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Old 6th May 2009, 09:27 PM   #1
louie 3 is offline louie 3  United States
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Unhappy transformer volume control (TVC)

I have a Chinese built transformer volume control on trial.

It is typical Chinese gear, very nice case, well made.

But....it has way, like way, too much gain for my normal amps (Classe' DR8 mono blocks)

Even with an XM radio tuner turned almost off, all I can do is raise the volume one click (3db).

I can't imagine a system with low enough sensitivity to allow using this.

What gives? A mistake?

Finally got it to work with a small tube amp with much less input sensitivity, sounds absolutely gorgeous, but useless.
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Old 6th May 2009, 09:35 PM   #2
udailey is offline udailey  United States
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The output impedance of a preamp is very important in the amp you are driving. The amp you are hooking it up to is obviously a bad match for it and it will work great with tubes. Preamps wont drive everything, just certain things.
What amp are you trying to drive with it?
Uriah

edit; Oh, you mentioned the Classe'. If those are solid state then it sounds like you have a great pre for driving tubes only.
Popular passive pot output impedances are 10k, 25k, 50k, 100k, 250k.
You would use 100k and 250k for tubes almost exclusively.
I drive LM3886 SS Chip amps with 25k and 50k, and I drive a MyRefC with about 10k.
So you need to find out the output impedance of the pre then you can know better what to drive with it. Then you will need a great passive for the SS but you will have to know its input impedance.
Uriah
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Old 6th May 2009, 09:42 PM   #3
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A TVC has no gain -- it's an attenuator. If you have too much gain, then it means that there is a mismatch between your source and your power amps. Fixing that is where you should focus your energy.
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Old 6th May 2009, 09:48 PM   #4
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Quote:
Originally posted by dsavitsk
A TVC has no gain --
Well, S&B TX 102 can be wired for 6dB gain.
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Old 6th May 2009, 09:56 PM   #5
udailey is offline udailey  United States
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I am betting its the TVC thats mismatched. He has probably been using the same source and amp for some time before getting this TVC.
Doesnt that make sense or is there something I am missing about impedance matching? Its a question not a challenge.
Uriah
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Old 6th May 2009, 10:06 PM   #6
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Quote:
Originally posted by Peter Daniel


Well, S&B TX 102 can be wired for 6dB gain.
Yes, as can many of them. But, unless he has it hooked up incorrectly, it does not seem likely that this is the issue.


Quote:
Originally posted by udailey
I am betting its the TVC thats mismatched. He has probably been using the same source and amp for some time before getting this TVC.
Doesnt that make sense or is there something I am missing about impedance matching? Its a question not a challenge.
Uriah
I think you are missing something. This is a voltage issue, not an impedance issue.

Unless it is set to a 6db increae as Peter mentions, the Zout of a TVC is always lower than the Zout of the driving stage. The Zin of the power amp is likely similar to the Zin of the former preamp. So, if his source could drive the preamp, it can drive the power amp, too.
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Old 6th May 2009, 10:24 PM   #7
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Too much gain from a TVC does not sound right. Even if it provides a +6db position. More info is needed. How many positions? What attenuation range? Pictures? Links?

Most active preamps will provide more gain anyway.
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Old 6th May 2009, 10:29 PM   #8
louie 3 is offline louie 3  United States
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Default Classe' impedance

In stereo mode, the input impedance of the DR 8 is 70K ohms, suspect it changes fairly significantly in mono, but can find no specs....it is definitely about 10 db more sensitive to input when in mono.

The tube amp is a Dyna St 35 Clone, input impedance is typically 470K ohms.

But....even with the ST 35 Clone, I could only get one click, so something is going on here I don't understand.

People rave about these TVC's, maybe this one is wired wrong or something?
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Old 6th May 2009, 11:17 PM   #9
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The input impedance has nothing to do with this. Whether it is 10K or 1000K, it will make little difference (you can prove this to yourself my putting a 10K resistor from input to ground of the dynaco, lowering the input Z to under 10K, and seeing what happens. What will happen is, in terms of volume, not much). The issue is the gain (sensitivity) of the power amp.

Download a 60Hz tone, play it through your source. Use your multimeter set to AC volts to measure the voltage on the output of your source. Then, connect your old preamp, set it to the volume you liked, and measure the AC volts on its output. Try this with the TVC and see what it's voltage is -- it will be higher, though maybe only by a small amount. The issue is that the TVC does not attenuate as much as your old preamp, and that your source has too high of an output for the combination of the TVC with your power amp.
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Old 6th May 2009, 11:44 PM   #10
tinitus is offline tinitus  Europe
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I must admit that after reading how much people are fiddling with their Intact trafos, and changing the sound significantly, I have completely lost interest
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