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

[andYz00m]

Thanks, Jeff.

 

[andYz00m]

I used one of the transformers from the second unit I haven’t built yet and it works great. Sent you an email.

Thanks again.

 

[WillDuc]

Hi guys,

I'm having a problem with a VP28 unit i built myself. When i am in line mode, pad engaged, there seems to be a substantial increase in the high end when i run tracks through it. I set up Q clone using my daw to verify that and it turns out that when the pad is engaged in line mode, there's kind of a high shelf (see picture). When i am in mic mode though, the frequency response stays flat whether or not the pad is engaged.

Is this something normal ? If not, where should i start as for as troubleshooting ? Bad solder joint, wrong capacitor or resistor value etc...

Here are my test points :
TP1=101mV
TP2=698mV
TP3=1,241V
TP4=305mV
TP5=305mV
TP6=305mV
TP7=642mV
XLR output = 1,233V

Regards,

Can someone give me hand with that ? I've yet to resolve this issue, if it is one.

If someone would be kind enough to pass some audio files provided by me in line mode, i would be better positioned to judge if my unit is ok or not.

Please reach out to me if you're open to help me.

Cheers,

 

[jsteiger]

Can someone give me hand with that ? I've yet to resolve this issue, if it is one.

If someone would be kind enough to pass some audio files provided by me in line mode, i would be better positioned to judge if my unit is ok or not.

Please reach out to me if you're open to help me.

Cheers,

Using the Mic Pad when in Line mode is not something that ever needs to be done. The Pad is only designed to be used when in Mic mode. The module is essentially flat in Line mode and flat in Mic mode (with or without the Pad engaged).

 

[WillDuc]

Using the Mic Pad when in Line mode is not something that ever needs to be done. The Pad is only designed to be used when in Mic mode. The module is essentially flat in Line mode and flat in Mic mode (with or without the Pad engaged).

Thanks for the lighting fast response Jeff, and thanks for clarifying the pad use.

I get what you're saying when you say the pad shouldnt ever need to be engaged. It makes sense because in line mode, the incoming signal is line level to begin with. Weirdly though, the frequency response is clearly not flat using my two modules in line mode, pad engaged. I've measured it with Q-Clone in my DAW to confirm what i was hearing.

My units are flat in line mode, pad depressed, so it's reassuring in a way.

Again, not trying to be a pain here, i just want to confirm the units are sounding as they should.

Thanks,

 

[jsteiger]

Thanks for the lighting fast response Jeff, and thanks for clarifying the pad use.

I get what you're saying when you say the pad shouldnt ever need to be engaged. It makes sense because in line mode, the incoming signal is line level to begin with. Weirdly though, the frequency response is clearly not flat using my two modules in line mode, pad engaged. I've measured it with Q-Clone in my DAW to confirm what i was hearing.

My units are flat in line mode, pad depressed, so it's reassuring in a way.

Again, not trying to be a pain here, i just want to confirm the units are sounding as they should.

Thanks,

I have never ran a sweep that way. Its putting 2 u-pads in series. If its flat in Line mode and flat in Mic mode with or without pad you are golden!

 

[WillDuc]

I have never ran a sweep that way. Its putting 2 u-pads in series. If its flat in Line mode and flat in Mic mode with or without pad you are golden!

Excellent, thank you mister Steiger!

 

[alesjob]

Hello good!

I have built two VP28 Ver C,

One of them has burned the resistors PR1 and PR3, when turning on the phantom (48V), the BC161 and BC141 were boiling after that.

The BC161 and BC141 are in their respective places, as are the diodes on the preamp board.

Could you help me please, I'm new putting this together.

I don't want to connect the other VP28 for fear of the same thing happening.

Greetings

 

[Ricardus]

So you must have a short on the phantom rails somewhere, and if those two transistors are hot, are they reversed? Is the 161 where the 141 belongs and vice versa?

 

[alesjob]

Así que debes tener un cortocircuito en los rieles fantasma en alguna parte, y si esos dos transistores están calientes, ¿están invertidos? ¿Es el 161 donde pertenece el 141 y viceversa?

Thanks for the reply!

The 161 and 141 are each in their place, they are not reversed.

It strikes me that when activating the 48v it has burned that part.

What would be the rails of the phantom?

 

[Ricardus]

Well, I think it's pin 15 on the edge connector, but Jeff hasn't published a schematic for this one, so he might have to help you with this.

 

[Ricardus]

Thanks for the reply!

The 161 and 141 are each in their place, they are not reversed.

It strikes me that when activating the 48v it has burned that part.

What would be the rails of the phantom?

Take some hi res photos of the top and bottom of the board and post them.

 

[alesjob]

Tome algunas fotos de alta resolución de la parte superior e inferior del tablero y publíquelas.

 

[alesjob]

2

 

[Ricardus]

Hmmm, well, the soldering is a little rough. You most certainly have a solder bridge somewhere there, and any number of cold joints.

You need to go over the board with a magnifying glass and make sure there are no gobs of solder connecting 2 pads that shouldn't be connected, and you need to clean up many other joints and make sure they are making good connections.

 

[jsteiger]

Phantom power does not get anywhere near the opamps so it can only be a coincidence that the R's burned when you engaged phantom. Those 10R's burning up are a tell tale sign of an opamp problem. If the opamps look like the same style of work as the main board then you likely have shorts on them as well.

 

[alesjob]

Phantom power does not get anywhere near the opamps so it can only be a coincidence that the R's burned when you engaged phantom. Those 10R's burning up are a tell tale sign of an opamp problem. If the opamps look like the same style of work as the main board then you likely have shorts on them as well.

Thanks Jeff for the response! The BC, even though the PR resistances have been burned, can I use them again or is it better to change them?

 

[jsteiger]

Thanks Jeff for the response! The BC, even though the PR resistances have been burned, can I use them again or is it better to change them?

Its hard to say not knowing what's wrong with the opamp.

 

[PaulSmith]

Hello! I have a VP28 that’s quite low in level to others.
I got the output reading 1.22vAC with gain/fader set to unity and here are the measurements:

1 - 419 mVAC
2 - 1853 mVAC
3 - 1.17 VAC
4 - 291 mVAC
5 - 291 mVAC
6 - 291 mVAC
7 - 613 mVAC
As you can see the TP1/2 are the ones that are quite far off!

Any idea where to look based on this?

Cheers!

 

[alesjob]

Good back!
Change the burnt resistors of the VP28, verify that everything is in order and we tried with a friend, the two preamps worked very well for now!. If something happened to us and I would like you to guide me, because we are new with this. We had the box turned on and we took out one of the cards to put them in another slot, but when we moved it, PR1 and PR3 burned again, I changed the resistors again and they didn't burn anymore. It could have been caused by the fact that the box was turned on?

Regards!