View Full Version : Which pre amps do the least damage?
Last night I found myself reading round the HiFi critic forum and noted comments by Martin Colloms regarding passive pre amps. His opinion is that unless you can afford a really good pre amp then passives often do less 'damage' to the signal than most active pre amps. It's an interesting point which I'm sure Richard from NVA would support.
In my own home system ditching the pre amp when I bought the Wadia CD player ( feeds the power amps directly) was a step forwards in terms of clarity and system dynamics - I wouldn't care to go back.
So my challenge is this: if you prefer the sound of your active pre amp to a passive in your system do you prefer it because it provides a higher fidelity signal to your power amp or just because it makes the system sound 'better' ie you prefer the sound so created regardless of how the signal is being manipulated or 'damaged' as MC would have it?
Leading on from the above is your system all about high fidelity to the original source or creating a musically satisfying sound you like? Are the two different things?
Covenant
27-08-2011, 15:41
I shall follow this thread with interest. I use a Beresford dac as a pre-amp and a Croft power amp. I am tempted to get a pre-amp but wonder if it will simply offer a different presentation rather than a genuine improvement. Perhaps I should just borrow one!
The 'less is more' argument is convincing.
MC did also mention the need for short-ish interconnects on passive systems. 1m is fine though he suggested he'd seen up to 3m work in some circumstances.
Martin Colloms is living in cloud cuckoo land of he's suggesting a "good" preamp is going to cost loads. What planet does he live on - don't answer that, he has his reputation as Top End Guru to consider with his silly numerical scores...
IMO, all you need is a line buffer with enough current and a low enough output impedance to be able to drive either low input impedance input amps, and/or long lengths of interconnect. It's my belief that these requirements can be met for very little money these days and all the rest is bling/male jewellery!!!!! The case won't be flashy, but the money will go on the innards instead, where it's needed.
I thought one reason for the Gator mod was to beef up the output stage to enable the caiman's use as a preamp? PLEASE put me straight Stan if I'm wrong.
Darren, I don't know your power amps, but of the input impedance is around 50K or higher, you may be able to safely use a passive preamp as long as the cables are the lowest capacitance you can find and very short in length (some of the better RF coax cables may be ideal for this and are very cheap if you're good at soldering). I think the thing with active preamps these days is to keep them as simple as possible. The Croft Micro Basic is a wonderful commercial starting point I think, as will this, if you have remote power amps -
http://spl.info/index.php?id=184&L=1
http://i132.photobucket.com/albums/q8/DSJR_photos/volume2_315x225.jpg
I think it's around £250 tops. - edit - looks like £300
For balanced sources, one of the best is this : http://www.thomann.de/gb/spl_2control_black_b_stock.htm
Personally I don't like volume controls, too many things to think of (impedance, cables etc) I prefer a good preamp. ;)
A friend had both (the 2volume and the 2control), he ended up keeping the 2control.
jandl100
28-08-2011, 07:18
Passive and active pre-amps have a different sort of presentation.
Which will "sound best" will depend on your taste and how they interact with the rest of the system.
IME active pre's can have more drive and oomph, but can lose out on the transparency available from a good passive.
But that is far from a general rule - I've heard passive pre's which are quite cloudy sounding, and actives which are impressively transparent.
Also, if you have inefficient speakers, you may need the signal gain from an active pre to get the in-room volume levels you want.
I have inefficient speakers these days (83dB/W) so I need the gain from an active pre ... and I tend to prefer the extra presence, power and grip in the mid and lower freqs that a good active pre can provide as well.
......
As an aside, I'm always puzzled by folks who say that using a DAC or CDP with a built-in volume control is in some way avoiding the use of a pre-amp.
A pre-amp is a volume control of some kind, and usually an input selector switch.
If you have a DAC/CDP with onboard volume control/switching then the pre-amp is still there, it's just in the same box as the CD/digital components.
At least, that's the way I look at it. :)
Jerry, what you're describing may well be an impedance mismatch I suspect. Maybe one of our resident engineers could elaborate.
A number of the simpler integrated amps out there are basically a power amp fed by a volume control and input switch and I seem to remember that NVA amps have an input circuit especially designed for a passive style preamp source. On the other hand, the AVI preamp I use has relay switching to the volume control, which feeds a Class A line driver of very low output impedance and, in my opinion, it sounds best actually driving long interconnects (since many of them were sold with ATC actives in the mid to late 90's, just the job).
Covenant
28-08-2011, 11:30
......
As an aside, I'm always puzzled by folks who say that using a DAC or CDP with a built-in volume control is in some way avoiding the use of a pre-amp.
A pre-amp is a volume control of some kind, and usually an input selector switch.
If you have a DAC/CDP with onboard volume control/switching then the pre-amp is still there, it's just in the same box as the CD/digital components.
At least, that's the way I look at it. :)[/QUOTE]
But the Beresford gives you the opportunity to feed a pre-amp directly, avoiding the volume control.
Hi DSJR,
I don't want to be cast into the Roll of Colloms defender but I'm not sure he does suggest that you have to spend fortunes on a pre amp. It's more that a passive will pound for pound spent be more transparent than an active pre amp?
Hi Jerry,
C'mon you as an ex Wadia owner will know that the volume control is digital and and that no switching or analogue processing is involved.
No point in feeding this through another set of interconnects to an active pre amp, through it's gain stages and then on to the power amp is there?
Hi DSJR, I don't need a pre amp for my home system at all the Wadia drives both my power amps really well. I'm just interested in MCs remarks..... You'd have to admit that he's heard a lot of kit( I know you have too!)
Well, I have experience of true passive pre-amps (just a switch and a volume control), buffer stages (no added gain), transformer coupled passive pre-amps and active pre-amps. In my experience, passive pre-amps and buffer stages significantly limit the dynamic performance of the system - transformer coupled pre-amps, and active pre-amps, seem to be much better in this regard. However, as always, system matching plays a huge role. I think it is true that passive amps can be more transparent, but they can also be very much less dynamic (surely this is part of system transparency). My idea of system transparency does not mean that you should feel as though you are listening from the bar.
I agree, there's nothing worse than a weedy, opaque sounding, passive preamp that you have to turn up nearly all the way in order to obtain any sense of scale or dynamics from your system! :nono:
Quality transformer-coupled passive preamps (such as those from Music First) are the only passive preamps I could live with, otherwise give me a quality active (valve) preamp, any day, with oodles of useful gain (but not too much - there is a sweet spot to be had), so that the sound obtained from your system has plenty of balls, drive, dynamics and impact!! :fingers: :hairmetal:
And I say that even though I use huge 95db efficient speakers, driven by 50W of Pure Class A valve power, so I'm not exactly lacking in the system power or sensitivity stakes.....! ;)
Marco.
Spectral Morn
28-08-2011, 12:23
Hi Jerry,
C'mon you as an ex Wadia owner will know that the volume control is digital and and that no switching or analogue processing is involved.
No point in feeding this through another set of interconnects to an active pre amp, through it's gain stages and then on to the power amp is there?
My own experience with Wadias such as the 861s are that you had to adjust the internal settings to maximise the amount of adjustment on the volume control. If you had very little adjustment you lost resolution. Personally though having used a Wadia direct into several power amplifiers even with very good volume control (near ideal) I much preferred the sound with a good active pre in the system.
Regards D S D L
Spectral Morn
28-08-2011, 12:24
I agree, there's nothing worse than a weedy, opaque sounding, passive preamp that you have to turn up nearly all the way in order to obtain any sense of scale or dynamics from your system! :nono:
Quality transformer-coupled passive preamps (such as those from Music First) are the only passive preamps I could live with, otherwise give me a quality active (valve) preamp, any day, with oodles of useful gain (but not too much -there is a sweet spot to be had), so that the sound obtained from your system has plenty of balls, drive, dynamics and impact!! :fingers: :hairmetal:
And I say that even though I use huge 95db efficient speakers, driven by 50W of Pure Class A valve power, so I'm not exactly lacking in the system power or sensitivity stakes.....! ;)
Marco.
Hi Marco
I agree with that, Transformer passive magnetic is the only way to go re passives.
Regards D S D L
I agree. I believe Hi-Fi Critic are comparing some transformer passive pre-amps in their next issue.
Truly passive (pot and stepped attenuator) is only really viable where the following situations apply:
- The source output is high (>2v) and the source output impedance is both low and able to drive a low impedance load cleanly with low distortion. Tubes often won't do this, and nor will some op amps which deteriorate markedly as loading impedance falls.
- The power amplifier has high input impedance (typically >50k Ohms). Many valve amplifiers do and also have high sensitivity which helps.
- Low capacitance is a must on both cables and load. No more than a couple of hundred pf.
Satisfy those criteria and truly passive can be superb, as in 'disappears' form the chain.
Put passive into an inappropriate circuit and you get the sound Marco rightly describes. TVC can help in that situation but brings other problems to the party.
I don't agree with Martin Colloms on the need to spend large sums to get a transparent pre. Good active is easy enough to implement around a couple of high performance op amps, or with tubes.
I'm not convinced with regard to the op-amp option.
Someone I know used an Audio Synthesis Passion passive pre-amp for many years (into valve power amps). In the end he concluded that it was just too sensitive to the interconnects and that an active pre-amp west just more dynamic - which is what he now uses (it still sounds pretty polite to me).
I know I'm going against the grain here, but I still feel it's ALL measurable, with no foo whatsoever involved, apart from perhaps knowing how to read and interpret the results...
Transformers can't add anything from mid-air, only transform volts into current at less voltage or vice-versa? If the output of the source allows this, then fine :)
IC op-amps work if properly implemented I think, but I reckon you need to know what you're doing if you're not going to throw baby out with bath-water.
Rob is spot on above. Valve gear with high input impedance and reasonable sensitivity should be fine with passive pre's and I believe this extra sensitivity is what NVA use, as well as the old Quad 303 and 405 designs, the latter offering high sensitivity and a reasonable 50k+ input impedance.
Before I sink without trace, I should add in the MC discussion that yes of course, he's reviewed most of the really important stuff (and profitably "consulted" on a lot of it too - cough - ) over the last 35 years or so (wasn't he the reviewer "Hugh Ford" in an early life, or was this Gordon J King?), but he has to play to his top end market "living" and this market wouldn't take him seriously if he suddenly found a £400 preamp that in most respects beats an ARC Reference pre at £10K (it probably would in all if it was stuffed with Clarity-Caps :lol:)
Hmm.. well Quad produced active pre-amp designs to go with the 303 and 405.
Perhaps everything regarding pre-amp design can be measured (I've heard technicaly sophisticated pre-amps that sound pretty crap though - particularly ones based on op-amps) - manufacturers don't provide such a level of measurement though, so it is somewhat academic. Certainly distortion isn't the absolute arbiter of sound quality though, as most transistor designs produce a level of distortion that is supposed to be below audibility, and most valve designs produce levels of distortion that are well above the threshold of audibility. This doesn't stop many transistor designs from sounding distinctly pedestrian, or some valve amps from sounding excellent.
________________
Have you got your hi-fi cynic hat on today Dave? Have you forgotten how much you like your valve (Croft) active pre-amp?
Where's Richard from NVA when you need him. Is he banned again?
Well, as NVA produce passive pre-amps (volume control and a switch) - it seems unlikely he would endorse any other approach.
Well, as NVA produce passive pre-amps (volume control and a switch) - it seems unlikely he would endorse any other approach.
But that doesn't stop his opinion being interesting does it?
Hmm.. well Quad produced active pre-amp designs to go with the 303 and 405.
Have you got your hi-fi cynic hat on today Dave? Have you forgotten how much you like your valve (Croft) active pre-amp?
Ages ago, an engineer at Quad told a prospective customer I was trying to sell a preamp to that a QED passive control would be perfect and all he'd need for his 303... result, I lost a preamp sale and QED made a tenner or two on their product.
Mark, my Crown power amps only offer 25K on their input and they're not as sensitive as my 303. I suppose it would be ok for the Quad II's which have a higher impedance, but they're even less sensitive in Crofted form and need a gain stage.
Nah, I'll take Rob Holt's excellent advice and just stick to what I have, 'cos it works well and although not absolutely finished, the Croft preamp is a transparent as I need it to be and I love it to bits :) :ner:
Where's Richard from NVA when you need him. Is he banned again?
Yes, and unfortunately this time, permanently.
Marco.
But that doesn't stop his (RD's) opinion being interesting does it?
I tried to give NVA's thinking in my earlier post. I seem to remember the input sensitivity and/or loading of the power amps to be optimised specifically for a passive front end.
Rob is spot on above. Valve gear with high input impedance and reasonable sensitivity should be fine with passive pre's...
And yet, despite that, active valve preamps still sound markedly better in my system (more 'balls and drive' and dynamic alacrity).... My preamp isn't lacking in gain, nor my power amp or speakers in sensitivity, and I mostly use 0.5m interconnects, together with a 7m pair of speaker cables (types listed in my sig below).
I guess, however, that "fine" might satisfy some people! I don't do "fine".... ;)
However, I haven't yet had the pleasure of listening to one of Richard's passive designs.
Marco.
Perhaps Anthony could answer that one, as he designed and built-rebuilt your amps Marco. I wouldn't say that the average output of a CD player, no matter how exalted, would be enough to drive a power amp - they weren't designed to, hence the rather lovely preamp you use :)
Yup.
Well, Anthony designed my power amp, and matched its sensitivity to the gain of my preamp, which itself is non-standard, particularly in terms of gain (one of the reasons why RD's argument about 'line level rules', and their effects, don't apply in my system), but the basic design of my preamp is all Glenn's :)
I like recorded music on my system to have as much of the energy, drive and vitality of live music, as possible, and I find that high-quality active valve preamps, so far, best serve the achievement of those goals. The passive preamps I've tried, in comparison, soften the sound to the detriment of creating that ultra-vivid and 'alive' sound I'm so used to hearing from my system, and love.
Marco.
anthonyTD
28-08-2011, 21:53
hi all,
i have to agree, i prefer active preamps to most passives, my own soul-mate preamps are of course active, however, they are not like a lot of actives out there, where you have the volume control at the begining, or the end, in the soul-mate the volume control is between two active stages and driven by a low impedence, high current capable device, so the volume control poses no bottleneck at any position.
the output is also a low impedence, high current circuit, so will drive difficult loads and long lengths of cables with ease. Combine this with my own bespoke active regulator circuits, huge bandwidth,very low noise floor etc, ultra reliability [compared to valve equivilents] and you have as near as posible [IMHO] the perfect active preamp topology.
Anthony,TD...
Just a point on the Quad power amps, yes they are sensitive but have pretty standard input impedance for SS at 20k Ohms. I believe this was to ensure some backwards compatibility with older units as Quad were big on allowing existing customers to upgrade with minimum fuss or inconvenience.
FWIW, 'correcting' the gain structure of a Quad pre/power combo is one of the few useful upgrades. Drop the power amp gain to give 1.5v input sensitivity (0.5v as standard) and reconfigure the padding resistors in the quad pre to raise output.
Drops the noise floor markedly, reduces distortion in the power amp input stage and has no negatives at all.......other than backwards compatibility of course.
hi all,
i have to agree, i prefer active preamps to most passives, my own soul-mate preamps are of course active, however, they are not like a lot of actives out there, where you have the volume control at the begining, or the end, in the soul-mate the volume control is between two active stages and driven by a low impedence, high current capable device, so the volume control poses no bottleneck at any position.
the output is also a low impedence, high current circuit, so will drive difficult loads and long lengths of cables with ease. Combine this with my own bespoke active regulator circuits, huge bandwidth,very low noise floor etc, ultra reliability [compared to valve equivilents] and you have as near as posible [IMHO] the perfect active preamp topology.
Anthony,TD...
In other words, proper, sensible implementation that delivers the goods :)
It's always his approach, Rob! :)
Marco.
anthonyTD
28-08-2011, 22:39
In other words, proper, sensible implementation that delivers the goods :)
:)
A...
For me ir all depends on the system
In my system I prefer an active I need that extra drive and clout a good active can bring but when I heard the Bastanis Crystal drivers with their 105db efficency the passive using 300b gives plenty of drive and authority but I think few people will have speakers this efficent so for most of us a active pre will be the preamp of choice
jandl100
29-08-2011, 08:30
......
JANDL100: As an aside, I'm always puzzled by folks who say that using a DAC or CDP with a built-in volume control is in some way avoiding the use of a pre-amp.
A pre-amp is a volume control of some kind, and usually an input selector switch.
If you have a DAC/CDP with onboard volume control/switching then the pre-amp is still there, it's just in the same box as the CD/digital components.
At least, that's the way I look at it. :)
Covenant: But the Beresford gives you the opportunity to feed a pre-amp directly, avoiding the volume control.
But there's a volume control pot in the Beresford - probably quite a cheap one (yes, it still sounds good!) - you're not bypassing a volume control at all! Sure you may not want to add an extra pre-amp - but you've got one already inside the Beresford. :)
jandl100
29-08-2011, 08:56
Hi Jerry,
C'mon you as an ex Wadia owner will know that the volume control is digital and and that no switching or analogue processing is involved.
No point in feeding this through another set of interconnects to an active pre amp, through it's gain stages and then on to the power amp is there?
Hi Darren - yes, you're right. I fed my old Wadia 830 straight to a power amp at times, and it worked surpisingly well. In fact I recall that I preferred it to going thru an active pre with the Wadia's digital volume set at max, which I found surprising.
But if you aren't VERY careful with overall system sensitivity matching, or tweaking the Wadia's internal settings, you are lopping significant bits from the signal and losing resolution when you use a digital volume control.
And most CDPs with volume control don't do it as well as Wadia does! ;)
Mind you, I used to have a Mark Levinson 39 CDP which had an analog volume control on board, which was bypassable. Very nice it was, too!
Nope, there aren't any hard and fast rules in this game, imho. :)
StanleyB
29-08-2011, 09:11
But there's a volume control pot in the Beresford - probably quite a cheap one (yes, it still sounds good!) )
I could have fitted a U$10 Alps one, but that works out at around £25 extra on the final retail price.
Mind you, I am not sold on digital volume controls. Once you know how they chop bits out of the signal in order to reduce the volume level, it's hard to know if those chopped out bits had any relevant musical details in them that are no longer audible in the final reproduced signal.
It's funny how things work out... the giant Sony 777es amp I've been using at work blew a pair of output fets this afternoon. So an emergency replacement was drafted in: my Harman Kardon power amp driven directly by the MSB dac with volume control provided via the Squeezebox Touch.
It has to be said that the sound is great, the DAC drives the arse off the H K, there is endless headroom and this combination rocks with dynamics and detail forever.
I'm currently sat on my work sofa listening to Semisonic and feeling strangely fine. No pre amp in sight and great sound. I do have fun with my work system.
An old friend of mine had his lovely old Sony 5650 blow it's V-FET's, taking some equally lovely but old Harbeth HL5's with it. The amp went to the skip without me knowing, and the 20 year old speakers had to have third party bass units fitted, since Audax don't make these custom made pre-"Radial" drivers any more...
Hi Dave,
Happily my 777 has excellent protection circuits and no harm was done beyond a bang noise and a nasty smell. New fets are £1.25 each and will be fitted for me soon.
Alan Sircom
30-08-2011, 09:03
I could have fitted a U$10 Alps one, but that works out at around £25 extra on the final retail price.
Mind you, I am not sold on digital volume controls. Once you know how they chop bits out of the signal in order to reduce the volume level, it's hard to know if those chopped out bits had any relevant musical details in them that are no longer audible in the final reproduced signal.
Some digital volume attenuation systems work by oversampling the signal prior to bit chopping. This seems to work without removing musical detail. However, i've heard some good, some bad, and I'm not altogether sure whether that hangs on the software or hardware implementation.
hifinutt
31-08-2011, 17:26
I agree. I believe Hi-Fi Critic are comparing some transformer passive pre-amps in their next issue.
yes i am waiting for a review of the music first reference which i nearly bought recently
hifinutt
31-08-2011, 17:29
i personally think systems sound better with pre amps but intersting to read views of those who use their volume controlled dacs into power amps
seen a great deal of threads recently which suggest a pre is nearly always better to have in system
i recently tried my 3.3k dac with volume control straight into my power amps and yes it was very detailed but when my teen came in [who is quite a good judge of sound] he said dad wheres all the oomph!
also went over to a friend who was running a volume control dac into 2 monoblocks with b&w 803d in a very big room. wife there too who was a musician . the sound was analytical and deatiled but a bit fatiguing .
put the music first mark 2 into the system and the bass dropped, the windows started shaking[i kid you not!] and the soundstage went round the room. no longer fatiging and just brilliant. needless to say they bought a mfa a few days later
Ali Tait
31-08-2011, 17:54
Aye, an active pre often gives better impedance matching, which yields the better sound.
StanleyB
31-08-2011, 18:00
I experimented with an adjustable impedance bridge at the output of a preamp many nearly three decades ago. Might be worth trying to design a new bridge with the same functionality.
Ali Tait
31-08-2011, 22:17
Interesting Stan. What were your conclusions?
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