[BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread

[mxz174]

Jeff, I did already check the polarity switch (you can see this in my post on the previous page of this thread.  It's been a while so I could certainly go over those again for good measure, but I recall checking the continuity on the pins in both engages and disengaged states and it looked like it was working perfectly.

 

[jsteiger]

Jeff, I did already check the polarity switch (you can see this in my post on the previous page of this thread.  It's been a while so I could certainly go over those again for good measure, but I recall checking the continuity on the pins in both engages and disengaged states and it looked like it was working perfectly.

10-4. Well, there is nothing else between the opamp and output transformer but the polarity switch, mute switch and some PCB tracks. Have you check the mute switch out? I don't see how the 20k R or the 100pF cap could have any affect like this.

 

[mxz174]

I have not checked out the mute switch yet.  I'll do that and go over the polarity switch again to see if I may have missed something

thanks again for your help Jeff!  I'll report back once I've checked those out

 

[jsteiger]

I have not checked out the mute switch yet.  I'll do that and go over the polarity switch again to see if I may have missed something

thanks again for your help Jeff!  I'll report back once I've checked those out

If it were me and those 2 switches look OK, I would lift the - end of the 470µF cap from the PCB and solder the primary lead of the transformer directly to it. Solder the other primary lead to a ground ref on the PCB. Do not use the standard transformer pads for this. Make sure the proper 2 secondary leads are soldered together (not to the PCB) and then take your final output from the remaining 2 secondary leads, again not connected to the PCB. Hope this makes sense. This will hard bypass everything in question between the opamp and the output transformer, as well as the t-pad.

 

[mxz174]

WOW, after all this time I FINALLY found the problem.  It's the mute switch.  I had checked that polarity switch inside and out but never tested the mute.  The pins do not show continuity for the appropriate switch state.  I double checked this against a known working module and indeed it is the switch that is faulty.  It looks fine from the outside and feels OK when you engage it, but it's not making connections on one side...

 

[jsteiger]

WOW, after all this time I FINALLY found the problem.  It's the mute switch.  I had checked that polarity switch inside and out but never tested the mute.  The pins do not show continuity for the appropriate switch state.  I double checked this against a known working module and indeed it is the switch that is faulty.  It looks fine from the outside and feels OK when you engage it, but it's not making connections on one side...

Well sonuva b!tch. Glad that is sorted and major sorries for the faulty switch.

A lesson for all though, the schematic holds the key. Everything else was checked. The only other possibility was the Mute switch. Electrons flowing down the roadmap highway.....

 

[rocka]

Hi! New to the forum and new to the diy world here!

First build is a vp25... I checked everithing, and seems to be ok!, the test points on the assembliy guide meassure ok, all the switches work ok, it sounds really nice, but it have low gain... really low gain... with all the pots open, i still get moderated to low input.

Any clue where i can check if i made some mistake in the building stage?

thanks!

bests

N

 

[jsteiger]

Hi! New to the forum and new to the diy world here!

First build is a vp25... I checked everithing, and seems to be ok!, the test points on the assembliy guide meassure ok, all the switches work ok, it sounds really nice, but it have low gain... really low gain... with all the pots open, i still get moderated to low input.

Any clue where i can check if i made some mistake in the building stage?

thanks!

bests

N

First rule for posting about these types of module builds....what opamp is it and who built it?

 

[rocka]

sorry! neewbie here....

The op amp is a SL2520 red dot, i bought it with the vp25 kit... the opamp came already asembled

thanks for your reply jeff

 

[jsteiger]

sorry! neewbie here....

The op amp is a SL2520 red dot, i bought it with the vp25 kit... the opamp came already asembled

thanks for your reply jeff

OK good to know. Is it fully seated? http://capi-gear.com/catalog/DOA_Install.php

The biggest issue folks have with these builds are faulty solder joints. I run my iron at 800˚F.

 

[rocka]

I rechecked everithing... and the only thing i noticed is when i make the testing procedure, without the opamp, and without a power source, i dont have the 600Kohms measurment... all the other procedures are ok, i have +/- 16 volts...

i rechecked the solder points and they are ok...

bad opamp could be?

thanks!!

 

[jsteiger]

bad opamp could be?

No it won't be that. Scott burns in and checks each and every opamp before he ships to me.

 

[TillM]

seams to me, that you insert a wrong resistor or maybe a electrolytic capacitor has the wrong polarize.
Check your resistors first. Its easy to confound a 10R with a 10k resistor.

 

[rocka]

thanks! will re check that!

 

[PetezaSlice]

Accidentally mixed 750r resistors on a dual VP26 build... This matter? Possible to rematch using a DMR-4200 DMM?

Doh whops

Thanks

*edit*

Also, if I'm doing two preamps, am I then taking 1 resistor from each taped pair, and putting it into each preamp? ie, the orange dotted 6k8 (R7, R8) - am I splitting a taped pair for R7 in each, and splitting a second taped pair for R8 in each?

 

[jsteiger]

Accidentally mixed 750r resistors on a dual VP26 build... This matter? Possible to rematch using a DMR-4200 DMM?

Doh whops

Thanks

*edit*

Also, if I'm doing two preamps, am I then taking 1 resistor from each taped pair, and putting it into each preamp? ie, the orange dotted 6k8 (R7, R8) - am I splitting a taped pair for R7 in each, and splitting a second taped pair for R8 in each?

No worries with matching. All of the supplied parts are more than precision enough for their respective uses.

 

[iturnknobs]

Anybody know if a Cinemag  CM75101-APC will work as an input trafo for the VP25? I just did  a build(2) that do not work. I have used  CMOQ-2S and CMOQ-2L for output trafos.

PCB color      ---------  CM color

  red                                          brn
  brn                                          yel
  blu                                            grn
  grn                                            blu
  yel                                            vio
  org                                            gry
                                              red &org tied together

Any help is appreciated.

Thanks.

 

[iturnknobs]

...I do believe my secondaries(CMOQ-2) are phase reversed, but I should still have something...

 

[Potato Cakes]

If your transformer wiring is correct, it's either a bad DOA or the eternally classic bad solder joint/misplaced component combination.

The spec sheet for the CM75101-APC has a higher secondary impedance than the EA2622, but sound in some type of form should still be happening.

Thanks!

Paul

 

[iturnknobs]

Struggling here with output trafo.  The "tap" on the ea2503 data sheet provided does not appear to match the VP25 rev B schemo.    The "tap" colors are reversed when drawings are compared to each other. I am going to assume the cinemag literature is correct.  Any ideas?

Is there a VP25 rev C schemo anywhere... or is VP26 rev C same except for output trafo?


http://www.capi-gear.com/catalog/images/gallery/2503/2503-specs.pdf
http://www.capi-gear.com/catalog/images/gallery/VP26/VP25-Rev-B-schematic.pdf

http://cinemag.biz/output/PDF/CMOQ-2.pdf

DOA is fucntional