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Best Valve pre-amp match for ME 550 amp

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Hi, I am looking for a hi Q valve pre-amp kit/plans that would have an <10 ohm (preferably) or up to 100 ohm output impedance, ... to match a ME 550 amp.
The ME 550 has a balanced input of 2 ohms, and unbalanced 1000 ohms.

...any suggestions??

UPDATE!!

I have decided to go with the Analog Metric Jadis based JP200, which all builders who built it have been impressed by its sonic qualities, however the Z-output is ~3Kohms, so I need to be able to reduce that to <10ohms, without degrading sonic quality...
 
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The ME 550 has a balanced input of 2 ohms, and unbalanced 1000 ohms.

I looked up the specs an found a very different answer. What I found was a very conventional 100K input impedance. But then there might be more than one amp called "ME 550" Do you have a link to this amp's specs?


That said if you ever have the open to use balanced inputs, then use the balanced inputs.

If building with tubes you really are going to need a transformer to get such low impedance and I seriously doubt anyone would be selling a kit with such uncommon specs. Check the specs again 2 ohm balanced seems wrong and so does 1000 ohms
 
...yes, I emailed the designer/producer of the ME amps, Peter Stein, who gave me that information.

Part of email reply...

"In standard configuration the ME 500 has a 2Kohm balanced input (or 1K unbalanced)..... Output impedance would need to be 100 ohms or lower (all good solid state high end preamps can do this easily) ...It is always good engineering practice to have at least 10 times lower driving impedance for Audio. 100 times is better."

I think he meant 2ohm balanced and 1K unbalanced....

the model is a ME 550 Type I
 
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No, a 2K balanced input makes sense, particularly in conjunction with a 1K unbalanced input.. No one makes a balanced input of 2 ohms - driving it would require more power than most solid state pre-amps are capable of.

If you want to drive this thing with a tube pre-amp a design using a 600 ohm line transformer or White cathode follower output would be good choices. The octal version of the Aikido using a 6BX7 as the output tube with large output coupling caps probably work.
 
...yes, I emailed the designer/producer of the ME amps, Peter Stein, who gave me that information.

Part of email reply...

"In standard configuration the ME 500 has a 2Kohm balanced input (or 1K unbalanced)..... Output impedance would need to be 100 ohms or lower (all good solid state high end preamps can do this easily) ...It is always good engineering practice to have at least 10 times lower driving impedance for Audio. 100 times is better."

I think he meant 2ohm balanced and 1K unbalanced....

the model is a ME 550 Type I

No, he meant 2K balanced and if you use only one of the two sides you have 1K unbalanced.

You want to use the balanced input. the way to get there with a tube amp is with a transformer. Yes you might use cathode followers or whatever. But that just adds more tubes. Transformers are noiseless and provide perfect galvanic isolation. and the transformer will have perfect balance too.

What you would be building is a very low powered stereo amplifier. You will not find kits or plans for this. It will be a design exercise. Likely take some Spice simulation and bread boarding. Not rocket science as it need not be complex.

The simplest approach is just to go single ended class A. Use something like a parallels 12AU7 or 6sn7 as an output tube.
 
No, he meant 2K balanced and if you use only one of the two sides you have 1K unbalanced.

" In a follow up email, he stated: "I also mentioned a 2 K ohm input impedance but as I now understand this is irrelevant as you have an ME 550 and not an ME 500 - the input impedance in standard form is 1K ohm or 1000 ohms. To get good performance from any preamplifier connected to a standard ME 550 I would suggest an output impedance (from the preamplifier) of 100 ohms or less."

...are there any hi-Q DIY plans I can use as a base plan and modify to suit, that you know of...Im entirely new to all this, but have modified some output caps on some NAD's with Nichicon Muse etc, with noticable improvement in clarity - definition - musicality ?
 
Curious suggestion. How much experience have you had with the ME550, when connected to a valve preamp?

Are you suggesting that the ME550 owner should trust the opinions of someone who has no experience with the combination?

Perhaps the ME550 owner should consult someone who actually knows the capabilities and limitations of the combination.
 
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I made the original suggestion he endorsed..

I thought it was reasonable given the original OP's interest in driving this amplifier with a tube pre-amp.. The version I suggested can drive 64 ohm headphones, but there are still a lot of issues to be considered including things like turn on/turn off transients which could be dealt with using a shunt relay and appropriate timer circuitry, along with appropriate power sequencing of the pre-amp and power amp..

I'd be the first to admit that the idea is not without risk, I have done it with with other solid state amps and tube pre-amps, but nothing with an unbalanced input with a 1K input impedance. He'll have to decide whether or not it is worth the risk - the designer with whom he has contact should be able to provide guidance as to whether or not this is a risky proposition.

Personally I would choose transformer coupling and avoid any risk of dc following the amplifier's input circuitry. One could also do a parafeed output transformer arrangement with the white CF in the Aikido, ratios could be 1:1 to 3:1 for 0 to -10dB of attenuation. The 3:1 would reflect a 9K load to the Aikido which is not a difficult load for the version I suggested, would allow the use of a much smaller and presumably higher quality film coupling cap at the output, and still leave you with about 12dB of gain which is enough for most applications.
 
I made the original suggestion he endorsed..

I understand that. I confined my comments to those made by cjcc67.
I thought it was reasonable given the original OP's interest in driving this amplifier with a tube pre-amp..

Indeed, given your lack of knowledge about the specific product, your comments were reasonable. Which is why I did not address them.

The version I suggested can drive 64 ohm headphones, but there are still a lot of issues to be considered including things like turn on/turn off transients which could be dealt with using a shunt relay and appropriate timer circuitry, along with appropriate power sequencing of the pre-amp and power amp..

Precisely. The ME550 is fundamentally unsuited to a large number of preamps that are commonly available. That includes even quite heroic valve preamps, such as suggested by you. The ME550 SHOULD be driven by a source impedance of less than 10 Ohms. 100 Ohms would provide average to poor results. The ME550 has:

* DC coupling throughout.
* No DC protection system, outside full power shutdown, if DC is detected.

It is perfectly suited to any preamp which:

* Exhibits a source impedance of less than 10 Ohms.
* Is completely stable, with better than 1 or 2mV of offset.
* Does not deliver any switch on thumps, DC shifts or other nasties.

I'd be the first to admit that the idea is not without risk, I have done it with with other solid state amps and tube pre-amps, but nothing with an unbalanced input with a 1K input impedance. He'll have to decide whether or not it is worth the risk - the designer with whom he has contact should be able to provide guidance as to whether or not this is a risky proposition.

Tigerscent has already been provided with appropriate guidance by those who have very long experience with the ME550, used with a very wide range of suitable and unsuitable sources. That includes the person who designed and manufactured the ME550. He was clearly and unequivocally told that use of a valve preamp would provide sub-optimal (at the very least) results.

Personally I would choose transformer coupling and avoid any risk of dc following the amplifier's input circuitry.

And excellent suggestion.

One could also do a parafeed output transformer arrangement with the white CF in the Aikido, ratios could be 1:1 to 3:1 for 0 to -10dB of attenuation. The 3:1 would reflect a 9K load to the Aikido which is not a difficult load for the version I suggested, would allow the use of a much smaller and presumably higher quality film coupling cap at the output, and still leave you with about 12dB of gain which is enough for most applications.

Or Tigerscent could use the preamp that was expressly designed for the ME550. That preamp exhibits a 2 Ohm (open loop) output impedance, unconditional stability, a frequency response from DC ~ 150kHz, low distortion, no DC shifts at switch on and zero global NFB. It is the safest, most appropriate option. And one that Tigerscent has yet to try.

I am not against the use of a valve preamp, per se. In fact, I would encourage Tigerscent to try an appropriate, low output impedance one, AFTER he has tried the preamp that the manufacturer suggests.

If Porsche suggsts the use of (say) Pirelli P-zero tyres, then would you fit (say) $100.00 tyres to one and expect the vehicle to perform?

Same deal with the ME550. A fine amplifier deserves the most appropriate match in preamp. A suitable preamp from ME, Krell, Mark Levinson or Gryphon are likely candidates. Most valve preamps are not suitable. Unless quite heroic alterations are made.
 
The things I could do with a third hand....
 

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I understand that. I confined my comments to those made by cjcc67.


Indeed, given your lack of knowledge about the specific product, your comments were reasonable. Which is why I did not address them.



<snip>

If Porsche suggsts the use of (say) Pirelli P-zero tyres, then would you fit (say) $100.00 tyres to one and expect the vehicle to perform?

Same deal with the ME550. A fine amplifier deserves the most appropriate match in preamp. A suitable preamp from ME, Krell, Mark Levinson or Gryphon are likely candidates. Most valve preamps are not suitable. Unless quite heroic alterations are made.

Your comments do make sense, and nothing I would inherently disagree with.. There are purpose built designs that would be suitable but that presupposes the OP has the ability to build such a design. It does seem to me that the matching pre-amp ought to be evaluated as a minimum.. FWIW there are not too many SS pre-amps that have such low output Z either if for no other reason than the series resistors generally found at their outputs.
 
Your comments do make sense, and nothing I would inherently disagree with.. There are purpose built designs that would be suitable but that presupposes the OP has the ability to build such a design. It does seem to me that the matching pre-amp ought to be evaluated as a minimum..

My point exactly. It always makes sense to start with a known yardstick and move on from there. Once Tigerscent has evaluated the 'standard' he can move onto other ideas and see how they compare. My point to Tigerscent has always been that the matching preamps are plentiful and modestly priced in Australia. He should have little difficulty in borrowing or buying one to try.

FWIW there are not too many SS pre-amps that have such low output Z either if for no other reason than the series resistors generally found at their outputs.

Indeed. I've long wondered at the laziness/incompetence of SS designers who build such devices, given the ease that a low source impedance can be accomplished with SS devices. At least valve designers have an excuse, though it would seem 100 Ohms is pretty easy to acheive using cathode followers. And, as you say, transformers could reduce this still further, albeit at the a monetary and sonic cost.
 
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<snip>

Indeed. I've long wondered at the laziness/incompetence of SS designers who build such devices, given the ease that a low source impedance can be accomplished with SS devices. At least valve designers have an excuse, though it would seem 100 Ohms is pretty easy to acheive using cathode followers. And, as you say, transformers could reduce this still further, albeit at the a monetary and sonic cost.

I suspect it has more than a little to do with the massive amounts of feedback employed to get good looking numbers and insufficient phase margin to safely drive typical audiophile capacitors, err.. cables.. :D

Long ago I did a tube phono stage and specifically told the dealer who was evaluating it that it needed to used with low capacitance cables into a 100K load minimum - they ignored my comments and the cables they used had about 500pF of capacitance and needless to say this design did not acquit itself very well under the circumstances - this was supposed to be a very minimalist phono stage that would retail for under $500. I learned a valuable lesson, that most dealers and audiophiles ain't that bright, and that I should not design things with a 10K output impedance.. :D
 
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