PX-1100 Reverberator

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untune

Well-known member
Joined
Oct 28, 2016
Messages
227
Location
Manchester, UK
I recently posted in the black market about tracking down a fuse holder from a Ukranian-produced effects unit. It's a digital chorus/delay unit that was manufactured for a short time in the early 1990s, and they are often referred to as an "Estradin PX-1100" online (due to the factory they were produced at.) These don't come up often in the UK and I missed out on one a few years ago, so I took a punt this one when I saw it. My original intention was to test it without doing anything too intrusive on the provision I could send it back if it wasn't working. The fuse holder cap was missing and also it uses a non-standard 2-pin power connector (which was also slightly damaged). The power cable was long gone, the parts are very old and specific therefore in order to test it safely I replaced both the fuse holder and power plug—I fashioned a plastic plate to hold the new pieces as they didn't quite match the case dimensions of the originals. This modification essentially means that I've committed to keeping it.

Bearing in mind I had to break two plastic seals to get inside the unit (which were stamped with the manufacture date, December '91) it's safe to say that there has been no maintenance at any point in the last thirty years. Everything looks clean inside, no obvious bad caps etc. I cleaned the pots and re-glued a few plastic button surrounds that had come loose with age. Powering it up, the unit does work, but it clearly has some issues.

Firstly, it sounds quiet. Even with the output volume on maximum, the input clips without the output getting to a decent level. I ran a synth through it, adjusted the input/output to various degrees but there was no change. There also seems to be considerable low-frequency loss. I thought it may be an impedance issue, but testing it with a passive bass resulted in a quiet and heavily distorted output, sounding like it was going through a distortion pedal. I'm not 100% sure but I think input impedance is ~220K and output is ~2K (according to the manual specs) and should be happy with most things.

Secondly, engaging the delay results in spitty, harsh and distorted repeats. I'm hoping that issue one is the root cause of issue two, considering that all the ICs appear to be esoteric Russian chips that are likely to be almost impossible to replace. Other than that, everything seems to function correctly (as in, all controls engage and disengage and effect the signal as they are supposed to.)

Anyone have ideas on where to start troubleshooting? Current/power supply issue perhaps? I can get access to most of the board without too much hassle and parts should be easy enough to replace. I've managed to find some literature, including schematic/manual but they aren't in English. I've attached the block diagram with a rough translation (can't vouch for accuracy but I think it's near enough to understand); not sure what some of those blocks in the middle translate to but I expect they're filter stages for clock noise or something similar.

Any help would be greatly appreciated. Thanks!
 

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Mike Havok

Active member
Joined
Feb 26, 2017
Messages
41
You will probably have more luck posting this in "The Lab" as opposed to the "Dynamic Processors" section
 

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