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Old 18th December 2004, 07:18 PM   #1
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Question Volume control for tube amplifier ??

HI !!

Im buildin my firts tube amplifier and i have few questions.

I have ordered almoust all components to the amp, but one thing what i need to know is, that what kind of volume control i should use with that amplifier??

My friend told that i should use passive preamp, but what kind of potentiometer i should use??

Im planning to do fully dual mono amplifier with two separated chassis.
Both contains two 6P3C powertubes and two ECC82 pretubes.

Guy who wrote the article of that amp im buildin said that it sounds like fart of an angel =))) So i want to use pretty good components with volume control.

The volume control will be in separate chassis, so i have two monoblocks and one passive preamp.

Is that potentiometer good, what that thailand guy sells in Ebay ??


Thanks !!
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Old 18th December 2004, 09:21 PM   #2
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RadioShack, err Tandy, or whoever is local to "Tre" will work fine.

"Cheap" doesn't have to mean "sounds bad"...

Tim
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Old 18th December 2004, 11:42 PM   #3
jlsem is offline jlsem  United States
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Quote:
"Cheap" doesn't have to mean "sounds bad"...
Usually mediocre, though...
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Old 19th December 2004, 12:26 AM   #4
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Hi,

Quote:
Is that potentiometer good, what that thailand guy sells in Ebay ??
Is it a true potentiometer or a switched attenuator?

Among the better pots:

- Thel (by far the best)

-Panasonic

-Alps Black Velvet

-Some older Noble carbon track pots

Attenuators:

-Shallco

-Seiden

-Elma

Best of all mercury wetted contact reed relays.

+ good quality metal film/bulkfoil resistors.

Using a potentiometer/volume control on its own in a box between stuck between (a rock) source and amplifier (a hard place) usually isn't the best solution.

I'd recommend either a buffered volume controle or an active preamp with little or no gain but of low Zout and good current capability.

The 12B4A preamp as suggested by Brett on this forum is IMO among the best of the active examples.

Personally I have presented a buffered volume control on the forum here which seems to have some following among those that built it.

As is often the case, much of the final results will be proportional to the effort spent on getting the best out of a given circuit.

Cheers,
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Old 19th December 2004, 06:09 AM   #5
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[quote]"Cheap" doesn't have to mean "sounds bad"... [\quote]

For example those noble carbon pots.. costs next to nothing here..
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Old 19th December 2004, 12:47 PM   #6
mcs is offline mcs  Denmark
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Default Re: Volume control for tube amplifier ??

Quote:
Originally posted by hannes86
The volume control will be in separate chassis, so i have two monoblocks and one passive preamp.
If you do this, then place the three boxes very close together and use 50cm interconnects. The output impedance of a passive pre is high, so the cable capacitance can cause treble loss.

Quote:
Is that potentiometer good, what that thailand guy sells in Ebay ??
I don't feel like spending time looking for "that Thailand guy" on eBay, so why not descibe the pot better, or provide a link?

The Alps pots sound fine to me (the RK18, RK27 etc.). For some possible relay attenuator circuits, see the links below

Best regards,

Mikkel C. Simonsen
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Old 19th December 2004, 12:59 PM   #7
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I have used the Rat Shack 100K dual pot with good results. I have found very little difference between it and an Alps stepped control. I good sounding piece for less than $7.
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Old 19th December 2004, 01:15 PM   #8
Prune is offline Prune  Canada
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Some Asian guy on eBay sells from time to time fake Alps potentiometers for little money; they are not really potentiometers but cheaply made attenuators (series type). I've used one in my headphone OTL tube amp and it works fine, but others at headwize.com and head-fi.org have had worse experiences, so they probably vary in interchannel matching. It needs a big knob as the torque necessary to turn it is pretty large.

Electroswitch makes rotary switches that work for attenuators and are of good quality for a smaller price than most others, but make-before-break versions are hard to find (break-before-make can be ordered from Digikey). Check out Borbely's site for resistor recommendations.
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Old 19th December 2004, 01:47 PM   #9
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OK. Thank you all !!

With potentiometer i met stepped attenuator, but first i didn´t knew that what that was in english =)

I havent decided yet, that do i put those amplifiers in two boxes or in one box with attenuator. If attenuator causes treble loss, than i quess it better to put all in the same box. I just tought that channel separation would be better in two different boxes.

That thailand guy makes those attenuator for 50€ including shipping. What does that relay attenuator will cost that mcs gave?? I quess that components cost much, because its better to use high quality components ??
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Old 19th December 2004, 02:31 PM   #10
mcs is offline mcs  Denmark
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Quote:
Originally posted by hannes86
What does that relay attenuator will cost that mcs gave??
The small 6-relay type with control section is 43€. Is it better than the rotary switch attenuator from Thailand? I don't know

Best regards,

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