Using hifi amp a signal tracer

[diydidi]

Hi all.
I would like to know if it is advisable to use my hifi bench test amplifier as a signal tracer, or should i rather get a dedicated amplifier/ speaker for this. What type of circuitry will I need front- end to add this to my hifi amp? I want to be able to probe valve amps etc.
Any advice please.

[Tom Phillips]

That will work if you take some precautions to protect the amp input from overload such as:
Add a DC blocking capacitor between the pint being probed and the amp input.
Use a resistive divider as required to attenuate the signal down to an acceptable level.
That's pretty much all a dedicated signal tracer is.
Google signal tracer for more information.

[Leo_Gnardo]

should i rather get a dedicated amplifier/ speaker for this.

Yes.

Why put your SS (presumably) hi fi amp at risk?

Slap together a rudimentary single-ended tube amp, sort of a downmarket Champ. Tubes will survive electrical insults that would smoke your hi fi amp, and leave you frustrated A) without entertainment whilst working and B) another @#$%! repair.

[Tom Phillips]

FYI there is a posting about home brew signal tracers in the MEF thread http://music-electronics-forum.com/t15825/ , post #7.
Tom

[diydidi]

Can I use a little practice amp such a Fender 15R amp modified for signal tracing? What type of input impedance will I need for signal tracing?

[J M Fahey]

This is a simple safe signal tracing adaptor, good for most you can find inside an SS amp ,pedal, or passive/active guitar. (< 1.2 V RMS)


If you want it to stand higher voltages, you can use instead my PC-Scope adapter/attenuator, but connecting to a guitar plug as above, and using Leds instead of plain diodes:



build the attenuator into a shielded and insulated box, it must be *impossible* to touch any internal part, switch contacts or resistors.


Note: the original use of the PC scope attenuator is to be able to use one of the free Soundcard based "PC-Scopes" available, without killing the Soundcard input with high voltage or transients.

It's meant for the Soundcard "Line" input, with around 100mV sensitivity, not the "Microphone" one.

I designed and built it to carry it everywhere in my Service bag, has saved my bacon more than once when away from the Lab.


Some useful ones:
Zelscope: Sound card oscilloscope and spectrum analyzer
Soundcard Scope

Beware they do not show DC but are great to see weird stuff happening: oscillations, distortion, noise, hum, ripple, crackling, etc.

[Tom Phillips]

This is a simple safe signal tracing adaptor...

That file / image didn't make it through. Would you try to re-post?
Thanks,
T

[J M Fahey]

Oh, probably one of the latter MEF server quirks.
*I* can see them as soon as I open this page, but just in case, these are the direct links, open 2 new empty tabs (or windows) and paste a link on each one.
They should open straight from ImageShack, without passing through MEF .
http://img694.imageshack.us/img694/9909/traceprobe.png
http://img189.imageshack.us/img189/6...attenuator.gif

Work or not, please post results, so I confirm if this shortcut works.
Thanks.

[Enzo]

It appears on the page for me.

[Tom Phillips]

Juan,
I was a guest using a network connection that blocked the images as it turned out. I can see them when I use my own connection.
Your imageshack shortcuts work in both locations.
Thanks,
Tom

[J M Fahey]

Thanks, good to know, so as to waste *a little* less times chasing ghosts which aren't really there.








Although many times I feel like:

[diydidi]

thanx guys awesome answers.