TVC Passive preamp with Sowter TVC transformers.

[disarmamant]

Passive TVC preamp using Sowter 9335 24 step TVC transformers.

http://www.sowter.co.uk/transformer-attenuators.php

One XLR balanced input and three unbalanced RCA inputs.

One XLR balanced output and one unbalanced RCA output. Will not provide unbalanced to balanced output, balanced and unbalanced outputs cannot be used together.

Quality Elma input selector switches.

High quality volume selector switch.

Solid silver internal switch wiring.

Solid aluminium case with 8mm thick front panel.

£325 plus RMSD postage at cost.

[anubisgrau]

a nice work! probably very close to music first TVC.

[disarmamant]

Price reduced to £295

[mikeyb]

I can't decide on this or the Pass DCB1 over on PFM

[lordmortlock]

Martins Work is second to none Mike. I had a tvc he built and it was superb.

[Lawrence001]

Nice looking piece of kit, May I clarify a few points please? Are the source selectors "dual mono" mechanically linked? Is the volume selector branded? Lastly, is the balanced operation "true balanced"? Thanks

[disarmamant]

Nice looking piece of kit, May I clarify a few points please? Are the source selectors "dual mono" mechanically linked? Is the volume selector branded? Lastly, is the balanced operation "true balanced"? Thanks

The source selectors are dual mono, 2 x 6 way 2 pole Elma switches with a linking bar between the two.

They are wired so both the hot and ground side of all the inputs are switched. This is so that a balanced input and output can be achieved.

It’s not ‘true’ balanced, as that would require four transformers, but with a balanced input and output with both the hot and ground isolated by the selector switches the primary and secondaries of the transformers are floating, so it will work with a single balanced source and a single balanced output.

Take a look at the Sowter link in my original post at the application diagram near the bottom left of the page. This shows the balanced use of the transformer.

The volume selector is a copy of a Seiden type switch.


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[disarmamant]

Martins Work is second to none Mike. I had a tvc he built and it was superb.

Thanks Jake. This one uses exactly the same transformers.


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[disarmamant]

I can't decide on this or the Pass DCB1 over on PFM

You’d need to look at what your source(s) impedances are. These are 10K transformers.

The application notes say the transformer needs to be driven with a low source impedance, but works well up to 10K. The impedance of the load, or your power amp, should be as high as possible, the higher the better. I’d be aiming for 20K or more, in the case of a valve amplifier that’s not normally an issue.

If you are driving an amplifier with a low input impedance, say around 10K or less, then you’d be better off with the DCB1.


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[mikeyb]

You’d need to look at what your source(s) impedances are. These are 10K transformers.

The application notes say the transformer needs to be driven with a low source impedance, but works well up to 10K. The impedance of the load, or your power amp, should be as high as possible, the higher the better. I’d be aiming for 20K or more, in the case of a valve amplifier that’s not normally an issue.

If you are driving an amplifier with a low input impedance, say around 10K or less, then you’d be better off with the DCB1.


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Ok thanks, I think the power amp I'm looking at is 100k Ohm.

Edited impedance figure