Modifying an Alesis 3630

[Blue Jinn]

Picked up one of these for cheap, so thought I'd install the gate switch and maybe swap the VCAs. Quick question, the voltage regulators have pretty lame (at least from my limited perspective) heatsinks, and there's recommendations to beef up the wall wart and some of the PSU components. I thought instead of doing that, just wire it up to an external power supply. I have other DIY gear (PAiA mostly) which I've built an external PSU so I thought I'd just gut the 3630 PSU and use an external one. I think is might actually be less work.

 

[Script]

Pots with switch sell cheap in China (plus import though for your region?).

No space inside for retrofitting PSU, as you say. If external, maybe add extra CRCR filtering.

Didn't swap the VCA. It's an FX comp after all.

 

[thomasdf]

Hello

Does anyone have the 3630 schematics ?

I tried to add a true bypass to mine, and for some reason the left channel is showing compression but is not compressing a single bit... even thought I reversed my mod, resoldered the traces i've cut back to original and removed the switch and all.
Maybe I fried a chip ?
Any document and help is welcome

Cheers

Thomas

Edit : found this

 

[JohnRoberts]

The newer more modern VCA will make a measurable improvement at least during bench testing (but not necessarily audible). As I wrote years ago, in this same thread, side chain design will dominate the sound quality experience.

Swapping out with very expensive new op amps is a good idea if you have too much money and want to end up with less, and/or to be able to brag about how much money you spent.

JR

 

[thomasdf]

Hello JR,

I wasn't thinking of swapping anything inside of the unit. I like it's squishy sound for some reason, on certain sources. I just wanted to add a true bypass, and in the process I ended up having the right channel sounding bypassed even when switched in... The GR display works, but the channel sounds like it's bypassed. Sound going through it, but no GR or gain happening. Right channel works as expected.

 

[metalockpick]

I have not used nor seen the inside of the 3630, but I have modded the previous gen "Micro Limiter". The biggest issue I had was with the voltage tripler circuit being noisy. I replaced the 9VAC adapter with an external 24VCT transformer and bridge rectifier, added more filtering, rewired the diodes and used the existing regulators. Big improvement. I used this for radical compression on band limited signal to great effect.

 

[thomasdf]

Hello JR,

I wasn't thinking of swapping anything inside of the unit. I like it's squishy sound for some reason, on certain sources. I just wanted to add a true bypass, and in the process I ended up having the right channel sounding bypassed even when switched in... The GR display works, but the channel sounds like it's bypassed. Sound going through it, but no GR or gain happening. Right channel works as expected.

Stock bypass (not true bypass at all) is achieved by grounding pin 2 of the main VCA with the bypass switch.
On my unit, that point of the circuit is always grounded, no matter the switch position. I have tried unsoldering the switch and the VCA, and that net is still grounded so I believe a component as failed somewhere... now I need to find which one

 

[thomasdf]

Problem solved : while redoing the trace I had cut I soldered two pads that weren't supposed to be linked. It's now back in business
Onto the true bypass again !

Edit : What resistor value should I add before the input in order to have something like 6dB of attenuation ? The input doesn't like high levels, for sure...

 

[gyraf]

NOTE: in that schematic, some of the opamps, e.g. U2 and U8.1 and U4.2, are drawn with + and - inputs reversed.. (that, or they are using bootstrapping in a really strange way)

 

[thomasdf]

I am not sure which revision this schemo is referring to (f ?) but I have a D version and there are some differences, too, and some weird stuff. I thing it’s good enough to understand the general design blocks but in detail I couldn’t rely on it too much.