michaelgb

Are passive preamps really transparent ?

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Posted (edited)

So let me get this right. 

If I like the sound of my Dac going straight into a power amp, then adding a passive preamp should not change anything sonically ?

Looking at both the Tisbury and Schiit sys.

Edited by michaelgb

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2 hours ago, michaelgb said:

So let me get this right. 

If I like the sound of my Dac going straight into a power amp, then adding a passive preamp should not change anything sonically ?

Looking at both the Tisbury and Schiit sys.

Hi michaelgb :)

I tried direct dac volume control and also SS and tube preamps. Direct volume control gave the blackest back ground and the best clarity. The preamps added some noise and colouration of their own. With tubes being pleasantly sweet ( probably distorted )

Just on a hunch I got my first passive preamp. But yet to try it out. 

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Super Wammer

Hifi collective used to do a 'loan' system on their Glasshouse TVC's ....not sure if they still offer it but worth a look at.

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Super Dealer

I have found Music First TVC type passives to be very very close and the nearest in transparency to taking my Dave DAC direct to a power amp and using the Dave volume control. Especially the silver wound V2, the copper wound was slightly less transparent to my ears.

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Super Wammer

I made a simple passive pre, using a Alps potentiometer silver hook up wire in Teflon, and Elma rotary selector. I made it because at the time I needed 5 inputs, and passives with more than 3 were hard to come by and expensive. To my ears it is completely neutral and silent. 

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So let me get this right. 
If I like the sound of my Dac going straight into a power amp, then adding a passive preamp should not change anything sonically ?
Looking at both the Tisbury and Schiit sys.
A pre can't help if the DAC output level and impedance is suitable for the power amp input sensitivity and impedance. If it isn't it might help, might not. Some like the sound or convenience of TVC/resistive ladders &c. Others worry about the transparency of digital volume controls. For me, long ago, I realised that digi volume is sonically superior to pots/trafos and the like. But that's me. Your options are of the 'if it ain't broke' variant and the 'suck it and see' variant.

Sent from my BLA-L09 using Tapatalk

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3 minutes ago, Jazid said:

For me, long ago, I realised that digi volume is sonically superior to pots/trafos and the like. But that's me. Your options are of the 'if it ain't broke' variant and the 'suck it and see' variant. emoji4.png

As long as the digital control has enough bits, so that turning it down doesn't lose so many that it becomes audible.  Newer ones (my DAC has a 32 bit control) are generally better than older ones.

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Moderator

Like everything in hifi, the answer is 'it depends'.

On the basis that the impedance match is OK between the source and amplifier, the output level of the source is high enough and (for a resistor-based passive) cable length is reasonably short, it should be fine. Most cases where people's experience is that passives 'flatten the dynamics' or similar are a result of one or the other of the above not being ideal, or are (as in my case) that people simply like the added things an active preamp gives.

Everything in the signal path has some dort of effect, even if vanishingly small. A transformer passive is the ideal, as anything else has a greater effect of some sort. However, you then get the problem that good transformers for signal-level audio don't grow on trees.

An active here just gives me more of what I like, plus a great deal more flexibility, and allows me to use sources that would not necessarily normally be an ideal impedance match. I am more than aware that it adds something, but I'm also more than aware that I'm very happy with what it adds.

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Posted (edited)

I've fitted a simple passive pre to my lounge system, based on a Chinese remote control kit, with 4 inputs and a motorised Alps pot. Mostly for convenience because I can turn the amps on, change input and volume from my armchair, which being a lazy bastard suits me well. I honestly can't detect any difference between direct DAC to amp and going via the passive pre. YMMV.

Edited by Tony_J
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Super Wammer

@michaelgb If you are just interested in finding out before you look at buying a passive unit drop me a PM . I have a couple of passive preamps and you are welcome to borrow one to try out and see if passives are for you . Both units are very transparent to me but may not be to you . One is a stepped attenuator the other is a normal passive log pot .

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11 minutes ago, rabski said:

 A transformer passive is the ideal, as anything else has a greater effect of some sort. However, you then get the problem that good transformers for signal-level audio don't grow on trees.

Or an autoformer, something I have yet to try. I do like TVCs, though.  And DHT valve preamps!

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Depends. Some DACs reduce volume by bit stripping and do not have enough bits to give good resolution at low volumes. Others have an analogue pot in the DAC. If you have a DAC with an analogue volume control then stick with that.  Do you know how yours works?

If you are not sure or don't know then try to hear a passive. if you go for a 'pot in a box' then you need to be careful about impedance matching. Normally a CD will work OK if you keep cable lengths down to sensible lengths (1m?) and you do not have really unusal items with odd impedances.You can normally find the impedances in the DAC/amp specifications. 

If you want to use a transformer volume control then there is greater flexibility and a lot of people believe they sound better.

Sometimes it is easier to try and see what you hear.

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A pre can't help if the DAC output level and impedance is suitable for the power amp input sensitivity and impedance. If it isn't it might help, might not. Some like the sound or convenience of TVC/resistive ladders &c. Others worry about the transparency of digital volume controls. For me, long ago, I realised that digi volume is sonically superior to pots/trafos and the like. But that's me. Your options are of the 'if it ain't broke' variant and the 'suck it and see' variant.

Sent from my BLA-L09 using Tapatalk

I prefer my Glasshouse stepped attenuator (resistive) to the digital volume control in my Sabre Dac (which uses the inbuilt volume control in the chip).

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Some power amps these days have very low input impedances.  10k even.  They would probably suffer most from impedance mismatches, even with short ICs.  Valve power amps often have 100k input  impedance, but by no means all.
Mainly class D or other types too?

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