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Best Valve pre-amp match for ME 550 amp

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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.

And yet, THD and IMD remain below audible levels at all times. Methinks you are searching for a problem that does not exist.

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.

The designer of the ME550 has constantly challenged the conventional paradigms of amplifier design. Many people, like you, have laughed off his design ideas as dumb. Nonetheless, not only have his radical ideas been copied by many, much larger companies (and smaller ones), but some of his ideas have yet to be duplicated. The low input impedance idea has been proven, via blind testing, to be a good one.

I have no inability to source valve types I wish to use. So they eventually wear out? They still work better at EOL...LOL

I note you have carefully avoided responding to my other comments about the weak points attributable to valve preamps. Why is that?

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

You need to get out more. Valve preamps have a considerable number of very serious deficiencies. Few of which you have cared to acknowledge. Valves offer no tangible advantages over a well designed and implemented solid state preamp. Unless, of course, you regard the various distortions generated by valve preamps (microphonic issues, phase shift and distortion problems, etc) as good things. For my part, I prefer accuracy over such distortions.
 
IN order:
you can think what ever you want.

As far as addressing things, you are waaaay to far behind to go attempting to request somebody pay attention to something you consider important to your argument.

Valve pre-amps have no weakness-es like you mention. Well, at least what comes of my bench does not.

You know, I was thinking just exactly the same thing about you, only less politely. Like I said, do please go and believe, and as follows such belief, spread The Word as far as you can.
cheers,
Douglas
 
IN order:
you can think what ever you want.

As far as addressing things, you are waaaay to far behind to go attempting to request somebody pay attention to something you consider important to your argument.

Unfortunately, part of high fidelity listening involves the elimination of any sonic effects from the reproduction equipment. Microphonics, noise and distortion are all audible flaws that are attributable to many valve preamps. For many listeners, these faults are unacceptable. Mid-fi and uncritical listeners may not find a problem with these faults. That's OK.

Valve pre-amps have no weakness-es like you mention. Well, at least what comes of my bench does not.

Oh yes, they do. The faults mentioned are audible and measurable in many cases.

You know, I was thinking just exactly the same thing about you, only less politely. Like I said, do please go and believe, and as follows such belief, spread The Word as far as you can.
cheers,
Douglas

I should mention, at this point, that I have built, owned, listened to and measured a very large number of valve preamps over the past 40-odd years. Some are better than others. NONE are superior to the best solid state designs. Even those where enormous attention has been paid to microphonic problems (compliant PCB mounting, etc), noise problems (highly regulated power supplies, etc) and the other things. Transistors just do the job better and have done so for many years. And, make no mistake: There are some horrible solid state preamps out there 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.

Hi Bandersnatch & Audiowize ...

What would you suggest in terms of a schematic with details of components - to add-onto the schematic attached? With gain and no loss of audio quality <10ohms??
...maybe a simple circuit that can be attached as a add-on to output of the JP200 pre??

Cheers
 

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  • JP200 Preamplifier Schematic.pdf
    15.7 KB · Views: 83
Hi Bandersnatch & Audiowize ...

What would you suggest in terms of a schematic with details of components - to add-onto the schematic attached? With gain and no loss of audio quality <10ohms??
...maybe a simple circuit that can be attached as a add-on to output of the JP200 pre??

Cheers

Or, you could just use an ME preamp. You know, the preamp that your power amp was designed to be used with.

Just a thought.
 
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It is difficult to assist TigerScent if he persists in ignoring much of the advice that has been offered to his oft repeated queries. I am at a loss to understand if he is in possession of just the JP 200 board kit or if he has the full pre-amplifier with the case ,power supply, input selector and all the other bells and whistles to suit his source requirements. As such ,whilst it would not be my choice to run this pre-amp with a solid state amplifier, let alone the more specialist M.E. one, his solution is still the same as I previously suggested; namely 'The Champ' audio amplifier* ( x2 ) available from Jaycar or Altronics. This is the easiest and cheapest solution.

* Silicon Chip Magazine, Feb., 1994
 
... surely you are not implying that I forego my valve preamp project??
I cannot help but feel you may be hinting at this :eek:

The real question is this:

WHY do you think a valve preamp is appropriate, or even superior to an ME, or another low output impedance design?

Precisely what technical details do you think the ME preamps lack, that a valve (any valve preamp, apparently) possess?

Valves are noisy, inconvenient, change their characteristics, from the moment they are switched on, require coupling components that shift phase, add distortion and generally bugger up sound quality. Which is not to say that some of these problems can be minimised (but not eliminated), but at huge cost.
 
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Hi Zaphod Beeblebrox,
No, the real question is why you are taking someone to task over a curiosity they are exploring. They don't have to answer to your line of questioning, and I couldn't help but notice that you didn't offer any information or helpful ideas in your posts.

If you disagree with this technology, you should ask yourself why you are even in this forum to begin with. I don't believe it is so you can be helpful, so therefore you are looking for something else.

I'm going to ask you nicely to leave this area and go post on subjects you can offer help or positive ideas on.

-Chris
 
It is difficult to assist TigerScent if he persists in ignoring much of the advice that has been offered to his oft repeated queries. <snip>

I was looking for a solution that would not rely on any IC componentry in the preamp valve section...

...interestingly Peter Stein who designed and manufactured the ME, knew what I was doing and gave me information I asked him about...he did not have an issue with me doing what I am trying to do, so I don't know why anyone else would...
 
TigerScent,

I have no idea of the exact I/P impedance of the ME amp. However, the O/P impedance of a cathode follower is the reciprocal of the tube's transconductance (gm). The gm of New Sensor's in production 6H30Π (6n30p) is 18 mA./V. So, the O/P impedance of a 6H30Π cathode follower is 55.6 Ω. Even if ME's I/P impedance is a silly low 600 Ω, the situation is acceptable.

If an absolutely no SS design is an objective, choke load the cathode followers. Good loading chokes are expensive. A 25 H. part of sufficient current capability and bandwidth will do the job. You can't use a part intended for PSU filter duty in this application. TANSTAAFL!
 
Hi Zaphod Beeblebrox,
No, the real question is why you are taking someone to task over a curiosity they are exploring. They don't have to answer to your line of questioning, and I couldn't help but notice that you didn't offer any information or helpful ideas in your posts.

If you disagree with this technology, you should ask yourself why you are even in this forum to begin with. I don't believe it is so you can be helpful, so therefore you are looking for something else.

I'm going to ask you nicely to leave this area and go post on subjects you can offer help or positive ideas on.

-Chris

Honestly, I never took any notice of the section that this thread was in. Not once. I ONLY took notice of the header and responded accordingly. I supplied all the information required for the poster to achieve his stated aims. I will respect your request and leave this thread.
 
...moving along

TigerScent,

I have no idea of the exact I/P impedance of the ME amp. <snip>

Hi Eli, thanks for your response.

Peter Stein the designer/manufacturer of the ME amps, informed me in an email, that the ME 550 series 1 is an unbalanced connection of 1kohm.

He went on to inform me that I would need a minimum of 10x less impedance for the preamp bottom line: in comparision to the power amp input, however 'preferably' 100x less for optimal performance.

His preamp he went on to tell me, was 2ohms which enabled it to drive virtually any power amp optimally, so I have been aspiring to have ~10ohm or less as a modification/add-on module for this preamp.

Peter Stein suggested in his email that I relay all this information to this forum so that all the details are clear. He was quite well-natured and helpful knowing that I was trying to get a valve pre-amp to work with his power-amp, and did not try to dissuade me whatsoever, but be helpful instead.

Its difficult to understand why some would be so opposed to my pursuit in this direction, however Peter was helpful and a pleasant chap to communicate with.

I have purchased most of the components for this pre-amp, valves, solid silver wired caps, etc ... and have been just looking at responses in case I might need to make a modification on the circuit board which is pre-stamped and rather solid and good quality.

I am not a great expert in designing circuit boards and where components should be placed, so giving general information that it needs this and that is nice, but I have no idea where to put then in relation to the circuit itself, so it would be good to have some helpful advice in that regard. I have posted the circuit diagram in previous posts.

The mods I have made to date have only consisted of modifying speaker crossovers with regards to cap replacement and resoldering with Mundorf silver solder, annealing solid silver strips and replacing the speaker wiring and baffling. I have also re-capped some audio equipement, all with astounding superior results in terms of sonic quality.

So I am keen on building this valve preamp as I have seen what difference just a cheap chinese knock-off - from alleged 'mattisse' valve preamp makes when used as a buffer between pre-amp and main amp in a integrated surround amp (NAD T773) ... which is very distinct. I have also used this buffer preamp (guanzo - $50 preamp ebay) with a Rotel power amp (990BX) which sounds amazing for what it is.

So...therefore...I would like to build this Jardis based valve preamp as it has had a lot of good reviews, for the ME 550 Series I. I also have had the idea that I could have 3 outputs from it, one to drive the Rotel for front speakers (Celestion Ditton 44 with modified solid silver circuitry), and the other for the ME 550 driving the Pro-Ac tablettes (also modified with solid silver - sounds amazing). I can then use the preamp with only the front amp, or rear amp - or both... yet I am wondering if doing this might affect the capacitance overall when both are working together switched on connected to the same preamp...The 3rd I considered to leave open for the option of possibly attaching a subwoofer...perhaps...

...so, it would be good to actually get some sound (forgive the pun) advice with suggested circuit and placement of components in some kind of add-on circuit board scenario, or mod to the main circuit board without altering it as it is pre-made - now that the element of criticism have appeared to have receded... :)
 
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Oh...I need to mention...I emailed AnalogMetric about their Jardis based 'JP200' valve preamp to find out what the output impedance is; and their response eventually was that it was ~3Kohms...

Given the load impedance and the source impedance requirement it almost seems that transformer coupling is close to ideal. I assume you are already committed to another path, and honestly haven't read much of this very long thread. :D

Hi Kevin,

No I have not committed to any other path (no SS circuitry tho) ... as nothing is clear enough in how to go about things circuit and layout component wise.

Yes...I do want the 'ideal' sonic pathway...and as far as transformer coupling goes (some said 'chokes etc) I have no idea on how to go about this, what values/components to use, nor where to place them in relation to the main circuit - which is what I am asking assistance for...

thanks - cheers...

Where would I put the transformers and what value would I use??

TigerScent,

I have no idea of the exact I/P impedance of the ME amp. <snip>

Can you give me an idea of where to place the chokes and how to connect them looking at the schematic??
 

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  • JP200 Preamplifier Schematic.pdf
    15.7 KB · Views: 44
Dude, you are hammering a square peg into a round hole. :(

Let's start with the IHF "standard", which is a 10 Kohm I/P impedance. Notice that ME is a rule breaker and I attribute unkind motivations to that fact, sorry.

It's very well established that the ratio between driving "box" O/P impedance and driven "box" I/P impedance be at least 1:10. ME agrees.

The O/P impedance of the JP200 circuit 3 Kohms. Given that setup uses 12AX7s, a wretched tube for line stage service. The very bad number is anything but surprising. The JP200 is also a rule breaker, given its complete inability to drive the IHF "standard" load. Quite frankly, I would not use the JP200 circuitry, even if offered a considerable amount of $.

All good designs incorporate compromises of some kind. Emphasizing strengths and minimizing weaknesses is (obviously) in order.

The 1st order of business is gain structure determination. What level of drive does the ME power amp need to produce full power?

BTW, a 6H30Π (6n30p) cathode follower is quite adequate as the driver of that ME stuff. As SS parts are acceptable in ancillary roles, the cathode follower will be constant current sink (CCS) loaded. CCS loading is much less costly than choke loading and performs at least as well.
 
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Dude, you are hammering a square peg into a round hole. :(

Let's start with the IHF "standard", which is a 10 Kohm I/P impedance. Notice that ME is a rule breaker and I attribute unkind motivations to that fact, sorry.

I feel the need to return to explain a few things about the ME550. I will comment solely on that.

ME power amps are not typical SS power amps. They are very different. Briefly, all ME power amps:

* Use no global NFB. They do employ around 15dB of NFB around the Voltage amplifier for gain stabilisation and linearisation. Obviously, local NFB is used for current amplification. The output devices are coupled to the load via collectors.
* Current limiting occurs at 40 Amps.
* ALL transistors are matched to within 1% tolerance for hFE and Vbe.
* Front end consists of two differential pairs.
* Non-inverting input is terminated via a 1,000 Ohm resistance. This is not an unusual figure for any SS amp. Peter Stein theorised that, since the -ve input (feedback line) is terminated with 1k, then the +ve input should be similarly terminated. Hence, input impedance is 1k. DBTs have confirmed that a 1k input impedance sounds better than significantly higher (68k) input impedance figures.
* The ME550 is further complicated (as opposed to other ME models), because one channel is operated anti-phase. This makes converting to a higher input impedance a difficult task.
* Since building a low output impedance preamp is a VERY simple thing to do, Peter Stein decided that releasing such an amp to market was appropriate.

It's very well established that the ratio between driving "box" O/P impedance and driven "box" I/P impedance be at least 1:10. ME agrees.

1:100 is a better number to aim for.

The O/P impedance of the JP200 circuit 3 Kohms. Given that setup uses 12AX7s, a wretched tube for line stage service. The very bad number is anything but surprising. The JP200 is also a rule breaker, given its complete inability to drive the IHF "standard" load. Quite frankly, I would not use the JP200 circuitry, even if offered a considerable amount of $.

All good designs incorporate compromises of some kind. Emphasizing strengths and minimizing weaknesses is (obviously) in order.

The 1st order of business is gain structure determination. What level of drive does the ME power amp need to produce full power?

1 VRMS. 30dB Voltage gain.
 
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1 VRMS. 30dB Voltage gain.

So, the 2 VRMS produced by a "standard" CDP is more than enough to drive the ME power amp into clipping. Therefore, a buffered volume control plus source selection capability is all that's needed in the control center ("preamp").

If the OP wants an effects machine, he'll have to find somebody other than me to help in designing it. OTOH, if transparency and good matching between signal source(s) and the very nasty load the ME power amp presents are the goal, the task is quite straight forward.

A bipolar PSU employing "noise free" Schottky diodes allows the setup to have but 1 cap. (the O/P coupler) in the signal path. A single bottle, 6H30Π (6n30p) wired as cathode followers (1/channel) "sits" between the source selection/volume control stuff and the downstream load. That's all of it, no fuss, no muss, just music.
 
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"...The 1st order of business is gain structure determination. What level of drive does the ME power amp need to produce full power?

Peter Stein from an email:

"The gain of the amplifier is 30db (in standard ex factory status) - if we assume 100 watts that translates to approx 1 volt or so. Note that clipping or maximum power will depend a little on speaker load and mains voltage - so it could be as high as 1.2V RMS."

So whatever 80W RMS translates to... ie: 0.8 volt
 
If the OP wants an effects machine, he'll have to find somebody other than me to help in designing it. OTOH, if transparency and good matching between signal source(s) and the very nasty load the ME power amp presents are the goal, the task is quite straight forward.

A bipolar PSU employing "noise free" Schottky diodes allows the setup to have but 1 cap. (the O/P coupler) in the signal path. A single bottle, 6H30Π (6n30p) wired as cathode followers (1/channel) "sits" between the source selection/volume control stuff and the downstream load. That's all of it, no fuss, no muss, just music.

Effects machine?? not at all...!!

I just want to use the ME550 to drive some ProAC tablettes and get the best sound from them...
 
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