EWBrown wrote:The CCCCS board on top runs at approximately 4 mA per 6DJ8 triode. The silicon is essentially outside of the signal path, but it can still "color" the sound, some folks like it better, some prefer plain old fashioned resistors. My ears aren't good enough to tell the difference... Yellow_Light_Colorz_PDT_05 Yellow_Light_Colorz_PDT_02
I have done some tests a while back in regards to ss v.s. tube power supplies, and the diodes in the power supply can create noise and other 'artifacts' in the sound, but this is more true of the power supply in the presence of higher gain stages. This usually is remedied by using more filter sections or even a choke filter. So that can negate that benefit of the tube rectifier. In a guitar amplifier, a class AB amp can 'pull down' a tube rectifier and as such, when you nail the amp, the voltage drops further enhancing that 'playing the amp' feel. This is why many guitar amp purists WANT a tube rectifier. However, this only works with class AB amps. Class A amps draw constant current and the effect isn't as noticeable. BUT still a tube rectifier makes less noise.
I think that one of the biggest assets of a tube rectifier is that you can create a 'slow heat' circuit on the filament. This way you only need one power switch when you turn on the amp. In other words you can set the amp so that the B+ comes up after the rest of the amp has warmed up. You also don't have the nasty inrush as you would with silicon rectifiers.
But despite all of this, I still don't mind having silicon rectifiers in the power supply. But when you put them in the signal path, then I pull on the reins a bit.
The C4S has too many "moving parts" for my liking, I'd probably go with an IXYS IXCP10M45S and a current set resistor, use two components, instead of six, per tube plate. There are some neat 10M45S "tricks", but I'll go into those elsewhere.
The reason for the C4S (or any CCS) plate load is that with its very high effective impedance, the tube stage can allegedly deliver more gain, and wider bandwidth.
Agreed, this design falls out of the "KISS" concept and would normally be a design I would avoid. As for high impedance plate loading...well, that is what an SRPP gain stage is for...and it is all tube :).
That EL34 SE would be a perfect one to try the red LED on the 6SL7 cathodes. The voltage is in the right range for common red LEDs.
Good, then I can build my breadboard with one channel using the resistor and cap and the other using a LED. Then I can compare.
It runs the two sections of each 6SL7 in parallel, which doubles the gm and halves the rp, and the mu stays the same. This allegedly increases the dynamic range and lowers noise. Looks like they run at 1.7 mA (1.7V thru a 1K resistor). Or 0.85 mA per section.
Yeah, they mentioned the benefits of paralleling the sections in the document with the amp. I actually prefer this to 'sharing' stereo amp sections in one bottle. I always believed that there could be some crosstalk or 'bleed over' when building two sections of a stereo stage in one bottle. However, I have not tested that theory, so I am not sure what the truth is in that matter.
I'd start t with the red LED (cathode to ground, anode to the tube's cathodes).
It is easy enough to take the LED out and install the resistor and cap, and then compare which sounds better.
Or you could build one channel with the LED and the other with the resistor and cap and get a real-time side by side comparison.
/ed B
Yup, that is what I mentioned above and that seems like a good way to go. I have a dual trace scope too, so feeding the same signal into both amp sections, I can lay one trace on top of the other and do simultaneous comparisons.
Last night I was orienting some parts on the 'board' that I am going to put everything on. However, since I was using shelving material, I realized that my board was not actual pine, but a wood 'image' overlay glued onto press board (El Cheapo wood). Given the weight of the transformers, I am sure the board would snap in half if I tried to carry it with that weight. So I need to find a nice solid piece of pine to lay everything out on.
Geo