Solid state preamp grain compared to valves

[Ali Tait]

Does that matter though, if they sound impressive (read as good)?

Valve amps don't measure as well in some areas, as their SS counterparts, but it hasn't stopped you or I (who know what a good sound is) from using them as our preferred choice. As ever, feck measurements, and instead use yer lugs: the classic AoS mantra!



Marco.

Yes indeed, however Nick measured some fairly high odd order harmonics-

http://www.audio-talk.co.uk/phpBB3/v...5720&hilit=Ldr

[Marco]

This matching of complementary components is, of course, something that is mentioned repeatedly on this forum with respect to all sorts of units, not just passive pre's. But back to passive pre amps, I suspect there is more to this than just the pre-/power-amp matching, but also what's happening upstream with the source components and their output, as well as downstream with the speakers and their demand, have some impact on how well a passive pre will work in a given system. Synergy, in other words.

That's also my view, based on considerable experience, but in terms of my observations on LDRs, it would be good for someone technically knowledgeable to say, 'Yes, that's true, and this is why'.

Marco.

[Marco]

Ok, fair enough. At the moment then, it'll remain as a very real mystery!

Marco.

[Marco]

Switching contacts are one of the biggest compromises in audio. DIP switches too. I wonder if it has to do with increased impedance / decreased conductivity at the switch contacts, something that an active can deal with...

Good shout, Neil. I guess it's possible. I'll see if I can get Chris, from LDR, to comment.

Marco.

[Haselsh1]

Ok, fair enough. At the moment then, it'll remain as a very real mystery!

Marco.

Yes it sure is and I'm still searching for a clue because a lot of what is going on here is akin to proving ghosts exist. We know damn well that something is going on because a lot of us can hear it but trying to tag it with a label is slightly difficult.

[anthonyTD]

The non linearity that some who have tested LDR's elude to, could be key in explaining why LDR's when used as a passive attenuator' seem to overcome some of the shortfalls experienced by those who have been underwhelmed with conventional "pots in boxes" attenuators, eg; by perhaps working in a similar fasion to the loudness controls found on many older type amplifiers, and preamps.
A...

[Marco]

I think that's a good point, and valid, and could explain what I've been hearing, now that you've outlined the relevance of "non-linearity" to the discussion

I'll try and explain as best as I can the problems I've found with some passives, highlighted in particular by the Goldpoint (metal-filmed stepped attenuator) unit I spent considerable time and money modifying, which markedly improved aspects of its sound, but never cured it's lack of 'life', and tendency to sound 'dynamically soft', compared with the Croft.

What used to annoy me was that every time I took the Croft out of my system, and put the Goldpoint in, I'd always have to crank up the volume much more to achieve the same loudness levels, at identical points on their respective volume controls, and it would result in a 'softness'/wooly aspect to the sound, which no amount of increasing the volume on the Goldpoint would cure - all that would happen is I'd end up clipping the power amp, chasing the 'lost dynamics', my ears told me were missing...

So in an attempt to solve that problem, I kept changing the value of the resistors (Z-foils) on the Goldpoint, by fitting new ones of a lower value, in a vain attempt to give the sound the 'boost' it needed, at the lower steps of the volume control, and 'equalise' the loudness levels, as well as trying to give it more 'punch' and 'attack', the same as I got from the Croft.

In that respect, I started off with 50K resistors, and ended up using 10k ones! Still to no avail... All that happened was that the sound became too loud, too quickly, and regardless, that lack of 'life', which was very clearly evident, still persisted, and so in the end the Goldpoint was sold.

I've also tried other, much more expensive stepped attenuator-type passives in my system, with very similar results.

Some managed to level the playing field more, in terms of 'punch' and 'drive', compared with the Croft, but ultimately still exhibited the same 'softness', dynamically, ably highlighted when reproducing things like very well-produced (close-miked) recordings of drum solos, where instead of hearing a crisp 'THWACK', of sticks hitting skin, as one would do in real life, with a passive it'd sound as if someone had covered the drumsticks in cotton wool, so it 'padded out' and softened the visceral impact, which that sound should've had.

Popping the Croft in instead though, completely cured the problem, and restored the required 'life' to the sound, in order to make the drum recording in question sound real/lifelike, so that it would make you blink when the sticks hit the skin. That just didn't happen, to anything like the same degree, with any of the passives I've tried.

Now, when I use an LDR, there are no such issues of 'chasing lost dynamics', or trying to equalise loudness levels, as the sound has all the 'balls', 'guts' and 'drive' of the Croft, but sounds like an LDR, exhibiting the beguiling nature of its style of music-making, not a high-end (extensively modified) valve preamp, which does things a little differently, but equally as valuably. That's why I'd like to have access to both types of presentations, and I'm having a Stereo Coffee LDR built.

I hope my ramblings above make some sense, in terms of what I've tried to describe as the problem I perceive with passives, and even better if someone could explain why. I can assure you it's an effect I can genuinely hear, repeatedly too with all different types of music, and that my system is perfectly suited for showing what a good passive can do, which I acknowledge. For me, it's just not as good as what the best actives do, especially the Croft

I just don't like equipment that, to my ears, artificially softens the sound of recordings and reduces dynamic impact, to ANY discernible degree - and so far, LDRs aside, that's precisely what I can hear from passives, *in comparison* with the best active designs.

Marco.

[anthonyTD]

What your describing ie; the issue with conventional passive attenuators is probably very similar to most folk who dont get on with them in their systems, the point you made about the differences acheived by changing the resistor values in the Gold point is key in understanding why its sometimes difficult to get conventional passives to work, its all to do with the way the resistor value, and network interact with the source equipment, cabling, and power amp, with an active preamp that has a relatively low output impedance, the issues associated with the passive attenuator resistor networks is pretty much eliminated.

I think that's a good point, and valid, and could explain what I've been hearing, now that you've outlined the relevance of "non-linearity" to the discussion

I'll try and explain as best as I can the problems I've found with some passives, highlighted in particular by the Goldpoint (metal-filmed stepped attenuator) unit I spent considerable time and money modifying, which markedly improved aspects of its sound, but never cured it's lack of 'life', and tendency to sound 'dynamically soft', compared with the Croft.

What used to annoy me was that every time I took the Croft out of my system, and put the Goldpoint in, I'd always have to crank up the volume much more to achieve the same loudness levels, at identical points on their respective volume controls, and it would result in a 'softness'/wooly aspect to the sound, which no amount of increasing the volume on the Goldpoint would cure - all that would happen is I'd end up clipping the power amp, chasing the 'lost dynamics', my ears told me were missing...

So in an attempt to solve that problem, I kept changing the value of the resistors (Z-foils) on the Goldpoint, by fitting new ones of a lower value, in a vain attempt to give the sound the 'boost' it needed, at the lower steps of the volume control, and 'equalise' the loudness levels, as well as trying to give it more 'punch' and 'attack', the same as I got from the Croft.

In that respect, I started off with 50K resistors, and ended up using 10k ones! Still to no avail... All that happened was that the sound became too loud, too quickly, and regardless, that lack of 'life', which was very clearly evident, still persisted, and so in the end the Goldpoint was sold.

I've also tried other, much more expensive stepped attenuator-type passives in my system, with very similar results.

Some managed to level the playing field more, in terms of 'punch' and 'drive', compared with the Croft, but ultimately still exhibited the same 'softness', dynamically, ably highlighted when reproducing things like very well-produced (close-miked) recordings of drum solos, where instead of hearing a crisp 'THWACK', of sticks hitting skin, as one would do in real life, with a passive it'd sound as if someone had covered the drumsticks in cotton wool, so it 'padded out' and softened the visceral dynamics that that sound should've had.

Popping the Croft in instead though, completely cured the problem, and restored the required 'life' to the sound, in order to make the drum recording in question sound real/lifelike, so that it would make you blink when the sticks hit the skin. That just didn't happen, to anything like the same degree, with any of the passives I've tried.

Now, when I use an LDR, there are no such issues of 'chasing lost dynamics', or trying to equalise loudness levels, as the sound has all the 'balls', 'guts' and 'drive' of the Croft, but sounds like an LDR, exhibiting the beguiling nature of its style of music-making, not a high-end (extensively modified) valve preamp, which does things a little differently, but equally as valuably. That's why I'd like to have access to both types of presentations, and I'm having a Stereo Coffee LDR built.

I hope my ramblings above make some sense, in terms of what I've tried to describe as the problem I perceive with passives, and even better if someone could explain why. I can assure you it's an effect I can genuinely hear, repeatedly too with all different types of music, and that my system is perfectly suited for showing what a good passive can do, which I acknowledge. For me, it's just not as good as what the best actives do, especially the Croft

Marco.

[Marco]

But don't forget, passives automatically offer 'greater fidelity', because they're measurably more accurate!! [Sorry, Macca]

However, yes, thanks for that. You've offered a reasonable technical explanation for what I can clearly hear, and that's why I've given up now with conventional passives.

Marco.

[Firebottle]

I have been trying to understand just what causes the difference with passive attenuators, I have heard the effect with a few.
I will put forward this hypothesis, so feel free to discuss.

Frequency response and phase response are inextricably linked, so although we cannot hear very high frequencies we CAN discern small phase differences.
When the frequency response of an amplifier or system is limited there is always a phase shift as the frequency limit is approached.

Now keeping things simple, imagine the output of the passive/active preamp driving the capacitance of the interconnect leads:

With a passive with its associated larger output resistance the hf frequency response is always curtailed, very much in the ultrasonic range (to our ears) in virtually all cases, BUT even though we cannot hear the frequency where the response falls there is always an alteration to the phase response.

With an active preamp with a much lower output resistance there is much more drive to charge/discharge the capacitance of the interconnect leads, so the hf response is affected much less, with the correspondingly smaller effect on the phase response.

So my hypothesis is that the missing bit with the passive approach is phase accuracy.