The VP28's are currently out of stock. I am waiting on 2623-1's to arrive. They should be here any day now.
[BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
- Thread starter jsteiger
- Start date
Help Support GroupDIY Audio Forum:
kante1603
Well-known member
Hello,erol said:
no,just leave the mic switch in the off position.This is the line mode.
Unity gain means the in and output level will be equal then.E.g. if you feed a say +4dBu signal the output will be the same in line mode set to unity gain.
This "zero"gain point (no boost,no loss) normally is the reference level that audio units work at.
Mic and line modes are different in their input impedance.You use the pad when an incoming signal is too hot.
Best regards,
Udo.
Luc, replace C9. It was installed backwards the first time.
Hey Jeff,
I want to thank you so much for your products, I have 8 working modules and cannot be happier with my rack setup and the sound of my project studio.
I do, however, have one oddity that I just can't wrap my head around.
The first two VP28s I built are working flawlessly, however the last 3 all have the same problem and I am stumped. The 3 modules sound beautiful both pushed and left with a cleaner gain-stage, however on all three the Signal Presence indicator is constantly lit at Unity Gain and below on the preamp gain knob at the top. Once I switch the preamp gain knob past unity gain the signal presense indicator turns off and works as intended when signal is present and sent through the preamp.
I thought it may had been a fluke on my third module, but after the next two were built with the same issue, I figured I must be doing something else. There actually is no signal at the input or output stages when the signal presense LED is lit at or below unity gain so the issue appears cosmetic at worst.
Hopefully it is something that wont damage the pre in the long-run, could it be something with the standoff/LED attachment? there are no shorts on the PCB that I can tell, and the plastic sheath adequately coveres each leg. I also thought it may have been a bad solder joint in the first few resistors, but they all work as intended sonically and none of the joints look disturbed.
Hoping to get some advice here, the issue is inaudible so either way I can live with the fault on my part if I can't figure it out.
Thanks!
I want to thank you so much for your products, I have 8 working modules and cannot be happier with my rack setup and the sound of my project studio.
I do, however, have one oddity that I just can't wrap my head around.
The first two VP28s I built are working flawlessly, however the last 3 all have the same problem and I am stumped. The 3 modules sound beautiful both pushed and left with a cleaner gain-stage, however on all three the Signal Presence indicator is constantly lit at Unity Gain and below on the preamp gain knob at the top. Once I switch the preamp gain knob past unity gain the signal presense indicator turns off and works as intended when signal is present and sent through the preamp.
I thought it may had been a fluke on my third module, but after the next two were built with the same issue, I figured I must be doing something else. There actually is no signal at the input or output stages when the signal presense LED is lit at or below unity gain so the issue appears cosmetic at worst.
Hopefully it is something that wont damage the pre in the long-run, could it be something with the standoff/LED attachment? there are no shorts on the PCB that I can tell, and the plastic sheath adequately coveres each leg. I also thought it may have been a bad solder joint in the first few resistors, but they all work as intended sonically and none of the joints look disturbed.
Hoping to get some advice here, the issue is inaudible so either way I can live with the fault on my part if I can't figure it out.
Thanks!
Is it possible some R's got flipped with each other around the 4558 chip?
lawrenceames
New member
- Joined
- Apr 19, 2014
- Messages
- 1
Hi guys,
First time building and I've run into a couple problems
Had a few components fry on me from incorrect placement, so I've replaced those.
My VP28 has really low output in both mic and line modes, could you have a look at the attached picture and see if theres anything noticeably wrong?
Thanks
Lawrence
First time building and I've run into a couple problems
Had a few components fry on me from incorrect placement, so I've replaced those.
My VP28 has really low output in both mic and line modes, could you have a look at the attached picture and see if theres anything noticeably wrong?
Thanks
Lawrence
Attachments
jswagler55
Member
- Joined
- Apr 13, 2014
- Messages
- 7
So I have completed 4 of these guys, 3 of them work 100%. 1 of them the Signal light only comes on basically when the signal is clipping, everything else seems to be working fine. Changed out the 4558 and op amps it still has them same issue.
Triple check the components around the IC opamp.
Hi all - So I finally found some time to assemble the pair of these I purchased back last year, and firstly thank you to Jeff for putting together yet another great kit. The assembly went smoothly and one of the units behaved perfectly on first power up, unfortunately the other unit is not so happy and is posing a bit of a problem, that I was hoping someone around here would be willing to give me a few pointers on.
Essentially the faulty unit heats up the DOA installed in A1 to an alarming level, and beyond testing the voltage at the DOA pins I have been reluctant to leave the unit powered up with DOAs installed for more than a minute or so for fear of cooking them. Each of the DOAs installed for testing were known to be good at the time of testing, although the same is not so true of them now. The DOA installed is A3 doesn't heat up in the same way and appears to operate normally from what I can tell.
The voltages at the DOA pins for the faulty unit are as follows:
A1 - Gets very hot when powered
C to +V = +15.28v
C to -V = -15.44v
C to O = +1.06v
+ to - = +1.06v
A3
C to +V = +15.28v
C to -V = -15.44v
C to O = -0.49v
+ to - = -0.49v
The voltage between the signal pins alarms me somewhat, especially as the working unit measures:
A1
C to +V = +15.29v
C to -V = -15.44v
C to O = +0.15v
+ to - = +0.15v
A3
C to +V = +15.29v
C to -V = -15.44v
C to O = +0.01v
+ to - = +0.01v
From this I assume I must have a short somewhere to account for the voltage in the signal path without DOAs installed on the faulty unit, but I'll be damned if I have managed to find it thus far.
Any pointers anyone can offer on where to start looking would be most appreciated.
Many thanks in advance…
Justin
Essentially the faulty unit heats up the DOA installed in A1 to an alarming level, and beyond testing the voltage at the DOA pins I have been reluctant to leave the unit powered up with DOAs installed for more than a minute or so for fear of cooking them. Each of the DOAs installed for testing were known to be good at the time of testing, although the same is not so true of them now. The DOA installed is A3 doesn't heat up in the same way and appears to operate normally from what I can tell.
The voltages at the DOA pins for the faulty unit are as follows:
A1 - Gets very hot when powered
C to +V = +15.28v
C to -V = -15.44v
C to O = +1.06v
+ to - = +1.06v
A3
C to +V = +15.28v
C to -V = -15.44v
C to O = -0.49v
+ to - = -0.49v
The voltage between the signal pins alarms me somewhat, especially as the working unit measures:
A1
C to +V = +15.29v
C to -V = -15.44v
C to O = +0.15v
+ to - = +0.15v
A3
C to +V = +15.29v
C to -V = -15.44v
C to O = +0.01v
+ to - = +0.01v
From this I assume I must have a short somewhere to account for the voltage in the signal path without DOAs installed on the faulty unit, but I'll be damned if I have managed to find it thus far.
Any pointers anyone can offer on where to start looking would be most appreciated.
Many thanks in advance…
Justin
Have you moved opamps to another unit to see if the problem stays with the pre or follows the opamps? Are the opamps seated properly? http://classicapi.com/catalog/DOA_Install.php
Hi Jeff - Thank you for the swift reply. Having thought I had eliminated the op amps when testing previously, I thought it best to take another look, and test them again… Schoolboy error discovered. These Gar 2520s were made up a while ago, and I don't recall testing them, and it would turn out I didn't, they simply got moved from the "to test" section of the bench to being marked "tested" by mistake.
As a result, it would seem two op amps from my stockpile have the same silly fault of the BD139 and BD140 swapped, hence the issue with the VP28. Seems like I shall be ordering a couple more Gar 2520s from you, which isn't an issue except for dealing with the shipping and import to the UK. C'est-la-vie…
Good news is the VP28s are working perfectly, down side is that I currently can't use them both at the same time without "borrowing" op amps from another piece of gear.
On another note, in testing the phantom on the VP28s it seems the current is carried by the hot conductor with the screen or cold forming the return, it also only measures about 28v. Where as with the phantom my VP312DIs the current seems to be carried on the screen with the hot or cold forming the return and it is the full 48v (which in my understanding is correct). Is this normal behaviour for a VP28?
Once again many thanks for all you help and patience.
Best Wishes
Justin
As a result, it would seem two op amps from my stockpile have the same silly fault of the BD139 and BD140 swapped, hence the issue with the VP28. Seems like I shall be ordering a couple more Gar 2520s from you, which isn't an issue except for dealing with the shipping and import to the UK. C'est-la-vie…
Good news is the VP28s are working perfectly, down side is that I currently can't use them both at the same time without "borrowing" op amps from another piece of gear.
On another note, in testing the phantom on the VP28s it seems the current is carried by the hot conductor with the screen or cold forming the return, it also only measures about 28v. Where as with the phantom my VP312DIs the current seems to be carried on the screen with the hot or cold forming the return and it is the full 48v (which in my understanding is correct). Is this normal behaviour for a VP28?
Once again many thanks for all you help and patience.
Best Wishes
Justin
The phantom part of both pre's is identical. The screen is always the return path but that is not exactly module related but rack related. I would maybe check your cabling.
Gigantic thanks to Jeff and gar for their work and to chunger and everyone who's posted such helpful information.
Just finished building a pair of these yesterday. Was quite difficult for a beginner like me, but they worked right off the bat and sound incredible.
Thank you all so much.
Just finished building a pair of these yesterday. Was quite difficult for a beginner like me, but they worked right off the bat and sound incredible.
Thank you all so much.
I finished another VP28 and tested it with some other op amps (gar2520s) and it works great, but when I put in a 1731 I built the power transistors get really hot in a very short period even though it works just fine. I checked for shorts in the places indicated in the build guide and didn't find any.Any ideas what this could be? Thanks!
Yes, visit the gar1731 support thread. These seem to be common problems. You will find the solutions there.
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