Eliminating volume pot?

losacco · 27th April 2010, 12:42 PM

I'm thinking of eliminating the 100k volume pot on this schematic but not sure what I need to change.

TheGimp · 27th April 2010, 12:52 PM

Is this a guitar amp? or designed for normal audio listening?

You can remove the pot by placing a resistor from grid to ground, then you are driving the grid directly. Not the best design. Options are add a small (10K series resistor on the input, or add a coupling cap.

What are the tubes?

Your gain going to be pretty high with the second stage cathode bypass. I'd be inclined to leave the gain pot in place.

Others are more familiar with DHTs and such stages and may have more insight.

SGregory · 27th April 2010, 12:53 PM

replace it with a 100k resistor to ground. I would consider a small grid stopper of about 1k though.

Gimp makes some valid points as well.

Psychobiker · 27th April 2010, 01:08 PM

Also, is that a pot I see under the output tube...?!

DougL · 27th April 2010, 02:57 PM

Quote:

Also, is that a pot I see under the output tube...?!

That is a common hum null pot for DHT.
I second the 100k resistor plus grid stopper.

Doug

Psychobiker · 27th April 2010, 04:12 PM

Doug,

To quash the hum from the AC heaters? Apologies, never looked at DHT before.

L

losacco · 27th April 2010, 04:14 PM

A Walton Audio design. Tubes are 5692 and 300b. I have finished one mono block. I use my computer to play mp3 and have noticed little volume increase and poor clarity from the computer source. Basically I turn volume up 100% and I get poor gain and sound quality. When I use my line stage/preamp, things sound great.

SGregory · 27th April 2010, 04:41 PM

Not sure that replacing the volume pot with a resistor will correct the above issue.

rotaspec · 28th April 2010, 02:57 AM

Quote:

Originally Posted by losacco

A Walton Audio design. Tubes are 5692 and 300b. I have finished one mono block. I use my computer to play mp3 and have noticed little volume increase and poor clarity from the computer source. Basically I turn volume up 100% and I get poor gain and sound quality. When I use my line stage/preamp, things sound great.

I don't know what computer/sound card you are using, but my Mac Mini audio output is about 1/3 the level of a typical CD player (mine also suffers from induced noise from the big LCD display, a common problem afflicting Mini's).
Either way, you are not going to solve the level problem by removing the volume pot unless the computer's expected load impedance is way higher than the pot value.
Ooh! Just had a thought! If you don't have a coupling capacitor on the amp input before the vol control, maybe the computer has some DC on the output line (and your preamp doesn't). It wouldn't take much DC getting to the amp's first stage grid to really mess things up.

alexg · 28th April 2010, 03:35 PM

Quote:

Originally Posted by losacco

A Walton Audio design. Tubes are 5692 and 300b. I have finished one mono block. I use my computer to play mp3 and have noticed little volume increase and poor clarity from the computer source. Basically I turn volume up 100% and I get poor gain and sound quality. When I use my line stage/preamp, things sound great.

Is that Walton design or Joseph Esmilla's? Can't remember now.

27th April 2010, 12:53 PM	#3
SGregory Tubie Noobie diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	replace it with a 100k resistor to ground. I would consider a small grid stopper of about 1k though. Gimp makes some valid points as well. __________________ Living Life Doing the Waltz in 4/4 meter.

27th April 2010, 01:08 PM	#4
Psychobiker diyAudio Member Join Date: Jul 2005 Location: Montréal QC	Also, is that a pot I see under the output tube...?! __________________ http://blog.liammartin.com

27th April 2010, 04:12 PM	#6
Psychobiker diyAudio Member Join Date: Jul 2005 Location: Montréal QC	Doug, To quash the hum from the AC heaters? Apologies, never looked at DHT before. L __________________ http://blog.liammartin.com

27th April 2010, 04:41 PM	#8
SGregory Tubie Noobie diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	Not sure that replacing the volume pot with a resistor will correct the above issue. __________________ Living Life Doing the Waltz in 4/4 meter.

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27th April 2010, 12:52 PM	#2
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Is this a guitar amp? or designed for normal audio listening? You can remove the pot by placing a resistor from grid to ground, then you are driving the grid directly. Not the best design. Options are add a small (10K series resistor on the input, or add a coupling cap. What are the tubes? Your gain going to be pretty high with the second stage cathode bypass. I'd be inclined to leave the gain pot in place. Others are more familiar with DHTs and such stages and may have more insight.

27th April 2010, 04:14 PM	#7
losacco diyAudio Member Join Date: Dec 2008	A Walton Audio design. Tubes are 5692 and 300b. I have finished one mono block. I use my computer to play mp3 and have noticed little volume increase and poor clarity from the computer source. Basically I turn volume up 100% and I get poor gain and sound quality. When I use my line stage/preamp, things sound great.

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