2 band transistor tone control

maouna

Member
2008-10-28 8:55 am
3 years later , i decided to build a transistor based tone control. i found a schematic in magazine wireless world from 1974. what do you think?
 

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Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
The WW schematic is OK, provided you realise that noise levels will be high, relative to modern designs, as there is no indication or provision of regulation, filtering of the power rail or suggestions for what to do about RFI or EMI if they become a problem in your board layout and wiring.

You will be on your own unless it is detailed in an article there, possibly relying on lots of bypassing, filtering and careful grounding. Personally, I would shield this or keep it separate in a freestanding preamp. The adjustment of R18,21 seems quite a strange feature. Is the setting explained in the text?
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
I remember a very similar circuit in Practical Wireless, probably around 1976 ? It looked very similar from memory but just had the two conventional pots.

Anyhow... I couldn't resist seeing how this worked in simulation. Its very much of its time, probably sounds "nice" but ultimately lacks the precision that opamps bring to the response. The response here is with the pots centred, looks awful, but look at the scale. Perhaps not so bad in context.
 

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maouna

Member
2008-10-28 8:55 am
no i havent reworked anything yet. the only thing i did was to add 0.47u bypass capacitors to all electrolytic caps that pass signal,added base collector capacitor to first transistors,added rail bypass capacitors and 100ohm resistor at output. the writer used 25V supply rail and a boost cut of +-18db. i will have to recalculate values for +-10db boost/cut and maybe i use 30V for supply rail.
 
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maouna

Member
2008-10-28 8:55 am
Mooly , i also made 2 pcb layouts for 2 band tone control using opamps this time. both pcbs include input filter,but the main difference is that the one pcb includes fets for class A biasing of opamps and the other one not. which version do you think is better to etch?
 

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