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Stepped Potentiometer

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Posted on July 31, 2014 at 14:13:18
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I have a PAIR of Parasound A-23. They have channel level controls on the back. I'm curious if anyone has the schematic for these amps and if so, what the value for the potentiometer is?

My goal is to replace it with a switched resistor ladder type. That way I'll get repeatable exact levels of attenuation. Right now, I really can't use most of the preamp gain, which is a matching Parasound P5. If i turn it up to 'noon' that is pretty darn loud!

And while I AM biamping, the speaker sensitivity is very low, being Maggie Panels. I have trouble imagining this combo with more sensitive speakers!
Too much is never enough

 

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RE: Stepped Potentiometer, posted on July 31, 2014 at 16:03:55
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 You could remove the cover and measure the pot.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Stepped Potentiometer, posted on July 31, 2014 at 19:22:40
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I'm more concerned with the space inside, now that I think about it. And I don't know if 'mono' stepped attenuators are even available.

If the stock pot is say, 50k, I and many others only use it from zero to about 10k. I'd be OK with a 25k pot, since I want to get more gain out of my pre and I'd like the adjustment to be both repeatable and easily duplicated between all 4 channels = 2x stereo amps.

The pots are on the back panel, next to the blue 'things', caps or ?

I would also probably void the warranty if I cracked into the case right now.

Too much is never enough

 

RE: Stepped Potentiometer, posted on July 31, 2014 at 20:32:29
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 I would stay with the original value.

Also there doesn't seem to be a lot of room there.

Those pots are soldered to the circuit board.

If you can get mono stepped attenuators (and I think you can) that will fit, you will have to bring wires out from the circuit board to the attenuator.

I don't think you will find circuit board mount stepped attenuators.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

Where are the tubes? (nt), posted on July 31, 2014 at 22:24:45
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 nada aqui

 

RE: Stepped Potentiometer, posted on August 1, 2014 at 12:11:57
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I just knocked a quick note off to Richard Schramm asking my questions.

I'll have an answer by mid-week, next.

Thanks, Tre` for your help.
Too much is never enough

 

RE: Stepped Potentiometer, posted on August 1, 2014 at 20:16:52
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 The 'stock' part is a 100k pot. And Richard suggested replacing with 1/4watt resistors to 'fix' the value if I really think I have too much gain. And suggested it might sound SLIGHTLY better.
My preamp at 'noon' is VERY LOUD.
After reading the Stereophile test (measures) I think the P5 is good to about 7 volts, which is pretty good for a pre…..
I may adjust the gain using test tones, than after a music test, crack the case and MEASURE the pot and get some 1% resistors for test.
Do they make 1/2% or better?
Too much is never enough

 

RE: Stepped Potentiometer, posted on August 2, 2014 at 10:44:29
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 That's a good plan.

I've seen .1% resistors.

Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Stepped Potentiometer, posted on August 2, 2014 at 16:30:13
Abacus Music
Audiophile

Posts: 97
Joined: February 13, 2012
 Let me make a radical suggestion: eliminate the pot and replace your preamp with passive. Too much gain wasted in your current setup.

 

RE: Stepped Potentiometer, posted on August 14, 2014 at 00:08:00
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Plan 'B' would be to do something like:
Turn amp gains DOWN, Way Down. All of 'em.
Turn gain UP on preamp to about '2pm'. This assumes it is a 300 degree pot, which would go from 7 clockwise around to 5.
Turn gain UP on the amps until it is as loud as you can stand.
Gain on preamp will now be fine and within normal range.
Pull cover on amps and MEASURE the potentiometer. It is a 100k pot, per Richard at Parasound. Measure ALL FOUR channels. Take an average and find the nearest standard 1/4 watt resistor values which add to 100k. That is the replacement for the pot which will yield MAX gain in my system / speakers. With a little left over, just in case.
Richard said (not direct quote = paraphrase) that it was just possible the resistor solution would sound somewhat better than the potentiometer as issued. Even so-called hi-end resistors are commodity cheap. I need a total of 8 of 'em and not even any interconnect wire.

I understand that the Passive Crowd can get passionate about that approach. However, my P5 does quite a few things quite well. Tone controls for use LATE at night to provide a sort-of loudness contour. MM/MC phono input. Bass Mangement w/sub output. The ability to drive 8 foot cables TO the amps. (amps located behind each speaker, w/only 3feet of speaker cable)
and so on.
Too much is never enough

 

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