Ok... not exactly a stomp box, but it is an interesting circuit; passive limiter (as in no batteries - there are "active" devices in the circuit)
http://www.canford.co.uk/Products/24-00 ... TER-EP529C
There are two identical circuits inside the box (not identical here, as one of them is snapped in half)
http://yfrog.com/09dscf2509bjx
The printed resistors on the back side of the board are each individually shorted out with a little wire... seems a shame, as they appear to have been laser trimmed.
comp markings;
ICM 267A - transformer
K974 J 1C - big fets(?). probably 2SK974S N-channel FET
73 R030 - orange cap
DA5 - sot23 parts. Probably BAR43S dual schottky diode
BBC - EP5/29C Headphone limiter
Information
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- Joined: 15 Oct 2012, 01:26
I know it's an old thread, but did you get any further with it ?
I've been trying to find the circuit for this one as the old BBC stuff is often available online, but other than the Canford audio page; http://www.canford.co.uk/ProductResources/ig/2864.pdf (your links don't seem to work now)
and the original BBC spec sheet; http://www.bbceng.info/EDI%20Sheets/10481.pdf ,
I couldn't find anything.
Any chance you could repost the pic (I assume that's what the yfrog link was), and any other info you have.
It seems quite an interesting circuit, and certainly useful for anyone, like myself, considering in ear monitoring and not wanting their hearing destroyed by some idiot dropping, unplugging or even screaming into, a mic.
I'm assuming the dual schottky is the "fast acting voltage clipper" protecting against dangerous spikes, although the circuit can't just be a diode clamp across the output as I think the BAR43S would be too low a level , and is the FET being used as a VCR controlled by the transformer output from the signal to provide the main limiter, with the capacitor providing the "averaging" mentioned, and the transformer itself providing the 6db/Octave high pass weighting on the detector ? Or is there something more complicated going on ?
The laser trimmed resistors with jump wires fit nicely with the description of "setting level by cutting links", so the engineer can set the unit to match any headphones they already know the specs for just by clipping the pre determined links, thus Canford only charging for setting up for unknown headphones.
Would love to see the circuit rather than guessing ;¬)
I've been trying to find the circuit for this one as the old BBC stuff is often available online, but other than the Canford audio page; http://www.canford.co.uk/ProductResources/ig/2864.pdf (your links don't seem to work now)
and the original BBC spec sheet; http://www.bbceng.info/EDI%20Sheets/10481.pdf ,
I couldn't find anything.
Any chance you could repost the pic (I assume that's what the yfrog link was), and any other info you have.
It seems quite an interesting circuit, and certainly useful for anyone, like myself, considering in ear monitoring and not wanting their hearing destroyed by some idiot dropping, unplugging or even screaming into, a mic.
I'm assuming the dual schottky is the "fast acting voltage clipper" protecting against dangerous spikes, although the circuit can't just be a diode clamp across the output as I think the BAR43S would be too low a level , and is the FET being used as a VCR controlled by the transformer output from the signal to provide the main limiter, with the capacitor providing the "averaging" mentioned, and the transformer itself providing the 6db/Octave high pass weighting on the detector ? Or is there something more complicated going on ?
The laser trimmed resistors with jump wires fit nicely with the description of "setting level by cutting links", so the engineer can set the unit to match any headphones they already know the specs for just by clipping the pre determined links, thus Canford only charging for setting up for unknown headphones.
Would love to see the circuit rather than guessing ;¬)
Great little headphone limiter..
The 1:15 transformer boosts the input to a passive rectifier integrator which then drives the fets which shunt the output.
the laser trimmed resistors form a series chain to set the level into the cans at limiting..the unused r's are shorted by the jumpers.
Enjoy
The 1:15 transformer boosts the input to a passive rectifier integrator which then drives the fets which shunt the output.
the laser trimmed resistors form a series chain to set the level into the cans at limiting..the unused r's are shorted by the jumpers.
Enjoy