you mentioned removing the ac coupling caps, try re fitting them again and see if the problem (DC offset) is fixxed... if it does, its probably in the opamp buffer board...
since you mentioned removing the ac coupling caps, try re fitting them again and see if the problem (DC offset) is fixxed... if it does, its probably in the opamp buffer board...
Is it just the one module with the HF noise?
Maybe check solder connections on the entire input stage, from the signal pins to the op amp.
I have found I've totally eliminated any HF type cross talk noise. Gone. At the source like I said before, kill it before it happens, which is probably easy with the UCD's.
Take your DAC out of the equation test with something known good, that includes MP3's..
Maybe try replacing the bootstrap cap just for kicks.
Maybe check solder connections on the entire input stage, from the signal pins to the op amp.
I have found I've totally eliminated any HF type cross talk noise. Gone. At the source like I said before, kill it before it happens, which is probably easy with the UCD's.
Take your DAC out of the equation test with something known good, that includes MP3's..
Maybe try replacing the bootstrap cap just for kicks.
Update:
Last night I checked the signal input circuit: it looked OK to me. Anyway, I resoldered the signal wire to the PCB.
Chris:
I did not have a suitable exact value cap to replace the bootstrap cap. Did you hear improvement with this mod?
While I was there I tried to change the small low voltage decoupling electros near the transistors (whose exact type I can't read). I aborted because the underside of the PCB was too crowded.
Instead, I paralelled there a couple a 100nf film caps.
I remember that I bought some Black Gate N type for that task, but I used them on other project. It's funny so few appear to have tweaked that low voltage PS! Instead we all are dreaming of a dedicated external PS.
Today I think the HF improved significantly: in fact now this channel sounds opaque compared with the other one. I think it is still burning-in. DC offset is still there...🙁
Today I will try this on the other amp: Panasonic FC 47uf?/50V //Wima MKS 100nf. If it is any good I will buy some small Tantalums "á la ClassD" 😉
Appart that, I received a kind reply from Hypex 🙂
I will attack this DC problem with both backups.
Regards
M
Last night I checked the signal input circuit: it looked OK to me. Anyway, I resoldered the signal wire to the PCB.
Chris:
I did not have a suitable exact value cap to replace the bootstrap cap. Did you hear improvement with this mod?
While I was there I tried to change the small low voltage decoupling electros near the transistors (whose exact type I can't read). I aborted because the underside of the PCB was too crowded.
Instead, I paralelled there a couple a 100nf film caps.
I remember that I bought some Black Gate N type for that task, but I used them on other project. It's funny so few appear to have tweaked that low voltage PS! Instead we all are dreaming of a dedicated external PS.
Today I think the HF improved significantly: in fact now this channel sounds opaque compared with the other one. I think it is still burning-in. DC offset is still there...🙁
Today I will try this on the other amp: Panasonic FC 47uf?/50V //Wima MKS 100nf. If it is any good I will buy some small Tantalums "á la ClassD" 😉
Appart that, I received a kind reply from Hypex 🙂
I will attack this DC problem with both backups.
Regards
M
Hi,
So what did Hypex have to say on the matter?
So it's the ones closest to the transistors your messed with and wound up bypassing. There's a good chance your tweak did more harm than good. Try re opening your mind and give it a careful listen again, see if perhaps you've fooled yourself. Saying it sounds more "opaque".... like a wall of sound? That's, a bad amp, with a flattened soundstage and no imaging.
Your bypassing could have had the opposite effect desired... parasitics/resonances etc.
When you're being bothered by HF hiss it's easy to make a "tweak" that chops off the HF air/microdetail (very bad tweak) and think it's an improvement because you noticed a reduction in the hiss, but you also reduced all the good stuff in that frequency range, which makes for a very dull amp. Sounds to me like this is the trap you've fallen into.
Reconsider your tweak, look for the source of the hiss to cure it. Maybe have another look at your layout/wiring again.
Don't just jump in changing those electrolytics with low impedance ones either, for they're also there to act as dampers, being considered the equivalent of more elaborate bypass+snubbers. See Bruno's old posts around somewhere, hotrod thread maybe.
I did change the bootstrap on the 180's, I did in conjuction with the bigger decoupling caps so I can't comment on how much or little they actually do for the sound. I just thought it may be leaking a bit much perhaps causing your DC problem. I guess the same could be true for the input stage caps. How do those rails measure?
So what did Hypex have to say on the matter?
So it's the ones closest to the transistors your messed with and wound up bypassing. There's a good chance your tweak did more harm than good. Try re opening your mind and give it a careful listen again, see if perhaps you've fooled yourself. Saying it sounds more "opaque".... like a wall of sound? That's, a bad amp, with a flattened soundstage and no imaging.
Your bypassing could have had the opposite effect desired... parasitics/resonances etc.
When you're being bothered by HF hiss it's easy to make a "tweak" that chops off the HF air/microdetail (very bad tweak) and think it's an improvement because you noticed a reduction in the hiss, but you also reduced all the good stuff in that frequency range, which makes for a very dull amp. Sounds to me like this is the trap you've fallen into.
Reconsider your tweak, look for the source of the hiss to cure it. Maybe have another look at your layout/wiring again.
Don't just jump in changing those electrolytics with low impedance ones either, for they're also there to act as dampers, being considered the equivalent of more elaborate bypass+snubbers. See Bruno's old posts around somewhere, hotrod thread maybe.
I did change the bootstrap on the 180's, I did in conjuction with the bigger decoupling caps so I can't comment on how much or little they actually do for the sound. I just thought it may be leaking a bit much perhaps causing your DC problem. I guess the same could be true for the input stage caps. How do those rails measure?
My dc offsets are 1mV, 5mV, 12mV, and 31mV.
The one with 31mV measures as such even with the inputs shorted (and the inputs are connected directly to the ucd modulator). Do you think I may have damaged it in any way? I would say it still sounds fine, though its hard to pick up subtleties when the amp powers just one driver.
The one with 31mV measures as such even with the inputs shorted (and the inputs are connected directly to the ucd modulator). Do you think I may have damaged it in any way? I would say it still sounds fine, though its hard to pick up subtleties when the amp powers just one driver.
Eaaasy now. If you have a look at the data sheet you'll see they're rated at the norm of 50mV dc offset max. I wouldn't even cry with a few mV extra.
Hi Chris:
I'm always open minded 😉 and give each tweak a three day option to allow burning-in.
Sound is not opaque now but open and very detailed. I tested with some Vivaldi's string concertos.
I did the mod on the other amp and now the sound presentation is comparable, so soundstaging improved. HF is very good, bording stellar, IMHO.
I could not help myself to make a mod also on my transport so I will have to allow a few days listening for things to settle down and evaluate.
Thanks for your help and interest 🙂
M
Re-reply still pending.
Sorry, maybe I induced you to confusion. It is not the Mosfets but the ones wich I think are BDX33C/34C Darlingtons, that I'm talking about.
I'm always open minded 😉 and give each tweak a three day option to allow burning-in.
Sound is not opaque now but open and very detailed. I tested with some Vivaldi's string concertos.
I did the mod on the other amp and now the sound presentation is comparable, so soundstaging improved. HF is very good, bording stellar, IMHO.
I could not help myself to make a mod also on my transport so I will have to allow a few days listening for things to settle down and evaluate.
Thanks for your help and interest 🙂
M
Update:
I first replaced the pair of electrolytic caps for the low voltage circuit that powers the opamp with 47uF/50V Panasonic FC // 100nF film (Wima). This made the sound very clean, with little HF noise, good detail but lack of dynamics and punch. Bass was lacking also.
Then, as I am a big fun of Rubycon's and as we could not find dealers who carry 63VDC versions, I used some Rubycon ZL that i have on my project box, to replace the Panasonic//wima. They are bigger: 270uF/35v? they do not fit very well on the PCB space. One of them lies in "Pizza Tower style" now 😀
After 3 days, this is what i hear: best, deepest bass I have heard on my Tannoy Definition 500, whose bass is "acurate" (some say it's shy). The rest of the presentation is more up-front (wich is good because UCD tend to sound laid-back), with better (more energetic) detail, like hearing distinctly the bow on violins and cello. the HF noise suffered a bit. I will paralel again the little film caps and see what happens 😎
Conclusion: the input opamps deserve better power than we presently offer to them 😡
I guess we will have to take a deep breath and build some dedicated PS when time and funds allow.
Cheers
M
I first replaced the pair of electrolytic caps for the low voltage circuit that powers the opamp with 47uF/50V Panasonic FC // 100nF film (Wima). This made the sound very clean, with little HF noise, good detail but lack of dynamics and punch. Bass was lacking also.
Then, as I am a big fun of Rubycon's and as we could not find dealers who carry 63VDC versions, I used some Rubycon ZL that i have on my project box, to replace the Panasonic//wima. They are bigger: 270uF/35v? they do not fit very well on the PCB space. One of them lies in "Pizza Tower style" now 😀
After 3 days, this is what i hear: best, deepest bass I have heard on my Tannoy Definition 500, whose bass is "acurate" (some say it's shy). The rest of the presentation is more up-front (wich is good because UCD tend to sound laid-back), with better (more energetic) detail, like hearing distinctly the bow on violins and cello. the HF noise suffered a bit. I will paralel again the little film caps and see what happens 😎
Conclusion: the input opamps deserve better power than we presently offer to them 😡
I guess we will have to take a deep breath and build some dedicated PS when time and funds allow.
Cheers
M
Hi,
Paralleling film caps is very likely to make HF worse as it will further encourage resonance. The point to using electrolytics there is to use somewhat high ESR ones in order to act as an all in one bypass + snubber and damp any HF noise, key is to find one that sounds decent. Low ESR caps aren't the answer in this location unfortunately.
What you could possibly do is just use one ZL, and leave the other a cheap high ESR?
Paralleling film caps is very likely to make HF worse as it will further encourage resonance. The point to using electrolytics there is to use somewhat high ESR ones in order to act as an all in one bypass + snubber and damp any HF noise, key is to find one that sounds decent. Low ESR caps aren't the answer in this location unfortunately.
What you could possibly do is just use one ZL, and leave the other a cheap high ESR?
classd4sure said:
He meant the +/- 12V decoupling caps... I used Rubycon ZA 47uf/16V (perfect fit in there) and the sound seems to be according to what Max said.
Low ESR is no problem in that position, the next decoupling cap is a couple of cm away on those lines.
Thanks Lucpes 🙂
Yes, that was the exact cap that I wanted for me! Or was it 35VDC?
Update:
I had a recklessness attack last night and I took off the small ceramic power supply decoupling caps that are near the OPA2134, and soldered there Black Gate NX-100nF*2 in superE-cap configuration (encouraged by Klaus', AKA soundcheck, experience). I only did one module. I had to drill the PCB
It's still burning-in as you can imagine.
Lower HF noise is all I can report to date, listening monoaural my best mono CD: Bartok's second violin concerto, 1953, Menuhin-Furtwängler, EMI reissue 😎
The gentleman at Hypex offered me to take a look at my odd DC offset-module 🙂
I will make the BG mod on it anyway!
Regards
M
Yes, that was the exact cap that I wanted for me! Or was it 35VDC?
Update:
I had a recklessness attack last night and I took off the small ceramic power supply decoupling caps that are near the OPA2134, and soldered there Black Gate NX-100nF*2 in superE-cap configuration (encouraged by Klaus', AKA soundcheck, experience). I only did one module. I had to drill the PCB
It's still burning-in as you can imagine.
Lower HF noise is all I can report to date, listening monoaural my best mono CD: Bartok's second violin concerto, 1953, Menuhin-Furtwängler, EMI reissue 😎
The gentleman at Hypex offered me to take a look at my odd DC offset-module 🙂
I will make the BG mod on it anyway!
Regards
M
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