DB54 - 2254 style compressor {update 22.10.19}

[dirty1_1garry]

I’m using a 0.5w meter, so should I use a meter gain pot?
I think the audio maintenance schematic has one but I might be wrong?
Do you have a schematic you could share so I could check my build please?
As I seem to be having some of the same problems mentioned here

What do you mean - 0.5W meter?
You can send me e-mail for more direct contact. I'm ready to help!)

 

[mrdarwin]

What do you mean - 0.5W meter?
You can send me e-mail for more direct contact. I'm ready to help!)

He's talking about 1/2mA meter, like on Neve's schematic.
Please share problems and solutions on this thread, it could helps other diyer, thx.

 

[Spencerleehorton]

Yes sorry typo!! 0.5mA meter I’m using, I have one channel nearly working but doesn’t setup quite right and low ish output the other channel is all over the place!

 

[mrdarwin]

Update.
Removed and put new transistors on BA283, and oscillation still here, only when the unit is plugged on another unit.
Removed jumper r12 and put a 50k trimmer. Tracking is now more accurate.
I highly recommend to mount psu outside the unit, with a toroid inside I have a big 50hz hum...

 

[Spencerleehorton]

I’ve got two channels inside a 2U with toroidal inside and channel 1 doesn’t hum but channel two does, I haven’t worked out yet whether this is noise due to both channels being off one LM317 or due to the position of channel two being closer to toroidal?
Still need some sort of schematic to know what R12 is?

 

[mrdarwin]

R12 is the jumper on ba185 near the edac connector.

 

[Spencerleehorton]

Ah ok r12 on ba185, will look to see what I’ve put in there and change for 50k trim

I’ve had success before with wrapping the toroidal with lams from txf to minimise 50/60hum.

Would be more helpful to have a schematic if anyone could msg me or email please?

 

[Spencerleehorton]

I’ve got 7.5k as R12 on ba185

 

[Spencerleehorton]

as i thought, it always goes quiet when anyone mentions a schematic!!!

 

[mrdarwin]

R12 jumper on BOM, 7k5 on neve schematic...
Igor?

 

[Spencerleehorton]

and you've put in 50k trimmer? confused? what should be in there?

 

[Spencerleehorton]

also ive noticed R8 on neve schematic on BA192 is 10k where as on the audio maintenance schematic R75 which is the same as R8 is 100k?
any ideas on this one?

no sign of it on the DB54 BOM?

 

[Spencerleehorton]

found errors in the schematics and info im using and have spent a couple of hours cross referencing, seems the error is repeated, so will change all of what ive found and see what results i get tomorrow.
If it can help anyone im happy to pass on the info.

 

[dirty1_1garry]

Hi folks!
Due to quarantine was out of town. Now I'm here. Let me comment.

Removed jumper r12 and put a 50k trimmer. Tracking is now more accurate.

That's a good news.

I highly recommend to mount psu outside the unit, with a toroid inside I have a big 50hz hum...

I can recommend the same. Mine was assembled with outside psu box. Topology of 2254 (as all others diode bridge compressor)  mean that signal goes down to microphone level, down to -60dBu and then gained up to line level. Every high hum source as 50Hz power  transformer can give a problem. May be that's necessary to try high quality  AC-DC impulse converters as alternative.

I’ve got two channels inside a 2U with toroidal inside and channel 1 doesn’t hum but channel two does, I haven’t worked out yet whether this is noise due to both channels being off one LM317 or due to the position of channel two being closer to toroidal?

I think it's more position. You can try unscrew your toroid, make a longer wires, trun on your unit and try to move toroid around enclosure to find best place.

 

[Spencerleehorton]

Well I’ve gone back to just testing one channel again now and changed R8 from 10k ( As per Neve schematic) to 100k as per audio maintenance schematic, DB54 doesn’t have a schematic so I don’t know what you’ve used?
It’s the 100k resistor down to gnd on S on the 183, 191 and 192 pcbs.
The other schematics I had were marked 10k?
The other resister was the 100k down to gnd on P, this was marked as 51k so I’ve changed this on all 3 mic amps.

 

[Spencerleehorton]

Channel 1 is now behaving much better but I can’t hear the compression now?
I can see it’s working better and see the controls are responding better but can’t hear the compression?
Ran out of time today but will investigate tomorrow!
I’ll also put in the 5k pot and 1k resistor for the meter.

 

[Spencerleehorton]

Changing the 10k to 100k and 51k to 100k was wrong.
I’ve now seen my error! Ba183 has the 100ks the ba283 has the 10k and 51k.
One channel is working perfectly now, had left out a 5.1k on 283, came to life once this was in!!
The other channel I have a low cut on 191 Pcb, so just need to go through sc and see why this is happening?

 

[Ilya]

I’ve got two channels inside a 2U with toroidal inside and channel 1 doesn’t hum but channel two does, I haven’t worked out yet whether this is noise due to both channels being off one LM317 or due to the position of channel two being closer to toroidal?
Still need some sort of schematic to know what R12 is?

Have you found the culprit of your hum problem? My experience shows that hum in Neve is very difficult to fight when you have several channels. Especially if they run from a common supply. Grounding is ultimately important in this situation.
Is your hum 50/60Hz or 100Hz?

 

[jona]

can't  find this diode BZX79B2V7.. is there a replacement i can buy at mouser  ?
thanks!

 

[Rob Flinn]

can't  find this diode BZX79B2V7.. is there a replacement i can buy at mouser  ?
thanks!

Looks like its a 2.7v zener diode.  Probably a 1/4w one will do.