ECC88 tube buffer NEEDED !

[vmed_cha_gr]

Hi
I have about 10 ecc88 tubes from different brands (philips bugle-boy, avirex, toshiba, svetlana & sovtek) . I want to make some tube buffers so i can give an analogue kind of sound to digital sources (like cd players).
Does anyone have a simple circuit to share with me?
Many Thanks
Vassilis

[DF96]

Search for a thread started by Wavebourn in which he presented a circuit which allows you to adjust how much distortion to add to a signal.

[bigwill]

Seconding DF96, a (properly designed) ECC88 buffer / follower will not have a sound and you may be disappointed.

[v4lve lover]

ecc88 is terribly lineair if you want coloured sound go for something whit horrible distortion btw dont forget it was made to operate at about 90vdc plate so dont go higher

[DF96]

Run a 12AX7/ECC83 from a +12V supply and you can get as much distortion as you want. Or use a low gain remote cutoff valve like EF92 as a cathode follower - plenty of second order distortion so it could sound quite 'musical'.

[kevinkr]

Seems like the ECC82 run on a low plate voltage might also be a choice. Generally if you want to warm up bad digital sound it means designing a bad (distorting) tube amplifier stage to do that - hence the many comments to that effect. Ideally you would want to bias for maximal 2nd harmonic..

[SemperFi]

Originally Posted by v4lve lover

... btw dont forget it was made to operate at about 90vdc plate so dont go higher

I've used these at > 200V with no issues. Usually I run them at 50-140V on the plates depending on usage, but they can take 200V and more. Look at some old HP oscilloscope schems, and you'll see them with b+ up to 400V.

With only 40-50volts you'll probably get some 2nd Harmones but it might not be enough to hear. Also at such low voltages you may start to pull some grid current, but an iPhone or other digital devices will probably handle that fine.

[suntechnik]

Originally Posted by vmed_cha_gr

I want to make some tube buffers so i can give an analogue kind of sound to digital sources (like cd players).

You can get good interpolated DAC instead might be a much better option.

Wadia decoding computers are good could be purchased second hand form Audiogon at decent price. Pioneer Legatto Link fairly inexpensive however not on a par with Wadia or dSC.

6DJ8 and similarities like ECC88 tubes were designed to be used in oscilloscopes like Tektronix.

BTW I am owning Graaf 13.5 II powered by 6922 it is the best preamp I ever heard.

You can Google ECC88 mu-follower to let your tubes be implemented.

[ChrisA]

Originally Posted by vmed_cha_gr

Hi
I have about 10 ecc88 tubes from different brands (philips bugle-boy, avirex, toshiba, svetlana & sovtek) . I want to make some tube buffers so i can give an analogue kind of sound to digital sources (like cd players).
Does anyone have a simple circuit to share with me?
Many Thanks
Vassilis

If you find a good design it will not do what you want. The "tube sound" requires that the tube be used to provide some gain. Even bette if the tube provides some gain in an open loop with no NFB.

The common way to do that is found in most guitar amps. The use the tube to provide abot 50X voltage gain and then squash all of that with a voltage divider (aka "gain pot"). Such a stage can produce at least 10% THD. More if you abuse it.

But almost all buffer designs you see will be very conservative and will sound just like a short length of good wire.

What you want is easy to design. build a common cathode gain stage with a smallish plate load and then a 10:1 resistive divider.

[ChrisA]

Originally Posted by kevinkr

Seems like the ECC82 run on a low plate voltage might also be a choice. Generally if you want to warm up bad digital sound it means designing a bad (distorting) tube amplifier stage to do that - hence the many comments to that effect. Ideally you would want to bias for maximal 2nd harmonic..

YES. Exactly. Don't think "HiFI". Look instead to musical instrument amps for inspiration and ideas. These kinds of amps are NOT designed to reproduce music, but to create music. Very different goals.

In technical terms what you are looking for is adding a bit of compression to transients so they clip softly and in a 'musical way' and at the same time actually adding some low numbered harmonics.

BTW "maximal" 2nd harmonic might be more than you want. But adding 5% to 10% is not unreasonable.