Tube preamp tone control

  
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The +/- 3 dB point for the treble is about 2, 5 KHz, with about 12 dB boost/cut at 10 KHz. Perhaps you should check the wiring (again ) or perhaps componentvalues Do you have access to a signal generator yeah i checked wiring and components again and again, i used linear pots cuz there s no log pot here, but still it s not working, in fact the the u-hi switch
Tube preamp tone control - schematic

has a very very small change in output tone too, i donno where s the problem in treble section. i used regular caps in whole circuit, should i use anything special But first: I presume that "Ultra High" switch is meant for some high treble accentuation (presence ), but it does not do that at all! I simulated your circuit on a computer programme. Firstly, the U-H circuit will be volume control dependent as you are probably aware of. But with the volume control set about half-ways, the treble is +3 dB already at a frequency of 650 Hz, and 8 dB up at 10 KHz. With the volume control further down (15% from 0), the +3 dB point is 400Hz and the response at 10 KHz up by 15 dB. That is not at all "ultra-high", and also quite a substantial treble increase! I would imagine you can do without it at all, but let us at least do things one at a time, and keep that switch off until the rest of the pre-amp is working. Also then, with the substantial difference that switch should make but does not, may I suggest you first check whether the tubes are working at all, i. e. measure the voltages (with a digital meter if you can). I would place the ECC83 anode voltages at 90V - 150V, with the cathodes at a volt or two. Use the signal generator to determine that you have reasonable gain at all. Do you have a scope Further to that you can check the tone control circuit alone, by detaching it from the 2nd ECC83 anode and feeding it directly with...



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