smallbutfine

Alesis 3630 - the cheap noise machine
« on: June 07, 2004, 11:37:18 AM »
First thread about this *****...
 :grin:
Since this one is a *very* cheap buy (ebay), it's a good thing for experiments with a soldering iron...
I checked the sound for a few days in several settings - almost useless, maybe if you are in "house" music, you can get a special *mud* sound ...
So opened up this thingie and tried 2 mods so far, seen on the old TT...
First one:
I got my Knipex and cutted two jumpers to eliminate the almost useless noisegate (does a lot "fluttering"). Very easy, much effect! A vast amound of "colourful" distortion was gone...
But now i had a crackling oscillation in the heights...
So i went on modding and tried a mod posted a while ago, old TT again...
Very easy as well, i soldered a bridge from the tip of a sidechain insert to the tip of the corresponding out (this was a very cool idea, whoever came to this first... ).
Sound was completely changing, much more warmth, crackling is gone...(as well as the possibility to use the output knob in a useful way :wink: ).
The ratio knob is working very different now... the thread i read mentioned this before, but no matter, it sounded unusable before, and now it doesnt make my ears bleeding anymore....
Since now i can say: i didn't expected this one to be useful from the beginning, but with this little afford i'm very surprised to get this big changes in sound.
I don't believe changing the opamps could get as much improvement as this "design change" mods!
But now i'm stuck...
i think there's alot of interest in this device, since it sells this often and is mostely hated for his sound...

Detector ciruit has to be modded for proper operation now...
Someone was much more into it as me, but...who?
Any help appreciated...
"In the past we suffered from crimes, today we suffer from laws."
Tacitus

www.audiomh.de


Jonathan Hayward

Alesis 3630 - the cheap noise machine
« Reply #1 on: June 07, 2004, 11:45:29 AM »
any chance of a more detailed explanation of where you put the bridge - turn left at the vca etc..?

smallbutfine

It's back in the rack...will make pics later
« Reply #2 on: June 07, 2004, 12:25:18 PM »
unfortunately it is back in the rack now...
i'm trying to borrow a digital cam later this evening. It may be useful to get an actual pic showing the mods...
 :cool:
then it'll go back down into reengineering...  :twisted:
sorry, not so much time in the moment...
maybe later this evening.
"In the past we suffered from crimes, today we suffer from laws."
Tacitus

www.audiomh.de

smallbutfine

pics follow tomorrow
« Reply #3 on: June 07, 2004, 12:59:02 PM »
...since i have to use my rack today in making music and patch another patch at the patchbay...
nevertheless: much more tomorrow...
got a package from Reichelt today :grin:

soldering time tomorrow after work...
"In the past we suffered from crimes, today we suffer from laws."
Tacitus

www.audiomh.de

Alesis 3630 - the cheap noise machine
« Reply #4 on: June 07, 2004, 01:00:27 PM »
Someone really cleaned on of these up about 2 years back by replacing some caps and op amps.

I will look to see if I can find the article. It made it into something "much better" than before.

Preben Friis

Alesis 3630 - the cheap noise machine
« Reply #5 on: June 07, 2004, 02:18:31 PM »
The description of the 3630 modifications of Peter Purpose are still on "that other site". I do however still doubt that the difference is
that big... - but I've never done it myself.

For the interested:  Here are the bridges to remove if you want to disable the gates and get rid of the HF oscilliations:



/Preben Friis

dale116dot7

Alesis 3630 - the cheap noise machine
« Reply #6 on: June 07, 2004, 02:21:10 PM »
I've been working on other things but I've got a couple of modded 3630's. The last one I've been working on has the following done:

-changing it to feedback (remove jumper feeding side chain jack and attaching to the output of the final output buffer but before the -10/+4 attenuator.
-removed the whole noise gate IC (LM339)
-Hijacked the noise gate output op-amp to use in a modified attack-release circuit
-removed the LM339 used in the attack/release circuit and replaced the LM339 between the attack and release section with a PNP buffer. Also, the output LM339 has been replaced using the freed up noise gate op-amp stage.

My theory there is the LM339 is a comparator and if you're using it as an amplifier it'll not work well.

Advice to anyone using an op-amp as a comparator or vice-versa... it's the same advice asking when to get married. Don't. :grin:

Alesis 3630 - the cheap noise machine
« Reply #7 on: June 07, 2004, 03:55:15 PM »
Quote
Detector ciruit has to be modded for proper operation now...
Someone was much more into it as me, but...who?


There are a great deal of problems with the 3630's detector circuit...where should I begin?

For one, the RC network that controls detector release rate is a poor choice of values.  The detector IC is underbiased and timing is too short.  This is what causes so much of the popping and distortion problems that the 3630 has.  Sure, you can remove or disable the gating network, but there are better ways to get around this problem and improve that gate while you're at it.  Detector feedback resistor values might also be an interesting value to play around with as well.

Quote
But now i had a crackling oscillation in the heights...

I've seen situations in the 3630 whereby excessive current in the Threshold control circuit results in oscillations on the control port of the VCA.  I think that the gating circuit might be no different.  It's my understanding that these VCA's are very susceptible to this kind of thing,  thus the use of the 33-ohm source impedance resistors on the +/- control ports.

Quote
Someone really cleaned on of these up about 2 years back by replacing some caps and op amps.

Oh, there's much more to it than that, boys.  The 3630 needs much more than simple signal chain upgrades--I think that whoever designed this bad boy had no idea what they were doing.  

Quote
My theory there is the LM339 is a comparator and if you're using it as an amplifier it'll not work well.

Now this is an interesting observation, Dale, and I admire the direction you took to solve this problem (the PNP buffer).  As I stated earlier, though, there's a simpler way to solve it.  Switching from a feedforward topology to feedback topology is a good idea, as well.

I'm hesitant to spill my proverbial guts on this one, though...I'm interested to see what solutions other people propose.

Jonathan Hayward

Alesis 3630 - the cheap noise machine
« Reply #8 on: June 07, 2004, 04:19:33 PM »
please do, I think many of us with these things would like to keep them around rather than never use them.
I have never seen the schematic to this either which would help clarify things enormously, what you say about the RC values in the detector circuit is interesting; maybe the THAT non-linear capacitor circuit could be used here...

Alesis 3630 - the cheap noise machine
« Reply #9 on: June 08, 2004, 01:03:24 PM »
Quote
I have never seen the schematic to this either which would help clarify things enormously

That's a funny issue--Alesis is so protective of the 3630's design.  They want $100 USD for the schematic, plus they make you sign a non-disclosure form.  To me, it's akin to a bag lady being overly protective of her stacks of trash and old milk containers.

Ironically, though, I must admit that I'm somewhat protective of my findings about the 3630's circuitry as well...I have a 3630 modification kit that I sell, so I'm hesitant to divulge some of this information...
I'm certainly not trying to impose myself on anyone here, or use this as an attempt to hock my wares--I suppose I'm just curious to see how folks in this forum approach solving the problems that Alesis' circuit design presents.

I can tell you that, so far, the mod ideas presented here are pretty good, although you're missing a few key issues.  Good luck, I hope I haven't offended anyone.


StrayCat

Alesis 3630 - the cheap noise machine
« Reply #10 on: June 14, 2004, 09:17:10 AM »
Hello, never saw this "Post" before I wrote my "Post" about looking for sPace to "Post" Pics. I have also done the 3630 MOD described by Peter Purpose. I used the SOIC chip instead of the original DIPP since Burr Brown has discontinued the "AP" DIPP. You must utilize a SOIC to DIPP adaptor. I have openly answered all and any question pertaining to this MOD that I have freely received information for. The kits you described are a great way for a DIY MOD newbie or advanced modder to facilitate this MOD. Post on the Black Market will ya. DR. Foster. Your R&D into improving the design is a value to all DIY'ers but also should be recognized for it's value for your time and expenses. Hmmm. I'm posting pics to get DIY people afraid to OPEN their ill sounding magic box to crack it open, look at all the pieces, identify the parts for the mod, swap em out and fire it back up. (without fire). The mod for me saved this unit and created a useable piece of Semi-Pro audio gear. I still have to strap the output and input grounds as per the article by Peter Purpose. The component and design changes are a value to DIY. I guess I can also do some experimenting but maybe a fire in the computer room isn't wise until I get the sprinkler system in. I don't remember a tip side chain to tip out. What would that do? or am I completely missing something here. The unit does NOT have balanced ins and outs so this could cause noise crud on the signal carrying wire since ring sleeve are now combined. +4/-10 settings do not create balanced unbalanced signals just a pad. Everyone says the 3630 has little headroom and distorts easily. Maybe people are using it as a balanced piece of gear trying to drive +4dB. Won't really work out very well. I have since only used unbalanced cables to the unit and from the unit and it seems to work better. less clipping. Not as much high end but more clear at least. Hope to share more pictures and ideas. I will not steal anyone?s R&D that they require or expect payment for. DR. Foster if your ideas require payment. Excellent, free enterprise is really valuable to us all. I can't burn up 3630's everyday to achieve better results. If you have developed a superior unit, formulated in a kit. post it on the black market. If you also could post some MP3's of the sonic difference or some scope screen captures with explanations. You may have made a ton of kit sales already. We "cheapies" are hungry for better sound and are willing to pay for it. My audio Hypocritical Oath
 :grin:

Cheers

Paul
Later
Chemira Music Studio

StrayCat

Alesis 3630 - the cheap noise machine
« Reply #11 on: June 14, 2004, 09:56:52 AM »
Another note, check out the design notes at THAT corporation for the 2180 improvements over the THAT 2150's when coupled with the 2252's.
If THAT Corporation even posts that there is a sonic improvement over their original spec VCA then (apart from improving their sales) then why not concede to the sonic spec improvement potential. Everyone changes op amp chips to better spec ones with some improvement. Even power savings can have an improvement, better slew rate etc. The only limiting factor of course is the circuit design. It may not respond to op amp improvement if that is not the only weakness in the design. Ah crap what do I know. Read the specs at THAT corp. "That" will say what I'm tripping and stumbling over.

Paul
Later
Chemira Music Studio


 

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