Increase treble boost? - UK Vintage Radio Repair and Restoration Discussion Forum

Ian - G4JQT · 19th Sep 2021, 3:46 pm

Is it possible to increase the treble boost of this circuit? I've played with the values of R4, C5, C7 but not made much difference. Or should I be looking at R3, R5, C8, C9? But VR2 adjusts the bass response.

Input pin 6, output C10.

Thanks.

Ian

Radio Wrangler · 19th Sep 2021, 4:04 pm

?

Which circuit?

I sometimes miss with attached photos.

David

19th Sep 2021, 4:06 pm

I think Ian has edited the post to include the circuit now.

19th Sep 2021, 4:07 pm

I do wonder what C11 is doing, can we have a bit more of the circuit?

Ian - G4JQT · 19th Sep 2021, 4:35 pm

Quote:

Originally Posted by merlinmaxwell

I do wonder what C11 is doing, can we have a bit more of the circuit?

It's just RF decoupling. It's part of my 'pantry' tx I made years ago. It would be nice to get a bit more treble boost to overcome the Q of the output cct and IF bandwidths.

Radio Wrangler · 19th Sep 2021, 4:48 pm

It doesn't look like it ought to work.

The opamp has o/p connected straight to - input so its output is voltage following the divided and decoupled supply line. So the left and right inputs go through passive tone control networks and get shorted to a fixed DC virtual ground.

Either I've missed something, there is an error in the diagram, or that's a rather disappointing circuit.

David

Ian - G4JQT · 19th Sep 2021, 5:01 pm

Yes, you're right David. An error in my redrawing from the original! It works OK, but just want a bit more treble...

G.Castle · 19th Sep 2021, 5:27 pm

Try reducing R4 on your diagram to the wiper of the treble pot, also you seem to have too big a capacitor bounding the op amp, 1n not 82p, beware too much boost will make it unstable.

Greg.

Diabolical Artificer · 19th Sep 2021, 5:59 pm

Some useful formula's here for such a problem - http://www.aikenamps.com/index.php/tone-control-scaling hope that helps.

Andy.

kalee20 · 19th Sep 2021, 7:33 pm

I'd say, take the signal to the - input of the op-amp from the other end of the 4.7kΩ resistor, ie direct to the treble wiper!

Then you can have the boost or cut extending to 0 or infinity.

(Though, as others have pointed out, watch for instability in the op-amp at maximum either!)

19th Sep 2021, 3:46 pm	#1
Ian - G4JQT Octode Join Date: Jun 2004 Location: Reading/Fakenham, UK. Posts: 1,323	Increase treble boost? Is it possible to increase the treble boost of this circuit? I've played with the values of R4, C5, C7 but not made much difference. Or should I be looking at R3, R5, C8, C9? But VR2 adjusts the bass response. Input pin 6, output C10. Thanks. Ian Attached Thumbnails Last edited by Ian - G4JQT; 19th Sep 2021 at 4:03 pm.

19th Sep 2021, 4:04 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,869	Re: Increase treble boost? ? Which circuit? I sometimes miss with attached photos. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

19th Sep 2021, 4:06 pm	#3
Guest Guest Posts: n/a	Re: Increase treble boost? I think Ian has edited the post to include the circuit now.

19th Sep 2021, 4:07 pm	#4
Guest Guest Posts: n/a	Re: Increase treble boost? I do wonder what C11 is doing, can we have a bit more of the circuit?

19th Sep 2021, 4:48 pm	#6
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,869	Re: Increase treble boost? It doesn't look like it ought to work. The opamp has o/p connected straight to - input so its output is voltage following the divided and decoupled supply line. So the left and right inputs go through passive tone control networks and get shorted to a fixed DC virtual ground. Either I've missed something, there is an error in the diagram, or that's a rather disappointing circuit. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

19th Sep 2021, 5:01 pm	#7
Ian - G4JQT Octode Join Date: Jun 2004 Location: Reading/Fakenham, UK. Posts: 1,323	Re: Increase treble boost? Yes, you're right David. An error in my redrawing from the original! It works OK, but just want a bit more treble... Attached Thumbnails

19th Sep 2021, 5:27 pm	#8
G.Castle Heptode Join Date: Dec 2020 Location: Swaffham, Norfolk, UK. Posts: 586	Re: Increase treble boost? Try reducing R4 on your diagram to the wiper of the treble pot, also you seem to have too big a capacitor bounding the op amp, 1n not 82p, beware too much boost will make it unstable. Greg. Last edited by G.Castle; 19th Sep 2021 at 5:34 pm. Reason: clarity

19th Sep 2021, 5:59 pm	#9
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Re: Increase treble boost? Some useful formula's here for such a problem - http://www.aikenamps.com/index.php/tone-control-scaling hope that helps. Andy. __________________ Curiosity hasn't killed this cat...so far.

19th Sep 2021, 7:33 pm	#10
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: Increase treble boost? I'd say, take the signal to the - input of the op-amp from the other end of the 4.7kΩ resistor, ie direct to the treble wiper! Then you can have the boost or cut extending to 0 or infinity. (Though, as others have pointed out, watch for instability in the op-amp at maximum either!)