Mystery Coponent in Subwoofer Schematics

[abid_rehan]

In my endeavour to build a subwoofer circuit myself I ame across this awesome schematics by NHT, however while I was trying to plot it in circuit maker 2000 to print pCB I came across this mystery component whose symbol is attached can anyone help identifying it and suggets alternate components.

[analog_sa]

Surely you can get optocouplers in Pakistan. If you really have to you can replace with a LED/LDR combo in a home made housing.

[Konrad]

IF you're sure the component is a light dependent resistor it can bee somthing like : VTL5C3, VTL5C3/2
If its a opto kopled transistor it can bee somthing like the well known CNY17. Found bouth at http://www.elfa.se/en/

[abid_rehan]

Well the BMP is exactly what is mentioned in the schematic and is located at htt://www.nhthifi.com under support, and then schematics by the name of NHT sub 2i controller on page 4 of the PDF file in the section of overshoot controller, appreciate if you could have a look at it, however there is no harm in using a combo of LDR-LED but need further help in this respect,

[abid_rehan]

KONRAD, analog_sa guys thanks for the tip however as I mentioned that this compnent is locted in overshoot control section of the sub and any more help would be appreciated.

[janneman]

abidr,

I can't located the .pdf you mentioned above. Can you cut-and-past the full link to that page, I don't want to wander all over the net in vain.

Jan Didden

[sam9]

If it is a VTL... device here is more info:

http://optoelectronics.perkinelmer.c...e=VTL5C+Series


An aside: for those interested in ultra low noise volume pots for their preamp there may be potential in these devices.

[sam9]

More: the main use I've seem for them in an audio context is in limiters on professional equipment. Possibly in the subwoofer amp bentioned it is being used that way-- to limit "gently" before clipping.

[Steven]

Here is the link for easier finding:
http://www.nhthifi.com/scripts/nhtte...ted=1062781024 (I hope this works). Otherwise go to Techhelp --> Vintage and do a search on SubTwo i Controller & Amplifier - Schematic.

Anyway, I copied a part below.

The circuit is supposed to be an overshoot controller, part of a loudspeaker processor.
The input signal is amplified by U14b and U15a. U15b helps in doubling the maximum output current of U14b to quickly charge C85 if the signal gets too big. Diodes D7..D10 form a diode bridge to act both on negative and positive overshoots. If the voltage over C85 is big enough to light the LED of the optocoupler, then the LDR will be illuminated and its resistance will be reduced. This will attenuate the input signal by means of the resistive divider R107 and ISO1. This circuit is just a limiter.

LED/LDR optocouplers are often used for limiters and compressors. Noise and distortion can be low and such circuits often do not need adjustments like many VCAs.

If you want to use such an LED/LDR optocoupler as volume control for hi-end use, be careful with the selection of impedance and signal level for operation. I once read an article (I think some 25 years ago, written by Wim Jak, a dutchman, in the dutch magazine Radio Bulletin) where he found that LDRs can be quite non-linear. He observed some sort of crossover distortion, caused by the LDR resistance not only being dependant on the light, but also on the voltage across the LDR. LDRs might be voltage dependant too!.

Steven

[mwmkravchenko]

http://www.nhthifi.com/scripts/nhtte...YWdlPTE*&p_li=

The link I think

Mark