Valve pre-amp.......

[RogerCook]

I wonder if reducing the value of the .47uF caps might help the treble?

[ecca]

Do you think so Rog ?
I might try that.

[Bojan]

Ecca, please stop torturing us and post a sound file with the valve pre-amp and etap2HW combination . . .

[ecca]

Boingy.... I will as soon as I'm satisfied.

[Amanda]

I found a schematic of the valve preamp that I used with the eTap2hw online.
This is obviously 1/2 of it and there's an error inasmuch as the heater supply is shown as AC when in fact it's rectified.

valve preamp.jpg

Try 0.1uF caps as the couplers that should improve the treble or even go to 0.01uF.

Usual Anode load resistor in meazzis is 100k Grid leak caps could go to 1 meg, 10k is a bit low for
a guitar input bearing in mind that single coil pickups are usually around 250k impedance and humbuckers
500k.

the 10k and 3.3 uF are a feedback circuit to adjust the gain of the amp..

Amanda

[ecca]

I'm taking all this onboard and will today be modifying things a little.
The input impedance at 10K is low as Amanda said so that will be changed.
I'll see what the effects of this will be before I change any capacitors and also I await the better valves from Russia.
Piet has also sent me a modified program but, again, I'll wait and see what effect the other mods have first.
Bear in mind that the circuit shown is only half of it. I have a pre-amp before the eTap2hw module and the same thing again after it so the requirements will be different.
There is a common, ganged pot level control for both channels which will be changed so as to be able to adjust each channel separately thereby providing separate input and output level controls.

[ecca]

What's the point of green LEDs under the valve bases ?
Damn clever these Chinese.

[rogera]

Those green LEDs are in fact 16th century hand carved jade from the dynasty of Ming the Merciless !!

[ecca]

Wel I never got round to modifying anything yesterday, it was too cold down the shed.
I did design a new front label on Autocad though with much help and a great template from Panchodiaz.
Back at it on Monday.....

[ecca]

NOS valves arrived today and bloody Autocad is driving me mad.