About volume control and input switching

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

Janne

ps. My first post here :)
 
Hi there Janne,
Good luck in your preamplifier. The use of a relay is a very good idea. You don´t have to worry about any stresses on the relays. The currents are so small you won´t have any problems. So don´t 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 don´t 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
Greetings
Ilias
 
volume ctrl

Hi,

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:
http://www.passlabs.com/pdf/Apserv10.pdf
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.

Thanks,
Timo
 

wessol

Member
2001-08-14 12:11 am
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.