drd c3g/300b - help needed - Page 2

audiousername · 20th December 2004, 08:25 AM

Nice Work

Love the big oil cap.

garbage · 31st December 2004, 01:57 PM

hi all

thanks for the kind words regarding the chassis. this is my first attempt at building chassis from scratch (my first attempt at building tube stuff also)

did the other channel... and put in shuguang 300bsc tubes and played for an hour or so.

there is still the slight hum that i hear when i was doing my breadboard... seems it is not due to the drd choke in between the 2 psu chokes... not sure how i can reduce this hum.

the lm338 regulator for the 300b filaments seem to have been busted somehow... all of a sudden my 300b and 83 were glowing.. i rushed to switch off both the supply... not sure why both channels died at the same time. the lm338 is mounted to a large heatsink somemore...

now am using dc but not regulated on the 300b filaments... using them via dropping resistors of 1R each on pins 1 and 4 of the 300b to get abt 5.2v - 5.3v. but one channel only... cos no more 1R. need to get some on monday. can't wait to listen to stereo again.

when there was stereo, the soundstage is slightly forward, bass is tight, vocals sweet, highs with sparkle but not overly bright. driving my totem to levels loud enough for my smallish room.

here's a pic of the amp with the tubes all in, but both side panels opened bcos of troubleshooting.

cheers
garbage

garbage · 5th January 2005, 12:00 PM

after putting in the 1R resistors for the other channel's 300b filaments

with an intent listener staring at the speakers

night view, lights out

bobhayes · 1st February 2005, 06:35 AM

Do you still have hum problems?

I see that you have two identical mono blocks, and assuming the hum problem remains in both, from breadboarding to final assembly, I can only think that after trying all your previous remedies, that it might be ground loop induced.

Where is the audio source coming from to your amps?

If your amps are earthed to chassis, and the chassis is the 0v of the circuit, and the source audio device (dac or preamp etc) is also built similarly and earthed, then the RCA leads complete a ground loop circuit which acts like a dirty great bit antenna, picking up all sorts of nasty noise, especially ac hum.

Try connecting an signal lead from the source to the amp but disconnecting the wire screening from ONE of the RCA plugs, or just leave the plug partially out of the socket so as the outer cylinder is not in contact.

Its a long shot mind you.

audiousername · 1st February 2005, 06:42 AM

Quote:

Originally posted by bobhayes
Do you still have hum problems?

He still does. There are some posts about it in this thread.

garbage · 1st February 2005, 11:33 AM

Quote:

Originally posted by bobhayes

If your amps are earthed to chassis, and the chassis is the 0v of the circuit, and the source audio device (dac or preamp etc) is also built similarly and earthed, then the RCA leads complete a ground loop circuit which acts like a dirty great bit antenna, picking up all sorts of nasty noise, especially ac hum.

Try connecting an signal lead from the source to the amp but disconnecting the wire screening from ONE of the RCA plugs, or just leave the plug partially out of the socket so as the outer cylinder is not in contact.

Its a long shot mind you.

anything's worth a try...

my chassis is not at 0v of the circuit. seems like i have some problem when doing so.

i just tried to switch the amp on without a signal at one of them. it hums louder.

5th January 2005, 12:00 PM	#13
garbage diyAudio Member Join Date: Apr 2004 Location: Singapore	a couple more pics after putting in the 1R resistors for the other channel's 300b filaments with an intent listener staring at the speakers night view, lights out

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20th December 2004, 08:25 AM	#11
audiousername diyAudio Member Join Date: Jul 2004 Location: Melbourne, Victoria	Nice Work Love the big oil cap.

31st December 2004, 01:57 PM	#12
garbage diyAudio Member Join Date: Apr 2004 Location: Singapore	hi all thanks for the kind words regarding the chassis. this is my first attempt at building chassis from scratch (my first attempt at building tube stuff also) did the other channel... and put in shuguang 300bsc tubes and played for an hour or so. there is still the slight hum that i hear when i was doing my breadboard... seems it is not due to the drd choke in between the 2 psu chokes... not sure how i can reduce this hum. the lm338 regulator for the 300b filaments seem to have been busted somehow... all of a sudden my 300b and 83 were glowing.. i rushed to switch off both the supply... not sure why both channels died at the same time. the lm338 is mounted to a large heatsink somemore... now am using dc but not regulated on the 300b filaments... using them via dropping resistors of 1R each on pins 1 and 4 of the 300b to get abt 5.2v - 5.3v. but one channel only... cos no more 1R. need to get some on monday. can't wait to listen to stereo again. when there was stereo, the soundstage is slightly forward, bass is tight, vocals sweet, highs with sparkle but not overly bright. driving my totem to levels loud enough for my smallish room. here's a pic of the amp with the tubes all in, but both side panels opened bcos of troubleshooting. cheers garbage

1st February 2005, 06:35 AM	#14
bobhayes diyAudio Member Join Date: Sep 2004 Location: Bungawalbyn, NSW	Do you still have hum problems? I see that you have two identical mono blocks, and assuming the hum problem remains in both, from breadboarding to final assembly, I can only think that after trying all your previous remedies, that it might be ground loop induced. Where is the audio source coming from to your amps? If your amps are earthed to chassis, and the chassis is the 0v of the circuit, and the source audio device (dac or preamp etc) is also built similarly and earthed, then the RCA leads complete a ground loop circuit which acts like a dirty great bit antenna, picking up all sorts of nasty noise, especially ac hum. Try connecting an signal lead from the source to the amp but disconnecting the wire screening from ONE of the RCA plugs, or just leave the plug partially out of the socket so as the outer cylinder is not in contact. Its a long shot mind you.