Quote:
Originally Posted by Electronpusher0
Hi Andy, you have got me curious, I will put the pre-amp back on the bench and check the output again.
In my setup the volume control is at the input of the main amp, so after the cathode follower in the pre-amp.
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Hi Andy,
I put the pre-amp on the bench as promised. I attached a modified schematic, seems I used a zener stabilised HT supply when I built it. I also used a regulated DC supply for the heaters and even fitted mesh screening over the mains lead! Photos attached.
As to results. I deliberately kept the gain down by using an ECC82 in the V2 position, this yields an overall gain of 65 at 1KHz ie a 5mV input will give 325mV output which is perfect for my application. However clipping occurs at 29V rms output!!!!! yes thats volts.
I tried changing the ECC82 for an ECC83 to see it would be more suitable for your application.
This changed the Anode voltage from 91V to 205V not surprisingly.
The gain of this version is now 291 at 1KHz which would give 1.5V for 5mV input, much closer to what you need.
Clipping now occurs at only (only!) 21V rms which represents an input of 72mV rms, which is 23dB above the 5mV nominal
Peter