If people knew how to do proper distortion measurements. They would not be ordering boards but would do point to point. The boards just make it that much easier (and neater).
The only distortion measurements I know of are on John Broskie's site.
http://www.tubecad.com/2005/January/blog0032.htm
Mine is P-to-P, 220V B+ circuit in Blog 30. 6CG7 into 5687. CLCRCRC PS with regulated 12V DC heaters. I built it on a chassis from a AES AE3 preamp using mostly the existing power supply.
Sound is better than the AE3, which was a typical voltage amp-cathode follower 6SN7 affair. Better in every way. Dead quiet, more dynamic and detailed. More true to life for lack of a better term. Piano sounds like piano - nothing soft or muddled, nothing edgy.
No measurements except the one that counts - listening pleasure.
MG
Sound is better than the AE3, which was a typical voltage amp-cathode follower 6SN7 affair. Better in every way. Dead quiet, more dynamic and detailed. More true to life for lack of a better term. Piano sounds like piano - nothing soft or muddled, nothing edgy.
No measurements except the one that counts - listening pleasure.
MG
Bas Horneman said:
Yeah, I saw those, and that was a good starting point. I'm quite interested in the effects of tubes, operating point, and circuit trimming.
BTW, I'm an exception to your rule- I have it built on a board (one of Broskie's- it is a heroic PCB), yet I know how to do proper distortion measurements...
Well, certainly that, but also to probe what the circuit can and can't do, to get an idea of how to really optimize linearity for different applications. I can build about a million variations, but that will take me a million years. So I'm playing around with a couple, but the collective efforts of other guys in their workshops would help map out the design landscape a bit more than it is now.
Ummmm... I have done the measurements.... but only on a Pentode Aikido... so not really relevant...
On the pentode Aikido the distortion and spectrum at the output look the same as the distortion and spectrum on the pentode anode i.e. measure the same and has the same spectrum - as far as my measurement setup can tell (say to 5% of measurement).
This using a 6B8-G pentode and driving two PT15s in triode mode PP through and IT phase splitter.
I haven't bothered to measure the all triode Aikido as it sounds so open and transparent that I just listen to it
(6N1P and 6N6P)
James
On the pentode Aikido the distortion and spectrum at the output look the same as the distortion and spectrum on the pentode anode i.e. measure the same and has the same spectrum - as far as my measurement setup can tell (say to 5% of measurement).
This using a 6B8-G pentode and driving two PT15s in triode mode PP through and IT phase splitter.
I haven't bothered to measure the all triode Aikido as it sounds so open and transparent that I just listen to it
(6N1P and 6N6P)James
Thanks, guys. With triodes, I find the gain to run about 40-45% of mu, so pentode definitely had me curious.
Distortion results I've gotten so far are quite good, but not blow-away. Distortion reduction requires a LOT of supply voltage, and JB's boards are set up so that the same tube envelope carries both top and bottom triode (to more easily allow voltage amp and follower to be different tubes). This means that the tubes' heater-to-cathode voltage ends up being strained. For the case of ECC88-family, one has to take the plate-to-cathode voltage well above the rated maximum to get the distortion to fall below that of a common-cathode stage.
At output voltages more typical of line stages (2-3VRMS) and a 160V supply, 2nd HD is the only one visible at -55dB for the best-selected tube sample and the resistor ratios tweaked for the best distortion null.
Distortion results I've gotten so far are quite good, but not blow-away. Distortion reduction requires a LOT of supply voltage, and JB's boards are set up so that the same tube envelope carries both top and bottom triode (to more easily allow voltage amp and follower to be different tubes). This means that the tubes' heater-to-cathode voltage ends up being strained. For the case of ECC88-family, one has to take the plate-to-cathode voltage well above the rated maximum to get the distortion to fall below that of a common-cathode stage.
At output voltages more typical of line stages (2-3VRMS) and a 160V supply, 2nd HD is the only one visible at -55dB for the best-selected tube sample and the resistor ratios tweaked for the best distortion null.
As another example Dave Dove posted his pentode aikido into 300BXLS design a little while ago. I designed the aikido stage and that runs the pentode at a gain of about 110 times.
I have run a pentode aikido at 200 times gain on the bench with no problems and a cascode aikido at a gain of 360 times... yes I'm playing with Aikido RIAA cicuits for a DL103
James
I have run a pentode aikido at 200 times gain on the bench with no problems and a cascode aikido at a gain of 360 times... yes I'm playing with Aikido RIAA cicuits for a DL103
James