6V6 line preamp

[disco]

.... and maybe better sound!

Hi Massimo, long time ago since we spoke

that really depends what load is ....... and is also more tube dependable

some tubes , when properly loaded according to their Ri , have no difference with or without cathode res. bypass , sound-wise

Right now I'm watching a bunch of square waves being amplified. I'll do the same without caps. Removing the caps will introduce local feedback, so the change ought to be noticable.

Salas, what was your impression with degenerated cathodes? Hope I won't upset you, tearing apart your design

 

[massimo]

Hi Jaap. We missed U

 

[Zen Mod]

....... so the change ought to be noticable.

.......

not necessarily

 

[disco]

M: Thank you.

not necessarily

Is it from experience you speak or can you underbuild your statement?

 

[Salas]

Salas, what was your impression with degenerated cathodes? Hope I won't upset you, tearing apart your design

They sound leaner.

 

[Zen Mod]

@disco

whatever

don't let me guide you , make your own conclusions

you'll see the difference on scope only in most severe conditions (hard load) , where degenerated iteration will behave better , anyway.

 

[Salas]

A few green Leds have less impedance than the resistor needed. Its another thing I do some times.

 

[disco]

Zen Mod: Indeed, the 6V6 is working with two fingers in its nose in this setup. The difference we might hear because of the feedback is a small loss of harmonics.

Salas: leaner and not cleaner you ment? You're not upset, are you? Really?

 

[Salas]

Leaner, in FFT it had only 2ndH anyway, so its maybe some lowering of it, not a distributional change. Why I be upset? Its a platform idea, you do whatever you like, you are valve experts.

 

[Zen Mod]

.........you are valve experts.

not me , Bubba

I'm just ZM

 

[Salas]

not me , Bubba

I'm just ZM

Zodiac Master valve psychologist then.

 

[disco]

Anyway, I took some actual measurements (in which I'm certainly not an expert). In my setup the pre is driving a 27 triode, having a grid to cathode capacitance of 3.1 pF. As a load I paralleled a 10K ohm resisor and a 3.3pF capacitor.

In the first setup (with cathode bypass) a 1KHz square wave of 200mV rms gave an output of 990mV rms (5 times amplification). In the second setup (without cathode bypass) a 1 KHz square wave of 200mV rms gave 460mV rms output (2.3 times amplification).

Here you'll find some results. Voltages are derived from a Fluke 87 true RMS multi meter. Don't know what frequency domain it can handle.

 

[buzzforb]

I picture him as being like the guy in white coat who use to give me electroshock when i starting talking to my special friends.

 

[Salas]

You lost half your gain without the cathode cap, expected. Don't load it under 20K btw, it has about 1.5K Zo in common cathode and bypass mode for instance.

 

[triode_al]

You lost half your gain without the cathode cap, expected. Don't load it under 20K btw, it has about 1.5K Zo in common cathode and bypass mode for instance.

Agree. I had 3k9 on my R120 and EL34-triode at 240V. The amplification was low of course, and the sound was very 'warm' - second harmonics. But I drove a Hitachi FET output directly with it and that worked like a charm. At the end I thought it too - well - vague.

 

[buzzforb]

Ran my PSU setup in PSUD last night. According to it, should be ideal. Guess that means i will spend this weekend scoping and rewiring PSU. Salas, ZM, what is your impression, if any, about high quality cap like PEH169 in prefilter vs motor run cap? Got my order queued up, and can add peh or bhc to the list. Not sure if it is woth the coin for an electrolytic, that in theory at least, should not be as good as film/motor run cap.

 

[stajo]

Ran my PSU setup in PSUD last night. According to it, should be ideal. Guess that means i will spend this weekend scoping and rewiring PSU. Salas, ZM, what is your impression, if any, about high quality cap like PEH169 in prefilter vs motor run cap? Got my order queued up, and can add peh or bhc to the list. Not sure if it is woth the coin for an electrolytic, that in theory at least, should not be as good as film/motor run cap.

Try PEG124, 33 or 47 uF on second C in filter and parallell up to a value where it gets silent with the ear in the cone. No need to go as big as PEH169 HV stuff for a start. IMHO.

Staffan

 

[buzzforb]

more a question of sound difference, if any. I am audiophool trying to learn secrets of audiophoolery

 

[stajo]

more a question of sound difference, if any. I am audiophool trying to learn secrets of audiophoolery

That might be a bit application dependent but my last little EL84-amp ended up with a combination in second C. 50 uF motorrun and 100-ish PEG124. To much plastic narrowed the sound to my ears. I actually prefer good electrolytics to plastic as base.

Do some listening tests, its fun and it might surprice you.

Staffan

 

[buzzforb]

Exactly what i was looking for. THnaks