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Old 11th August 2001, 08:51 PM   #1
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Join Date: Aug 2001
Location: Kouvola, Finland
Hello all DIYers!

I'm having a preamplifier project going on (I am not the only one, I guess ). At first I thought the preamp would have semiconductor input switches and volume control (MAX4662 and CS3310), but then I looked at the Pass Labs Aleph P 1.0 service manual and saw how simplified the input switching and volume control was. Now I'm re-considering my own preamp design and I have some questions:

1. What kind of relays you would use for audio switching (of what brand / model).

2. Wouldn't the relays be really stressed when used in volume controlling (especially the "LSB" relay)? Do they last? Do I have to be afraid of connection failures and "static" in the sound?

3. Hasn't the development in solid state switches made them an alternative worth considering (recent switches have on resistance something like 2.5 ohms or less)?

Thanks in advance


ps. My first post here
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Old 12th August 2001, 09:36 AM   #2
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Join Date: Jan 2001
Location: Germany
Hi there Janne,
Good luck in your preamplifier. The use of a relay is a very good idea. You donīt have to worry about any stresses on the relays. The currents are so small you wonīt have any problems. So donīt use big relays rated 5-10A. You can use ones rated at 1-2A. Try to find relays that are sealed from the enviroment like omron or siemens have . They are small in size and a few models are offered with gold or rhodium contacts for very long life. So if you find sealed relays with good contact material thats what you need.
About semiconductors, now that hard to say. They donīt seem to have the sound of simple circuits even if theoreticaly they are perfect. They are never used in high end circuits.
Anyway good luck again
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Old 12th August 2001, 01:24 PM   #3
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Join Date: Apr 2001
Location: Germany
Default volume ctrl


i find the aleph P 1.0 volume control very interesting.
It seems to be much simpler than the P 1.7's.
ADC0804 is a cheap 8-bit AD-Converter and the investment in 6 relays per channel seems reasonable.
Unfortunately the drive circuit is not shown in the service manual.
Service Manual location:
volume ctrl circuit is on page 7.
What kind of input is expected on the "Ref B" input?

How can you make this attenuator move one step up and down?

The only thing that i want is a remote controlled ladder attenuator that can do without complex control computer etc (or at least i don't want to build the control computer).
I would use a kit remote control/receiver.
Any pointers to similar projects are appreciated.

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Old 13th August 2001, 10:19 PM   #4
hifi is offline hifi  Sweden
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Join Date: Mar 2001
Location: sweden
what is not shown ?? the layout hmm ref b is from the PS thik it is 9,1 or 18,2 V from the zener stack...

if any body decides to draw a layout for the AD chip...plz mail it to me on hifi@hotbrev.com

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Old 13th August 2001, 11:20 PM   #5
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Join Date: Aug 2001
The Sutherland Engineering Preamp uses the MAX335 serial switch for switching instead of relays and for volume control uses the LM1972. The only draw back is you will have to program a microcontroller to control both.

I have been told that the "Build Your
Own High-End Audio Equipment" book, available
through Old Coloney Sound Labs has some good volume
control schematics

For what its worth.
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Old 14th August 2001, 04:52 PM   #6
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Join Date: Apr 2001
Location: Germany
Hi Micke,

Ok, only a voltage on Ref B. Fine.

And you adjust volume with what? The 100 k pot??

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Old 14th August 2001, 05:40 PM   #7
hifi is offline hifi  Sweden
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to my understandign yes...if you draw (a working) layout of the input part plz mail it to me on hifi@hotbrev.com

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Old 15th August 2001, 05:50 AM   #8
Ignite is offline Ignite  Canada
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I actually went with a high-power l-pad. It works well. Thanks for the input, everybody.
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