Preamp popps............

[Bernardduur]

OK, so I try to rehouse an Alembic preamp. The first issue was that it was not DC biased, so I put a cap (1 uF, NP) from ring to ground (isolated jack) to overcome this problem.

The next problem I have is that the unit pops like a madman. Turn it on and off is a pain for the amp because a loud pop can be heard. I tried using a pulldown resistor, but no difference can be heard with that. I tried to replace the switch; no difference.

Is there another way to elimate this?

[aron]

If it's really loud there must be DC somewhere. Measure your output using a multimeter set to DC and see how much voltage you've got there. Maybe a simple capacitor at the end will fix this or maybe there is one but it's leaking.

[Sir H C]

Often a relay on the output to force the pre-amp outputs to ground on power down is used in the audio world.  Then you guarantee no pop.  Otherwise you have to do a lot of work to determine how everything will gracefully decay as the supply goes away.  Can be a big pain hence the relay on the output.

[Bernardduur]

OK, I tried these things;

The cap on the end does not fix it, as does the relais (I guess you meant Sir H C) that the signal of the preamp is fed into the ground when the unit is switched off??)

I can't get a voltage reading (DC) at the end

[Rob Strand]

There's two possible problems.  I'm not 100% sure what you mean by "turn it on".  Is it when you plug the jack into the 6.5mm socket for the first time, or, do you have some sort of switch where you can select preamp and no preamp?

Assuming the second case.  You may need to put a 1uF cap in series with each input (the hot one and the grounded one).   Then put a large resistor 1M to 2M2 from the input side of the hot cap to ground.  (As a precaution you might have to put a large resistor between the *original* inputs).

See how you go.

[Bernardduur]

Sorry, I guess I wasn't clear to mention it was a simple onboard preamp I try to build into a box...... I didn't know Alembic made bigger preamps also.....

So it is just a simple onboard preamp, one input, one output and a switch to bypass the effect.


I will try Rob's thought.

[Bernardduur]

Rob's also does not work;

I get a louder pop when the power is plugged in, a small pop (and not a working effect) when it is unplugged

[jrc4558]

try buffering input and output. sometimes an impedance mismatch causes a pop (an empirical finding of yours truly)...

[Bernardduur]

Wow, that worked great; now I only have a small pop

[Bernardduur]

Wow, that worked great; now I only have a small pop

And now not anymore; I added a millenium bypass to switch a LED on and off and now the popping is back, also with the LED removed

%^%$#$%##@

[Bernardduur]

Just for the records; I fixed it

It only needed an input buffer; with an input and an output buffer it popps like a madman, with only an input buffer (IC) there is absolutely no popping.......

Should've known this a long time ago

Thanks all!