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

[all-over-again]

Do you live anywhere near Brighton. I could take a look. Other than that I will be starting to build a pair of VP28 for a friend when the kits arrive later today. Therefore since I will have the units in front of me it will be easier for me to help you.

I got 0.02v on the second LED down
I live in London
Any help would be appreciated
and i was flowing the joints on the switches and one of the Leds lit up, im guess it was power from one of the caps, but seems strange, on that note, i will go over everything again and check all the correct parts are in there correct places, 2nd time and sort of 3rd////...

 

[all-over-again]

Do you live anywhere near Brighton. I could take a look. Other than that I will be starting to build a pair of VP28 for a friend when the kits arrive later today. Therefore since I will have the units in front of me it will be easier for me to help you.

I got power on the second LED down 0.02v
I live in London
any help is appreciated

 

[all-over-again]

Do you live anywhere near Brighton. I could take a look. Other than that I will be starting to build a pair of VP28 for a friend when the kits arrive later today. Therefore since I will have the units in front of me it will be easier for me to help you.

Do you live anywhere near Brighton. I could take a look. Other than that I will be starting to build a pair of VP28 for a friend when the kits arrive later today. Therefore since I will have the units in front of me it will be easier for me to help you.

one led has 0.02v second one down ..... after i disconnect from power , the leds come on if i run a screw driver across the switches, the leds light up for a second
I live london so a bit far, but now considering a trip in the coming weeks , maybe i will buy another one soon and try again or get someone else to try for me
any help is appreciated

btw something is strange with this forum at this moment, sorry for the excessive posts

 

[all-over-again]

all leds are showing values,
0.015 and the rest 0.001, they do light up, i think i should change the buttons on the front, i mean as they lit up on accident, when i was passing the solder iron over them when it was turn off and two of them lit up, which is discharge from the caps i guess, i would see why all four could be faulty, but will change all 7....

 

[Rob Flinn]

all leds are showing values,
0.015 and the rest 0.001, they do light up, i think i should change the buttons on the front, i mean as they lit up on accident, when i was passing the solder iron over them when it was turn off and two of them lit up, which is discharge from the caps i guess, i would see why all four could be faulty, but will change all 7....

Led's normally need 1.6v to maybe 3 volts across them to light up depending on their colour.

 

[jsteiger]

The 4 indication LEDs are all in the same constant current string. The supply voltage starts at the 48V red LED and goes upward. If an LED is in backwards it will stop the voltage to the remaining ones.

 

[all-over-again]

The 4 indication LEDs are all in the same constant current string. The supply voltage starts at the 48V red LED and goes upward. If an LED is in backwards it will stop the voltage to the remaining ones.

After reading this i looked at the board, maybe this is the answer, on the leds , one of them or four of them are orientated the wrong way , i noticed on a led there is a line that goes diagonally and one side fatter than the other , now i got to find out which side is - and which side is + , i will turn the cap around also, i had a funny feeling about it all yesterday,
every other vp 28 build has the dot facing the front of the board, because it has a dot im guessing it has orientation, but doesn't say anything about it on the build guide, i should of followed my instincts ....

it is possible the green led is the wrong way round as it fell out a few times, i had already cut the lead and bent it, although i left one side longer, maybe after it was bent my judgement was off ..

/// the green light comes on briefly when i power it up// still no lights on the other leds///

Thanks

(i know it's something very simple, but i have simple knowledge of these things, but even simple things can present complications)

 

[Rob Flinn]

After reading this i looked at the board, maybe this is the answer, on the leds , one of them or four of them are orientated the wrong way , i noticed on a led there is a line that goes diagonally and one side fatter than the other , now i got to find out which side is - and which side is + , i will turn the cap around also, i had a funny feeling about it all yesterday,
every other vp 28 build has the dot facing the front of the board, because it has a dot im guessing it has orientation, but doesn't say anything about it on the build guide, i should of followed my instincts ....

it is possible the green led is the wrong way round as it fell out a few times, i had already cut the lead and bent it, although i left one side longer, maybe after it was bent my judgement was off ..

/// the green light comes on briefly when i power it up// still no lights on the other leds///

Thanks

(i know it's something very simple, but i have simple knowledge of these things, but even simple things can present complications)

The longer lead on an led is positive. This may not help you much if you have already cut them ......

 

[jsteiger]

The green signal present LED is not in the constant current string. Only the 4 pushbutton indication LEDs are.

 

[all-over-again]

The green signal present LED is not in the constant current string. Only the 4 pushbutton indication LEDs are.

I've given up, will buy a new one next month after I've paid for my mac, I'm doing a free short electronics course online, so will look at this one more in depth at a later date when i gain a little more knowledge around testing procedures , hopefully i will be able to measure everything and find the fault ...

Trying to get my head around the mathematics and understand the terminology within electronics... Music will have to wait for a while ...

 

[cmac]

Hello, I am having problems with my CAPI VP28 preamp. It worked fine for years of use. I did botch soldering the PR (10R) resistors on the Rev B board between the two Op Amps. As I said, the preamp worked fine for a long time but finally stopped working. I will attach a picture of the top, and bottom of the PCB where these resistors are located. PR4 on the PCB may have lost the pad, but I did try to re-solder the connection with the 10R resistor and it appears to be holding properly. Is it possible to add a jumper for these PR resistors I messed up? I cannot find a schematic for this preamp, any help would be appreciated. If it is not worth attempting to add jumpers to this section, I did see on the CAPI site, I could order a "partial kit" for this preamp. I am certain I could at least get the transformers off to reuse on a new build. This could be an option.

These were my test point results. It should be noted that the green signal present light worked right when I sent the test tone to the preamp. All the front panel pushbutton lights work, although I did leave all of them disengaged for line level as instructed.

**Proper Results**
TP1 = 111.1mV AC
TP2 = 697mV AC
TP3 = 1.26V AC
TP4 = 310.8mV AC
TP5 = 310.8mV AC
TP6 = 310.8mV AC
TP7 = 651.5mV AC
Module’s output = 1.297V AC

**My Results**
TP1 = 73mV AC
TP2 = 463mV AC
TP3 = OL
TP4 = 210mV AC
TP5 = 0.0mV AC
TP6 = 0.0mV AC
TP7 = 0.0mV AC
Module’s output = 0.0V AC

 

[bigmood]

what's up gang. looks like it's my turn to do some troubleshooting. i recently built two VP28 preamps: one works exactly as expected and the other has about -8db lower output. the db also changes when the phase button is pushed. i reflowed/cleaned up some solder joints but for the most part they look solid. i swapped (0252) opamps with the working one and nothing changed. i compared resistors to the working one and it looks like they're all correctly placed. i tried different chassis slots, cables, interface i/o, scrolled through this thread, etc. i noticed my issue sounds very similar to PerspectiveSound's post on page 46, though I didn't see a resolution posted. i've done everything i can think of for now so here are my test point results:

TP1 = 109mV AC
TP2 = 695mV AC
TP3 = 450mV AC
TP4 = 110mV AC
TP5 = 110mV AC
TP6 = 110mV AC
TP7 = 232mV AC

looks like something's going wrong between TP2 and TP3. without a schematic its hard to tell which components to focus on, so that's what I'd like to know for now.

to get 1.227-1.228V AC, I'm running 400hz out of my daw at -16.21dBFS. at unity gain, zero fader, line level it's around -24.69 dBFS. after engaging the phase switch it's at -25.17dbBFS. with the mic switch engaged, the phase switch takes the volume from -1.32dBFS to -10.4dBFS or so, though I had to terminate my test because the dBFS number kept slowly going down and the metal transistors on A1 started to smell bad and get really hot. i swapped opamps with the other VP28 and the same thing happened again. i realized that this was only happening when i was passing the test signal through it and had both phase and mic switches were engaged. the mic switch alone didn't do it. hopefully this symptom helps narrow down the problem

 

[jsteiger]

If the polarity button changes level drastically the I would check the T2 windings for shorts.

 

[cmac]

If the polarity button changes level drastically the I would check the T2 windings for shorts.

Hey Jeff, I posted an issue I am having with one of my VP28s just above what you replied to. I would greatly appreciate your insight/advice on how to proceed! Thanks much.

 

[jsteiger]

Hey Jeff, I posted an issue I am having with one of my VP28s just above what you replied to. I would greatly appreciate your insight/advice on how to proceed! Thanks much.

Wow, that board looks rough. If the rest of the build looks like that then the issue could be anywhere. If those 10Rs smoke then its an opamp related issue. Are you able to test the opamps?

 

[bigmood]

If the polarity button changes level drastically the I would check the T2 windings for shorts.

I think I found the short! forgot to mention I'm using the Litz transformers. I'm getting 32ohm between Grey and Red (I assume this is abnormal) and then .5ohm between Red and Pink. The rest of my readings look good (correct me if these pairings are wrong—I pulled them from this thread):

Black to Red, appx 16.2Ω
Pink to Gray, appx 32Ω
Violet to Orange appx 32.2Ω

I assume this means I'll need a replacement transformer?

 

[jsteiger]

I think I found the short! forgot to mention I'm using the Litz transformers. I'm getting 32ohm between Grey and Red (I assume this is abnormal) and then .5ohm between Red and Pink. The rest of my readings look good (correct me if these pairings are wrong—I pulled them from this thread):

Black to Red, appx 16.2Ω
Pink to Gray, appx 32Ω
Violet to Orange appx 32.2Ω

I assume this means I'll need a replacement transformer?

I assume all leads were isolated during the DCR check? Red and Pink should read "OL" so your result indicates an internal short. Please send me an email thru the store with your order # and I'll get you sorted.

 

[bigmood]

I assume all leads were isolated during the DCR check? Red and Pink should read "OL" so your result indicates an internal short. Please send me an email thru the store with your order # and I'll get you sorted.

Yep they were isolated. just checked them again to be sure and it was coming up ~.3ohm. okay sounds good! thank you for the super quick reply. it really lowered my blood pressure lol

 

[cmac]

Wow, that board looks rough. If the rest of the build looks like that then the issue could be anywhere. If those 10Rs smoke then its an opamp related issue. Are you able to test the opamps?

Yes, the 10R spots on the PCB look rough... The rest of the board does not look that bad! I did swap the op amps out with a another working VP28 and it was not the issue.