i have the revision D board. can someone describe what to disconnect, if i want to try the amp with no negative feedback? i have it open and i just am not clever enough to figure it out...
thanks
negative feedback loop
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negative feedback loop
by nyazzip » Sat Nov 13, 2010 7:18 pm
<i>the poor craftsman blames his tools</i>
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nyazzip - KT88
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by SVinzant » Sat Nov 13, 2010 8:19 pm
I think you want to disconnect the wires that are connected to terminal strip J3 Pin 3 and terminal strip J4 Pin 3.
Tape them up so they don't accidently short out against anything.
I would also wait until you get one of the more seasoned tube guys chime in here and confirm what I think is correct.
I'm still learning this stuff and by no means an expert.
Scott
Tape them up so they don't accidently short out against anything.
I would also wait until you get one of the more seasoned tube guys chime in here and confirm what I think is correct.
I'm still learning this stuff and by no means an expert.
Scott
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by Ty_Bower » Sat Nov 13, 2010 8:36 pm
This is a Rev C board, but the connections are the same. On this amp, you're looking at the twisted pair of black/red or white/red wiring leading from the yellow and black speaker binding posts back to the board.
Feedback connected:
Feedback not connected:
Feedback connected:
Feedback not connected:
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Ty_Bower - KT88
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by nyazzip » Sat Nov 13, 2010 9:06 pm
ah thank you. i was only expecting one wire per channel, not two. also can anyone tell me what the function of adjustable resistors 30 and 31 are for? i haven't had the amp open since i assembled it 3 years ago
in playing with the bias, no amount of turning seems to affect the DMM readings on R22...it reads about 0.450vdc(yes i tried the adjacent test point to make sure i was on the right one
)...do those screws turn indefinitely or what?
this spring i smoked R17 and R26 pretty bad by using some cheap ebay tubes without a bias check. could this be my problem...?
the amp does work, for the record
thanks again
in playing with the bias, no amount of turning seems to affect the DMM readings on R22...it reads about 0.450vdc(yes i tried the adjacent test point to make sure i was on the right one
)...do those screws turn indefinitely or what?
this spring i smoked R17 and R26 pretty bad by using some cheap ebay tubes without a bias check. could this be my problem...?
the amp does work, for the record
thanks again
<i>the poor craftsman blames his tools</i>
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nyazzip - KT88
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- Joined: Wed Jan 09, 2008 1:24 am
by Ty_Bower » Sun Nov 14, 2010 7:44 am
nyazzip wrote:ah thank you. i was only expecting one wire per channel, not two.
You can leave the wire going to the black (common) speaker binding post connected. Actually, it's probably a good idea to keep the output secondary grounded even if you're not using NFB. Although with this amp (as with all UL and pentode amps) you will probably need at least a little NFB.
also can anyone tell me what the function of adjustable resistors 30 and 31 are for?
They adjust the amount of NFB you get. For example, moving the NFB connection from the 16 ohm tap to the 8 ohm tap would require adjustment. See the manual for details.
in playing with the bias, no amount of turning seems to affect the DMM readings on R22...it reads about 0.450vdc(yes i tried the adjacent test point to make sure i was on the right one
No, they only move ten turns. There is a little nylon worm gear inside and a metal spring finger that travels along it. If you reach the end, the finger will jump the track and land in the adjacent one. Be gentle with them, as excessive "fiddling" can damage the mechanism.
this spring i smoked R17 and R26 pretty bad by using some cheap ebay tubes without a bias check. could this be my problem...?
That don't sound good.
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Ty_Bower - KT88
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by nyazzip » Sun Nov 14, 2010 12:33 pm
i received a paper assembly packet with my st-35 kit, but the bulk of it is diagrams....certainly no mention of NFB loops or resistors or fun stuff regarding operation. is there a procedure/online literature for adjusting resistors 30 and 31?
<i>the poor craftsman blames his tools</i>
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nyazzip - KT88
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by Ty_Bower » Sun Nov 14, 2010 12:43 pm
The manual is here: http://www.diytube.com/phpBB2/viewtopic.php?t=837
Look on page 6, "Initial Settings: Feedback and Bias".
Look on page 6, "Initial Settings: Feedback and Bias".
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Ty_Bower - KT88
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by nyazzip » Sun Nov 14, 2010 5:26 pm
man, i have no idea how i kept missing that; i do have it in my packetr after all. so all this time i have been running the amp with random NFB resistor settings...wow
i had it all apart/disconnected last night, now i have to do it all over again...grr
i had it all apart/disconnected last night, now i have to do it all over again...grr
<i>the poor craftsman blames his tools</i>
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nyazzip - KT88
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