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

[Homestudio]

Yeah the builds look good except for the bridges, everything's in the right position nothing's wrong there. The only resistors I could find local are 10 ohm .25watt  2% (instead of 5%). Will these be alright in the vp28? Thanks again,Patrick

 

[jsteiger]

...The only resistors I could find local are 10 ohm .25watt  2% (instead of 5%). Will these be alright in the vp28?

Yes, perfectly fine.

 

[Homestudio]

Thanks again Jeff. Awesome support!

 

[Potato Cakes]

A fun thing I just found out about my VP28's is what happens when I really push it with program material. On a rock mix where the peaks are -3dBFS and RMS is around -12dBFS, I inserted my VP28's with Red Dots and BA512s and turned the input gain to just before two clicks to fully open and turned down the output fader to -16. The result is this almost finished mastered sound with everything moving forward in the sound field and increased perceived loudness. The peaks were now hitting around -6dB but the RMS was at -9dB, which would explain the volume feeling as it was greater than before. I could faintly hear the low end start to break up, but without any static sounding artifacts like the preamp was giving up. Maybe the kids would call what I'm hearing as wooly. Whatever it may be in the subjective audio dictionary, it seemed to immediately put me really close to what sounded like something ready to be released.

For mastering projects I incorporate two different sounding compressed mixes parallel to the original and then limit for overs, but I think for the next project I'm going have to incorporate this signal chain somewhere in the process.

Thanks!

Paul

 

[WillDuc]

Hi guys,  just want to make sure my unit is working as it should. I noticed that in line mode (mic button depressed) the sound changes quite a bit. I would describe it as hi fi, almost to the point of harshness. After running a test tone i noticed that while in line mode, i don't get any harmonics even if i drive the input quite hard. In mic mode however, i get plenty of them (see attachments). Reading from the forum it is not something that this preamp is known for (pronounced highs). Is the unit working as it should ?


Regards,
William

 

[jsteiger]

Hi guys,  just want to make sure my unit is working as it should. I noticed that in line mode (mic button depressed) the sound changes quite a bit. I would describe it as hi fi, almost to the point of harshness. After running a test tone i noticed that while in line mode, i don't get any harmonics even if i drive the input quite hard. In mic mode however, i get plenty of them (see attachments). Reading from the forum it is not something that this preamp is known for (pronounced highs). Is the unit working as it should ?

There is nothing more than a u-pad before the input transformer for line mode. Basically only the level should change going in, nothing else.

 

[WillDuc]

Ok so there's definitely something going on with the unit. Can you suggest a starting point ? Debugging without a schematic is tough.

Thanks

 

[jsteiger]

Ok so there's definitely something going on with the unit. Can you suggest a starting point ? Debugging without a schematic is tough.

Thanks

We have a test points guide for this. Ruling out the opamps is always the first step.

 

[WillDuc]

Thanks jeff for your quick reply. Here are the results i got.

TP1=101mV
TP2=698mV
TP3=1,241V
TP4=305mV
TP5=305mV
TP6=305mV
TP7=642mV
XLR output = 1,233V

Judging from the numbers i guess everything is working fine. As it's my first colored preamp, i guess it's the sound of a cranked preamp that i am not used to hear. That being said, i still find it weird that in line mode i don't see the harmonic content i see in mic mode when i feed a test tone.

Regards
Guillaume

 

[jsteiger]

...As it's my first colored preamp, i guess it's the sound of a cranked preamp that i am not used to hear. That being said, i still find it weird that in line mode i don't see the harmonic content i see in mic mode when i feed a test tone.

Not sure what type of levels you are sending it but hit the line input with appx 40dB more level than when in mic mode. We run 0dB in to measure line mode things and -40dB for mic mode. What level are you feeding it in mic mode?

 

[WillDuc]

Not sure what scale you are referring to when you say 0dB. I read approx 1.23V on the input xlr using a DAW as a tone gen. Now using this level in line mode i can't get the preamp to distort and add harmonics like in mic mode (i obviously turn the level down when using the mic mode, can't tell how much in dB though) . In line mode, I push the signal with the channel fader and/or the preamp gain and when i start to hear the tone distorts it's when my converters start to clip. Maybe it's me and the line mode is cleaner than the mic mode? Keep in mind it's my first experience with your products.

 

[aka-pablo]

Hello groupdiyers - I am new to this forum - I have just built 2 CAPI VP28 preamp mounting 2 capi gar2520 each. I built the 2 units at the same time using a "carbon copy" approach, if I can say that. When testing them I get 2 sort of issues:

1) one of the unit works and I get signal, while the other one does not get any signal (the leds light up though). Basically one of the gar2520 (the Fader Booster) warmed up to the point that i can smell the warming plastic and I had to remove the unit.

2) When I test the other unit, the one that works, I get a distorted signal as an output. I have double checked if there is any bridge between capacitors and parts but everything seems to be relatively clean.

Is there a way to isolate the problem? I have seen the document that shows how to test teh unit using the test points however at the moment I haven't got a signal generator. Do I necessarily need a signal generator to test the unit?

Thanks in advance
P

 

[jsteiger]

Testing a newly built preamp with newly built opamps is near impossible. You really need 2 known to be good working opamps. Short of that, we are just stabbing in the dark if there are problems at startup.

 

[csweet08]

Hello, I've noticed some slight browning of a single resistor on a couple of my VP28's and my FC526s. I'm told this resistor protects against ground faults or power problems but I'm not sure of this. I haven't noticed any extra noise on these units vs others without the browning. Anyone know the possible cause and whether its cause for concern? My best theory is it could be from a few hot swaps I accidentally did. I attached a couple  photo's here https://groupdiy.com/index.php?topic=69678.new;topicseen#new

 

[WillDuc]

Hey ya’ll,

Building a pair of VP28s and I’m to the output transformers. The leads on my EA2623’s don’t match, however, the colors on the PCB. Can anyone help me get these in the right place? My leads are blck/red/grey/pink/purple/orange...

Thanks! Sorry if this has already been addressed.

Ryan

There you go Ryan :

http://www.capi-gear.com/catalog/images/gallery/2623/2623-1-L-specs.pdf

Judging from the colors you mentionned I guess you have Litz transformers in your unit. You can find the conversion table on the lower left.

Cheers

 

[Studio Mollan]

Hi,
I would like to make a line in patch point to the VP28. Planning on using the spare card edge connectors 9 can 11 for this. I already have this wired to an XLR in my Fredenstein 500 rack.  Would be easy if i got the schematics but i know and understand you won't make them public Jeff.  So if you could please pinot me in the direction on where to inject it on the PCB.

Best possible scenario would also be to make this input 48v free. Probably via a pair of capacitors. If i could get a value on these too would be great.
Thanks! Great kit this!

 

[jsteiger]

Hi,
I would like to make a line in patch point to the VP28. Planning on using the spare card edge connectors 9 can 11 for this. I already have this wired to an XLR in my Fredenstein 500 rack.  Would be easy if i got the schematics but i know and understand you won't make them public Jeff.  So if you could please pinot me in the direction on where to inject it on the PCB.

Best possible scenario would also be to make this input 48v free. Probably via a pair of capacitors. If i could get a value on these too would be great.
Thanks! Great kit this!

Mic or Line shares the same input path which is the typical card edge pins 8 and 10. I would make this selectable somewhere outside of the rack. Also just make sure phantom on the pre is off. If you try to connect 2 sources without switching one of them out of the path, the 2 devices outputs would drive each other. I'm not sure I see the need or want to support something like this.

 

[jkmang]

Just checking something real quick. Organizing BOM before building 4 units. 

C3 - listed 33uf 25V on the BOM. I have all 4 33uf 63V.  I'm sure this is fine. Just checking.

 

[jsteiger]

Just checking something real quick. Organizing BOM before building 4 units. 

C3 - listed 33uf 25V on the BOM. I have all 4 33uf 63V.  I'm sure this is fine. Just checking.

Yes this is correct. BC/Vishay discontinued the previous 25V part so the new 63V part is all that's available.

 

[brewhouse75]

Just finished my first build of (2) VP28s. Not sure why, but on one of the units the polarity switch must be engaged to get any decent amount of gain. When disengaged the signal is very weak and lacks any low end. No idea how to track down what component is to blame without a schematic. Second unit, which I built at the exact same time, works just fine.