Valley 400 Pre (Self etch & Gerber)

[hymentoptera]

Hey I've got one of these sitting in my closet. I didn't know it was anything worth building. Sound good, huh?

I bought it for like $20 a while ago, dead, and I think I determined all it needs is a full recapping. If I remember correctly the voltages were fine and the EQ and dynamics worked, but the mic pro had no or distorted output or something. Maybe I should fix it up and give it a go.

If anyone needs to see anything, closeup pics, actual component values, etc, from a real unit, mine's got a 6000's serial and it would be nothing for me to pop it open and have a look.

 

[pucho812]

Did you try it again?

Yes... I made a second one as I trashed the old one pretty good.  I cut the trace as suggested and put in the 10K(r20) resistor as suggested and added the jumper at r20 . .  I then tested with my AP system one. I get nothing. But if I leave out the 10K resistor(r20) all together keep the jumper at r20 and reconnect the trace with a wire, I get a large amount of gain and oscillation noise  on the output(-40dbu into the pre, +20dbu  at the output of the pre). I can hear it and see it on the scope. I can remove the wire jumper to disconnect the trace but then  I do not get any gain or signal on the output.  I do have an original valley schematic for the transamp as a mic pre if you would like to look at it, I can add it to the tech documents.  I am certain it's is a layout issue, and  that I  just can't see it.  this is with all the correct parts including the 1K rev log pot.  I have been able to scope signal at the input and on both boards the input is working fine.  I have had to put it down for the moment as I have been taken away with work duties on an old RCA desk... I posted some info in the tech documents for the uoab(universal operational amplifier board) which is the epicenter of the RCA console...  The console sounds amazing...

 

[ForthMonkey]

Did you try it again?

Yes... I made a second one as I trashed the old one pretty good.  I cut the trace as suggested and put in the 10K(r20) resistor as suggested and added the jumper at r20 . .  I then tested with my AP system one. I get nothing. But if I leave out the 10K resistor(r20) all together keep the jumper at r20 and reconnect the trace with a wire, I get a large amount of gain and oscillation noise  on the output(-40dbu into the pre, +20dbu  at the output of the pre). I can hear it and see it on the scope. I can remove the wire jumper to disconnect the trace but then  I do not get any gain or signal on the output.  I do have an original valley schematic for the transamp as a mic pre if you would like to look at it, I can add it to the tech documents.  I am certain it's is a layout issue, and  that I  just can't see it.  this is with all the correct parts including the 1K rev log pot.  I have been able to scope signal at the input and on both boards the input is working fine.  I have had to put it down for the moment as I have been taken away with work duties on an old RCA desk... I posted some info in the tech documents for the uoab(universal operational amplifier board) which is the epicenter of the RCA console...  The console sounds amazing...

In short,you say it's not working.Really interesting.I can't see any error.Eagle and Spice circuit is same.I didn't try this preamp but in theory everything is ok.I have original circuit,too.I have no idea what's going on about this circuit but i'll try one day.Sorry about trouble again.

 

[pucho812]

Everything is good, not working but life is good.  I will get it right eventually.