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Best Valve pre-amp match for ME 550 amp

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No idea. There is no schematic supplied.

...also, what are the steps in transformer coupling with regards to the JP200

The transformer is the easy part. Connect it to the output. You will also need to alter the gain of the preamp to compensate. This will alter the sound of the preamp.

...and what mods would you suggest to help with the loop feedback?

I wouldn't. The preamp is designed to incorporate global NFB. Removing it would be difficult and time-consuming for someone (else) to work out.

(As I do this in stages, Its more affordable, and I end up using better components)

Once I build this, I still would like to try the ME preamp:installments work well with me ... :)

You should try the ME preamp FIRST, not last. The ME preamp is as good as the best valve preamps available and far better than cheap crap. And by the best I mean products like the Conrad Johnson Premier 16, et al.
 
No idea. There is no schematic supplied.



The transformer is the easy part. Connect it to the output. You will also need to alter the gain of the preamp to compensate. This will alter the sound of the preamp.

Can you elaborate a bit on how to do this?

I wouldn't. The preamp is designed to incorporate global NFB. Removing it would be difficult and time-consuming for someone (else) to work out.

how is global NFB in the preamp going to affect the ME 550 sound quality typically?

You should try the ME preamp FIRST, not last. The ME preamp is as good as the best valve preamps available and far better than cheap crap. And by the best I mean products like the Conrad Johnson Premier 16, et al.

Which ME preamp would you suggest as a best performance/value match for the 550, which includes a phono stage?
 
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They were well designed products and sounded special - especially with low impedance brute speakers like Apogee, Thiel, Duntech, Ambience etc lots of control and dynamics where others amps could sound kinda muted and flat. Mr Stein is an accomplished designer certainly and the temperature thing does make a difference to dynamics and linearity. The ME15 isn't too expensive s/h. I see units go for 400-600 on ebay pretty regularly and the 25 for 800 or so with the phono stage. You can pay more for the latest "upgrades". Details of what exactly (components please if anyone knows enough to talk about them) they are might be would be nice else it's tricky to know what you're paying for of course.

Fair question. Here are the differences between the old and new ME preamps:

Old:
Power Transformer: 4VA, EI core type.
2,000uF in external power supply box.
Total of 6,000uF capacitance on internal power supply PCB.
Regulation provided by LM340T15, with series pass transistor for -ve rail.

New:
Power transformer: 40VA, 'R' core type.
20,000uF in external power supply box.
23,000uF on internal power supply PCB.
Pre-regulation and capacitance multiplication, via series pass transistors.
Line level regulation via LM317T/LM337T devices.
Phono regulation via LM317T/LM337T devices.
Muting on board.
Provision for remote control if required.


All alterations are centred on power supply and regulation.

The 15 is nice enough (same line board) if you don't need two tape loops and phono. They (the pre's) also make a nifty headphone amp if you have high impedance (>300ohm) cans - with a very similar sonic signature to the power amps - dynamic and open and clear. A possible config might be source>tube buffer>me pre>me power to give you some tubey goodness. My unit also got a slight power hum when it was converted to high impedance operation (in only one channel) so be aware of that if you have silly efficient lowthers or something..unless you like humming.. :D

It's more likely something else was wrong. Converting to high input impedance has never, IME, ever led to more noise (though there will be a VERY slight increase in theoretical noise performance - in reality, the difference will be academic).
 
Can you elaborate a bit on how to do this?

Connect one pair of terminals of the primary of the transformer to the output and earth of the preamp. Take the secondary connections to the power amp.

Which ME preamp would you suggest as a best performance/value match for the 550, which includes a phono stage?

An ME15 or ME25 will suffice. The ME15 is less expensive but far less commonly available. Both are sonically identical. If you are in/near Sydney, I will be happy to loan you an ME preamp. If you are outside the Sydney area, then I will post one to you for evaluation. You pay freight both ways.
 
Connect one pair of terminals of the primary of the transformer to the output and earth of the preamp. Take the secondary connections to the power amp.

So the Primary of the transformer used in the preamp; has one pair of terminals connected to the preamp - while the secondary connections go to 'where' in the power amp?

(I assume they are also connected to the preamp : as well as wherever (please specify) on the 550 right?)
 
The secondary windings are connected to the input of the ME550.

So the 550 is not plugged into 240v power, but instead is powered by the secondary windings of the preamp transformer. What about the secondary windings that connect to the preamp as well, are they secondaries then connected to preamp and the input of the 550 (instead of it being plugged in) or am I missing something ??
 
So the 550 is not plugged into 240v power, but instead is powered by the secondary windings of the preamp transformer.

NO! You are buying a pair of AUDIO COUPLING transformers to add to your preamp, in order to lower the output impedance to a suitable figure. Those transformers (one for left and one for right) are connected between the output of the preamp and the audio input of the power amp.

What about the secondary windings that connect to the preamp as well, are they secondaries then connected to preamp and the input of the 550 (instead of it being plugged in) or am I missing something ??

Consider my offer of a loan ME preamp. You will rapidly dispense with your experiment that I suspect you are not qualified to perform.
 
NO! You are buying a pair of AUDIO COUPLING transformers to add to your preamp, in order to lower the output impedance to a suitable figure. Those transformers (one for left and one for right) are connected between the output of the preamp and the audio input of the power amp.

ahhhh, well now its making more sense...lol (It didnt make much sense to me, but in case there was some esoteric element to the whole thing ie: using the secondary in both the secondary in the preamp and secondary in the power amp at the same time, is what I was actually thinking, but the way you wrote it, made it hard to follow, so just 'asking'. I knew you would correct me :)

so, can you specify the audio coupling transformers I should use (ie: RS components or element14), based on the pcb and 550?


Consider my offer of a loan ME preamp. You will rapidly dispense with your experiment that I suspect you are not qualified to perform.

I am a beginner - we all start somewhere. I am learning as I go along --- which is why I ask questions :)

I might take you up on your loan offer when I put the silver wiring in my 550...
 
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Avoid them. Use the appropriate technology to deal with the problem. Valves are not the appropriate technology to deal with your problem. SS is. That said, high quality transformers (which are expensive) will do pretty much all you require, without serious degradation of performance. Frankly though, I can't see why you would bother. A zero GNFB, low output impedance SS preamp is exactly what you need. Think of it this way:

Take a crappy, 20 year old Hyundai Excel, with bad tyres. Bolt a fifth wheel to it and you may well gain an improvement.

Now take a new Porsche 911, shod with Pirelli P-Zeros. Bolt a fifth wheel to it and you can pretty much guarantee that you will damage it's performance. That is what you are trying to do with your ME550 - cripple it's performance.
 
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