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DAC + Passive Preamp

striped67

striped67

Active Member
Still patiently waiting for the Audiolab DQ, but also weighing up my options. Frustrated with the lack of alternative DAC + Pre units in the same price range (sub £1k) has got me thinking about using a "Passive Pre".

A good example might be a Rega DAC and a Creek OBH-22, which together would come in at roughly the same price as a DQ. It ticks all the right boxes, except for a remote control for the DAC.

Anyone using a similar setup?
 
I use the Young DAC (M2Tech) into an EVA II LDR pre. It is a super solution, and I have been using a passive pre for a while. The EVA bests my old NVA P90 quite nicely and consistently in my system, which is a surprise as they are both supposed to be transparent.

The EVA uses an apple remote control, which is really handy.
 
i have an immaculate creek obh-22 for sale. it's hardly been used except for the remote, which is used , but in good condition. I used the obh-22 as a remote control for a naim 32.5 for a while.
 
M@ver1ck said:
what's a passive pre?
Click to expand...

I'm not very good with tech, but this is my understanding: A 'Passive Pre-Amplifier' is an oxymoron - it doesn't amplify anything. It attenuates the signal from the input device (CD player, or DAC in this case) before the signal reaches the power amp. Not all amplifiers like a passive pre though, because different sources have different outputs and impedances.

A passive pre, when used in a system where it really works, is very transparent as it does nothing to the signal. There is usually a source selector as well.

Hope that helps - Wikipaedia might also be useful. :)
 
Alan Brown said:
I'm not very good with tech, but this is my understanding: A 'Passive Pre-Amplifier' is an oxymoron - it doesn't amplify anything. It attenuates the signal from the input device (CD player, or DAC in this case) before the signal reaches the power amp. Not all amplifiers like a passive pre though, because different sources have different outputs and impedances.

A passive pre, when used in a system where it really works, is very transparent as it does nothing to the signal. There is usually a source selector as well.

Hope that helps - Wikipaedia might also be useful. :)
Click to expand...

There are (over simplifying) two approaches a) a simple potentiometer b) transformer coupling. At the low end you will have a) and this WILL in most cases affect the signal and can give poor results. Using b) can be very expensive indeed but can offer very good performance.

In the end I have found that the best results that I have is with no preamp in the chain rather the input devices themselves have their own very high quality pre-amplification. The Metric Halo stuff mentioned above does have this functionality. Not only is it a DAC/preamp but also an ADC so you can rip yer LPs too.

Cheers,

DV
 
Darth Vader said:
There are (over simplifying) two approaches a) a simple potentiometer b) transformer coupling. At the low end you will have a) and this WILL in most cases affect the signal and can give poor results. Using b) can be very expensive indeed but can offer very good performance.
Click to expand...

There's also 'c' a stepped attenuator passive pre, this is basically a fancy switch with resistors of different values to give the attenuation one would get from a pot. As such you end up with just a high quality resistor in the signal path at any given level, as near to 'no preamp' as it's possible to get.

I use an old Audio Synthasis PAS-02 in my second system:

4045528161_1d8c0af367_z.jpg


It's just a fancy stepped attenuator and an input selector in a box with some RCA sockets on the back.

Tony.
 
I don't think so, but they kind of look like it! The volume knob is a dual gang so you can really precisely set the level; 3db steps at the back, 0.5db at the front. Very useful as the problem with stepped attenuators IME tends to be too little adjustment, i.e. you get to choose between just too loud and just too quiet!

Tony.
 
I use a 'D' type - an LDR (Light Dependant Resistor). It is a single 'variable' resistor in the signal path, with no contact points within the actual volume control.

I like it!:)
 
Tony L said:
There's also 'c' a stepped attenuator passive pre, this is basically a fancy switch with resistors of different values to give the attenuation one would get from a pot. As such you end up with just a high quality resistor in the signal path at any given level, as near to 'no preamp' as it's possible to get.

I use an old Audio Synthasis PAS-02 in my second system:

4045528161_1d8c0af367_z.jpg


It's just a fancy stepped attenuator and an input selector in a box with some RCA sockets on the back.

Tony.
Click to expand...

Tony, I did say that I was over simplifying. I also have a stepped attenuator - its still a variable resistor but in discrete steps rather than 'analogue'. The end result is still the same.

There is no such thing as a passive pre-amp. The nearest that you can get is with a very very expensive transformer option. I still question the validity though.

Cheers,

DV
 
Alan Brown said:
I use a 'D' type - an LDR (Light Dependant Resistor). It is a single 'variable' resistor in the signal path, with no contact points within the actual volume control.

I like it!:)
Click to expand...

I was going to comment but I gave up. Whats the point when peeps have no idea............

Cheers,

DV
 
Darth Vader said:
There is no such thing as a passive pre-amp. The nearest that you can get is with a very very expensive transformer option.
Click to expand...

I agree the term 'passive preamp' is a daft one as it amplifies nothing, merely attenuates. I guess 'passive control unit' would make more sense. I'd have thought whether a transformer based solution would be better or not is purely down to individual circumstance, i.e. the loads at either side. There is a strong argument for not sending the signal down miles of thin cable after all! Theoretically a stepped attenuator should be little different than sticking a resistor of the appropriate value for your chosen listening level at either the output of the source component or input of the power amp, i.e. it is as simple a solution as is imaginable.

Tony.
 
Darth Vader said:
I was going to comment but I gave up. Whats the point when peeps have no idea............

Cheers,

DV
Click to expand...

I'm sorry DV, I don't have any idea where I lost/managed to irritate you - I started by giving a potted explanation of what I understand a passive pre to do (as well as saying I'm not too good at tech)- and I did say it amplifies nothing at all. I think I described the term 'Passive Pre Amp' as an oxymoron.

Now I'm quite prepared to admit I may be the moron here, but it seems to me we're in broad agreement?

An LDR passive control unit (Like it Tony) does the same job as any other passive pre, the only difference being what I tried to describe earlier - the lack of contacts in the signal path. I have borrowed a quote from Uriah Dailey on DIYAudioProjects, who published some instructions for building and LDR passive: "What makes this passive preamplifier interesting is that there are no contact points in the form of a "wiper" as in the case of a potentiometer or "switches" as may be with a discrete stepped attenuator." As far as I see it the obvious weakness in this approach is whether the LDRs in question are of decent quality for an audio application compared to nice resistors in a stepped atenuator - and indeed, if there is an issue there, if the alleged benefits of no contact points offsets the quality of the LDRs.

I simply wanted to help M@ver1ck with an explanation in response to his query - which seemed relevant to the original post as well. I think any more down these lines will be well and truly off topic, and we have (obviously;)) reached the limits of my technical understanding.
 
I agree the term 'passive preamp' is a daft one as it amplifies nothing, merely attenuates.
Click to expand...
OTOH it is quite possible, and in fact very sensible, to build an active preamp that has a maximum gain of 1. So no amplification, merely attenuation.... Of voltage at least.

I think 'passive pre' is actually a reasonable term. We know exactly what it means...

Paul
 
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