Passive preamp vs TVCs - please can you clarify ?

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wackyraces
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Re: Passive preamp vs TVCs - please can you clarify ?

Unread post by wackyraces »

Dr Bunsen Honeydew wrote: Mon Apr 29, 2019 6:14 pm Depends on the power amp. With NVA amps and most others NO. It depends on the input load in the power amp for the pre-amp, and cable capacitance as well which with a passive is important to keep low.. Valves always love passives (all), some transistor amps like Naim do not.

It is all marketing bullshit per usual, why do you want to read these eeediots, just borrow, loan, buy and return, use your ears with your music in your system. Why do you think these people know more than you do, they don't they just want your money. this thread is getting like Wigwam thread, there is only one answer to anything, you, your music, your room, your system, your available funds.
Thanks - I only needed clarification on this for my own education. You specialise in passive pres so I guess there's nothing simpler than using one in the audio chain without any disadvantages that are being banded around out there - good to know you chaps are there to square up the truth.

Except maybe - digital attenuation given enough 'bit' headroom - that should be as pure as it gets when it comes to altering the volume from a digital source. My Auralic Mini has a 'supposed' 64 bit software volume control option - and if I engage this, then attenuating 16 bit streams should be done losslessly in the digital domain (in theory). Only that should be better than any analogue volume control in existence.
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Re: Passive preamp vs TVCs - please can you clarify ?

Unread post by Vinyl-ant »

What a load of old shite that entire quote is.
A tvc is a transformer with a load of taps, on the primary side. turn it up or down and you add more taps or take away taps. The Series resistance and inductance is altered as you are effectively altering the coil length and inductance to change the turn ratio between the primary and secondary coils. A 1:1 transformer has a nominally equal primary and secondary, I. E. A 10 turn primary and a 10 turn secondary. It doesn't attenuate in this ratio. The taps on a tvc alter the ratio.
Output impedance remains the same as the secondary side doesn't change. That is the beneficial part, but you also form an lcr filter with the TX secondary, the cable capacitance and input capacitance of the amp, and the resistance of the secondary coil plus the cable.
There are no free lunches.

A pot is a voltage divider and shunts a proportion of the signal to either earth or the pot output. That proportion is determined by the position of the wiper in relation to either end. In the middle half goes to the output and half to earth. Turn it up, less goes to earth as there is more resistance in the earth side than the output side. Turn it down its the opposite. It doesn't convert signal to heat, an inline resistor does that and a rheostat does that.
What a load of crap
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Re: Passive preamp vs TVCs - please can you clarify ?

Unread post by Lurcher300b »

What a load of old shite that entire quote is.
Sorry but...
on the primary side
the ones I have seen have been on the secondary side, but it doesn’t matter much. And much of the same is true for ones based on autoformers.
Output impedance remains the same as the secondary side doesn't change.
Doesn't matter if the taps are on the primary or secondary, the output impedance changes as the source impedance on the other side is transformed by the square of the turns ratio, The input impedance likewise changes by the square of the turns ratio, reflecting the load impedance of what its driving.
It doesn't convert signal to heat,
All power dissipated in a resistor is converted to heat, both in the resistor between the source and the wiper. and the one from the wiper to ground. its what resistors do.

I am not offering a view on which is better, there are arguments for both, but I feel the need to correct the physics.

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Re: Passive preamp vs TVCs - please can you clarify ?

Unread post by TheMarlin »

Such nonsense. I’ve had tonnes of amps and Pre amps.

If you like the detail in the music, nothing is better than a quality passive Pre amp with quality attenuation.

I’ve had lots of big name Pre amps, two best I ever had were my Mark Levinson Cello Passive Pre amp with stepped attenuator, and my NVA Pre amp.

Powered Pre amps are signal thieves, and noise generators.
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Re: Passive preamp vs TVCs - please can you clarify ?

Unread post by Lurcher300b »

Powered Pre amps are signal thieves, and noise generators.
Possibly, but TVC's are not powered pre's

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Re: Passive preamp vs TVCs - please can you clarify ?

Unread post by Dr Bunsen Honeydew »

It is not so simplistic Marlin, there are horses for courses. Old Exposures and Naims didn't like passives, and some big muscle amps are made somewhat limp by them. It is IMO all to do with how the input stage of the power amp is configured, though I do agree with you in a majority of situations, it is just the exceptions don't prove the rule. For example (not my opinion or experience as I have none) that Krell prefers a half way house with a passive, inc a unity gain buffer stage.

God as always is your ears and your music, and it is fun process learning for yourself and not following the knob heads and brainwashed who so populate other forums.

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Re: Passive preamp vs TVCs - please can you clarify ?

Unread post by TheMarlin »

Maybe I should have said ‘with the amps I’ve experienced’... I’ve never needed monster wattage.

Where can I read up on TVC’s?
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Re: Passive preamp vs TVCs - please can you clarify ?

Unread post by Lindsayt »

Some sources don't work well with passive pre-amps.
Like the cylindrical Musical Fidelity phono stage that was a disaster with the passive pre-amp I heard it with at a bake-off. It sounded far too flat. With an active pre-amp it restored the life and dynamics to the music.

My CD players all sound fine with passive pre-amps as do my professional, radio broadcast turntables with built in phono amplification.

The Prometheus TVC that I had sounded fine in the midrange. But not so good in the bass and treble. I wondered if my professional sources were saturating it, or something?
It'd be intersting to try an MFA TVC to see how that would fare... Even though I'd struggle to justify the cost of an MFA, unless by some magic I saw one for a couple of hundred quid.

The (yeah I know highly toxic) LDR that I had, sounded fine. Very nicely transparent. Only trouble, over time the music got quieter and quieter at full volume, until eventually it was too quiet.

I never got to hear it in the same system at the same time as my NVA P50SA. But my highly provisional estimate is that the LDR was as good as the NVA at being transparent and letting the music through.

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Re: Passive preamp vs TVCs - please can you clarify ?

Unread post by Geoff.R.G »

Fretless wrote: Mon Apr 29, 2019 4:34 pm https://www.tortugaaudio.com/whats-wron ... e-control/

According to this, LDRs are better than TVCs.
If LDRs were any good camera manufacturers wouldn't have ditched CdS cells in favour of photo diodes in light meters. I can't remember when the changeover occurred but I believe around the 1970s.

If you believe the linked article, a stepped attenuator has a problem with the switch but a TVC doesn't! I find that strange because in theory one could use exactly the same switch with either resistors or a transformer. Exactly why the same mechanical characteristic has an adverse effect when used with resistors but doesn't with a transformer is beyond my comprehension. (Hint, wear in the switch will have exactly the same effect on either circuit) That it takes many years for wear to be a problem isn't mentioned.

Passive pre-amplifiers are very good as long as all the input sources have similar outputs, unfortunately my Leak Troughline tuner doesn't have sufficient output to work well with one.

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