Recommend me a preamp, please
- Thread starter Markus S
- Start date
If you have normal gain requirements then a second hand Music First TVC is possibly your best bet. They are as neutral as anything on the market, effectively 'invisible' and the transformer coupling means you get no issues with impedance matching.Because they have no electronicc parts, they are pretty wearproof. You could use one for years and lose virtually nothing.And while preferences are just that, an MFA preamp is noticably superior to an LS15 if you really do want something pretty 'invisible.'Many peopel don't...that's hi fi. Nothing wrong with a few well-chosen colorations.
Robert
Tapehead
The clatter tells audiophiles that there is something oh so special going on inside
They want stepped attenuators using discrete resistors, combined with remote control and definitely don't want any sort of chip solution which they see as bad.
So clatter clatter it is.
Tony L
Administrator
A passive attenuator is (assuming it's of a decent quality) it is entirely dependant upon it's surrounding equipment - it doesn't have a sound of it's own, only a context where it is happy or not. Any loss of dynamics would imply a mismatch somewhere else, the passive attenuator is effectively a piece of wire with a resistor in it connecting a source to a power amp. That's it. A straight wire with minus gain, to paraphrase Quad. It can't really impart any character. I understand the main symptom with passive preamps is that, in certain less than ideal situations, the top end rolls off a bit too early. I've never noticed this with mine, but in fairness I've only got ears that work to about 12-13Khz, so it may occur higher than I can assess. I have absolutely no idea what my Audio Synthesis PAS-02 sounds like, and I like that about it.
Robert
Tapehead
Top end can roll of a bit early where things aren't matched, and not all sources are happy driving a passive pot/attenuator where the loading can be closer to 1k Ohm (depending on the attenuator) than the 20k+ usually seen with active. Plus of course the load impedance is variable.
Some op amps found in line sources aren't at their best best into low loads. Not often a problem but worth a look if a passive solution appears not to work well when nothing looks amiss.
Some op amps found in line sources aren't at their best best into low loads. Not often a problem but worth a look if a passive solution appears not to work well when nothing looks amiss.
Tony / Robert, thanks to both. Am interested in your experiences and understanding this better. Have read elsewhere that a pre amp provides impedance matching between source and power amp. That it is this matching which preserves dynamics. I think this is what you're saying above.
Maybe I can ask about a specific example? Would a digital source output impedance of 10 or 20 ohms match well with a power amp that had a 18 kOhms input impedance?
Also understand the digital source 2v output would drive the power amp in terms of volume just fine.
I have also read that an output impedance to input impedance ratio of 50:1 works fine. The above easily meets that. So, what would change if I removed the NAC72 from this chain - no loss of drive and dynamics?
Maybe I can ask about a specific example? Would a digital source output impedance of 10 or 20 ohms match well with a power amp that had a 18 kOhms input impedance?
Also understand the digital source 2v output would drive the power amp in terms of volume just fine.
I have also read that an output impedance to input impedance ratio of 50:1 works fine. The above easily meets that. So, what would change if I removed the NAC72 from this chain - no loss of drive and dynamics?
Tony L
Administrator
Rob is the better one to answer as he understands the detail whereas I don't. All I can say is my current Rega DAC, which I think is 600 Ohms, has no issues at all with the Audio Synthesis passive and either a Leak Stereo 20, Quad 303, Exposure 2010 or the Musikelectronic Geithain actives downstream. Sounds great with them all. The leads are Gotham GAC 1 and 1m lengths aside from the actives, which are 5m. For some reason I really don't understand at all my Dynavector phono stage can be more temperamental and can sound a little gutless into some amps downstream, the most puzzling thing being that it seems at it's best into the MEGs, which technically should be the worst with a passive as they are only 10k input (half that of anything else). The maths / theory just doesn't play out in practice on this one, which is why I don't understand it!
anubisgrau
pfm Member
10-20 ohm source (any source) into 18k is just perfect.
can't get much better, i don't think a higher amp imp would bring anything. such a low imp sources can virtually drive any load.
can't get much better, i don't think a higher amp imp would bring anything. such a low imp sources can virtually drive any load.
martin clark
pinko bodger
An aside:
A low output impedance is always desirable from sources including pre-amps: this greatly helps shrug-off the effects of cable capacitance and the effect of input loading in what follows.
A high-ish input impedance on the driven item (preamp input or amplifier input) is desirable so it causes no extra loading on the source driving it. 10Kohms or more is a handy value; Naim uses >22K as do many others. This matters because really high quality coupling caps tend to be fairly small values and no one wants to throw away bass response unnecessarily. (A fairly standard value of 10uF output coupling cap into a 10Kohm load means bass rolls off -3dB at 1.6Hz, which is a sufficient degree of overkill for any purpose)
However - 'impedance matching' for voltage signals is a fundamental misunderstanding hanging over from the days when telephony did not include any amplifers in repeaters - i.e. pre-1920s. The idea of matching impedances for maximum power transfer persists from this root, and even people who really, really, really ought to know better (Jeff Rowland etc) go for it in a big way. It is pure waste - a 600ohm source and a 600ohm load means (1) it's a hard load to drive which usu. creates excess harmonic generation and (2) the overall result still chucks away half the signal voltage level. Just daft.
Fortunately, it's mostly nonsense. The preamp's function is control of level, low output impedance and, I think essential, a small measure of HF bandwidth limitation above the audio band to avoid upsetting whatever follows.
A low output impedance is always desirable from sources including pre-amps: this greatly helps shrug-off the effects of cable capacitance and the effect of input loading in what follows.
A high-ish input impedance on the driven item (preamp input or amplifier input) is desirable so it causes no extra loading on the source driving it. 10Kohms or more is a handy value; Naim uses >22K as do many others. This matters because really high quality coupling caps tend to be fairly small values and no one wants to throw away bass response unnecessarily. (A fairly standard value of 10uF output coupling cap into a 10Kohm load means bass rolls off -3dB at 1.6Hz, which is a sufficient degree of overkill for any purpose)
However - 'impedance matching' for voltage signals is a fundamental misunderstanding hanging over from the days when telephony did not include any amplifers in repeaters - i.e. pre-1920s. The idea of matching impedances for maximum power transfer persists from this root, and even people who really, really, really ought to know better (Jeff Rowland etc) go for it in a big way. It is pure waste - a 600ohm source and a 600ohm load means (1) it's a hard load to drive which usu. creates excess harmonic generation and (2) the overall result still chucks away half the signal voltage level. Just daft.
merlin
Avatar changed - Town names deemed offensive.
I just use phono to XLR adaptors on one set of outputs. I do the same on the Metric Halo for rips etc. Absolutely fine.
Tony L
Administrator
In my admittedly limited experience a good passive (in a scenario where it is happy) can often make even expensive active preamps sound rather hyped, coloured, grainy or slow in comparison. I'd argue that the passive adds nothing and may only subtract just a little, the active always brings something of it's own to the table - a good passive is entirely devoid of character, which is very rare for an audio component. Some will like that, some won't. Another thing is be careful of dynamics, they can be very misleading, e.g. if one preamp makes things sound fat 'fatter', 'bigger' and 'more punchy' it is almost certainly compressing the signal to some degree. I've certainly heard some tube preamps do this (more to do with specific tubes than the pre itself IME), but I'm used to studio compressors etc so I know exactly what I'm listening for in this regard. I'm not necessarily looking down on this trait either, e.g. I'd be the first to admit my Leak Stereo 20 does something similar, and I love it!
Have also read (must stop reading!) perspectives which say that an active pre preserves more of the sound than a passive pre. The argument that the latter is a misnomer. Expect this probably depends on precise implementation.
By losing the 72/HC combo I would also lose the net effect of the large trafo / caps in the HC. Whether this matters or not would anyone care to comment?
PS Apologies to the OP - hope this is at least of some interest.
By losing the 72/HC combo I would also lose the net effect of the large trafo / caps in the HC. Whether this matters or not would anyone care to comment?
PS Apologies to the OP - hope this is at least of some interest.
Tony L
Administrator
I don't think it's possible to generalise too much as not all pres of either genre are created equal plus with the passive context is everything. FWIW I'd describe a 72/HC as being fairly characterful. What power amp are you using? If Naim be wary of changing preamp as it apparently sets the safe operating parameters for the power amps of similar period (bandwidth limiting). It's a very long time since I ran a shoebox Naim pre (I had a 32.5) though I recall it sounded a hell of a lot better as a line stage with the phono stage and something else pulled out (tape buffer boards IIRC). Certainly worth a play.
Tony L
Administrator
I'd be inclined to consider it a full system and leave the pre alone in that case. Have a play with the boards though, i.e. try pulling out the phono stage if you are not using it (NA 322 or 323) and the tape buffer boards which I assume would still be called NA 324 (the 72 is pretty much a 32.5 wearing a new hat). I always felt the 32.5 sounded a fair bit cleaner and more open that way. Obviously you lose the tape out facility in the process, but who uses a tape recorder these days?! It's simple and easily reversible anyway.