Help with DCB1 developing background noise with F5T and Aleph J
Ok, so I tested the hotrod dcb1 with my DAC and a topping TP20 amplifier and it works just fine. I tried it on my main system using both F5 Turbo and Aleph J amplifiers and once powered on, it is quiet, but after a couple of minutes there is this strange background noise that kicks in, it's not a hum or a buzz but more of a shhhhhhhh. I recorded it and here is a link to the audio file (can't upload it to the forum).
My setup is laptop to dac (in the same box as the DCB1 - see picture), I bypassed the opamp output of the DAC, so the R+ G and L+ G go directly to volume pot (20k) the ground are soldered together and the 2 ground pins of the pot are connected together and to the input ground. Then the 3 wires go to the DCB1 input. The output wires go to the RCA pins. The DCB1 ground (Vout) is connected to the chassis through a CL60.
Any ideas what's wrong with this setup that upsets Mr. Pass' amplifiers
BTW, the amplifiers work fine with other preamps
Many thanks
KJ123
Ok, so I tested the hotrod dcb1 with my DAC and a topping TP20 amplifier and it works just fine. I tried it on my main system using both F5 Turbo and Aleph J amplifiers and once powered on, it is quiet, but after a couple of minutes there is this strange background noise that kicks in, it's not a hum or a buzz but more of a shhhhhhhh. I recorded it and here is a link to the audio file (can't upload it to the forum).
My setup is laptop to dac (in the same box as the DCB1 - see picture), I bypassed the opamp output of the DAC, so the R+ G and L+ G go directly to volume pot (20k) the ground are soldered together and the 2 ground pins of the pot are connected together and to the input ground. Then the 3 wires go to the DCB1 input. The output wires go to the RCA pins. The DCB1 ground (Vout) is connected to the chassis through a CL60.
Any ideas what's wrong with this setup that upsets Mr. Pass' amplifiers
BTW, the amplifiers work fine with other preamps
Many thanks
KJ123
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Hmm, as far as we know from the reports here many DCB1s are mated with Pass DIY power amps successfully. A particular system thing most probably. Try disconnecting the NTC ref to chassis. If no solution, rearrange grounds as straight as you can to and from PCB without intermediate bundling. But with twisted send & return pairs all the way to each RCA, to the pot. If some hum happens after that, connect PCB GND straight to chassis this time. Maybe the interconnects are much longer in this main system setup? Try extra 220 Ohm resistors in line with RCA outs. Lets hope that no semis decided to go erratic meantime and they are fooling us. Best is to scope from DAC output onwards to make sure the hiss is not entering from outside, and to just monitor on the scope the circuit points , the rails, all changes, not to be going to the system each time for a listen. Can be coming from the rails if something changes as it warms up for instance. Weak LEDs that turned noisy, too hot setting resistors, whatever.
Are you saying that the noise exists all the time and is just not reproduced/not picked up by the T-amp or is it caused by a higher impedance amp? Sorry for the ignorant question
And one more question, the BOZ preamp I built has its pot after the buffer, the DCB1 has it at the input (between the dac and dcb1), could the pot cause the problem? Should I move it to the output?
And one more question, the BOZ preamp I built has its pot after the buffer, the DCB1 has it at the input (between the dac and dcb1), could the pot cause the problem? Should I move it to the output?
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Higher impedance can let loop area (wideness of send and return signal routing) behave better like an antenna for interference. It can also allow easier reaction if its about oscillations. Pot after the pre attenuates noise on its input along with signal. So it can enhance SNR in lower volume settings but it does the opposite thing than buffering for current. Against the DCB1's purpose if put after it in other words. See to have the metal body of the pot grounded.
So it turned out the problem was not related to the DCb1 at all. It was the output from my DAC. I am bypassing the output opamps and I used the audio out + and - right from the dac chip pins. It turned out it was not a good idea to use the chip out -, I tried the regular audio neg. after the opamp stage and it worked perfectly.
Thank you Salas for your support.
KJ
Thank you Salas for your support.
KJ
It's been a while...
I finally got around finishing my build of the Mezmerize DCB1 buffer, after only 2+ years
Had it on the breadboard for many months and then slowly began casing it up.
My board is slightly hotrodded with TO220 rectifiers, running the CCS' at about 330mA. I am also using
quite a bit of added capacitance per side with a whole bunch of 330uF capacitors paralleled in two banks
(inspired by my former pre, a tube amp from small german manufacturer Steinmusic. Fast Forward:
Steinmusic pre went to Ebay, the Mez is clearly better ) Caps are pretty much as per BOM, only C1
is only 47uF FC but snubbered as per Salas' recommendation. Output resistors are those AMRG ones..
I didn't try any others.
The volume attenuator is one from hungarian member 8thNote driven by a mono detented Alps poti and
working absolutely beautiful and supposedly very neutral!
The case is fabricated around a solid front made from morroccan Thuya wood (sort of floating on 8mm
stainless steel dowels), with two knobs turned from Delrin.
The Mezemerize is my first piece of gear sporting the Toshiba semiconductors, and lately all my other
builds are following that line... --> Dynahi and a F5 headphone amplifier.
Seems like there will be no way back.
I finally got around finishing my build of the Mezmerize DCB1 buffer, after only 2+ years
Had it on the breadboard for many months and then slowly began casing it up.
My board is slightly hotrodded with TO220 rectifiers, running the CCS' at about 330mA. I am also using
quite a bit of added capacitance per side with a whole bunch of 330uF capacitors paralleled in two banks
(inspired by my former pre, a tube amp from small german manufacturer Steinmusic. Fast Forward:
Steinmusic pre went to Ebay, the Mez is clearly better
) Caps are pretty much as per BOM, only C1 is only 47uF FC but snubbered as per Salas' recommendation. Output resistors are those AMRG ones..
I didn't try any others.
The volume attenuator is one from hungarian member 8thNote driven by a mono detented Alps poti and
working absolutely beautiful and supposedly very neutral!
The case is fabricated around a solid front made from morroccan Thuya wood (sort of floating on 8mm
stainless steel dowels), with two knobs turned from Delrin.
The Mezemerize is my first piece of gear sporting the Toshiba semiconductors, and lately all my other
builds are following that line... --> Dynahi and a F5 headphone amplifier.
Seems like there will be no way back.
Attachments
Seriously !!
Every time this Stixx guy posts photos of a new piece of gear,it is uniquely original and beautiful.
You would think he would have the decency to botch something for once and build something ugly to let some of us feel a little less inferior.
If he says it took him a few days to design and build, I'm gonna put my fist through a wall !
Sorry, overtaken by envy for a bit.....nice work...congratulations......mutter, mutter,
Every time this Stixx guy posts photos of a new piece of gear,it is uniquely original and beautiful.
You would think he would have the decency to botch something for once and build something ugly to let some of us feel a little less inferior.
If he says it took him a few days to design and build, I'm gonna put my fist through a wall !
Sorry, overtaken by envy for a bit.....nice work...congratulations......mutter, mutter,
Seriously !!
Every time this Stixx guy posts photos of a new piece of gear,it is uniquely original and beautiful.
You would think he would have the decency to botch something for once and build something ugly to let some of us feel a little less inferior.
If he says it took him a few days to design and build, I'm gonna put my fist through a wall !
Sorry, overtaken by envy for a bit.....nice work...congratulations......mutter, mutter,
I assure you his talent did not happen right out of the womb. Tons of effort and time are needed, and I am sure he has made a mistake or two.
Of course, I am much more comfortable with imperfection, and I see some systems where they run all the boards without chassis as at all, and are thrilled as heck they got something running. It's that emotion I am shooting for. I also let go of mistakes I made, not beating myself up.
Any day I am not a jerk to myself or others is a good day in my book
Oops. Sorry Tea! I should have included some smileys to indicate my indignation was not serious at all. No slight of any kind was meant.
I really admire the man's aesthetic choices and how consistently superb they are. Even the little details like floating the panels on stainless rods. For me personally, I've been trying to make enclosures that don't look like a box but I keep overdoing it, and Stixx with a few very creative flourishes makes an enclosure that's elegant and not box like at all. Hence the mock grievance.
I agree that as long as your hobby brings you happiness, it's all good.
I really admire the man's aesthetic choices and how consistently superb they are. Even the little details like floating the panels on stainless rods. For me personally, I've been trying to make enclosures that don't look like a box but I keep overdoing it, and Stixx with a few very creative flourishes makes an enclosure that's elegant and not box like at all. Hence the mock grievance.
I agree that as long as your hobby brings you happiness, it's all good.
@ppap64: You made my day
@Nick @Joel: Thank you!
Very nice way of expressing your appreciation of my stuff, be assured it means a lot to me (although I am not building my pieces of audio gear for you guys entertainment ).
As one ages (I am well in my 50ies) the projects are getting nicer and with better executed details... but then it often takes even more time and effort. I am glad that I can still
count on some resources found at work (occasional cnc stuff for instance). Even though I have bare boards making music they get cased cup nicely when long term testing shows
they 'deserve' it... the Mezmerize sure did.
Thanks again!!
@Nick @Joel: Thank you!
Very nice way of expressing your appreciation of my stuff, be assured it means a lot to me (although I am not building my pieces of audio gear for you guys entertainment
).As one ages (I am well in my 50ies) the projects are getting nicer and with better executed details... but then it often takes even more time and effort. I am glad that I can still
count on some resources found at work (occasional cnc stuff for instance). Even though I have bare boards making music they get cased cup nicely when long term testing shows
they 'deserve' it... the Mezmerize sure did.
Thanks again!!
Hi!
Just finished my 600 mA hotrodded DCB1 and started testing. The right output has a dc offset of 19 mV and the left < 1 mV. The Vout is pretty much the same (stabilizes around +/- 9,55 V with a difference of 0,01 volt between the channels) but there is a difference of about 60 mV between the voltage drop over 3,3 R between the channels.
My amplifier has capacitors in the signal path, so I don't worry too much about the offset but should I look for some other problems in the DCB1 before connecting it to the amplifier?
Thanks for a fun kit=)
Just finished my 600 mA hotrodded DCB1 and started testing. The right output has a dc offset of 19 mV and the left < 1 mV. The Vout is pretty much the same (stabilizes around +/- 9,55 V with a difference of 0,01 volt between the channels) but there is a difference of about 60 mV between the voltage drop over 3,3 R between the channels.
My amplifier has capacitors in the signal path, so I don't worry too much about the offset but should I look for some other problems in the DCB1 before connecting it to the amplifier?
Thanks for a fun kit=)
Torb, hi
Your PSUs are very well matched, and their CCS also. Got around 2V across each setting resistor and the MOSFETS warm up?
The offset is 9 out of 10 times the idss matching of the JFETS themselves. You could swap positions between the two in the higher offset pair just in case it lowers. But ask Tea for a better pair if you got them from Tea.
Your PSUs are very well matched, and their CCS also. Got around 2V across each setting resistor and the MOSFETS warm up?
The offset is 9 out of 10 times the idss matching of the JFETS themselves. You could swap positions between the two in the higher offset pair just in case it lowers. But ask Tea for a better pair if you got them from Tea.
Thanks for your quick reply! The voltage across the setting resistors is about 1,5 V with the mosfets hot, but not painful to the touch.
I will ask tea if he would sell me some more jfets then.
Thanks for this amazing kit and for sharing your work (i just built a couple of reflektor regs, super nice!)