odd thing happening....

CoolCat

CoolCat

Well-known member
just seeking advice from those who might have suggestions...

dual preamp, with DI on each channel (Aphex 207) one knob unit for each channel.

so I lost the CH2, at times the Input LED's would light up, the buttons light up, but CH 2 dead.

then other times....CH2 will produce some sound but maybe 50% the gain as CH1.

this was tested out with the same Mic and same Cable as CH1.....CH2 has an issue.

then not being able to sell it broke, it sat for months...
I just put it in the Rack for the good channel.....and now both CH1 & CH 2 are working with the DI ? (3 days and counting anyway...skeptical)

No schematics to be found. Any inputs appreciated.... any similar stories might be helpful...
 
This is a preamp technology I’ve never even seen before. A solid state / tube hybrid—but different from starved plate designs. My first suspicion is the tube section going bad as that is the more likely section to do so. But I don’t know how important the tube section is in this preamp.
 
Stuff like this has always been the most maddening and simple failures, in my life.

Corroded jacks - especially shutoff/diverter jacks.
Cold solder joint. Only fails/works at the right temp or when the board flexes from install/removal.
Cracked resistor. Ditto.

All I can say is that I feel for ya, man. This is self-immolation territory for me.
 
The correct way to attempt a repair of this type even with no schematics is to send a signal in like 1KHz and then trace with a scope the signal as you see it progress and compare bad channel to good. This might not be a thing to do for beginners as even having a scape might not be the case but good scopes are around $300 these days not like when I started and they were like $2000. So in some things inflation went the other way- but the $2000 scope were large CRT types and the $300 are Rigol small computer with a TFT display which I am sure will not last like a 30 year Tektronix but then it does have a 5 years warranty. 100MHz dual channel storage scope is a deal. If you can not do the work then get it over to a good Technician as if he has the time to deal with it then it can be fixed. Gain wise, if the tube is involved- exchanging the tubes will cause the gain problem to follow the tube and if so get a new tube to put in there. I don't know what people want tubes anyway- the Tube is a transconductor amp and so are FET's.
 
Thanks for the inputs.
update"
This thing has worked perfectly since.....Im starting to think possibly the DI Guitar jack was the issue.
The DI guitar jack turns off the Mic/Line In when a guitar cable is plugged in, so was it "stuck"?
.....because ever since I stuck the guitar cable in the DI input worked....and then removed it plugged in mics and repeated etc...
theres not been a problem.

The oscope sounds like something I could do in retirement, get a 1khz freq generator....dabble in repairs and some audio stuff...build something.
I could use my DAW and interface for a Freq generator signal.

Ponder you might have got it... the old jack probably needed some exercise.
 
CoolCat said:
Thanks for the inputs.
update"
This thing has worked perfectly since.....Im starting to think possibly the DI Guitar jack was the issue.
The DI guitar jack turns off the Mic/Line In when a guitar cable is plugged in, so was it "stuck"?
.....because ever since I stuck the guitar cable in the DI input worked....and then removed it plugged in mics and repeated etc...
theres not been a problem.

The oscope sounds like something I could do in retirement, get a 1khz freq generator....dabble in repairs and some audio stuff...build something.
I could use my DAW and interface for a Freq generator signal.

Ponder you might have got it... the old jack probably needed some exercise.
Click to expand...
Oh....yeah, preamps do that. My ART MPA does that. If something is plugged into the DI it overrides the mic input.
 
These things called normalized jacks were even a pain in Broadcasting in that patch bays that were normalized need to be cleaned now and then- dust gets in everywhere and will cut a air chain signal out. Sometimes you need some rifle like brushes and some contact cleaner. Normally a squirt of D5 and working a plug in and out will do it. I have had some Tascam cassette decks with broken solder joints have problems. The have 1/4" jacks on the front.
 
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