Yamaha GC2020 Modification/component Upgrades

[illacov]

The lowly GC2020 is a compressor that was mainly a piece found in use in live rigs and occasionally the project studio. I had a pair at one point, but now I'm down to one.

I opened it up one day to find some decent capacitors (Rubichon), what appeared to be various ICs and instead of VCAs I found OTAs.

There were also some transistors here and there, most of which I was able to identify via Google but my parts hunt isn't quite complete. I have turned up nada in regards to a schemo, but I would be glad to post pics of the PCB.

Here's the grocery list of stock components that I identified.
NOTE: I haven't cataloged the capacitors or resistors yet, but after some time on the web I identified the ICs, transistors and OTAs

(2) 13600DB/JRC5005, (3) LA6324/4L8, (4) NJM2043SE/JRC5719, T TA75559S DOT 51, C2878 A SJ, A1015 GR51, TB 5 DOT H.

I've been kind of stuck on National Semi Conductor stuff so I kind of stuck with them as I used cross references to find replacement/upgrade parts.

Here's where I wound up:

Replace the 13600DB with Lm13700 or NE5517

Replace the LA6324 with National LM324N.

Replace the NJM2043 with National LM49720.

Replace TA75559S with National LM1458 or National LM8272.

Replace C2878 with Fairchild BC546B

Replace A1015 with Fairchild BC560C

I realize that some of the IC changes would require socket installation.

I figured this mod would be pretty cool if the GC2020 could be cleaned up, especially at the input and output amp stages. If the OTA is adding noise or haziness, then I'd definitely like to see some improvement there if possible.

I'm thinking that I'd love to go for clarity and transparency where possible.

I'd love to hear some thoughts especially on my upgrade choices.

I'll try to find out more from the unit if I can. I'm going to put a call into Yamaha customer support since their service manual for this compressor isn't on the site. They've helped me in the past with my PM700 project.

Peace
Illumination

 

[evilcat]

I would be interested in mod too : I also have one piece but it's not up to scratch with the other comp I have (Neve, TubeTech, Millenia...). It's a "hard comp", could be good, but it distorts the sound, cleaning it up would be great.

Ben

 

[PRR]

> Replace the 13600DB with ....NE5517

Is there any difference??

> Replace the LA6324 with National LM324N.

LA6324 seems to be a low-current LM324. Low-current is not a good direction for nice audio.

Either '324 is a terrible audio amplifier. Yamaha surely uses it only for side-chain or metering, no? Won't help your "sound".

> Replace TA75559S with National LM1458

1458 is an improved '741; TA75559 seems a slightly improved 1458. I think you'd have to squint very hard to hear ANY difference.

> cleaned up .... noise or haziness .... clarity and transparency

OTAs have limited dynamic range. If you hit them gentle, you hear hiss, if you hit them hard, they won't be transparent. Maybe you should consider a different box.

> especially at the input and output amp stages.

How does it sound when switched "OUT"? That leaves the in and out amps in the path, bypassing the OTA.

I assume you have digested the operator manual?
http://www2.yamaha.co.jp/manual/pdf/pa/english/signal/GC2020BIIE.pdf

Even in "+4", the input can be clipped by most modern balanced outputs. In fact there seems to be astonishingly little input headroom, or else the specs are un-clear. Such situations are NOT "chip swaps", but outright re-designs (gain-staging) or very careful driving.

 

[okgb]

Is it worth the effort to you ?
the one time i tried one i found it so unusable that
I wondered how it ever made it to market !

 

[illacov]

If Yamaha is open tmw I'll give them a shout about that service manual.

I'm very curious about the schematic. I'm kind of shooting blind here regarding components, of course if stuff isn't in the audio path, I'll leave it be.  I'm just curious if the unit can be cleaned up if at all.

PRR glad to have you in the thread!

I'd love to poke around the schemo and see if one could replace the OTA in this circuit with a VCA? Maybe a THAT 218x?

Just seems a shame to have these common place junk boxes floating around everywhere for pennies and there might be a hidden gem lurking.

Do you have better suggestions for replacing the ICs?

Regarding when the compressor is switched out? The unit is still hazy, not very clean. If I can get the schemo I'll scan it and post it so it can go into the archives, if for nothing more than a conversation piece.

Thoughts?

Thanks

Peace
Illumination

 

[Seditionary]

did you end up making these mods?  anyone else play with this box?  i think it is kind of cool as a color box -- sounds kind of like lo-fi vhs.  it would be fun to make it even more colorful though into a real effects box