SSL 552 Summing Box

[helterbelter]

I think I have a few 552's left.
I want to keep one as backup (in case my 557 breaks down), but in case I have another one.....

 

[jplebre]

hey
is it possible to use a 651?
I'll grab the schemos and look at it next week

 

[helterbelter]

651 ?
I have googled it... :
If it contains the 82E26 boards, yes, then it's possible.

 

[jplebre]

Hi

Yes, it does. I was not sure if it would work because the compressor is split through several boards. Not sure if it was split the same way
it's the one on the G+4000 series (quad). Not sure how much the bus amp actually differs probably nothing

 

[helterbelter]

The principle is exactly the same as what I did with the SL557 module, and the 552 module : Tap off the audiosignal before the VCA, wire that to the sidechain circuitry, and apply the CV that comes out of the SC to the VCAs.  Compare the schematics of the 82E26 + 82E27's to the Gyraf schematic, and you see how to do it.

http://www.ka-electronics.com/images/SSL/ssl_drawings_index.htm

 

[razzor]

got all the parts needed for the turning the 552 into a compressor and have a few questions .i am sure they wont be the last

1.if using a 2180a does pin 4 still need lifting

2. can i tap off the 2 47k resistors on the gyraf board with them soldered in place or  lift the leg and solder them in series

3. are the 10k resistors  on the input mix bus needed  or do they connect straight to the pins

4. just noticed that on your finished picture that on board 85152  H7 and H10 are not been removed and H11 12, IC 10 11 12 14 13 have been removed but they where not on the list  . i guess it would be ok to follow what has been done in the photo.
many thanks


R64 is not connecting to rv5 but R62 is .is this right ?  would be great if i could get the schematic

 

[helterbelter]

Hi Razzor,
I see this is your first post : Welcome !

got all the parts needed for the turning the 552 into a compressor and have a few questions .i am sure they wont be the last

Cool ! please post the updates on your project, and regarding questions : Shoot ! I'll do my best to help of course.

1. if using a 2180a does pin 4 still need lifting

Yes. The same rules apply as to the normal GSSL.

2. can i tap off the 2 47k resistors on the gyraf board with them soldered in place or  lift the leg and solder them in series

In case you have a readily stuffed GSSL : yes, lift the legs of both resistors and wire these to the 552. Of you have an empty board to start with, you can put the resistors in and solder wires to the legs.  In case you use a turbo board, one of these 2 resistors will be off-board.
To explain the use of the resistors :
The 47k resistors aren't in series either way. They're between the 552 boards and the input of the sidechain. The 47k resistors function as a small summingresistornetwork.

3. are the 10k resistors  on the input mix bus needed  or do they connect straight to the pins

Well, in case you have a 552 to start with, let's focus on the compressor first, and the summing bus as second. The inputs to the compressor part is on pins 27, outputs on pins 25. You can wire XLR's or TRS jacks to these.

Also, I still have to look at the correct values. 10k is not the right value, I guess 20k will be better. But this is also mentioned in the first post of this thread.

4. also just noticed that on your finished picture that on board 85152  H7 and H10 are not desoldered and H11 12, IC 10 11 12 14 13 have been removed but they where not on the list as being removed . i guess it would be ok to follow what has been done in the photo.

That's right, I haven't desoldered H7 and H10. The other hybrids are socketed so I took them out, but I didn't felt the necessity to take the H7 and H10 out.  It doesn't matter in regards to powerconsumption, H7 and 10 contain switching fets that won't function without the 85500 hybrids. Take them out or leave them in, whatever you prefer.

The other hybrids and IC's : ........You're right, I haven't listed these. I think I missed 1 paper when making the list, because they're all on this same paper. You can take them out.

And thanks for pointing this out, I have updated my first post. I might better rewrite the whole, it's a bit messy after all the updates and additions.....

 

[razzor]

The good news is i have sound ....... and it seems to be working gonna test it further .before i get really happy

i noticed on your pictures you removed the IMO gain pot from the 552 should i do the same. can it be of any use

 

[helterbelter]

The pot isn't used anymore, so, yes you can remove it. It's a dual deck pot, 10klin and 100kLin.

Regarding the VU that ain't moving : It should be a 1mA DC meter, not a VU (unless you use an Expat VU Mod board).

So, that the VU ain't moving, ok, but does the audio compress ?

I don't expect the VCA will be broken, I suggest you check the voltages first. Especially the + and -12v rails fail fast.

 

[razzor]

well it's finished apart from some minor work to the psu and maybe changing the led's in the meter . what a great compressor and summing unit . managed to get it calibrated and distortion set with a neutik A1 and got some spec's

with both summing and compressor in the chain
0.018 thd+n / -92 db Noise / 94db X talk with a good flat frequency response

using  22k 0.1% resistors worked well for the summing network and it got very close to 0db in and out . making minor adjustments to vr3 for the summing input  and vr5 for the compressor input  i was able to set the  gain and balance . using a 0db 1k signal i set the level to -0.7 as this was giving 0db when playing finished tracks and drums though it

i used 2180 THAT's with pin 4 not connected and  47k linear pots for gain and threshold
fitted with a turbo board and single sidechain working in gssl mode only  …. found this setup from stitch-o
original can be found here http://groupdiy.com/index.php?topic=16113.160  was great help

the unit give's 14db of makeup  gain and the threshold range is 0 to -20 or more

there is a minor worry that when the threshold is set  at maximum  with no signal going to the unit the meter reads -2db in gssl mode and don't move but in turbo with the same settings it hits -20 db in a ticking motion about one every second or so  but as soon as you back off a bit  from the maximum  it stops . i wont really be working in them extremes but it would be nice to sort it out.  could be a imbalance in the sidechain .any ideas?

was thinking of some more upgrades like the crush and blend but i am unable to find pcb's  so it might have to be done on variboard

the two extra female xlr's at the back are summing outputs i never had any more male ....
it was a bit of a tight fit in there as you can see from the photo's


dan ddt …gyraf  …pcb grinder...hairball …expat ….helterbelter

i have really enjoyed this project

many thanks

 

[helterbelter]

Nice !
Yes, it's a tight fit. That's why I have removed the DIN connectors from the PCB's in my prototype.

 

[tinwhiskers]

The principle is exactly the same as what I did with the SL557 module, and the 552 module : Tap off the audiosignal before the VCA, wire that to the sidechain circuitry, and apply the CV that comes out of the SC to the VCAs. Compare the schematics of the 82E26 + 82E27's to the Gyraf schematic, and you see how to do it.

http://www.ka-electronics.com/images/SSL/ssl_drawings_index.htm

Apologies for the thread necromancy, here—and my evident ignorance (v much still learning basics)—but it occurred to me...

AFAIK, the comp and mix amp in the G series are spread across the '26 and '27 boards; they are less distinct functional blocks, more one dispersed entity. If, as in this example, one may use the VCAs from the 552s, plus the Gyraf GSSL S/C, and one then has a perfectly happy combined set of summing amplifiers and compressor... Assuming one has a fully-built Gyraf GSSL w/ appropriate 202 or 2002 VCAs, and ofc a summing network w/ 10K resistors as @helterbelter employed... Is that then a perfectly happy summing amp—or is something crucial missing in the absent 552s (which I have missed)?

Thank you! Amazing work and knowledge—thanks for sharing with us beginner peons .

 

[r2d2]

This project is so cool,
and worthy of expansion
on a 2U box as well
with the addition of :
blender on the LR out insert
monitor selector switch for external input
2 dedicated vu meter / meterleds bar for LR master out
else more ?

Ps:
it would be really nice
that posts containing images that are not more visible
because of "expired" links
were updated by re-attaching the images.