...actually yes - I find the valve preamp/buffer gives a smoother more natural pleasant sound, when placed between the preamp of a receiver and amp section - in some amps, but not in others. Overall, I like the natural transparent warm valve quality sound - with the dynamics of the SS amp
Actually I quite like the ME550. I had it upgraded by the designer Peter Stein, and he modified it so that I could put solid silver strips in the output part on the + end. Quite good really - and I think it would sound super with balanced warmth, transparency and detail matched with an impedance matched valve preamp...
Dearest Zaph...
I believe your comment on 'audioreview' was:
"Bottom Line:
The ME25 is possibly the best high end bargain, on the planet. It's sound quality resembles that of the power amplifiers: Superb conrtol, very extended response, great detailing and transparency, holographic imaging and an almost 'tube-like' presentation."
ME Sound ME25 Preamplifiers reviews - Audioreview.com
In this comment, you are alluding to the fact that the ME25 is almost on par with a tube/valve preamp but not quite - from what I read of your remark...so it befuddles the minds of those with sound mind of how you could possibly now refer to this better element as 'distortion'...
Please - do tell ...
So-o-o ... with regards to my latest comment, based on this comment --- and comparing it to your latest comment --- and my subsequent response --- what is your esteemed qualified response in turn..., so curious we all are to know...
Dearest Zaph...
I believe your comment on 'audioreview' was:
"Bottom Line:
The ME25 is possibly the best high end bargain, on the planet. It's sound quality resembles that of the power amplifiers: Superb conrtol, very extended response, great detailing and transparency, holographic imaging and an almost 'tube-like' presentation."
ME Sound ME25 Preamplifiers reviews - Audioreview.com
In this comment, you are alluding to the fact that the ME25 is almost on par with a tube/valve preamp but not quite - from what I read of your remark...so it befuddles the minds of those with sound mind of how you could possibly now refer to this better element as 'distortion'...
Please - do tell ...
Many valve amps and preamps have SOME advantages over most SS amps and preamps. This is largely due to the fact that valve amps and preamps eschew the use of large amounts of global NFB. ALL ME power amps and preamps eschew the use of global NFB. As a consequence, they exhibit the nice features attributable to valve products, but without the (many) drawbacks. Unlike valve products, ME amps and preamps:
* Do not wear out (well, the transistors don't).
* Offer very good signal/noise figures.
* Offer very low levels of THD and IMD.
* Low power consumption.
* Are built using components that will probably be available for many decades to come.
* Are extremely reliable.
* Offer a flat frequency response from DC ~ 200kHz.
* Offer a flat phase response within the audible band.
So-o-o ... with regards to my latest comment, based on this comment --- and comparing it to your latest comment --- and my subsequent response --- what is your esteemed qualified response in turn..., so curious we all are to know...
My "esteemed qualified response"?
The same thing that I have been telling you for SIX YEARS.
You need to listen to the preamp that was expressly designed to work with your power amp, BEFORE you spend a single cent on a product that may not work properly with your power amp.
I cannot believe it has been six years and you are still resisting common-sense, logic and reason.
...are you suggesting that I abandon my beloved valve pre-amp project?? I cannot help but feel this is what you may be implying...however, would it not be best that on completing this project - I then compare it with an ME-preamp???
...the only thing is, I have been relying on you to give me some assistance in getting the ohms output low on the valve one, so that it would be fairer to make a comparison...
...I can't believe its SIX YEARS and you still have not offered to assist me, so that I can then compare the two...
Presuming that you have built up the full pre-amplifier kit for the JP200, which includes a case , input selection switching, volume control power supply with regulators and filtering ccts ; then I suggest that the simplest addition that you could try in order to allow matching to the ME amplifier, is to use two "Champ" 1/2 W audio kits as output buffers. They are available as low cost kits from Jaycar or Altronics. They can be powered via the positive regulator cct using a dropping resistor to give a 9 to 12 v supply.
The best preamp for your power amp is an ME preamp, or another preamp with an output impedance of less than 10 Ohms and a DC offset of less than 1mV. Valve preamps are spectacularly unsuitable for ME550 power amps. Few have sufficiently low output impedance and most employ an output coupling capacitor which rollsoff bass response into low impedance loads and may cause problems due to DC shifts at switch-on. I have been perfectly consistent in these points. Additionally and more importantly, you would not have to abandon anything, had you listened to my words in the first place.
No. The real question is this:
Why do you think that a valve preamp is more suitable than an ME preamp for your ME550 power amp?
...I can't believe its SIX YEARS and you still have not offered to assist me, so that I can then compare the two...
I have, many times, offered to assist you, by supplying a suitable preamp for your purposes. Send me suitable refundable funds and I will send you a preamp. Less freight costs, of course.
I don't see much of an issue to develop a valve pre capable of 10dB of gain to have an output Z of less than a hundred ohms. Balanced output too... No cathode followers, no capacitor coupled outputs. I am equally confident kevinkr can do a fine job of it too. It would be an interesting exercise.
cheers,
Douglas
No cathode followers, no capacitor coupled outputs. I am equally confident kevinkr can do a fine job of it too. It would be an interesting exercise.cheers,
Douglas
100 Ohms is easy and it will not provide optimum results. 10 (TEN) Ohms, or less is what I suggested is appropriate. That means a solid state buffer will be required. If using a solid state buffer, then there is no point in using valves for such a purpose, unless extra noise, distortion and microphonics is really desired. The ME550 owner is usually the kind of person who desires accuracy and fidelity, not additional distortion. Therefore, again, the optimal, economic solution is an ME preamp. I should add that it is a solution that thousands of owners acknowledge is the right one for them. Valve preamps should NEVER be used with an ME550. Not ever.
I stepped right over that ME550 with a pair of 4E27 tube amps. They are as easy to drive as I want them to be.
Your ridiculous input impedance is not as hard to drive as you think, given the proper circuit. I think I can do well under ten with an OPT and no triodes. How many volts does it take to run one of those amps to full power?
cheers,
Douglas
Your ridiculous input impedance is not as hard to drive as you think, given the proper circuit. I think I can do well under ten with an OPT and no triodes. How many volts does it take to run one of those amps to full power?
cheers,
Douglas
I don't see much of an issue to develop a valve pre capable of 10dB of gain to have an output Z of less than a hundred ohms. Balanced output too...
This is super easy. I'd parallel a pair of 7788s per channel and use a 2.5K gapped transformer for a 2A3. This would give maybe 6dB of gain and give an output impedance under 10 Ohms. More gain just requires another valve and lower step-down ratio.
It only takes 1.5VRMS for full power. Points:
* The input impedance is not "ridiculous". It was chosen for good, solid, technically valid reasons. It was chosen to provide a low noise floor and superior 'balance' between the two sides of the long tailed input pair. Significant DBTs have been performed over many years to verify that a low input impedance provides superior sonic results. So, before you make ignorant comments about the designers choice, I suggest you put in the hard yards first.
* It would be easy enough to use a phase shifting, distortion producing transformer to provide a 10 Ohm output impedance. It would be easier, cheaper, lower distortion, lower noise, zero microphonic to use a DC coupled solid state solution. Solid state solutions are vastly superior in every conceivable way. Unless the listener wants additional distortion, of course.
* I don't get the desire to re-invent the wheel. Valve preamps can be fine, in the right situation (though never any better than a high quality SS one). Compared to a high end solid state preamp, they are noisy, microphonic and cannot, without heroic efforts, provide a low output impedance.
* The ME preamp is a perfect, low cost, convenient solution to drive an ME550. A valve preamp is none of these things.
Zaphod, a few points you missed:
*The ignorance is yours for claiming it is mine. The benefits of low resistance are obvious.
*you are an uncultured bum for coming here with this bull cookie tripe, 'Unless the listener wants additional distortion, of course.'
*you are also mistaken about 'additional distortion' being the simplistic answer for liking tube and TX citcuits.
*ME550 designers chose a path, and you claim it is best answered with SS. I don't think you have a clue as to what is possible...especially given the 'points' you put forth as legitimate.
*The ignorance is yours for claiming it is mine. The benefits of low resistance are obvious.
*you are an uncultured bum for coming here with this bull cookie tripe, 'Unless the listener wants additional distortion, of course.'
*you are also mistaken about 'additional distortion' being the simplistic answer for liking tube and TX citcuits.
*ME550 designers chose a path, and you claim it is best answered with SS. I don't think you have a clue as to what is possible...especially given the 'points' you put forth as legitimate.
Anyone who can't see beyond this level of prejudice has sacrificed so much believability that one begins to doubt the basis of the whole decision making process.
Then why claim the low input impedance is "ridiculous"?
The you feel free to explain what possible technical advantages can be gained by using valves, rather than BJTs as amplification devices in low level applications. From any technical and audible perspective, there are no advantages, short of added distortion, noise and microphonics.
Really? What do you imagine are the advantages of using valves in low level circuits?
I make no such "claim". I state is as a fact. Unlike you, I have more than 20 years' experience with ME550 amps (and 40 years' experience with older models). I know which models can be successfully operated with valve preamps. The ME550 is not one of them. I also know that, after bench testing and extensively listening to some of the best valve preamps available commercially (Conrad Johnson Premier 16, ARC - various models, etc), that the ME preamps are the equal in most areas and superior in a couple.
OK, I'll bite: Tell us, PRECISELY, why you imagine a valve preamp is superior to an ME preamp (generally) and when connected to an ME550 power amp (specifically).
We await your in-depth explanation.
Just to start it, the variability of capacitance depending on voltage applied across the device. This applies to BJT and MOSFET.
On their temperature induced property changes, I will just quote Wavebourn:
The problem of gm doubling in ss amps is much worse, since they have much higher gm, and are very temperature-dependent. That affects the most critical listening region, adding dynamic distortions, i.e. distortions modulated by signal envelope that changes temperature of crystals instantly.
On the input impedance, choosing a set of devices that requires going so far off the reservation is POOR engineering. Or good marketing. Same sin IMO.
cheers,
Douglas
On their temperature induced property changes, I will just quote Wavebourn:
The problem of gm doubling in ss amps is much worse, since they have much higher gm, and are very temperature-dependent. That affects the most critical listening region, adding dynamic distortions, i.e. distortions modulated by signal envelope that changes temperature of crystals instantly.
On the input impedance, choosing a set of devices that requires going so far off the reservation is POOR engineering. Or good marketing. Same sin IMO.
cheers,
Douglas
Which should not present an issue in any correctly designed product, as such things are already allowed for in the design.
Several points:
* Like most preamps, the ME preamps are operated in Class A (down 100 Ohm loads). As I understand it, gm doubling is not a problem with Class A amplification.
* Since the amplification stages operate with significant bias currents, the semiconductors are all run at temperatures greater than ambient. AND, since they operate in Class A at all times, temperature changes are eliminated.
* THD, at any frequency from 20Hz ~ 20kHz and IMD remains below 0.05% at all times, provided load impedance remains above 100 Ohms. Such distortion levels are generally considered to be inaudible.
Your opinion is duly noted. You should note that the designer originally built amplifiers which exhibited the 'standard' 50k ~ 100k input impedance. Subsequent theorising, combined with DBTs confirmed his theory that a lower input impedance would perform better than a high input impedance.
How would you deal with the following problems that afflict valve preamplifiers?
* Microphonic problems.
* Noise problems.
* The fact that valves begin to wear out, the minute that they are powered up.
* The inability to source some, once popular, valve types.
* Distortion and phase shift problems inherent to coupling components.
Your interpretation of the heat generated in the Class A operation ignores the thermal inertia of the silicon itself. Taken over a long period, its average power dissipation is relatively constant, but as its output goes up it gets cooler, and as it goes down, it gets warmer...and thus the rot sets in. Correct this with NFB and you get more rot.
Their low impedance requirement for 'acceptable' performance is just evidence of poor engineering. What a surprise they noticed and dealt with it as you mention.
I have no inability to source valve types I wish to use. So they eventually wear out? They still work better at EOL...LOL
In any case, do us all a considerable favour, and go argue these points as widely as you can with a solid dedication, it will have a beneficial effect on any tube-based endeavor I choose to pursue. The folks who believe you deserve all they get and a dollar more besides...
cheers,
Douglas
Their low impedance requirement for 'acceptable' performance is just evidence of poor engineering. What a surprise they noticed and dealt with it as you mention.
I have no inability to source valve types I wish to use. So they eventually wear out? They still work better at EOL...LOL
In any case, do us all a considerable favour, and go argue these points as widely as you can with a solid dedication, it will have a beneficial effect on any tube-based endeavor I choose to pursue. The folks who believe you deserve all they get and a dollar more besides...
cheers,
Douglas
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