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Best Valve pre-amp match for ME 550 amp
Best Valve pre-amp match for ME 550 amp
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Old 2nd January 2018, 05:37 AM   #211
Eli Duttman is offline Eli Duttman  United States
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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!
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Old 2nd January 2018, 09:13 AM   #212
Zaphod Beeblebrox is offline Zaphod Beeblebrox  Australia
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Quote:
Originally Posted by anatech View Post
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.
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Old 2nd January 2018, 10:49 PM   #213
TigerScent is offline TigerScent  Australia
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Arrow ...moving along

Quote:
Originally Posted by Eli Duttman View Post
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... :-)

Last edited by TigerScent; 2nd January 2018 at 10:52 PM.
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Old 2nd January 2018, 11:16 PM   #214
kevinkr is offline kevinkr  United States
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Best Valve pre-amp match for ME 550 amp
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.
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Old 2nd January 2018, 11:52 PM   #215
TigerScent is offline TigerScent  Australia
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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...

Quote:
Originally Posted by kevinkr View Post
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.
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??

Quote:
Originally Posted by Eli Duttman View Post
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??
Attached Files
File Type: pdf JP200 Preamplifier Schematic.pdf (15.7 KB, 13 views)
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Old 3rd January 2018, 07:20 AM   #216
Eli Duttman is offline Eli Duttman  United States
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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.

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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Last edited by Eli Duttman; 3rd January 2018 at 07:21 AM. Reason: grammar
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Old 3rd January 2018, 08:12 PM   #217
Zaphod Beeblebrox is offline Zaphod Beeblebrox  Australia
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Quote:
Originally Posted by Eli Duttman View Post
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.

Quote:
Originally Posted by Eli Duttman View Post

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.

Quote:
Originally Posted by Eli Duttman View Post

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.

Last edited by Zaphod Beeblebrox; 3rd January 2018 at 08:27 PM.
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Old 4th January 2018, 02:15 AM   #218
Eli Duttman is offline Eli Duttman  United States
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Quote:
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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Last edited by Eli Duttman; 4th January 2018 at 02:18 AM. Reason: clarified remarks
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Old 4th January 2018, 02:17 AM   #219
TigerScent is offline TigerScent  Australia
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Quote:
Originally Posted by Eli Duttman View Post

"...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
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Old 4th January 2018, 02:22 AM   #220
TigerScent is offline TigerScent  Australia
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Quote:
Originally Posted by Eli Duttman View Post

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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