fooking green pre wierdness

Ptownkid · Aug 17, 2006

Built two channels, one works great, the other has an odd problem.

The output sounds great until you make a loud enough noise that is clips really bad, but it's not clipping within the audio program nor are the leds going into the red.

The pin voltages are all bang on on all 5532's, and all 5 chips have been taken from a working channel.

No idea what to check next.

Flatpicker · Aug 17, 2006

Can you put a hot signal through it so that it clips all the time and trace it out with a scope?

Ptownkid · Aug 18, 2006

I was thinking of doing that, what is considered "hot". Is there a certain frequency or voltage level I should be looking to use?

emrr · Aug 18, 2006

look for bad solder joints. Hell, re-touch them all and listen again.

Flatpicker · Aug 18, 2006

[quote author="Ptownkid"]...what is considered "hot"...[/quote]
Just hot enough for it to distort like you said it was doing. Start at the input and look at the output of each stage. Where you first see the distortion occur narrows it down to the section that's causing it.

peterc · Aug 18, 2006

Check that the voltages around the transistors are the same for both preamps. I've had BC550's go bad before.

Peter

Ptownkid · Aug 18, 2006

the two bc550's read identical to each other with no inupt, should I check em with input?

peterc · Aug 18, 2006

What I meant was to check the DC voltage conditions of the good channel against the bad. No signal necesary.

Peter

Ptownkid · Aug 18, 2006

good channel

E 12.27V
B -0.02
C -0.64

Bad channel

E 12.35
B -0.01
C -0.71

Mbira · Aug 18, 2006

The quickest way if you got the stuff is run an identical signal thru both and see where the one is fooking up at-bad solder joint or wri=ong value something or other is my guess...

Ptownkid · Aug 19, 2006

Ok, so I switched out the 550's for shit and giggles, and still the same dilemma. I am going to run a signal through them both and A/B em on my scope, but I'm just not entirely set up to do that at the present time.

Curiosity question, if I run a sine wave through it, will it make noise?

I know that's probably a dumb question, but I'm not entirely positive.

Flatpicker · Aug 19, 2006

[quote author="Ptownkid"]Curiosity question, if I run a sine wave through it, will it make noise?[/quote]
If you have the output connected to some amp/speaker it will. (Is that what you meant to ask?) I'd un-hook it's outputs before testing.

Ptownkid · Aug 19, 2006

yeah, that's what I was asking

So, i should send an audio file through them, assuming it's one that makes the bad channel clip, instead of a sine wave?

Mbira · Aug 19, 2006

Use a sine wave and just check the outpit pins on the 5532's as they go thru the stages. Then you'll know what's up and where...

Flatpicker · Aug 19, 2006

Yes, use a sign wave. If audio can make it distort, than a sine wave should too.

fooking green pre wierdness

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