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Old 9th January 2013, 10:01 AM   #51
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So, how would transformers be used to manage a low impedance, assuming I was to build the pre-amp - 12AU7 Balance Tube Valve Preamplifier Amplifier DIY Kit ref AR (No Tube) | eBay - rated at 400 ohms: to bring it to the required 2 - 10 ohm range?

Is there any other way as well?
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Old 9th January 2013, 11:38 PM   #52
treuben is offline treuben  Australia
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Someone seems a little invested in ME *me*thinks.. lol Anyhow, the impedance is just pro level 600ohm so any pro preamp designed to drive that impedance will be happy - (most hi-fi units will tell you what impedances they're happy with too in the specs) and yes, there was some reconfiguration besides the resistors. Turning the psu plug around (!) on one board. You know, I think these people would go a lot further toward giving people a positive view of their products if they weren't so obtuse about what actually was going on and trying to make service money. (My apologies if you aren't - perhaps I'm just overly sceptical) If you know (and it sounds like you might), upload the documents or description and help everyone! There are any number of capable people and they'd be delighted to have the info. For example; How about telling us which board (if it matters) to reverse the power connector on? Scan of instructions would be nice. Peter Stein did send those out on more than one occasion so I'm sure service people would have them. The reversing of the power connector put both channels in phase psu-wise and having them out of phase meant that you could bridge the channels (you can't do this one you put the amp into high impedance mode with psu back in phase) and also there is some advantage to bass transients coming off opposite rails allowing slightly greater dynamics in that config. I knew a man who distributed and repaired ME for many years and several owners so my failure opinions are anecdotal and not scientific certainly. Sadly the only people who could make a scientific study are people with vested interests so it doesn't make those accounts any more trustworthy. Perhaps we could make a poll sometime of owners concerning repair expense and failure. That would probably be more useful then either account. Careful of the fan cmos logic/counter chip - it's static sensitive and goes now and again. It's also socketed and on the fan board (pretty obvious as there's only one of those) If your fan goes full speed or stops with an error that might be the culprit. The service tech told me that lightening gets them (I don't see how) but hey. If you buy the amps online and get them shipped also check that the fans don't drop and jam because of being dropped by couriers. The impeller part is held in with a little cir-clip and occasionally fell down due to transit shock. Simple enough to put back after removing the sticker - same procedure as for lubrication if you've done that on sleeved units for pc's etc. Nice sounding dynamic amps. Pro's: dynamics, good low level detail for ss, good drive and openness. Cons: not particularly holographic soundstage (no way you can get that with low distortion though- it's an illusion coming from phase delays and harmonic distortion - read transformers and tubes or fets.)
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Old 9th January 2013, 11:54 PM   #53
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I decided to go with this one for now. It will be a work in progress, and it seems to be a good design so far --- I have a feeling it will match the ME 550 well, given a few adjustments here and there...

http://www.ebay.com.au/itm/JP-200-JP...item4ab888e981

Any thoughts on the design? Also, schematics of 550 would be nice to have with regards to making appropriate modifications --- so if they can be supplied would be good.

I would still like to compare this once finished to an ME pre-amp...

Last edited by TigerScent; 10th January 2013 at 12:01 AM.
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Old 9th January 2013, 11:58 PM   #54
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Originally Posted by TigerScent View Post
I decided to go with this one for now. eBay Australia: Buy new & used fashion, electronics & home d?r It will be a work in progress, and it seems to be a good design so far --- I have a feeling it will match the ME 550 well, given a few adjustments here and there...

Any thoughts on the design? Also, schematics of 550 would be nice to have with regards to making appropriate modifications --- so if they can be supplied would be good.

I would still like to compare this once finished to an ME pre-amp...
Item removed.
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Old 10th January 2013, 12:00 AM   #55
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Quote:
Originally Posted by Zaphod Beeblebrox View Post
Item removed.
yes, I saw that, I updated it: JP-200 JP200 Valve Tube Preamplifier Amplifier Bare PCB (Stereo), based on Jadis | eBay

Last edited by TigerScent; 10th January 2013 at 12:02 AM.
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Old 10th January 2013, 12:05 AM   #56
treuben is offline treuben  Australia
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Not that I'm insinuating reliability problems with the fan chips (I've had the same kind of cmos chip go in a Crown Powerline series (also nice and dynamic actually) and no-one complains about their reliability. In that circuit it was used as an error condition logic part and broken=error light and no starty. A pita but at least it only cost me $3.50 to fix as the schematic was freely available from Crown and that made repair easy and cheap. 8) That's the kind of support we like to see! There will always be companies that grind off part numbers (at least ME didn't do that to my knowledge) and don't provide schematics to owners. (Like Audio Research and Halcro - steer clear!) so think about what you're buying in terms of support too - we would if we were buying a car. The excuse that info in the wrong hands is dangerous doesn't wash with me. It's always better to be available to everyone. If one uses it and breaks the thing then you pay for someone who does know what they're doing or a dealer sanctioned repairer (if they're still around and don't cost more than a new amp - I bet those Halcro repairs are interesting now given the choice of repairers lol). As for building decent preamps, yes thats not too hard in diyaudio - plenty of matched quality transistors for sale cheap too. It's not rocket science. Impedance ratios of pre-out to main in are usually quoted as 1:10 as optimal with opinions varying slightly - plenty of info on the preamp building threads. Even 1:1 can work well for some people - like Mr Pass is fond of saying: listen and see! For the purposes of buying though.. Probably look for output Z less than 100ohms or get the info to convert your 550 to high impedance mode. No-one should charge you more than a minimal fee for lifting resistor leg and changing the plug around.
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Old 10th January 2013, 12:14 AM   #57
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Quote:
Originally Posted by treuben View Post
Not that I'm insinuating reliability problems with the fan chips (I've had the same kind of cmos chip go in a Crown Powerline series (also nice and dynamic actually) and no-one complains about their reliability. In that circuit it was used as an error condition logic part and broken=error light and no starty. A pita but at least it only cost me $3.50 to fix as the schematic was freely available from Crown and that made repair easy and cheap. 8) That's the kind of support we like to see! There will always be companies that grind off part numbers (at least ME didn't do that to my knowledge) and don't provide schematics to owners. (Like Audio Research and Halcro - steer clear!) so think about what you're buying in terms of support too - we would if we were buying a car. The excuse that info in the wrong hands is dangerous doesn't wash with me. It's always better to be available to everyone. If one uses it and breaks the thing then you pay for someone who does know what they're doing or a dealer sanctioned repairer (if they're still around and don't cost more than a new amp - I bet those Halcro repairs are interesting now given the choice of repairers lol). As for building decent preamps, yes thats not too hard in diyaudio - plenty of matched quality transistors for sale cheap too. It's not rocket science. Impedance ratios of pre-out to main in are usually quoted as 1:10 as optimal with opinions varying slightly - plenty of info on the preamp building threads. Even 1:1 can work well for some people - like Mr Pass is fond of saying: listen and see! For the purposes of buying though.. Probably look for output Z less than 100ohms or get the info to convert your 550 to high impedance mode. No-one should charge you more than a minimal fee for lifting resistor leg and changing the plug around.
Im sure Peter Stein would gladly give this info, where I to contact him. He is not so easy sometimes to get hold of, but when you do, he is on a roll...I found him to be a very helpful person. Dont know what he might think of my idea, but to date I have found him an amiable and well-meaning chap. He modified the internals so that I could easily wire silver wiring to output as well. I just dont want to contact him unless necassary and cannot get the info otherwise (its painful trying to reach him). I had him refurbish and modify my ME 550, (including fan) and it worked like a charm when I got it; havent plugged it in since.

I really would like the valve sound hybrid with it though, as I have experienced just a simple but effective chinese valve buffer (which I modified a bit) in a NAD unit, between pre-amp/amp giving greater soundstage and clarity. Once I have achieved this, then would like to compare the ME preamp (or vice:versa - whichever).

I think either way, this would only promote the ME and probably initiate a greater interest with innovation in the product. I was using an NAD 7150 preamp out with the 550, and the sound was good, in comparison to the NAD stock amp sound.

So ANY good ideas with regards to mods are welcome and encouraged
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Old 10th January 2013, 12:16 AM   #58
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Originally Posted by TigerScent View Post
The circuit will exhibit a hopelessly high output impedance (>1,000 Ohms), but you should be able to transformer couple it to deal with that issue. Also, it uses a loop feedback, which is not a great idea, sonically, given your ME550 eschews the use of global NFB. ME preamps also eschew the use of global NFB, as do most high end amps and preamps.

Have you costed the project? Using quality parts, it will cost a fair chunk of money. You could probably buy a nice, second hand ME preamp for the same money.
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Old 10th January 2013, 12:26 AM   #59
treuben is offline treuben  Australia
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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. 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..
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Old 10th January 2013, 12:27 AM   #60
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Quote:
Originally Posted by Zaphod Beeblebrox View Post
The circuit will exhibit a hopelessly high output impedance (>1,000 Ohms), but you should be able to transformer couple it to deal with that issue. Also, it uses a loop feedback, which is not a great idea, sonically, given your ME550 eschews the use of global NFB. ME preamps also eschew the use of global NFB, as do most high end amps and preamps.

Have you costed the project? Using quality parts, it will cost a fair chunk of money. You could probably buy a nice, second hand ME preamp for the same money.
How would you rate/compare this one: http://www.ebay.com.au/itm/320934868...84.m1438.l2649

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

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

(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 ...

Last edited by TigerScent; 10th January 2013 at 12:37 AM.
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