Tone feedback loop- can you spot the problem?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I've been trying to get this non inverting design from head-fi to work (TREBLE BOOST for PPA, Pimeta, MMM!), but the response drops 13db below 1kHz in modeling.
Can someone spot the problem with this design and suggest how to make the tone function work?
Thank you.

tone_control.gif
 
You are mistaken: The circuit in the diagram that I posted is active- the bandaxall tone stack constitutes the feedback network for a non-inverting linestage, replacing a lone 1k gain-resistor (but will benefit from a stability compensation capacitor. When implemented with proper values, there should be no loss or deviation from linearity when the controls are set to flat, as varying the feedback alters the gain for the target frequencies. There is however a problem with the design posted on Head-Fi that causes the large response shift.
 
Last edited:
Well i would say, yes it's got an active component, the OpAmp, but the actual tone circuit is typical of a passive one. It looks like someones tried to combine both together, but it doesn't work properly.

I simmed it exactly as in the diagram you posted.

The best thing about it, is the bypass position, but even then it's tragic ! For a .775mV RMS input signal @ 1kHz the output is 9V !

Not bypassed with the same input signal, & both pots centered, it's output is 10.25V !

Quite honestly i have to say, the options in the links i gave you earlier, will provide a must more satisfactory outcome, & are Proven to work !
 
It is a an active tone control, but not Baxandall, and designed for gain. That is why it has component values which look more like a typical passive circuit.

You need log pots (or antilog??), as 'flat' (usually mid-position) means 10% of resistance not the 50% of a typical Baxandall unity gain inverting circuit. You need to get this right for the simulation too!
 
@ DF96

It is a an active tone control, but not Baxandall, and designed for gain. That is why it has component values which look more like a typical passive circuit.

Hi, yes i realised it was active due to the OpAmp in circuit, but as you say, it does "look more like a typical passive circuit". Which is why it looked like a bit of both to me.

You need log pots (or antilog??)

Ahh, the screenie in Post #1 didn't show or mention that ! Good point ;) Well i still think the other circuits would be better, as they are proven to work.

@ kouiky

I'm sorry for the confusion, due to the above If you get it to work, let us know :)
 
Don't worry about the confusion, because all responses are helpful. It was kicking my butt, big time, but it would be great if we could get it to work; single opamp gain stage; non-inverting, with tone controls. What I would like even more would be stepped switched tone controls, so that center was direct, and each step could be individually tailored, rather than a fixed turnover frequency. Making a slightly different version work on an inverted input pin is easy, but non-inverted is being finicky.
 
If you want stepped switched tone controls, then John Linsley Hood designed one in the 80's which was considered very good. Also Rane has a more advanced circuit. Both are available on the www. I don't recall the actual www's but a search should locate them :)

If you stay with the passive/active approach, the using 2 OPA's won't hurt. Use the first one as a buffer to feed a passive network, which should be a Bipolar type for low noise with a low input impedance from the source.

The other one a JFET as it will better match the higher impedance of the passive network for lower noise than a Bipolar.

Select both for lowest noise/distortion you can.

EDIT

Found the JLH

a 'Clapham Junction' or spot-frequency step lift and cut-type tone control http://www.angelfire.com/sd/paulkemble/sound3.html

Let us know what you decide to do, & how it pans out afterwards :)
 
Last edited:
Hi kouiky,

Just in case you're interested here's mine. It's ben through a few different iterations in the last few years, but the latest is here, http://www.diyaudio.com/forums/chip-amps/199130-usable-tone-control-5.html, post # 45. It's actually an entire preamp including a baffle step compensation circuit that can be easily modified for a different frequency, or left out altogether if it's not needed. If only the tone circuit is needed, the volume, balance and output circuit can also be omitted.

Mike
 
The topology is all wrong.
No, the topology is just different.

The input is meant to be applied to . . .
In a Baxandall circuit, yes. In this circuit, no.

Google 'opamp baxandall tone control' to get a better idea of the sort of circuit you're trying to build.
No, that will tell him about a different circuit he is not trying to build.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.