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Old 20th March 2005, 03:50 PM   #11
sajti is offline sajti  Hungary
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Here is my buffer circuit, I used few years before. It contains input selector, and volume pot, and works as preamplifier. It use very low supply voltages, and it works well with ECC88/E88CC only.ű

sajti
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Old 20th March 2005, 07:45 PM   #12
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"I have this schematic somewhere from the forum, but I forget already :-)) from which thread. Could somebody give me more info abaout it? Is it a buffer or a preamp?"

Hi thats my schematic based on JoeRasmussen's Valve buffer. I am using mine as a preamp with unity gain. Works great and sounds excellent. The power supply is very critical. Something like a split rail RCRCRC will do the trick. I am using 4 UL85 single diode rectifiers to get the split supply. The bottom 1.2K resistor is a mistake and should be more like 220K (try a few values until you like the sound, your looking for a voltage drop of about 1.6V across the resistor). I also tried a green LED to bias the bottom valve, but eventually found the sound a bit strident and went back to the resistor. That was when I discovered the mistake with the bias resistor.

I say try the schematic as is, Joe Rasmussen spent a good deal of time designing the principle of this circuit and he obviously thought it worthwhile using the bottom Constant Current Source over a basic resistor. I tried a basic resistor biased version (Joes published valve buffer). A version with a Mosfet at the top and a bias resistor at the bottom, and finally the version with the valve at the bottom and the Mosfet at the top. I definately found the final version the most satisfying (but there were many other variables which make a definative statement difficult).
Joe even went to the extent of replacing the top Mosfet with a valve in one of his preamps and said it sounded even better.

No compromise !!!!

Shoog
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Old 21st March 2005, 05:10 PM   #13
Tyimo is offline Tyimo  Hungary
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Hi!

Thanks - köszi Sajti!

Thanks Soog!!

Could you tell me something more about Buffer-preamp's PSU?
I mean: regulated or not, regulated DC or simple AC heather, etc?

Thanks!

Tyimo
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Old 21st March 2005, 05:44 PM   #14
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Hi,
Te power supply I used was quite simple.
As I said I made a bridge rectifier out of four UY85 valves (dirt cheap). I then put them into a split supply. Each rail was filtered by;
a small inductor from a bass speaker crossover (has little effect, but should slow down inrush current)
next a 270 ohm resistor
next a 220 uf cap to earth
next a 22 ohm resistor
next another 220 uf
next another 22 ohm resistor
another 220 uf cap.
Finally I have an o.47uf mkp cap between the rails.

I have had no issues with overstretching the rectifier valves and the thing has been running for about 5months now.

Ther raw AC supply is a little difficult to pin down as I have used a 6.3V transformer to supply two speaker line output transformer, which step the supply up to about 100V per side. Its very difficult to source suitable 70-100V transformers.

This supply is very quiet.
At first I tried replacing the middle filter cap with a capacitance multiplier, but this had a bad effect on the sound, and so I removed it with no ill effects.

Any more questions, just ask.

Shoog
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Old 22nd March 2005, 05:10 PM   #15
Tyimo is offline Tyimo  Hungary
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Thanks a lot Shoog!!

Greets:
Tyimo
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Old 27th March 2005, 06:39 AM   #16
Tyimo is offline Tyimo  Hungary
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Sajti!

A tápodban hány Wattos az R6-7 ellenállás? 0.5-3W?

Köszi!


I would like to wish for every DIY-ers Happy Easter!
Tyimo
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Old 27th March 2005, 06:50 AM   #17
sajti is offline sajti  Hungary
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Quote:
Originally posted by Tyimo
Sajti!

A tápodban hány Wattos az R6-7 ellenállás? 0.5-3W?

Köszi!


I would like to wish for every DIY-ers Happy Easter!
Tyimo

Szia,

miután még sztereóban sem folyik rajta 10mA-nél nagyobb áram, ezért 0.5W-1W bőven elég. Én 1W-ost használtam

sajti
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Old 28th March 2005, 07:45 AM   #18
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Default Re: ECC85 or ECC88?

Quote:
Originally posted by Tyimo
Hi!
Could somebody give me some info about the attached schem: could I use it for tube buffer? Is it possible to use the circuit with ECC88 tube too? What would be the lowest voltage for?
Thanks

Tyimo
That circuit is called a super linear cathode follower SLCF.
To the best of my knowledge it was pioneered by
Allen Wright and Joe Rassmussen of Vacuumstate.

Cheers,

Terry
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Old 28th March 2005, 08:14 AM   #19
Will is offline Will  Malaysia
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Location: Kuala Lumpur
Quote:
Originally posted by Shoog
Hi,
Te power supply I used was quite simple.
As I said I made a bridge rectifier out of four UY85 valves (dirt cheap). I then put them into a split supply. Each rail was filtered by;
a small inductor from a bass speaker crossover (has little effect, but should slow down inrush current)
next a 270 ohm resistor
next a 220 uf cap to earth
next a 22 ohm resistor
next another 220 uf
next another 22 ohm resistor
another 220 uf cap.
Finally I have an o.47uf mkp cap between the rails.

I have had no issues with overstretching the rectifier valves and the thing has been running for about 5months now.

Ther raw AC supply is a little difficult to pin down as I have used a 6.3V transformer to supply two speaker line output transformer, which step the supply up to about 100V per side. Its very difficult to source suitable 70-100V transformers.

This supply is very quiet.
At first I tried replacing the middle filter cap with a capacitance multiplier, but this had a bad effect on the sound, and so I removed it with no ill effects.

Any more questions, just ask.

Shoog


Shoog,

To put things into perspective as the literature mentioned to operate the vavles in the proper cascode manner, which pin does the 1K input resistor connectes to ?


regards,
will.
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Old 28th March 2005, 10:27 AM   #20
Alkis is offline Alkis  Greece
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Let's say we have a CDp with a typical Zout of 50K and an amplifier with the same Zin.What's the purpose of using some buffer stage?Why does this change so much the tonal quality-which ever huppens, but I can't explain why.Is this just because of the elimination of capacitance that wires and pot injects?
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