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Old 13th Jul 2017, 6:29 am   #233
Diabolical Artificer
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Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
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Default Re: 807 (maybe) amplifier build. Now EL34

Thanks both. Theory aside amp now working like a good un. Frequency response is flat from 15hz to 6khz where it rolls off gently to a 3dB point at 20hz. THD is 0.3% at 50w rising to 0.8% at 112w. I have plenty of gain left; with a 1.3v RMS IP I have 136w before clipping. So can lose a few more DB on NFB, but think I'll stick there for now as any improvement in THD is negligable, unhearable and I'll probably run into instability again.

I'm going to struggle measuring THD lower than this as my Marconi TF2331 is at it's limit. My signal source is also a bit high over 1v.

So, all that's left to do is attach another protection device that will turn off the amp if the OP stage EL34's Ik goes over 100mA. I've breadboarded a circuit, just have to test. I also have to put a clipping indicator LED driver on the same PCB together with a VU driver. am in the process of trying out a few circuits. See att. I tried out the ESP one, but didn't like it. The first attached works well.

A.
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