[Zyca]

http://www.youtube.com/watch?v=tLKE4rUqMWU

Anyone interested in the Stepped attenuator shown in the URL above?

This kit is from KECES as well, and I'm thinking about offering it as a almost completed board, with everything except the volume resistor soldered.

The basic spec of the attenuator is as follows:

Input impedance varies from 10K to 20K, well within the comfort zone of most source and OP Amps.

Type B curve, but with 64 steps, it is not going to be to hard to find the right volume for most listeners, unlike 23 step attenuators.

Max output is 1/2 input VRMS, max handling input voltage is 70VRMS (Resistor used is capable of handling 1/2W, 1/2W @ 10K ohm means that you need 70VRMS input to reach 1/2W), but let's try not to do that.

Signal does not pass through the relays, as relay acts as shunts to ground, signal only passed through a resistor and then promptly wired to the output.

Since this is based on an ADC reading off the control pot, one must understand that there IS a possibility of setting the pot right between two steps, and thus causing the relay to literally "chatter", this can be solved by turning the relay just one hair to either side.  But this does not happen often unless one really tried to make it happen.


I'm thinking about offering it as an ALMOST completed kit, with only the volume resistor not soldered, so you can use whatever exotic resistor you prefer, or you can use the supplied 1% precision resistor.  A companion transformer (it won't be like the one in the video, it is way too much an overkill) will also be supplied in the kit to power the relay and ICs on the board.



I'm shooting for a target price of $50 USD plus shipping ($20USD or less anywhere in the world), is anyone interested in such things?  I'm thinking this can be perfect for modding your pre/headphone amp/integrated amp, or any new projects that needs a volume pot.

[Audiovista]

Cool video! I could not see the transformer you mentioned 

Are there ways to eliminate relay chatter? If you're using a microcontroller, that could be possible?

Well, you'll see what others say. The price certainly seems reasonable.

Boris

[JohnR]

Seems interesting... how many channels in the one module? Can they be ganged together? (to get, say, six channels)

[Zyca]

The relay chatter is not avoidable in this current design, even if we used a microcontroller with this design, which we didn't.



I forgot to mention that there's two channel per board, or one balanced channel per board.

you can easily gang up a bunch of the board together, I'm not sure if you can see a few through hole soldering points next to the IC, that's the control signals.  Just have one board act as MASTER with all the parts on it, and remove the IC from other boards to make them act as slave.  Each relay is driven by a transistor with high HFE, thus connecting a bunch of them together is not going to cause a lot of problem.  However, we have not tried to hook up much of them together, so we cannot say how many exactly is the max, but 6 boards is definitely withing reachable target.


The transformer is not in the pics, we are getting it from our supplier soon.  It will be 100~120V/200~240V selectable, so wiring it up properly and it should be easy to use it to build a pre or mod something with it.

[Mike B.]

There are a number of this type kit available from sources like DIYClub. The major concern for audiophiles seems to be the effect of the relay on the sound. Have you compared your unit to a discrete resistor rotary attenuator?

[Zyca]

There are a number of this type kit available from sources like DIYClub. The major concern for audiophiles seems to be the effect of the relay on the sound. Have you compared your unit to a discrete resistor rotary attenuator?

We have designed this unit so that the relay is NOT in the signal path, they are only used for connection to ground, the analog signal passed through a 10K fixed resistor, and the relay connects after that, shunting the desired amount of power into ground.  And thus creating a voltage divider.

I would say that the simplest advantage is that we have much more steps than rotary attenuator, and that we do not have any switches and contacts in the signal path, we try to keep as little "stuff" in the signal path as possible.

[KBK]

So..it is a relay enacted/controlled 64-step shunt volume. Very nice.

Just the way I'd do it myself.