[BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread

[kante1603]

....but did you listen to it?

Udo.

 

[cookiesuttle]

Yes sorry, everything works and sounds fine on it.  No hum or noise.  Just green led won't go off.  Strange. 

 

[jsteiger]

Post some build pics of around the IC opamp area.

 

[cookiesuttle]

ok will do when I get home tonight!

 

[kante1603]

Could it be killed when reversing it 180 degrees?

Udo.

 

[jsteiger]

I thought the same thing.

 

[kante1603]

Brothers in mind.......

 

[cookiesuttle]

nope, flipping the phase doesn't do anything.  Will take some pictures after I feed the pregnant wife before she kills me!  haha

 

[jsteiger]

nope, flipping the phase doesn't do anything.....

No, we meant when you turned the 4558 opamp 180 degrees.....

 

[cookiesuttle]

Yeah I tried that and none of the LEDs work then.

 

[cookiesuttle]

picture 1.  Is there a way to post more than 1 pic on a post?

 

[kante1603]

@cookiesuttle

Found a pdf for the 4558,found this:

"Notes 1.Reverse connection of supply voltage can cause destruction."

Supply voltage is on pins 4 & 8,by reversing the chip exactly this has happened.

I would give it a try and swap them out.It's a standard part,cost per chip bought as single part is 20 cent (Euro).
You have the Preamps in working condition and you said they sound good,so it's most likely that just this part is fried.A cheap way to check.....

Good luck,

Udo.

 

[cookiesuttle]

K ill give it a shot!

 

[cbarrett92]

Does anyone else think that the diode to the right of the 4558 looks destroyed or is that a bad look form the camera?

 

[jsteiger]

This is not related to the sig prez circuit but R10 looks like 150k in the pic not 137k? It could be the pic though. I would try replacing the 4558's like Udo and I were referring to. The rest of the R's for the sig prez look correct.

 

[cookiesuttle]

ok so no 4558's available locally. . argh.  Will order from capi

 

[New Soul Rebel]

Built a VP28 a couple of months back. Hardly used it to be honest.

It works fine in operation (sweet as in fact), but for some reason, ever since I built the thing, I get a big thump when I have phantom power on, and switch the mic line on. To be clear, that's... phantom power ON before I engage the mic switch.

Huge peaking thump. But then, like I say, it works and operates fine. Its obviously something not quite right there. I've another pair of these. They work perfectly, and I took great care on this build, so am a bit annoyed i've got this problem. :-[

Has anyone else experienced this on a new vp28 build? Any particular thoughts? (Jeff?)

Matt

 

[jsteiger]

Well, when you have phantom on, there is usually a pop or thump when engaging the standard pad. After all, when switching DC there will be some popping. It has always been a standard practice to engage phantom and the like with a pre's output muted by some means or not connected, It really can also be said for the mic/line switch.

 

[kante1603]

+1 on this,had a similar discussion why not to switch patterns on a ldc- mic while monitors are open... :
Udo.

 

[cookiesuttle]

So had the chance to try my 2 vp28's out on a session -- well a session setup.

2 different problems:

1) The preamp with the LED that stayed on the whole time:  I switched out the 4558 and that didn't do anything.  Other than that, works perfectly fine.

2) preamp 2: green led works fine on this one and overall seems to work fine, but by Shure KSM 32's will not pass signal.  Any other mic I have including other phantom powered mics work fine, but these mics will not work on this particular preamp.  The Shure's both work fine on my OTHER VP28, but not this one.  Do you think it's a phantom power issue on this one?  Maybe it's not quite enough voltage on it?