Another GSSL is born today

Another GSSL is born today. I've had it 95% done for a few months, but finally got around to putting the final touches on it, including a new front panel, a meter light, and trimming the meter properly.

This is probably some important info, some of which is burried in the GSSL help thread, but this is what I had to do to get the unit to respond properly using THAT 2180LA VCA's:

1) 100K resistor driving neg input of TL072 to VCA CV's replaced with 122K to get proper ratios for THAT 2180LA's.

2) 2K resistor feeding meter replaced with 1K +/-5% for 0-20dB range.
Note: I tried to get a 0-10 dB range, but there wasn't enough current with the resistor completely bypassed to drive the meter to full scale at 10 dB reduction (this is what the trimmer is for that you see by the ammeter).

3) Threshold potentimeter changed from +12/-12V range to 0/-12V range to get better precision (+12 leg replaced with ground). This has the threshold kick in at about -50 to -40 dBFS with the threshold at it's lowest setting (ratio dependant).

4) Pin 4 on the VCA's are bent up and away from the IC sockets to disconect from the trimmer circuit (I'm not sure if this is nesc, data sheets have pin 4 as N.C.)

Pardon the poor pictures, I can't find my digital camera and had to use my video camera's still function (no flash).









I also ran some attenuation response curves for the unit that I compiled into an excel sheet if anyone's interested. The curves show how the knee of the compressor behaves, gentler at lower ratios and sharper at higher.

http://www.emediatransfer.com/chris/GSSL_cal.xls

Damn, that is a nice DIY-setup you're collecting... :shock:

Jakob E.

very nice...


connecting the + side of the threshold pot to gnd means, there is no range of more than 0 db ??

I use a 15k resistor in series with the pos. leg of the pot....


is there a way to expand the threshold range in total ??


mat

Use a lower series resistor from the centre pin of the pot to the DC mixing opamp..

that's what I will try!!

:thumb:

Very good looking stuff you have there....

What's that cap for next to your meter light's?

[quote author="gyraf"]Damn, that is a nice DIY-setup you're collecting... :shock:

Jakob E.[/quote]

With many thanks to you sir! One of the GSSL's is a gift for a friend who lets me play in his studio when it isn't booked.


[quote author="radiance"]What's that cap for next to your meter light's?[/quote]

That's a 1K trimmer, used in conjunction with a 1K resistor for the meter range. I knew that the 2K resistor on the board was too resistive with the CV input adjustment I did (the meter barely moved). I decided to just trim the meter in place from 0-2K with the two resistors. Turns out 1K did the trick.

[quote author="matthias"]very nice...

connecting the + side of the threshold pot to gnd means, there is no range of more than 0 db ??

mat[/quote]

I found myself only using the threshold set from 12:00 to full. A 12:00 setting kicked in the compression at about -45 dBFS, while a full setting kicked it in about -2dBFS (+4 operation). I'm not sure if this is a typical response, or if this is affected by my tweaking. The 12:00 to full setting was basically 0 to -12V, so I changed the connection so that it was the pot's full range.

Thanks for all the nice comments!

-Chris

Just out of curiosity, where are you guys getting the front panels engraved/silk screened?

Nice work Emperor...

Sender,
Those panels look like they are from frontpanelexpress.com. Check them out.

TK,

Do you have a Front Panel File for that particular front panel and about how much did it run you?

My panels are laser engraved by Lenny at Vermont Laser:

http://www.vt-laser.com

I've done FPE in the past too. Here is how I see the pros and cons to laser engraving:

Pro:
1) Since laser is a raster scanning method and not a vector plot, the artwork is not limited to what an engraver can do. You could even put a photo of yourself on the front if you want.
2) Common file formats are OK. No HPGL or FPE proprietary software required.
3) Laser is charged by the square inch of surface you are engraving regardless of detail or density. This makes a panel with a zillion letters, scales, and logos MUCH cheeper than a FPE panel.
4) You will be the only kid on your block with a "Laser-tuned GSSL".

Con:
1) Without special post processing steps, laser can only ablate away a colored panel down to a bare oxide surface. In other words, it can only write "white" on colored anodized layers.
2) Slight raster lines show in the laser when you look closely.
3) The engraving is not deep like a mechanical engraving. Some folks prefer this look however.
4) My laser guy doesn't stock 19" front panels, so you need to order the panel and ship it to him, so it takes a little longer to get your part.

If anyone wants a copy of any of my artwork, I'd be glad to email the files. Most are in either Corel Draw or Illustrator formats.

Hope this helps,
Chris

That would be great. I'd appriecate the files (both Corel Draw and Illustrator). So where did you order your chassis/front panel from? Also, that cut out for the meter, what meter is that for?

My email is wsender*at*comcast.net

TK?

Check your email. The chasis/panel was from Par-Metal, the meter was a Modutec from Mouser.

-Chris

One more question TK. That 100K resistor you talked about replacing. Is that the one directly above the IC or a little bit above that other 100K in the a group of about 3 other resistors.

[quote author="Emperor-TK"]Another GSSL is born today. I've had it 95% done for a few months, but finally got around to putting the final touches on it, including a new front panel, a meter light, and trimming the meter properly.

This is probably some important info, some of which is burried in the GSSL help thread, but this is what I had to do to get the unit to respond properly using THAT 2180LA VCA's:

1) 100K resistor driving neg input of TL072 to VCA CV's replaced with 122K to get proper ratios for THAT 2180LA's.

[/quote]

is it recommended for THAT 2180LB also?

Yes, It should be the same tweek for the 2180LB's. The LA and LB VCA's differ only in thier distortion specs if I recall correctly.

-Chris

[quote author="Sender"]One more question TK. That 100K resistor you talked about replacing. Is that the one directly above the IC or a little bit above that other 100K in the a group of about 3 other resistors.[/quote]

i second that question-cos when i follow the one at leg 6 it connects to 620 k and not 470k :?: