Simple 'treble cut' opamp circuit needed.

[HankMcSpank]

Hi,

I've tried a search & also trawled the web....I can find lots of circuits with baxandall bass treble boost/cut circuits....all I seek is a simple treble cut circuit for a TL072 opamp. (or any opamp come to that!)

This is for a guitar with piezo pickups. Unprocessed these piezos sound a little harsh at the upper end, so I'd like to be able to roll this treble off a bit

I have magnetic pickups going through the same signal path (they are summed in TL072 opamp), which sound fine (no need for any treble cut), therefore I'd like the pot at one extremity *not* to affect the treble ...& at the other extremeity the treble to be rolled off (a bit like how a passive treble control rolls off the treble.

Many thanks in anticipation.

[nigelwright7557]

Originally posted by HankMcSpank
Hi,

I've tried a search & also trawled the web....I can find lots of circuits with baxandall bass treble boost/cut circuits....all I seek is a simple treble cut circuit for a TL072 opamp. (or any opamp come to that!)

This is for a guitar with piezo pickups. Unprocessed these piezos sound a little harsh at the upper end, so I'd like to be able to roll this treble off a bit

I have magnetic pickups going through the same signal path (they are summed in TL072 opamp), which sound fine (no need for any treble cut), therefore I'd like the pot at one extremity *not* to affect the treble ...& at the other extremeity the treble to be rolled off (a bit like how a passive treble control rolls off the treble.

Many thanks in anticipation.

I would have just gone for a standard Baxendale design.
I play guitar a lot and prefer a more trebly sound.
The Baxendale will give you what you want but with the added option of treble boost.

[mightydub]

1) see http://sound.westhost.com/projects-3.htm, indeed the entire site, all kinds of circuits, information, and ideas.

2) download a copy of LTspice and start messing about.

[HankMcSpank]

Nigel - The thing is about the baxandall it'd need an extra knob (bass), & I don't want to go putting another knob on my guitar!

Also, I don't want to emphasise the treble any more than it is at present (the piezos are *so* cutting already).

Like I say, all I need is a treble rolloff.


Mightydub - Re the linkl you gave. I'm aware of it - but I couldn't find anything that suits (I'm sure there is but I guess what I'm saying I'm not too sure how to hack one to suit my needs!)

[Mooly]

Do you even need an OpAmp. Simple = one pot ( 10k ) and one cap determined by experiment to suit you. Try values around 1000 pF to begin with.

[Eva]

Another potentiometer in series with the capacitor may be useful too. One determines shelf frequency and the other the amount of cut.

[nigelwright7557]

[QUOTE]Originally posted by HankMcSpank
[B]Nigel - The thing is about the baxandall it'd need an extra knob (bass), & I don't want to go putting another knob on my guitar!
QUOTE]

Why does it need a bass knob ?

Just remove the bass cct...........

[mightydub]

download Rod Elliot's crossover calculator:

http://sound.westhost.com/software/esp-lr13.exe

which has the abstract schematic and calculates values for 12dB or 24dB/octave Linkwitz-Riley filters. A very handy tool, makes it too easy really.

One disadvantage to doing this with an opamp is you need the +/- power supply, OK if the circuit goes in the amp but maybe a problem if it goes in the guitar. I suppose you could use 9V batteries.

[HankMcSpank]

Thanks guys.

in the end, (inspired by the simplicity of Mooly's suggestion), I continued searching & found this thread...

Tone circuit blues

Essentially that works for me!

I did try the baxandall, but I was getting faint ringing/static when turning the bass & treble controls (a bit like when tuning through an AM radio). Rather than try to get to the bottom of that (would anyone know what couldn have caused it?), I ripped all the associated extra components out - the simplicity of this solution suits me down to the groun.

many thanks once again.

[nigelwright7557]

Originally posted by HankMcSpank
Thanks guys.

in the end, (inspired by the simplicity of Mool's suggestion), I continued searching & founf this thread...

Tone circuit blues

Essentially that works for me.

I did try the baxandall, but I was getting faint ringing/static (a bit like when tuning through an AM radio) when turning the bass & treble controls. Rather than try to get to the bottom of that (would anyone know what couldn have caused it?), I ripped all the associated extra components out - the simplicity of this solution suits me down to the groun.

many thanks once again.

But did you read the next message ?

"It forms a low-pass filter (treble cut) in conjunction with the output impedance of the opamp. As that impedance is going to be pretty low you should try adding a resistor in the wire between the opamp and the top of the tone pot."

I would be adding a resistor just before that filter.

I suspect you were getting high frequency noise with the baxandall cct. But if you were just using treble cut then that shouldnt have been a problem.