0
\$\begingroup\$

I have made an input mod to increase the input impedance of my Creative T3100 speakers. Mod Schematic

But now even if the potentiometer is at the lowest level some sound from the input is coming off from the speakers, distorted and at constant low volume (not affected by the potentiometer level). Normally (e.g if I bypass the mod) there is some clean sound coming off the speakers bit is nearly inaudible even if you put your ear next to the speaker. Here are the pins I used (photo taken before I did anything) Speaker pins And here is a schematic I found of the speakers Speakers schematic

UPDATE: Apparently the output of the mod is too loud (measured after the filter): With the mod Without the mod: Before the mod

\$\endgroup\$
0
\$\begingroup\$

Stray inductive positive feedback and parasitic noise can be a difficult issue to diagnose when we are blind to your layout.

You show two grounds.(left gnd right) and (V+ and Gnd)

It seems the Op Amp (OA) has injected noise but from where?

  • Do some tests to find out where.

    • Short the input signal to local gnd with a sufficient cap if it has DC bias
    • the connections at that noise may be insufficiently shielded.
    • Change ground for connections to the one between the stereo signal.
    • Keep wires short and twisted to reduce stray effects.
  • last resort, use an inverting buffer to make the stray feedback inverted
| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ I don't think it is a connection, ground or wiring problem since if I remove the op amp from the socket and short the inputs with the outputs (before and after each capacitor respectively) it is fine. I think maybe the circuit needs improvement. \$\endgroup\$ – user170729 Mar 17 '18 at 18:05
  • \$\begingroup\$ The circuit added is unity gain followed by an attenuator and then non-inverting gain amp with stray coupling. What improvement do you think? My test was not what you did. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 17 '18 at 18:20
  • \$\begingroup\$ Maybe add low ESR ceramic cap on Vcc? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 17 '18 at 18:26
0
\$\begingroup\$

You're using a JFET opamp with a fairly high bandwidth, a very high input impedance, and no decoupling. As others have said, without any pictures of your construction it's hard to pinpoint the problem, but I'd expect you to have problems with parasitic oscillations.

If you do increase the input impedance of your speakers you might also want to check that the rest of the wiring to the speakers it up to the task, and that whatever's driving them can cope with such a high impedance.

| improve this answer | |
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy