[BUILD] All things RackNeve

[AW]

I am using the edcor PCW10K/600 for the interstage transformer
How do I check why the osc freq is changing when I switch ratios?
I was very careful assembling this unit, checked and double check my work???
I did add sockets for all the transistors maybe there might be a faulty one.
Are there dc voltage checks I could do across the transistors?

 

[Ilya]

You need to follow a signal. Check the level before and after the Edcor. Make sure the level after is greater than before. Check for DC action on the bridge. In 1:1 it should be grounded - you can check this at R64. In other positions it should have variable amounts of DC at that point.
Than you follow the bridge output down the sidechain circuit and see how it behaves when the level is changed. I suspect that somewhere down the road it gets corrupted and is not getting to the part that opens the pulses to the VT2.
There should be an error somewhere. Otherwise the unit should compress. No matter how thoroughly you checked, something is wrong. Don’t worry, this is normal.

 

[AW]

I rechecked the main board and found that I installed the wrong transistor for VT11, I had a BC550C installed instead of a BC560C I replaced it, but it still is not compressing.
I think I need a scope, unfortunately I can't afford one right now.
Maybe I fried one of the transistors by having the wrong one installed.

 

[AW]

I rechecked the main board and found that I installed the wrong transistor for VT11, I had a BC550C installed instead of a BC560C I replaced it, but it still is not compressing.
I think I need a scope, unfortunately I can't afford one right now.
Maybe I fried one of the transistors by having the wrong one installed.

Checked all the transistors, they are all good, don't know what else to look for

 

[AW]

This is the scope I am thinking on buying next month
https://www.amazon.com/DS1102Z-Digi...uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

 

[Ilya]

The wrong transistor in that position shouldn’t fry anything.
The scope looks fine. I have no experience with this particular scope, but I have one from Rigol, 2000 series. Works for me.

Check that your C19 is 82p. Check the orientation of the D1 and D2. The marking band on the diode should point towards the square pad.
VT11 is responsible for conducting pulses to the chopper VT2. VT11 should see variable DC on its base. The DC level depends on the level in the SC.
Check that you get pulses at the base of VT10

 

[AW]

I did install the 82p for C19, I do have the correct orientation for D1, and D2. I did some more checking and found that on the XLR's I connected my shielded wire input and output twisted pair cable to pin1, I removed the shielded connection on both as per your instructions.
I did ground pin 1 to chassis for both input and output. So I have pin 2 on both XLR's going to pin 1 on the molex input/output connectors, and pin 3 going to pin 2(molex connectors)

I do get a reading now on the threshold meter when i inject around 17dbu at 1khz, but when you get a little below that it doesn't register, also the led's on the threshold take a while to go off when you take the signal off, or turn the bypass on.

 

[Ilya]

on the XLR's I connected my shielded wire input and output twisted pair cable to pin1

You need to connect the cable screen to XLR pin1. On a single side of a cable only. On both input and output.

I do get a reading now on the threshold meter when i inject around 17dbu at 1khz, but when you get a little below that it doesn't register, also the led's on the threshold take a while to go off when you take the signal off, or turn the bypass on.

The reading on the meter doesn't mean anything if you didn't do calibration. So you need to check if actual compression action is going on. The LEDs turn off slowly - that's probably because your release is very long. You may also check if R55 is actually 390R. Also, disconnect the "decay" molex and measure the resistance at the switch side. You should read from 1.8K to 120k depending on the "Decay" switch setting.

 

[AW]

i was able to find the decay problem, I installed the stop pins when the shaft wasn't in the correct position. Still no compression action, I am getting 235khz at D1 cathode, but nothing at the collector of VT2 could it be possible VT2 is faulty or a cold solder joint?, I did install a NP electrolytic for C90 did notice it had a longer lead on one side, should that have been installed on the positive side? I never knew they made such a capacitor.

 

[Ilya]

You won't see anything at the VT2 collector. You have to check the base of VT2 for pulses.
The longer lead is of the cap not relevant in your situation.

 

[AW]

Sorry I meant I don't get a reading on my freq counter at the base of VT2
Would I be able to get a reading on my freq counter at the base, or do I need a scope?
Should i try replacing VT2??

 

[AW]

Sorry I meant I don't get a reading on my freq counter at the base of VT2
Would I be able to get a reading on my freq counter at the base, or do I need a scope?
Should i try replacing VT2??

I went ahead and ordered my replacement scope, Iet's look at my problem when I get it.
Thanks again for being here to help figure this out
Tony

 

[Ilya]

Sorry I meant I don't get a reading on my freq counter at the base of VT2
Would I be able to get a reading on my freq counter at the base, or do I need a scope?
Should i try replacing VT2??

If you don't see pulses at VT2 base this means they are not getting there. They are lost somewhere between the D1 and VT2. I'd check for DC conditions at R55 and VT11 and see how they change depending on the sidechain signal level. Also make sure you connected the attennuator correctly. If you didn't, it may mess up your SC signal level and it won't trip the threshold.
235 kHz is pretty much in spec. If it doesn't change with ratio, than your osc is working fine.

 

[AW]

Do these AC readings look right

 

[Ilya]

Yes, the trend looks correct. FYI Threshold settings are "-12" - "+10" in 2 db steps

 

[AW]

I figured while I wait to get my new scope delivered I took DC and AC(rms) readings throughout the entire circuit path. I applied a 1vrms input sig @ 1khz thresh set at "0"
Let me know if you see some readings that might indicate why I am not getting any compression.
Thanks tony

 

[Ilya]

I am using the edcor PCW10K/600 for the interstage transformer

Here's your problem. And your AC readings confirm this. Remember, this was one of my first questions - about the level after interstage transfrmer?
The transformer you are using is 4:1, it steps down instead of stepping up. You need to use 600/10K step-up instead.
You can either replace it or cut PCB traces and swap windings of the one you have currently installed.

 

[AW]

So what you are saying is I can remove the EDCOR transf and rotate it so pri is now sec, and sec is now pri
I understand the pins won't line up so I would have to do some modifications?

 

[AW]

I think I will just order the correct one PCW600/10K,,my bad

 

[Ilya]

Yes, in this situation you need to swap windings. So that your secondary winding becomes primary.
If you manage to desolder the transformer, I’d suggest using fly leads from its pins to PCB. This will make testing easier. And if the swap won’t work for some reason (although it should) it will be easy to install a proper transformer.

EDIT: This way you can play with the unit while waiting for a new part to arrive.