Sowter-based TVC

[leoduran]

Just ordered a pair of Sowter 9985's for my simple TVC:
- 3 ins (one direct), 2 outs; balanced all around
- 23-step attenuator with remote (kit from "Bent Audio")
- Optional balance control (tabs on primary windings)

The Sotwer has 26 tabs, but will be skipping 3 towards the top, to accommodate the Shallco switch in the remote kit).

I'd like to acknowledge some greats tips I received from John Chapman, at http://www.bentaudio.com/
And from Peter Daniel, at http://www.audiosector.com/

Here’s the schematic:
http://i272.photobucket.com/albums/jj163/cuernoslargos/LD-1-1.png

[Glowbug]

Don't forget to post pictures

[leoduran]

Originally Posted by Glowbug

Don't forget to post pictures

The 9985's will arrive in 4 to 6 weeks, so I look for pictures in the May time-frame.

[leoduran]

[leoduran]

Just got done drilling holes and mounting the (23-step) volume control kit:

[oshifis]

Is it possible to cascade two stepped attenuator transformers? 26 steps is too few for me, I would be more happy with ~50 steps.

[leoduran]

Originally Posted by oshifis

Is it possible to cascade two stepped attenuator transformers? 26 steps is too few for me, I would be more happy with ~50 steps.

I'm not sure I know what you mean by cascading... Is it like "Config #1" or "Config #2" on this drawing?

I suppose you'd double the steps, but I think you'd still have 2db's per step (which may not be what you're after)... But, to be honest, I'm not sure what the steps would be on "Config #1" (I'll send that question to Sowter).

[oshifis]

I mean Config #2. The tapers do not move in sync. Initially the right side taper is at the top position, and only the left side taper moves until its lowest position. Then it remains there and the right side taper moves from the top towards the bottom. Controlling the two tapers could be done by some electronic (remote) control logic.

[leoduran]

Originally Posted by oshifis

I mean Config #2. The tapers do not move in sync. Initially the right side taper is at the top position, and only the left side taper moves until its lowest position. Then it remains there and the right side taper moves from the top towards the bottom. Controlling the two tapers could be done by some electronic (remote) control logic.

Well, "Config #2" will definitely still yield 2dB's of attenuation per tab/step; are you OK with that?... You will, however, be able to double total attenuation - at the price of having to manage 2 separate knobs.

[leoduran]

Originally Posted by oshifis

I mean Config #2. The tapers do not move in sync. Initially the right side taper is at the top position, and only the left side taper moves until its lowest position. Then it remains there and the right side taper moves from the top towards the bottom. Controlling the two tapers could be done by some electronic (remote) control logic.

I just heard back from Sowter, and they said that although they can't add more tabs to a single transformer, upon request, they can make attenuation tabs at 1dB, instead of 2dB.... So, you could potentially cascade down to -50 dB, at 1dB per step, using 2 transformers per channel.