IRP Knowles DI-4019 Limiters

i bought a pair of these limiters for chump change, back around 2000,

one unit has issues that i would like to resolve.

before i get ahead of myself, does anybody have any knowledge of, or a schematic for this unit please.

best

Pb

Some Images











(not so) quick release solder jumpers connecting the daughter board

found (what i think) is the patent for this unit,

this daughter board has test points labelled, they seem to match the ones referred to in the patent.



block diagrams from patent

Nice detective work!  I have had a couple on my bench, but not for servicing.  Changed the trim pots to front panel controls.  It is a strange box.  Seems to have program dependent release time?

hey mjrippe,

i have been reading & re-reading the patent, trying go get my head around it.

it mentions a set attack of 1ms and a release of 500ms on one bit of circuit, the comp bit?

the is also a separate limiter circuit, i think? :-0

my head was hurting, so i went back to the jumpers.





teased them all up, and got a look at the underside of the board.









just looking at it, has occurred to me, that apart from two 1000uf caps at the power supply, there are no other electrolytic s, that i can see.

i found an online version of the patent & pasted it into a txt document attached below,  its more digestible, than the other one.


scratch my comments above, was talking shit.



if i see it right now,

post input transformer, is the 'over range limiter', point 37 in Fig2,

then 'gain controlled amplifier' driven by 2 detector circuits.

one  feed-forward

one  feedback

a 'magnitude selector gate' decides which of the 2 detector circuits gets to drive the 'gain controlled amplifier' .

gain controlled amplifier to output amp to output transformer.

more reading to do now on the detector circuits.

Knowles is still in business, though not that business.
www.knowles.com/
Try  email  [email protected]

Delta Audio does some IRP repairs, and could have docs, or know the designer. 
http://deltaaudio.biz/irp.html

hey PRR,

thank you for the delta link, potentially very useful.

they are based about 20km from the original factory,

have sent them an email.

best

I got this reply back from delta-audio,

"I'm sorry but we don't have any paperwork on those. What we did get was from when IRP went back to Germany and it was basically items they didn't want to take back with them so it was very limited on paperwork.
You could see if you can contact IRP in Germany, but the owner died this past year, so I don't know their situation now."

Resurrecting a 5-year-old thread because I've got a chance to snag one for $75 that appears to be in well-cared-for condition.

I love character compressors - especially the old broadcast stuff like the CBS Volumax, some of the Harris / Gates stuff, the Orban Optimod.

Still $75 is $75, so I'm interested to know if it's worth even that. I'm not expecting the next Distressor or LA2A here..., but an interesting squeeze box for wild card duties is the exact sort of thing I will always find rack space for.

gnarmageddon said:

Resurrecting a 5-year-old thread because I've got a chance to snag one for $75 that appears to be in well-cared-for condition.

I love character compressors - especially the old broadcast stuff like the CBS Volumax, some of the Harris / Gates stuff, the Orban Optimod.

Still $75 is $75, so I'm interested to know if it's worth even that. I'm not expecting the next Distressor or LA2A here..., but an interesting squeeze box for wild card duties is the exact sort of thing I will always find rack space for.

Click to expand...

Hey, did you ever end up with this unit? If so what are your thoughts?

The DI-4019 is a stand-alone version of the product DE-206 "Level-Matic", which was part of the so-called "Voice-Matic automixer" system from IRP. The purpose of the device was by no means for use in the studio area but in meeting rooms , where the speakers' microphones were mixed using an automatic microphone mixer. I had specified these products many times and really appreciated their performance at live events. It is a leveller with an infinitely long release time. This means the following: a talker enters the stage and speaks into the microphone, a (correctly set) Levelmatic device reduces the total gain of the automixer by approx. 5 dB. If the talker speaks at a constant volume, the Levelmatic device remains at -5 dB. The special thing is that the gain remains at -5 dB even when the talker leaves the speaker's desk. This means, in contrast to a compressor, the gain does not increase when there is no audio signal: So there is no increase of the room's background noise. If the next talker comes who speaks less loudly, the Level-Matic increases the gain and goes to -1 dB, for example. The reinforcement remains here until the next talker appears. If he is very loud, the Level-Matic reduces the volume to a maximum of 10 dB. Overall, the Levelmatic ensures a relatively constant speaker level during an event with several talkers, without the unpleasant breathing of a compressor.

The negative side of the device is a relatively high distortion factor, especially with strong gain reduction. At least that was my subjective impression; I never measured it. This is not audible with live voice amplification, but you can hear it on the tape recordings if you pay attention to it.

In my opinion the device is not suitable for (transparent) studio recordings.

A similar leveller with an infinitely long release time was available from IED (optional module 120P in their 4400/4800 series automixers).

ns