so here is a little update i was able to get the preamps working Success!! i didnt put the 10 k resistor in the r1 spot on the pcb it does say it in the instructions but in the pictures it is not populated so i didnt put that resistor in ..this also solved my problem with the led and everything is working great !!
[BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
- Thread starter jsteiger
- Start date
Help Support GroupDIY Audio Forum:
The only thing that explains this is the switches are not soldered tightly down to the PCB. There is a small flat spacer on each end of the PC pins. Use a magnifying glass to make sure both of those on each switch are tight to the board.weiss said:
jsteiger said:
Actually not. They are completely on the pcb. And when i tighten the screws of the potentiometers the L-Plate does not correctly align with the front plate and so the buttons stick together with the metal framework. Buttons and potentiometers show into slightly different directions
It must be the alignment of the pots then. The PCB, L-bracket and faceplate should be assembled together before the pots are soldered.
Hi All-
First post here but there's a ton of great knowledge on this forum I've been checking out. I built a VP26 stepped gain pre over the past few weeks. Super fun to build and everything is super high quality. Nice work Jeff.
I'm having one problem. Recording into a DAW and looking at the waveform reveals that half the wave has considerably less amplitude than the other half. This reverses with the phase switch and is clearly audible. Both the VP26 and the Gar2520 (and the 51x rack and power supply) were new builds so I ordered a Gar1731 to see if the problem went away. It didn't, so unless I made the exact same mistake on two different opamps the problem must lie with the VP26. I've reflowed every joint and inspected everything with a magnifying glass and don't see any bad joints or solder bridges. I pulled the output transformer and it measured with correct resistance and no shorts.
Anyone have any ideas what else I might look for? I just ordered a cheap signal generator to go with the scope my grandfather gave me a few years ago, I figure this problem is a good exercise to learn how to troubleshoot with a scope if no one has a quick solution. Does anyone have any tips for using a scope? I gather the general idea is to hook the signal source to the input and then trace the circuit with the scope to see where the waveform gets distorted.
Attached is a photo of the wave in logic swapping the phase a few times during an acoustic guitar part.
Thanks in advance for any advice!
-mike
First post here but there's a ton of great knowledge on this forum I've been checking out. I built a VP26 stepped gain pre over the past few weeks. Super fun to build and everything is super high quality. Nice work Jeff.
I'm having one problem. Recording into a DAW and looking at the waveform reveals that half the wave has considerably less amplitude than the other half. This reverses with the phase switch and is clearly audible. Both the VP26 and the Gar2520 (and the 51x rack and power supply) were new builds so I ordered a Gar1731 to see if the problem went away. It didn't, so unless I made the exact same mistake on two different opamps the problem must lie with the VP26. I've reflowed every joint and inspected everything with a magnifying glass and don't see any bad joints or solder bridges. I pulled the output transformer and it measured with correct resistance and no shorts.
Anyone have any ideas what else I might look for? I just ordered a cheap signal generator to go with the scope my grandfather gave me a few years ago, I figure this problem is a good exercise to learn how to troubleshoot with a scope if no one has a quick solution. Does anyone have any tips for using a scope? I gather the general idea is to hook the signal source to the input and then trace the circuit with the scope to see where the waveform gets distorted.
Attached is a photo of the wave in logic swapping the phase a few times during an acoustic guitar part.
Thanks in advance for any advice!
-mike
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I experienced a massive distortion when going out of my RME interface into the preamps and back to my DAW. i have to lower the send gain to about -60dB to prevent distortion but then the output signal is very low again.
Is this normal? what can i do if i want to integrate the preamps as an external effect on a buss and not as a gain stage?
thanks for your answers
weiss
Is this normal? what can i do if i want to integrate the preamps as an external effect on a buss and not as a gain stage?
thanks for your answers
weiss
Dr Gris said:
unfortunately, lowering the signal from +4 to -10dB does not make any change, as well as enabling the "pad" mode on the preamps. Still distorting.. I never had any problems with my other 19" gear in my studio, so that's basically why i ask.
Just build a simple u-pad with 4k99 series R's and a 160R shunt.
They can be built into Switchcraft XLR tubes like these http://classicapi.com/catalog/product_info.php?cPath=84_85_165&products_id=336
Okay, now i lowered the input signal so i can pull it up afterwards in the DAW (works as well).
But apparently i have some strange distortion anyway on either of the two preamps. Just hear for yourself..
(rename txt to zip first)
Numbers are the relative positions of the knobs
But apparently i have some strange distortion anyway on either of the two preamps. Just hear for yourself..
(rename txt to zip first)
Numbers are the relative positions of the knobs
![[silent:arts]](https://cdn.imagearchive.com/groupdiy/data/avatars/m/0/172.jpg?1620371656){kind=avatar}
[silent:arts]
Well-known member
Hi Mike,
this is normal. nothing wrong.
most acoustic signals ARE asymmetric
do you have any other preamp to compare?
you will see
this is normal. nothing wrong.
most acoustic signals ARE asymmetric
do you have any other preamp to compare?
you will see
I wondered that at first so I also tried the same source/mic/cable/converter with my vintech x73 and didn't have the audible change in sound when I used the polarity switch. The audible difference when using the polarity switch on the VP26 is very pronounced, one setting is very bass heavy and on the other the bass nearly disappears and the the mids are very pronounced.
The polarity switch should not make a drastic tonal change. I imagine you have a cold solder joint on either the mute and/or the polarity switch. Also double check you wiring for the output trafo as well as the soldering on the t-pad.
Hi All-
Thanks for the help so far. A quick update. I reflowed all the joints again, then desoldered, removed and tested the Tpad and replaced it (not fun, wow). I checked for bridged connections as best I could with a multi meter and triple checked the output transformer wiring and component values and placement. No luck yet.
I did learn to use my scope and signal generator though, so even if this pre never works I've gained a bit of knowledge.
Here's what my scope shows, and please feel free to correct my beginner mistakes.
I connect the scope and signal generators ground wires to pin one on the card connector. With the other lead of the signal generator I inject a 1K sin wave at R3. The scope probe shows the sin wav makes it all the way to the Opamp with no issues. Post Op amp the amplitude of the sin wave grows as I expected. With the phase switch out the sin wave shows up at the red lead of the output transformer and not at the orange, phase switch in shows the opposite. The mute switch eliminates the sin wave at both the orange and red leads. Unless I'm missing something this all looks good.
Where it starts to look funny is with the phase switch out the sin wav shows up at the Brown, Green and Black leads at about half the amplitude of the red but the blue lead shows a slightly higher amplitude than the red lead. The phase switch moves the larger amplitude sin wav to the black lead. The Tpad has no effect on the sin at the green or brown leads but both the black and blue lead's sin waves are slightly higher amplitude at the extremes of the Tpad and slightly lower amplitude at the center of it's travel.
At pin 2 of the edge connector you get a large amplitude sin wav with Tpad fully up. As you turn the Tpad down the sin diminishes to zero amplitude and then back up to half amplitude when the Tpad is all the way down. Pin 4 on the edge connector shows a similar phenomenon except the amplitude is not as high as pin 2 when the Tpad is all the way up and it doesn't diminish all the way to zero amplitude. If you reverse the phase switch Pin 2 does the same thing but opposite and pin 4 does the same thing except with a large amplitude sin wav.
I am now stuck, thanks so much to anyone that has any ideas. If anyone can confirm I'm using the scope right I'm thinking I'll post a few photos of how to hook things up and trace the signal. Might be a useful post for some other guys.
-mike
Thanks for the help so far. A quick update. I reflowed all the joints again, then desoldered, removed and tested the Tpad and replaced it (not fun, wow). I checked for bridged connections as best I could with a multi meter and triple checked the output transformer wiring and component values and placement. No luck yet.
I did learn to use my scope and signal generator though, so even if this pre never works I've gained a bit of knowledge.
Here's what my scope shows, and please feel free to correct my beginner mistakes.
I connect the scope and signal generators ground wires to pin one on the card connector. With the other lead of the signal generator I inject a 1K sin wave at R3. The scope probe shows the sin wav makes it all the way to the Opamp with no issues. Post Op amp the amplitude of the sin wave grows as I expected. With the phase switch out the sin wave shows up at the red lead of the output transformer and not at the orange, phase switch in shows the opposite. The mute switch eliminates the sin wave at both the orange and red leads. Unless I'm missing something this all looks good.
Where it starts to look funny is with the phase switch out the sin wav shows up at the Brown, Green and Black leads at about half the amplitude of the red but the blue lead shows a slightly higher amplitude than the red lead. The phase switch moves the larger amplitude sin wav to the black lead. The Tpad has no effect on the sin at the green or brown leads but both the black and blue lead's sin waves are slightly higher amplitude at the extremes of the Tpad and slightly lower amplitude at the center of it's travel.
At pin 2 of the edge connector you get a large amplitude sin wav with Tpad fully up. As you turn the Tpad down the sin diminishes to zero amplitude and then back up to half amplitude when the Tpad is all the way down. Pin 4 on the edge connector shows a similar phenomenon except the amplitude is not as high as pin 2 when the Tpad is all the way up and it doesn't diminish all the way to zero amplitude. If you reverse the phase switch Pin 2 does the same thing but opposite and pin 4 does the same thing except with a large amplitude sin wav.
I am now stuck, thanks so much to anyone that has any ideas. If anyone can confirm I'm using the scope right I'm thinking I'll post a few photos of how to hook things up and trace the signal. Might be a useful post for some other guys.
-mike
