Bell Electrolabs - ADT Automatic Double Tracker  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
Post Reply
User avatar
krystal
Information
Posts: 25
Joined: 27 Jan 2021, 10:52
Has thanked: 58 times
Been thanked: 36 times

Post by krystal »

I thought this might be of interest. It's a kind of modulated doubling delay.
This particular unit is quite distressed. I've traced it to help debug it.
Switching and power are not shown. It has it's own plug, and i couldn't be bothered to follow the wires around a transformer and bridge rectifier etc. There's a couple of regulators for +15V and -12V.
I'm not very experienced with this stuff, so please take it all with a grain of salt.

It seems like a previous owner tried some repairs/maintenance (like that Mod pot that's been replaced)
So far i've replaced a couple of electrolytics, a tropical fish and both cmos ICs that were damaged.
I've found some resistors to be way off spec and will be replacing those shortly.
Some of the tropical fish have some small cracks on their surface, should i be replacing those too?

I've got it running but not getting any modulation so far. The Delay and Dev(iation ?) seem to be working.
Probing indicates that U6 (on my schematic) is oscillating but i can't hear it at all when probing around the 4046.
R50 & R51 are two of the resistors that need replacing (R51 is that big resistor near the 4046 that seems to have been previously replaced)

I can upload/take more pictures if necessary.
Attachments
ADT SCHEM.jpg
IMG_5391.jpg
IMG_5384.jpg
IMG_5370.jpg
IMG_5368.jpg

User avatar
Dirk_Hendrik
Old Solderhand
Information
Posts: 4193
Joined: 03 Jul 2007, 08:44
Location: Old Amsterdam
Has thanked: 232 times
Been thanked: 887 times
Contact:

Post by Dirk_Hendrik »

Great work Krystal!!
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

User avatar
nihilandvoid66
Information
Posts: 3
Joined: 14 Nov 2023, 10:41

Post by nihilandvoid66 »

Hey Krystal

I have one of these myself, been trying to chase one down for over a decade and finally got one.
I'm very keen to get another however so if you wanted to sell this one as is, I'd be certainly interested!

So glad someone finally traced one of these! Thank you!
For years I thought these were the same as the pedal version, but when I got in contact with Tony Koorlander of Bell Electrolabs, he confirmed that PA:CE redesigned the circuit to a basic long delay time chorus and released this unit, which he often states is inferior to his design. I'm trying to get my hands on the pedal version too but this is much harder.
I also know the pedal version has been traced by someone I know but as they paid for someone to do it, they naturally don't want to release the schematic publicly. Needless to say Tony's original ADT design is very unique!

Cheers, if you are interested in selling this, I'm very keen!.
Alex

User avatar
krystal
Information
Posts: 25
Joined: 27 Jan 2021, 10:52
Has thanked: 58 times
Been thanked: 36 times

Post by krystal »

Hi there.
I'm afraid i finished fixing it and sold it already. It sounds pretty great, but it was just worth enough that i couldn't justify keeping it. I've been thinking of breadboarding it to try and see if i could get close with a charge pump and +9/-9v or something.
If you get your hands on a pedal version i'd be interested in seeing the differences in the circuit.

User avatar
nihilandvoid66
Information
Posts: 3
Joined: 14 Nov 2023, 10:41

Post by nihilandvoid66 »

Hey Krystal

No worries, I'll keep looking. There is one in Liverpool at the moment but I have no means of getting it unfortunately.
From what little I've seen of the schematic for the pedal version, it basically arranges the 4 delay chips into different configurations (series parallel etc) depending on which mode is selected, and the deviation control on the pedal version works much like the Intensity knob on the CE-1, where it just controls the speed of the LFO (but the depth is fixed).

Thanks!

Post Reply