DB54 - 2254 style compressor {update 22.10.19}

[MoJo]

I think you will be looking for 24 VDC after adjustment, but the build docs should tell you for sure.

For the trimpot, you might want to grab one of these. I find it very helpful and much less prone to hazards like accidental shorts than a screwdriver, although not absolutely necessary.

Thanks JMan! I actually have one of those and will use it. Can I ask you a couple of education questions? Like, do you by any chance know what CHA means? I think I see the wire shielding attached to that pole. Also, is 0V the same as the "return" or neutral path of a circuit?

 

[JMan]

Thanks JMan! I actually have one of those and will use it. Can I ask you a couple of education questions? Like, do you by any chance know what CHA means? I think I see the wire shielding attached to that pole. Also, is 0V the same as the "return" or neutral path of a circuit?

I haven't built this project (though I do have the PCBs somewhere in my stash here), so while I can't say for sure, I would assume CHA denotes the chassis connection. You'd run a nice chunky wire from that terminal to the same place near the power inlet where you have made your connection between chassis and IEC ground. Though I don't know the grounding scheme of this project, I'd reckon that's the path through which all grounds from the circuit (power ground and audio ground) return. I imagine if you check continuity between 0v and CHA, you will find the are connected. Again, I think this is all likely the case, but it will be important to double check the schematic and build documents.

Yes, 0v is the return path for your DC, which is then grounded to the chassis/IEC ground connection, assuming my guess above is correct.

 

[MoJo]

I haven't built this project (though I do have the PCBs somewhere in my stash here), so while I can't say for sure, I would assume CHA denotes the chassis connection. You'd run a nice chunky wire from that terminal to the same place near the power inlet where you have made your connection between chassis and IEC ground. Though I don't know the grounding scheme of this project, I'd reckon that's the path through which all grounds from the circuit (power ground and audio ground) return. I imagine if you check continuity between 0v and CHA, you will find the are connected. Again, I think this is all likely the case, but it will be important to double check the schematic and build documents.

Yes, 0v is the return path for your DC, which is then grounded to the chassis/IEC ground connection, assuming my guess above is correct.

I can't thank you enough for being patient with me JMan. I'm an excellent kit builder when I have step-by-step instructions, so this kit is a little scary to me because the kit designer definitely expects me to know these things. Thanks again JMan.

 

[JMan]

Not at all. That's what this forum is here for, right?

 

[MoJo]

Not at all. That's what this forum is here for, right?

Right, yay!

 

[MoJo]

I have some BA 191/185/283 boards here, which are either AVD or Garash; not sure how I'd tell tbh.
Anyway, working my way through the PCBs here:

R1->R11 stepped threshold
R13->R22 ratio values
R23->R28 stepped attack
R29 min attack time
R30->R38 release values
R39 makeup gain pot->gnd
R40->R49 stepped makeup
R51 parallel on interstage secondary
R52 BA283 T->gain trim
R53 power drop
R54 BA283 J->K feedback
R55 main power drop
R56 Op secondary zobel

Which leaves...
R12 7R5
R50 1k
R57 620ohm

Now, from the 2254E schematic, there should be two resistors forming a potential divider from BA283 F->R->gnd which drive the meter op feed; these are R31,R32 (560,1k5). I suspect that this is R50, and the meter is directly off BA185 B (GR signal).

R57 is suspiciously directly next to R56, so I wonder if it's an alternative value for the Zobel?
As for R12, no idea; it's almost trivially small and next to the ratio resistors.

I don't have PCB1/PCB2 here. Would anyone consider taking a look/photo of the PCB to confirm my theories?
I'll even have a go at making schematics!

Dave.

Hi Dave, did you ever take a shot at making a schematic for this project?

 

[MoJo]

Hi Everyone,

I think I have the wrong power supply transformer, but need to be sure. I am in the not-so-United States where our wall power is 120VAC. I purchased the TRT30215 Toroidal transformer because someone on this thread asked if this was the proper transformer for this kit. I did not realize that maybe that person was not in the US.

The spec on the TRT30215 says PRI: 230V/50-60Hz ge-ge (which I think means yellow)
SEC: 2X 15V/1A gn-rt/bn-bl

When I first saw the spec, I thought it would be OK because I would be feeding less voltage to the primary, and I didn't think that the windings would care. I thought the primary windings would just carry 120VAC.

But then I started thinking that maybe I would not get 2X 15V as the secondary output (wired in series); maybe I would only get roughly half of that, due to the primary winding having half of the rated input voltage.

So I started looking for a toroidal transformer with 120VAC primary and 30VAC/1A secondary, but can't find anything close. Can someone set me straight or suggest the proper toroidal transformer?

I am at a complete loss at this point.

 

[JMan]

I would look at the Triad VPT30-830 or VPT30-1670. The former doesn't quite give you a full 1A (does this unit really need that much?) but is a bit smaller, so it will be easier to fit inside a 1RU chassis. The latter can provide 1.67A which is definitely overkill and the physical size will be more of a hassle, although it will probably still fit. I don't know if that 1A requirement you mentioned is true to purpose or more of a ballpark "this will be plenty."

To your query more generally, yes, we have to get transformers with primaries designed for use with our local mains nominal voltage, so you can't sub a 230VAC transformer here in the US.

 

[MoJo]

You rock JMan! One person on another site said to fit a 330ma fuse to the mains input, so I believe that I don't need 1 amp. I will look at those transformers you mentioned. Thanks so much again JMan; you are greatly reducing my stress levels!

 

[JMan]

Glad I can help!

It's worth mentioning that current draw on the primary side of your transformer (where your fuse will be) is not necessarily equal to current draw on the secondary side. However, I would be seriously surprised if this circuit draws enough current to stress the 830 model. That said, if it punks out on you, you can always replace it with the beefier model.