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Old 8th June 2011, 08:34 AM   #1
Klakmuf is offline Klakmuf  Italy
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Default Quality line attenuator?

Hi, I bought a second hand power amplifier (brand is: Classic, model: 8.0b, power: 150 watt each channel on 8 Ohm) and I am looking for a simple but quality line attenuator to control the volume.
I own this device: "SM Pro Audio Nano Patch +" that I currently use to attenuate line signal that originates from the Pc (it goes to an external Dac via optical cable, then through the attenuator to powered bookshelves).
The Nano is a honest device but it is PA, and I am looking for a better quality attenuator for the main stereo equipment.
So what I ask is if you can kindly advise me about a commercial quality device that could do the work, without great expense, and/or about a related DIY project that could fit my needs.

Thanks,
Klakmuf
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Old 8th June 2011, 09:54 AM   #2
Mooly is offline Mooly  United Kingdom
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I think all you need is a simple volume control to work with line level sources.

All you need is the control, a box and some sockets. Its as simple as it gets really, and quality can be exceptional if you build it properly.

For most line level sources a 10 or 20K pot is ideal. A "logarithmic law" type is usually used although a linear will work just as well and often are better matched between the two gangs of the control.

ESP - A Better Volume Control

this suggests a 100k pot... personal choice I guess... the lower the pot the less influence stray and cable capacitance has on the high frequency roll off. Personally I would use 20k or 22k as a good all round choice and scale the resistor down accordingly.
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Old 8th June 2011, 10:24 AM   #3
Klakmuf is offline Klakmuf  Italy
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Thanks a lot for your anwer, still I don't understand if you suggest a) to build a volume control for the power amplifier or b) an attenuator for the incoming signal or if a) and b) are the same thing.
I guess what I need is some very simple instructions to build an attenuator that can lower the signal from a source (CDP, mainly).
The reason to this is that signal from my active tube preamplifier would be to high and would allow only the first fraction of the knob range, while I need a slow rising of the volume, so I thought better not to use the preamplifier and building instead an attenuator.
I will start studying the DIY materials you kindly indicated me.
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Old 8th June 2011, 11:17 AM   #4
ampmade is offline ampmade  Belgium
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Hello,

It's the same thing, the term attenuator is used for a fixed value of attenuation. The volume control is a variable attenuator.
You could also build your proper variable attenuator with some fixed values resistor and a rotary switch (i don't know if it's the good component name).

Fabrice
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Old 8th June 2011, 11:36 AM   #5
Mooly is offline Mooly  United Kingdom
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For a first attempt I would suggest something like this for the control,
OMEG|PC2G16ECO10KB|POT, DUAL GANG, LOG, 10K | CPC

this is similar but of extremely high quality,
ALPS|RK27111220K|POTENTIOMETER, 20K | CPC

If you are not used to soldering etc then I would go with the first type...

The volume control would connect between the output of the CD player and the input to the power amp... quality wise it's as good as gets as there are no active components involved or power supplies etc.

The control itself is very easy to wire. If you decide to have a go we can advise what to do.
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Old 8th June 2011, 12:19 PM   #6
Klakmuf is offline Klakmuf  Italy
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Yes, I am determined :-) I am not that good soldering but I have a skilled friend that volunteered to help.

I don't know if this device might fit:

VALAB 23 Step Attenuator Potentiometer 20K Stereo Log | eBay

It has 23 steps and this is one feature that interest me in order to slowly rise the volume, but I don't know if it has the right specs or involves a harder work to be installed. Most important thing to me is however the less possible effect on the signal quality that a attenuator might perform.
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Old 8th June 2011, 01:18 PM   #7
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An attenuator is merely a voltage divider circuit. The best is a stepped ladder attenuator, and is also the most expensive, naturally. Do a little Googling and you will find everything you need to know, and it's not very complicated.

Best, Bill
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Old 8th June 2011, 02:56 PM   #8
Klakmuf is offline Klakmuf  Italy
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I see Bill. And yes, I have in mind something very close to this Italian DIY work that use a stepped ladder attenuator:

http://www.audiocostruzioni.com/a_d/...o/image004.jpg

http://www.audiocostruzioni.com/a_d/...image005-5.jpg

I am familiar with wood working, that would not be a difficulty. I think the attenuator in picture is a stepped ladder one, and when this is correct, the K Omhs you may suggest are the same 20 as Mooly indicated?

Thanks a lot all of you
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Old 8th June 2011, 06:17 PM   #9
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Klakmuf View Post
Most important thing to me is however the less possible effect on the signal quality that a attenuator might perform.
There are advantages and disadvantages to both types. The switched type has of course the switch elements themselves as a (possible) problem and 23 steps may not be enough in practice at low levels... the pot of course is infinitely variable.

If you made a little box to put it in then providing it were large enough you could try both types.

Its up to you
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Old 8th June 2011, 07:54 PM   #10
Klakmuf is offline Klakmuf  Italy
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Right you are. When the power amplifier will be here I will make some tests with the Nano Patch at first, in the meanwhile there's a lot more about the attenuator matter that I need to study for my purposes. But also I will try not to assimilate too much information, otherwise I might get confused...
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