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
- 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
Sure thing (hopefully by May time-frame)...
The 9985's will arrive in 4 to 6 weeks, so I look for pictures in the May time-frame.
Here are some 'mock' pictures..
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Mechanical work is done..
Just got done drilling holes and mounting the (23-step) volume control kit:
Just got done drilling holes and mounting the (23-step) volume control kit:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Is it possible to cascade two stepped attenuator transformers? 26 steps is too few for me, I would be more happy with ~50 steps.
Ummh, interesting idea...
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).
I'm not sure I know what you mean by cascading... Is it like "Config #1" or "Config #2" on this drawing?
An externally hosted image should be here but it was not working when we last tested it.
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).
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 see...
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.
Actually...
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.
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... or even better 1.5 dB per steps. A buffer stage could be used between the individual transformers, if direct cascading is not possible for some reason (e.g. loading each other).
I'm staying the course...
For this go around (which I'm calling "LD-1"), I'm keeping things simple: a single transformer per channel (down to -50dB, @ 2dB/step), and no buffer stages... However, I did opt for the Sowter 1035 (which adds a +6dB tab on the primary side), in lieu of the 9985; and also went with the OCC wire option.
An externally hosted image should be here but it was not working when we last tested it.
On XLR connectors, the pin #1 is not part of the audio circuit! It is to connected directly to the chassis.
See the "Pin #1 Revisited" papers.
Audio Systems Group, Inc. Publications
See the "Pin #1 Revisited" papers.
Audio Systems Group, Inc. Publications
Pin #1 issue...
See "Ground lift in balanced connections", here:
Groundloop problem solving: Ground lift circuits
See "Isolation for balanced lines", here:
Your own audio isolator
In any event, if you look closely at the schematic, pin #1 is already connected to chassis ground on the output side, and optionally connected via the "LIFT" switch's down position, on the input side (i.e., LIFT means chassis ground "lifted" from pin#1 on the input side)... So, I think the "LIFT" option is fine, and is consistent with what I've seen on similar TVC applications.
Thanks for the link... Yep, much have been said & written about this "Pin #1" issue. For example:
See "Ground lift in balanced connections", here:
Groundloop problem solving: Ground lift circuits
See "Isolation for balanced lines", here:
Your own audio isolator
In any event, if you look closely at the schematic, pin #1 is already connected to chassis ground on the output side, and optionally connected via the "LIFT" switch's down position, on the input side (i.e., LIFT means chassis ground "lifted" from pin#1 on the input side)... So, I think the "LIFT" option is fine, and is consistent with what I've seen on similar TVC applications.
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Engraving work is done...
Engraved, to let silver show on the black-anodized aluminum. Also, notice the "red" (Sharpie) lines on the rear panel
Engraved, to let silver show on the black-anodized aluminum. Also, notice the "red" (Sharpie) lines on the rear panel
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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Transformers have arrived...
Just started soldering, and expect to be done by end of April (doing a little at a time, on spare time)... I'm anxious for a listening test!
Just started soldering, and expect to be done by end of April (doing a little at a time, on spare time)... I'm anxious for a listening test!
Done deal...sounds great!
Just finished the project on Friday night (April 30th)... It sounds clear and transparent, and I like it a lot!
Here are some parts-list revisions:
1) Volume knob (40mm dia) from AudioKit:
ManopVarie
2) TOCOS toggle switches (4PDT), and hook-up wire (solid-core silver, 23ga, cotton-wrap) from Michael Percy Audio: http://www.percyaudio.com/Catalog.pdf
Just finished the project on Friday night (April 30th)... It sounds clear and transparent, and I like it a lot!
Here are some parts-list revisions:
1) Volume knob (40mm dia) from AudioKit:
ManopVarie
2) TOCOS toggle switches (4PDT), and hook-up wire (solid-core silver, 23ga, cotton-wrap) from Michael Percy Audio: http://www.percyaudio.com/Catalog.pdf
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Update to schematic...
As shown in the updated schematic, I've added:
1) Input: Gain selector switch (0db/+6dB)
2) Output: RCA connectors & associated mode switch
3) Soft/Hard Grounding options (LIFT)
As shown in the updated schematic, I've added:
1) Input: Gain selector switch (0db/+6dB)
2) Output: RCA connectors & associated mode switch
3) Soft/Hard Grounding options (LIFT)
An externally hosted image should be here but it was not working when we last tested it.
BTW, with regards to more (50) attenuation steps...
The response I received from Sowter (back in March 2010) was:
"We can’t really increase the number of taps, but you could cascade two attenuators to get more attenuation steps, say at 1 dB per tap."
So, yes, you could get 50 (-1dB) steps with a cascaded configuration like this:
(NOTE: However, this would require 2 separate Volume "Trim" controls)
The response I received from Sowter (back in March 2010) was:
"We can’t really increase the number of taps, but you could cascade two attenuators to get more attenuation steps, say at 1 dB per tap."
So, yes, you could get 50 (-1dB) steps with a cascaded configuration like this:
(NOTE: However, this would require 2 separate Volume "Trim" controls)
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