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

Yes the 2503 is all fine. You can resolder those leads again.

Next, let's remove the t-pad from the circuit. Desolder the 3 leads where they connect to the main PCB. Leave the rest of the t-pad alone and set it to the side. Take another small jumper wire and solder from pad A to pad C on the main PCB (where the t-pad leads were). Make sure you do not touch pad B at all.

Power it up and check again.

Jeff

jsteiger said:

Yes the 2503 is all fine. You can resolder those leads again.

Next, let's remove the t-pad from the circuit. Desolder the 3 leads where they connect to the main PCB. Leave the rest of the t-pad alone and set it to the side. Take another small jumper wire and solder from pad A to pad C on the main PCB (where the t-pad leads were). Make sure you do not touch pad B at all.

Power it up and check again.

Jeff

Click to expand...

Ok. So I re-soldered the 2503 in there .. and plugged it back in to just double check that i was back at the same place.. then I pulled the T Pad out and put a jumper between A and C  - plugged it back in and i got nothing -

I did not clean the solder from the B hole - was that a mistake?

Thanks
Max

Max, no problem on cleaning the B hole as long as it's not shorting to A or C.

I would recommend starting form the beginning of this thread and skimming thru posts. It appears that you problem is more near the input of the circuit, not the output. We have covered this in earlier posts. Basically, you will have to do some diagnostic work while injecting a mic level signal and following the signal thru the circuit until it dies out.

The previous issues you described with the
Polarity switch make me still think it could be around the Mute and Polarity switches.

Jeff

Alright - will do! I remember reading over some posts bout injecting and tracing. I'll go back through and do the homework.

Thanks for all the help!
Max

Hey  Jeff - got one more question - Should i reconnect the T Pad when i start tracing the signal or leave it out for now?

Thanks
Max

Either way Max. If you leave it out and solve the problem, then putting it back in will be the only change so you will know what to look for if things don't work then.

jsteiger said:

Either way Max. If you leave it out and solve the problem, then putting it back in will be the only change so you will know what to look for if things don't work then.

Click to expand...

Alright - I'm back. Thanks for taking the time to answers these questions - I know I'm be presenting you all with some pretty 'amateur hour' problems. I've learned the hard way on just about every step of this project - glad for it though.

I built an injector and probe and started tracing signal through out.
I followed the tracing directions found on page 6 of this thread - ( starting somewhere around post 106 or 107 )

I was able to trace decent signal on the Input side of things following the directions - and i was able to trace decent signal on the Output side up until the output of the EA2503 transformer (blue, green, yellow, orange, grey and violet) - signal is significantly reduced in volume and sounds as if everything below 1K is rolled off.

I've discovered a few things of interest along the way that i don't quite understand.

1) - I can trace signal from the Input all the way to the Output with the OpAmp removed. Did I make some crazy mistake or is this normal? (same occurrence on the output side of the 2503 - low vol and sounds like a hpf)

2) - Once I honed in on the 2503 as the possible source of my issue - i removed it to test it, again - and while it was removed I randomly did some exploratory probing..  When i probed the top mounting hole of for the 2503 on the PCB ( the mounting hole opposite of the Grey, Violet, Yellow and Green points ) I get full signal coming through.
I'm not the best following a schematic.. but that really had be stumped.
the output trans tested fine again.

Through all of this, even more touching up of any remotely suspicious joints - and double checking all my resistors and caps - I still have the exact same issues. 

Seems to me either the 2503 or i made some gnarly mistake that kinda botched it all ??? ???

Thanks so much again.
Max

Max

Can you post some top and bottom pics please?

Was your last run thru with or without the t-pad? I helped a guy thru email last week that was describing a very similar problem. After he put his t-pad back in, he discovered it must have been something faulty with his original t-pad wiring as it was fine then.

Best, Jeff

jsteiger said:

Max

Can you post some top and bottom pics please?

Was your last run thru with or without the t-pad? I helped a guy thru email last week that was describing a very similar problem. After he put his t-pad back in, he discovered it must have been something faulty with his original t-pad wiring as it was fine then.

Best, Jeff

Click to expand...

Howdy -

I tested the unit both with the T Pad removed ( A and C jumpered ) and with the T Pad reinstalled.
Just like before I started tracing and retouching, the removed T-Pad testing yielded no signal on the second time around.
When i reinstalled the T-Pad  I was back to the same weak, HPF sounding signal.

Here are some photos of the top and bottom. Its all pretty ugly. At this point - i've mangled just about everything. This should serve as a solid lesson to any other DIY newbies. The part of your super detailed assembly guide that says "CHECK TWICE, SOLDER ONCE" is golden advice. Somewhere in there i think it also stresses taking your time. Like a fool I did not follow either rules that well.

You can see that I have a stepped gain switch in there. The tight space of that board was a stretch for my iron skills at that point.. any chance that a mistake at that stage could yield these results?

Thanks again - I'll track it down at some point - and hopefully not botch the whole build in the process.

-Max

one more

I don't see anything jumping right out at me although it seems strange that you had different (both not good) results with the t-pad in or out.

Does the gain switch seem to work at every position, even though the signal seems HPF sounding? We can easily eliminate it just for good measure. You can remove the 2 jumper wire connections that go to the main PCB. In their place, solder a short jumper wire from 1 to 3 on the main PCB for the gain pot area. WARNING!!! This is the equivalent to the gain switch being set to wide open, full gain, so be prepared for that. Let me know how that sounds.

Cheers, Jeff

I just tried removing the Stepped Gain and got the same result.

When it was installed, all the steps of it seemed to work just fine..

When I traced the signal through out the circuit - i noted a very similar HPF change in the sound on all of the output leads of the transformer... orange, blue, grey, violet, yellow and green -

Does that raise any flags? I've tested the 2503 multiple times.. but the similarity seems strange. I could also be a misunderstanding its significance.

The fact that the Phase switch cuts signal when engaged is still floating somewhere in this strange soup as well. I've touch those tips up way to many time - i can see that i've got flow from top to bottom on the board.. and tripled checked the resistor value, and cap value associated with it.

Just rambling now. Thanks for the help and ideas as usual.
-Max

Can you add a couple of small jumper wires from SW3 to SW4 as shown in the pic below? You can just solder them onto the solder lugs that are above the white epoxy sealant on those switches. If your 2503 leads are long enough, you can move Brown and Red to the respective solder lugs on SW3. Red towards the bottom of the switch, brown towards the plunger.

Report back with your findings. 

Best, Jeff

Well, I jumpered the two switches as you showed - and the problem remains. HPF sound and loss of signal when the Phase is engaged.

The leads Brown and Red leads on my transformer might be long enough.. but I've soldered and desoldered those points so many times already that I'm a little leery of pushing my luck. I'm gonna give it a better assessment and if doable, I'll give it a shot and report back those findings.

Dig it.
Max

Max,

I am starting to think it may be the 2503 even though all the winding's DCR measure out OK. You did say that you traced the signal to just before the 2503 and it was fine right? You could probe right on the solder lug of SW4 where the red lead goes to verify.

I asked ED via email last nite if he could think of a reason the 2503 would produce this result if all the winding's DCR was correct and he said nothing comes to mind but stranger things have happened.

Let me know and we'll go from there.

Cheers, Jeff

Heyo-

Strangers things have definitely happened.. and they've definitely happened to me.

Yes, the signal is good up to the 2503 - and i just double checked again - at the switch 4 lugs and right at the solder point of the leads to the board.

Can I attempt a similar sort of signal trace directly on the 2503? Should I change anything about my probe set up?

THANKS!
Max

Max

With the Polarity switch out, the signal will be coupled to the red lead of the 2503. You could check there by probing from the bottom of the PCB.

With Polarity switch engaged, signal will be coupled to the brown lead of the 2503. See if the signal is good at the brown lead with the switch in. It should be.

Best, Jeff

I get signal on the Red and Brown leads regardless off the position of the Phase switch.. In fact I can probe all 6 lugs of all 3 Switches and get good signal regardless of the switch position.  ???

My probe set up is an iPod wired to alligator clips attached to In Lo and In Hi (J8 and J10)
The probe is hooked up to a small set of speaker with a 10uf 100v Non-Polarized Capacitor inline.

-Max

Max

What about setting your DMM to ACV and probing for a mV reading. You can hook the black probe to the upper lead of R13, closest to the top edge of the board or the Bourns gain pot.

I am about to test a VP26 built for a customer so I will see if I get anything like what you are describing.

Best, Jeff

Hey Jeff -

I gave this probing a shot. I wasn't super sure about how to do this -

My DMM ACV settings only has 300V and 200V.
I set it at 200V and connected the Black lead to the top side of R13.
I then probed with the Red lead at J8 and J10 and I got a reading of approximately 3.4 from both inputs.
(both readings started a little higher and seemed to drop - the more that i double and triple checked)

I was a little unsure about the reading because you noted looking for a mV reading.. So I set the DMM to DCV  (which has a mV range) and conducted the same test -  I got a approximately 1.78 from both inputs.

Results were the same regardless of Switch 3 being engaged or not.

Not sure if this is what you were looking for.

-Max