Kepex Gates - Bringing them up to working condition..

spacecho

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Hey Guys,

I bought a rack of allison research gates in a pr10 powered rack,
i got them cheap as four are half working (pass signal and gate but sound slighly different - some crackels and hums in some settings) and three arent working, there is also a gain brain in there that amplifies signal (both in and out - but no compression at all)

I want to get them up to spec and at least have say 4 working well (drum kit duties)

I have print outs of the schematics and a basic manual, and have read all of the relevant posts on gdiy and gs

how should i go about fixing these.... (i can follow a schematic and have built a few things (1176, nite eq, guitar pedals) - but i have no formal training or experience)

i thought i might start by..

1) passing varied signals through all units in various settings and note what works as well as differences in settings

2) calibrate as described in manual

3) re cap and calibrate the broken ones to see if this fixes anything - (some of the caps look bloated at the lead ends)

the units all have those 100v lamps - most of these dont work and some flash on intermittently.
i have the feeling that these are adding to the zaps and noises in the signal.

i would be happy to disable these (and use my ears) if it made them more stable and free of artifacts ( i read a post on gs mentioning engineers who left them broken / blown so that they would not affect the audio..

i would be even happier if i could change them out to regular leds..

if any of you have experience in fixing / servicing these i'd appreciate your ideas

Thanks!




 

barclaycon

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Remove all the neons and replace them with Red LED's. I think it shows on later schematics how to bridge over from the +24v rail instead of the 110v line.
I would also suggest disabling the 110v power supply completely. I remember getting shocks from these many years ago when we had to borrow gates from different racks!
Everything should be straight forward from the lineup procedure. I think the only components that are hard to get are the matched FET's. (I never did discover the criteria for selecting these - even Valley Audio didn't seem to know).
But these are probably OK.
Good luck with restoring these - I still think they have the best 'release' characteristic of any noise gate.
I must get round to restoring my Gain Brains!
 

barclaycon

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Hello, barclayton here...
(or at least I will be after Christmas!)
Thanks very much for the offer but the Gain Brains work fine, it's just that I'm combining them into a stereo unit with dual gang pots etc. Just a little project I've had on the go for a while.
Like I said, I think all the parts for Kepexes are still available. If anybody has information on how the FETs are matched (I mean in the Kepex - not the Gain Brain). I'd love to know.
 

Silvas

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strangeandbouncy said:
Gain brains rule. Period. . I will am very jealous . . . my fav on acoustic gtr.



   Kindest Bah Humbug,


   AndyP

+1

Love the gain brains. Esp on snare and rooms.  Have 4 in the studio. Plus 4 kepex, which i never use. I have them as "spares" for pots and parts for the gain brains.
 

slor

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Hey any chance you could post (or PM) the Kepex manual? I just recapped my 6 units and would love to get them calibrated!

Many thanks,
Seth
 

slor

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Yes! One bad pot thus far, more to come I'm sure. "Built to last" these units are not....
 

NOON

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Hi, I'm currently restoring a couple of Kepex gates. Got them racked up, powered and working, pending a few niggly things. I'd like to properly calibrate them but can only find the schematic, not the service manual. Does anyone have a copy of the service manual / calibration procedure?
  Gain trim is pretty easy, just set for unity, high and low meter are not critical for operation but the fly in the ointment is the bias adjustment, trims bias for a few sections of the circuit.  It's about 2/3 of the way across the top section of the schem, just before the output amp.

    Schematic is here. http://www.waltzingbear.com/Schematics/Misc/Kepex_500.htm

Thanks!
 

NOON

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Amusing anecdote, I went to some trouble modifying a power supply to provide a 100V rail, based on the markings on the board and the schematic, before looking at the back of the PCB and realising the 100V rail went nowhere and the meter circuit was bridged to the 24V rail. I was wondering why they were using a 100v rail for LEDs, didn't realise until afterwards that they'd started with neons and moved to LEDs at the lower rail until I actually stopped and thought about it (who does that these days!)
  On a related note, anyone got any good projects that could use a 100V rail? ;)
 

Cutterwoller

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Does anyone have the calibration proceedure for the Kepex modules, I cant find them anywhere!  :'( :'(

Please help! Thanks
 

JohnRoberts

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NOON said:
Amusing anecdote, I went to some trouble modifying a power supply to provide a 100V rail, based on the markings on the board and the schematic, before looking at the back of the PCB and realising the 100V rail went nowhere and the meter circuit was bridged to the 24V rail. I was wondering why they were using a 100v rail for LEDs, didn't realise until afterwards that they'd started with neons and moved to LEDs at the lower rail until I actually stopped and thought about it (who does that these days!)
  On a related note, anyone got any good projects that could use a 100V rail? ;)
modern IC technology process is limited to around 36V maximum so 100V is not usable for other than discrete design.

Modern digital is moving toward 3.3V rails.

Have fun

JR

 

mjrippe

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JohnRoberts said:
modern IC technology process is limited to around 36V maximum so 100V is not usable for other than discrete design.

Modern digital is moving toward 3.3V rails.

Have fun

JR

So to complete that thought, forget modern and go retro!  I am sure there are some tube mic designs that will run on 100VDC, and even more circuits if you can adjust it upward from there.
 

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