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
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
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.
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.
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.
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.
The surest way to produce 2nd harmonic distortion is the circuit used to drive the tone stack of a Fender Bassman. A 12AX7 grounded cathode directly coupled to a cathode follower (the other half of the valve), biased to have some grid current. with 300Volts anodes, 100K loads and 1,8 K on the cathode of the 1st stage you are good to go.
Thanks !
I have to say that i'm amazed by the quality of your information & i thank you all. I would like a link for a decent tube buffer circuit using ecc88 tube that can be easily build & give me a chance to experiment a little. I have seen buffer devices sold on ebay by indeed hifi , even some well known audio brands.
I would really like to build a point to point buffer like those.
I have to say that i'm amazed by the quality of your information & i thank you all. I would like a link for a decent tube buffer circuit using ecc88 tube that can be easily build & give me a chance to experiment a little. I have seen buffer devices sold on ebay by indeed hifi , even some well known audio brands.
I would really like to build a point to point buffer like those.
The 6922/6DJ8/E88CC will also produce 2nds if designed 'right'. No need to build a Fender Bassman...the dude is wanting to use his E88CCs.
Try a common cathode stage with very low plate resistor, say 2kohms, running off a b+ of 75-80volts. Unbypassed cathode resistor of about 200-330ohms. The quiescent current will be ruffly 4mA, dropping 20volts over Rp. According to LTspice that gives you almost 10% 2nd harmones with a large input signal (2volts), but only 2-3% with a more common .5volts input. It will have gain, so it's not a buffer. You can take the signal off the cathode, with a 3-4dB loss, but that's probably even better in your application.
Try a common cathode stage with very low plate resistor, say 2kohms, running off a b+ of 75-80volts. Unbypassed cathode resistor of about 200-330ohms. The quiescent current will be ruffly 4mA, dropping 20volts over Rp. According to LTspice that gives you almost 10% 2nd harmones with a large input signal (2volts), but only 2-3% with a more common .5volts input. It will have gain, so it's not a buffer. You can take the signal off the cathode, with a 3-4dB loss, but that's probably even better in your application.
the chinese used the 6N2, a 12x7 equivalent as cathode followers in this amp, running them at +/12v rails....in case you are wondering the 2 5z4 rectifiers supply +/-6volts to a 4558 ic......
An externally hosted image should be here but it was not working when we last tested it.
some help.
Your suggestion looks very interesting. The tubes i have where bought to support my tube pre-amplifier which is now a killer with 2 siemens ecc88cc from the 70's installed inside. I have never build any tube circuit, i was always into transistorised audio equipment.
Can you draw a circuit (or any available from the net) with the one you propose? I have all the parts and transformers needed. No problem if the tube buffer amplifies things a bit.
Thanks
Your suggestion looks very interesting. The tubes i have where bought to support my tube pre-amplifier which is now a killer with 2 siemens ecc88cc from the 70's installed inside. I have never build any tube circuit, i was always into transistorised audio equipment.
Can you draw a circuit (or any available from the net) with the one you propose? I have all the parts and transformers needed. No problem if the tube buffer amplifies things a bit.
Thanks
Last edited:
Rather then draw one how about simply point you to one. Look at the schematic at the top of this page. It is what everyone here has been suggesting. It is very basic and easy to build. However is has a bunch of gain so you WILL need a volume control. Build this in an over sized chasis so you have room to modify it later and use shielded wire in the signal path, ground only one end of the shield. Layout matters a lot. The unlabeled cap that connects the cathode to ground can be omitted or use a 25uF 25V electrolytic.
The Valve Wizard
Also you might want to read that entire web site especially the "triode gain stage" link
How to design valve guitar amplifiers
About the volume control. My opinion is the best place for it is between the two triode sections but it could also go on the power amp. A third option is both Use fixed resistors between the triodes to cut, maybe 4:1. Try the buffer then adjust the ratio so the volume control pot has a good range
Last edited:
That is what I'd call and "effects box" not a "buffer". Running a 12*7 tube at such low voltage is totally unpredictable. Every brand of tube sounds different because the curves are mostly undefined. Any reasonable buffer design will use at least 100 volts DC power supply.
You can get a good 120V transformer for "free". You may even have the parts on hand.
I have built a buffer type box using two wall wort power cubes. What you do is find an AC power cube and then place it's twin inside the box and connect the 12VAC sides together. Basically, one power cube works as designed, the second one runs "backwards". Obviously you need AC power cubes. So if cost is an issue this is nearly free. One more thing use some of the 12VAC to run the heaters.
If you don't have AC power cubes then crack open DC cubes and remove the transformers. But this is much more work better to buy the AC units
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.