DB54 - 2254 style compressor {update 22.10.19}

[TwentyTrees]

Hi Zergonion,

This happened to me too, and alarmed the bejeezus out of me! I was able to get it fixed. I think it was about the ground wiring - I've a feeling that what I thought was a CT connection on the PSU board was in fact a ground connection, and I had to run the toroid secondaries in series without a centre tap, but I'd need to check my notes and photos as it was a little while ago. It'll be a couple of days before I get the chance to, but I'll post back here when I've checked!

I have to say that the DB54 sounds amazing when all done - buttery loveliness!

Andy

Hi all!
I need some help with the power trafo http://www.banzaimusic.com/Talema-TRT30215.html
I wired secondaries in serial, center tap (which should give me 30V ac), but when I connect it to the electricty the trafo gets really hot and the measured voltage on each wire is 7.5V. I used 250mA as well as 500mA fuse, but no luck. Shoud I get new trafo?

 

[Winetree]

Are full kits still available?
If so, cost?

 

[Lee_M]

Hi all!
I need some help with the power trafo http://www.banzaimusic.com/Talema-TRT30215.html
I wired secondaries in serial, center tap (which should give me 30V ac), but when I connect it to the electricty the trafo gets really hot and the measured voltage on each wire is 7.5V. I used 250mA as well as 500mA fuse, but no luck. Shoud I get new trafo?

What mains voltage are you on?

Going by the fact you're only getting 7.5v, is it possible you're using a 240v primary winding on 120v mains?

 

[TwentyTrees]

I've checked through my notes, and I was right - the '0V' connection on the PSU next to the power transformer secondary connection is not a centre tap but is, I think, signal ground. By connecting the toroid secondary windings in series to the 'VAC in' (isolating the join, natch), and connecting both the '0V' and 'Cha' points on the PSU to the chassis, I got the right voltages and my toroid stopped trying to melt itself(!). Pic of my build below, hopefully you can see the wiring bottom left to see what I mean.

A couple of other things that caught me out at first, from the notes: the 'Bypass' switch operated the other way round than I expected, so I had to hack the switch and rewire a couple of points to match my panel; audio polarity got flipped somewhere at first, easily fixed by swapping a couple of molex headers (possibly just my wiring!); and I can't  get the meters to accurately reflect gain reduction over their whole range, but it's not a huge problem as I set by ear anyway.

It is a lovely piece now that it's all working. I ran some overly thin string stems through it a couple of days ago, and quite apart from the gentle dynamic control it smoothed out all the spiky, harsh top end and left them sounding much more lush and full then before. Would love a sidechain HPF- something for the Mark II?

 

[TwentyTrees]

And the front (just because  ;D)...

 

[Zergonion]

Hi TwentyTrees!
Thank you for all infos. Yes at first I connected the CT to 0V on PSU board and the trafo . Now it's connected to the chasis/star ground and it works as it should
Yesterday I wanted to attach the front panel but quickly found out that the lips on top and bottom panels are hitting the vu meter, so more cutting and drilling.
BTW, nice looking stereo comp!

 

[TwentyTrees]

You're very welcome, glad to hear you got it all sorted out. Good luck with the panels and the meter! I hate metalwork...

BTW, nice looking stereo comp!

Thanks! I'm quite pleased with how it turned out.  8)

 

[Murdock]

Would love a sidechain HPF- something for the Mark II?

Yes please! If this would happen I would immediately build a stereo set!

 

[MrBlomski]

So a 30va 2x15v 1A is enough to power both channels?

 

[TwentyTrees]

Yep, 30VA 2x15V toroid works fine here.

So a 30va 2x15v 1A is enough to power both channels?

 

[Zergonion]

So, my unit is all wired up, power supply is working fine (+24V), I also did the "Bias calibration" 2,3VDC. Then I ran into a problem when trying to do the "unity gain cal." - when compression switch is off, the sound is coming through; but when I switch it on, the sound dissapperas (there's only a small ammount of bleed-through).
I checked all connections, there's no cold solder and I have no idea where to start with troubleshooting.  Is there a procedure how to check were the signal gets lost?

TwentyTrees - what transistors did you use for your unit, BC184 or a replacement?

 

[MrBlomski]

BC184c = BC550

 

[TwentyTrees]

TwentyTrees - what transistors did you use for your unit, BC184 or a replacement?

I used MPSA18 for the BC184 - flipped 180', and HFE matched as close as possible.

In terms of troubleshooting, before you get stuck in following the input, have you checked your voltages on the BA card connectors to make sure all is well there? There are schematics out there for each of the BA cards used in the 2254 which show what pins are what.

Once you're happy with that, do you have a scope that you can use to follow the signal through your unit? Alternatively, a "sniffer" probe? (I've used a test probe croc-clipped to a small battery powered speaker in a pinch - not elegant, but functional - there are doubtless better ways to put one together!) Then I'd just follow your input signal from the input xlr through each section of the circuit to see where it disappears. A proper schematic for the DB54 would make this much easier (hint hint Garry!), but the 2254 and BA card schematics should help.

Good luck!

 

[mrdarwin]

Hi there!
Stuffing my boards....
what about JP1 jumper 2 pins? It's not mentionned in calibration procedure... does it bypass/pass the unit without the front switch?

 

[TwentyTrees]

Good question! I jumped it and that was that. Looking at the PCB traces though, it looks like it might bypass a zobel network on the output transformer secondaries...

Hi there!
Stuffing my boards....
what about JP1 jumper 2 pins? It's not mentionned in calibration procedure... does it bypass/pass the unit without the front switch?

 

[zerodb]

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.

 

[djn111]

Hi,

I was wondering, is there still a pcb set available ?

Or someone who has not build his set jet ?

Kind regards DJN

 

[diystudiotoys]

Hello!
We have few kits in stock right now and waiting more in February.
check here www.diystudiotoys.com

Hi,

I was wondering, is there still a pcb set available ?

Or someone who has not build his set jet ?

Kind regards DJN

 

[mrdarwin]

Hi there!
How do I have to connect the meter? The "+" on molex Xmeter is on the right, like "+" on molex Xlight?
what resistor value for lighting 8027B meter?

 

[mrdarwin]

Unit finished... and some problems:

1. psu
loaded with 2x15v xformer, 30VAC, and around 45v dc out... 1k trim  not working...  so loaded with 18vac and around 24v ok
did you mount psu inside 1u rack case? got 100hz big hum when compression engaged... no hum with off board 24v psu.

2. BA283 bias
I can/t get 2.3vDC... max is 5/6v DC... my trimmer is a 4k7(?)

3. meter range
wrong range of compression indicated, and can't correct it with trimmer... probably due to my old 8027b, have to try with other one.