[mgalusha]

This doesn't quite fit with the how and why of audio but I know some of our members like projects in progress.

A friend of mine has asked me to investigate putting his Burson Buffer in a nicer chassis along with a remote controlled volume and source selector. There are a few options available for this but the least expensive are the products from China (imagine that).

LITE Audio sells the "V-03" volume control which is a relay based stepped attenuator with 4 inputs and 100 steps. A touch over $100 on eBay or from some of the Chinese DIY sites. I had one of these I picked up in late 2005 and never got around to using, so it was the logical place to start.

With that out of the way, I present, in all it's glory, a nude preamp. <hah>











Given that it's not shielded and the PS is right next to the volume board it's surprisingly quiet and sounds quite good. Of course the upside is the SB can run at 100% so there in no potential loss of information (even though the SB does it's volume control starting at 24 bits). Great dynamics, no apparent loss of bass or other information and of course rock solid imaging since it's a stepped attenuator.

If we decide to go ahead with this I'll post photos of the case (they make quite a nice one) and other details.

Mike

[Audiovista]

Pretty cool.

Mike, how do you like the remote volume control? Are the transitions smooth (no interruptions between different settings)? How about relays clicking - is it audible from a distance?

THanks,
Boris

[Occam]

Very, very cool!   

I'm looking forward to your progress/comparison reports.

[mgalusha]

Boris & Paul,

Thanks. To answer a few questions. The volume control is quite smooth and doesn't display any nasty clicks and pops thus far. I don't think it's logarithmic but it's not too bad. The relays are noisy but once inside a case, perhaps with some absorbent material they probably wouldn't be too bad.

Jerry really wants it to be remote controlled and have multiple inputs and short of rolling my own there are not a lot of ready made options. Obviously the Chinese parts and since I had one it was just a matter of screwing it to some wood to build a test version. It actually sounds very nice behind my phono stage as well. The Burson has 6dB of gain and I have plenty of output from my phono, Scheu/Benz cart, Jensen 1:10 step ups and a Hagerman Cornnet phono pre. Of course the 6dB of gain gets the output of the SB up to a more standard ~2V output.

Another option, which we can't hear first is this from Jos van Eijndhoven. It appears to be very nicely done and my gut tells me that he spent considerably more time optimizing it than the folks at LITE Audio did. It uses 1/2 the number of relays and sounds like it operates better. The Chinese version has some quirks with the PIC. It always goes to input 2 on power up and to a volume level of -88 while the unit from Jos does as you would expect and remembers what it was last set to.

There is some cost difference but it's only about $100 and I think the money would be well spent. The only thing the LITE piece has going for it is that some sellers on eBay offer a preamp case for it that is fully cut out and would look nice. Not that we can't put the other piece into a nice case, it will simply take more time as I'll have to machine the chassis, in particular the display opening. Not a huge deal but it does take time.

Twisted Pear audio also offers a nice PIC driven log attenuator but the don't quite have the IR portion done yet and that is one of the requirements for this project.

Mike

[MaxCast]

Sounds interesting, Mike, right up my alley. 
Is this a passive design?
Anyway to stick a couple tubes in there somewhere?

[mgalusha]

Rich,

The test bed isn't passive since it's using the Burson Buffer which is a solid state buffer with 6dB of gain. You could easily use such a volume control with a tube line buffer / gain stage. It's really no different than a preamp with a nice level control. The biggest benefit is the accuracy and (hopefully) the transparency of the volume control. Any "normal" volume potentiometer uses a wiping contact on a resistive surface and they are always a little noisy in comparison to a fixed resistor/switch arrangement such as a DACT or Gold Point. The other downside to a standard pot is the channel tracking. While good ones can be quite good they can't come close to what .1% matched resistor can in terms of accuracy.

You could use something like this as a purely passive attenuator but the same problems arise as with most other passives, impedance mismatching. The one that Jos in The Netherlands sells averages about 20K output impedance, pretty high unless you are driving a high impedance device. In this case this will be somewhat mitigated by having the buffer input boards a very short distance from the level control and eliminating the need to drive cables.

Mike