Trimpots sound better than equivalent resistors for biasing?

defect9 · 25th October 2009, 11:29 AM

I'm stumped. I used some trimpots to bias a pair of low-volt tubes (12DW8s, cathode follower) and had some awesome sound, but when replacing with an equivalent resistor, the sound goes to crap (clipping and bassfarts at a much lower level than with the trimpots). As it's a low-volt headphone amp I'm not worried about the trimpots so I'll likely just leave them there, but I'm trying to figure out what makes it so much amazingly better.

All I can think is that it's not just a resistor, but a voltage divider, and that has something to do with it.

Peter M. · 25th October 2009, 12:33 PM

You could try measuring the voltage across the resistor, and do the same across the trimpot.

peranders · 25th October 2009, 12:36 PM

Fixed resistors are always better if you want a fixed value

Gordy · 25th October 2009, 12:52 PM

It's possible that you measured the wrong part of the trim pot and hence installed the wrong value resistors. If you were using the trim pot in voltage divider mode then obviously replicate that with the fixed resistors. Replace a trim pot with exactly the same value resistors and the performance will be the same. If the performance suffers it's a measurement / installation issue, and nothing to do with "fixed vs variable resistance".

TheGimp · 25th October 2009, 02:38 PM

Difference in materia?l Carbon comp vs metal film?

Peter M. · 25th October 2009, 06:07 PM

The difference in material won`t make any difference in level before clipping.

Possibly the viper point of contact in the pot doesnt like the current, and increase resistanse value when current runs through it. So if measuring the voltage drop across the pot and across the resistor you can find out.

Sch3mat1c · 25th October 2009, 06:30 PM

I think *you* like trimpots better.

Measure it, you won't find a single difference, assuming you have indeed chosen your resistors the same.

It's all in your head. So follow your head. Don't bother trying to explain it, because there is no explanation. Likewise, disregard any who try to explain it, because they're most likely way off the mark.

Tim

P.S. Ya know what... I'm going to add that to my signature.

defect9 · 25th October 2009, 07:21 PM

I think it's gotta be that I measured it wrong or installed it wrong (which turned out to be right). Turning out to be a fun weekend if nothing else

25th October 2009, 11:29 AM	#1
defect9 diyAudio Member Join Date: Sep 2007 Location: Carson City, NV	Trimpots sound better than equivalent resistors for biasing? I'm stumped. I used some trimpots to bias a pair of low-volt tubes (12DW8s, cathode follower) and had some awesome sound, but when replacing with an equivalent resistor, the sound goes to crap (clipping and bassfarts at a much lower level than with the trimpots). As it's a low-volt headphone amp I'm not worried about the trimpots so I'll likely just leave them there, but I'm trying to figure out what makes it so much amazingly better. All I can think is that it's not just a resistor, but a voltage divider, and that has something to do with it.

25th October 2009, 12:33 PM	#2
Peter M. diyAudio Member Join Date: Jan 2005 Location: Østfold	You could try measuring the voltage across the resistor, and do the same across the trimpot. __________________ Note to myself: Never again use fingers to check if there still is voltage left in a capacitor...

25th October 2009, 12:36 PM	#3
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Fixed resistors are always better if you want a fixed value __________________ /Per-Anders (my first name) or P-A as my friends call me

25th October 2009, 06:07 PM	#6
Peter M. diyAudio Member Join Date: Jan 2005 Location: Østfold	The difference in material won`t make any difference in level before clipping. Possibly the viper point of contact in the pot doesnt like the current, and increase resistanse value when current runs through it. So if measuring the voltage drop across the pot and across the resistor you can find out. __________________ Note to myself: Never again use fingers to check if there still is voltage left in a capacitor...

25th October 2009, 06:30 PM	#7
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	I think you like trimpots better. Measure it, you won't find a single difference, assuming you have indeed chosen your resistors the same. It's all in your head. So follow your head. Don't bother trying to explain it, because there is no explanation. Likewise, disregard any who try to explain it, because they're most likely way off the mark. Tim P.S. Ya know what... I'm going to add that to my signature. __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

25th October 2009, 12:52 PM	#4
Gordy diyAudio Member Join Date: Nov 2006	It's possible that you measured the wrong part of the trim pot and hence installed the wrong value resistors. If you were using the trim pot in voltage divider mode then obviously replicate that with the fixed resistors. Replace a trim pot with exactly the same value resistors and the performance will be the same. If the performance suffers it's a measurement / installation issue, and nothing to do with "fixed vs variable resistance".

25th October 2009, 02:38 PM	#5
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Difference in materia?l Carbon comp vs metal film?

25th October 2009, 07:21 PM	#8
defect9 diyAudio Member Join Date: Sep 2007 Location: Carson City, NV	I think it's gotta be that I measured it wrong or installed it wrong (which turned out to be right). Turning out to be a fun weekend if nothing else

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Advice on trimpots.	Colescuttle	Parts	6	29th March 2009 04:37 PM
resistors and capacitor which one have the best sound ???	prorms	Solid State	28	4th March 2007 07:12 PM
T-Amp output biasing for better sound?	soundcheck	Class D	16	10th December 2006 03:12 AM
low-biasing or high biasing in Class-AB amps	Workhorse	Solid State	124	18th October 2005 04:45 AM
Dual Trimpots?	punchpeanut	Parts	1	17th June 2004 06:14 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read