Hi,
Read this thread with interest.
I finished recently my Mini-A (Zen Mod helped me with some gain questions).
At the time I discussed gain with Zen Mod I had only a temp PS (with only 30000uF per rail) so I obviously experienced hum but did not report it. Now I have 75000uF per rail, the hum went down, but it still there. Today in the morning (with fresh ears) I could even hear it from the listening position about 3.5m from the speakers. The speakers are pretty sensitive (95dB self brewed Troels Gravevesen's Vifa C17 d'Appolito).
My wiring is pretty much as Bengalli sketched in post #82, though I still do not have the R in CRC, so there should be no ground loops.
The other thing is the hiss. I can hear some hiss coming from the tweeter. It is definitely audible still 0.5-1m from the speaker. I should mention that I use Zetex ZVP3310 for the differential pair. I've read that the reason for this is the 9.1v zener setting reference voltage in the CCS of the differential pair (my zener by bypassed with 47nF cap following BrianGT).
Should I try to replace this zener with a different one (pretty random solution). I have seen that NP uses TL431 to set reference voltages. Would this help here? Or shall I replace it with a chain of LEDs? I do not see many people complaining about high freq noise in mini A.
The hum and his do not change regardless whether the preamp is on or off, the input is shorted or not.
Read this thread with interest.
I finished recently my Mini-A (Zen Mod helped me with some gain questions).
At the time I discussed gain with Zen Mod I had only a temp PS (with only 30000uF per rail) so I obviously experienced hum but did not report it. Now I have 75000uF per rail, the hum went down, but it still there. Today in the morning (with fresh ears) I could even hear it from the listening position about 3.5m from the speakers. The speakers are pretty sensitive (95dB self brewed Troels Gravevesen's Vifa C17 d'Appolito).
My wiring is pretty much as Bengalli sketched in post #82, though I still do not have the R in CRC, so there should be no ground loops.
The other thing is the hiss. I can hear some hiss coming from the tweeter. It is definitely audible still 0.5-1m from the speaker. I should mention that I use Zetex ZVP3310 for the differential pair. I've read that the reason for this is the 9.1v zener setting reference voltage in the CCS of the differential pair (my zener by bypassed with 47nF cap following BrianGT).
Should I try to replace this zener with a different one (pretty random solution). I have seen that NP uses TL431 to set reference voltages. Would this help here? Or shall I replace it with a chain of LEDs? I do not see many people complaining about high freq noise in mini A.
The hum and his do not change regardless whether the preamp is on or off, the input is shorted or not.
One can you can try is to run more current through the zener in question by
reducing the value of the resistor connecting the zener to ground. I'm
referring to R7 of the schematics here:
http://www.diyaudio.com/forums/attachments/pass-labs/88d1011505607-mini-mini-.zip
Cheers,
Dennis
reducing the value of the resistor connecting the zener to ground. I'm
referring to R7 of the schematics here:
http://www.diyaudio.com/forums/attachments/pass-labs/88d1011505607-mini-mini-.zip
Cheers,
Dennis
Any issues with DC offset on the output? I also used ZVP3310 but can't get my offset under control. It starts near +200mV, then wanders downward as the amp warms and settles at some -100mV. Not really hazardous to the speakers, but definitely unwanted... Perhaps my Vgs matching wasn't as good as I thought.
Hi,
These are the pictures. One is a general view of the inside.
The other one is lifted PS board. I have added some description there.
All the outputs from the PS board go to the BrianGT boards. In particular the RCA sockets grounds and the speaker terminals grounds go to the amp boards. There are no other connections to the ground.
These are the pictures. One is a general view of the inside.
The other one is lifted PS board. I have added some description there.
All the outputs from the PS board go to the BrianGT boards. In particular the RCA sockets grounds and the speaker terminals grounds go to the amp boards. There are no other connections to the ground.
Attachments
An update:
The resistors for the CRC filter have arrived. I have put 0.15Ohm for the R. So Now I have 30mF-0.15Ohm-45mF per rail. The improvement is huge. In one channel the hum is barely audible 10-15cm from the speaker. The other is somewhat louder, but still ok. Now I am probably picking up noise from somewhere. It cannot be inadequate filtering. I haven't investigated properly yet and I am not sure whether I can be bothered. We'll see.
The other issue I reported (in MY build - all issues are MY fault - not the design!) was the hiss. I suspected CSS zeners. I used some generic 1N5239 from ebay from China. Not so good as most of you would say. I ordered TL431, but I ordered also BZX55C which is not again anything special but from more legitimate source. I replaced the reference zeners with BZX55C and the hiss was gone completely. What a relief!
Since the improvement was so great I replaced also the input zeners with the new ones.
The old ones will be useful if I decide to build a noise generator.
Now I will spend some time listening!
Since the amp was open I added the bleeders in the PSU. More chance that I will come back to this site to report future progress!
The resistors for the CRC filter have arrived. I have put 0.15Ohm for the R. So Now I have 30mF-0.15Ohm-45mF per rail. The improvement is huge. In one channel the hum is barely audible 10-15cm from the speaker. The other is somewhat louder, but still ok. Now I am probably picking up noise from somewhere. It cannot be inadequate filtering. I haven't investigated properly yet and I am not sure whether I can be bothered. We'll see.
The other issue I reported (in MY build - all issues are MY fault - not the design!) was the hiss. I suspected CSS zeners. I used some generic 1N5239 from ebay from China. Not so good as most of you would say. I ordered TL431, but I ordered also BZX55C which is not again anything special but from more legitimate source. I replaced the reference zeners with BZX55C and the hiss was gone completely. What a relief!
Since the improvement was so great I replaced also the input zeners with the new ones.
The old ones will be useful if I decide to build a noise generator.
Now I will spend some time listening!
Since the amp was open I added the bleeders in the PSU. More chance that I will come back to this site to report future progress!
Last edited:
Spent sometime today to investigate the hum remaining in one channel.
I discovered that disconnecting the ground of the input of the other channel reduces this hum (but the hum in the channel with disconnected input ground goes slightly up).
The other way around disconnecting the input ground of the humming channel makes the hum slightly worse.
I have read somewhere in the forum that people indeed disconnect the input ground in one channel.
I discovered that disconnecting the ground of the input of the other channel reduces this hum (but the hum in the channel with disconnected input ground goes slightly up).
The other way around disconnecting the input ground of the humming channel makes the hum slightly worse.
I have read somewhere in the forum that people indeed disconnect the input ground in one channel.
this seems like one channel has a big loop in the return.
You MUST ensure that EACH channel has it's own two wire closely coupled pair all the way from the source to the amplifier PCB.
good.
The coax screens/shields are the Signal Returns.
Are the screens/shields connected at both ends?
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