Measuring low noise circuits

[BYacey]

These meters were somewhat obscure when in production. Now they are probably close to unobtainium.

I have the schematic for the 310 meter; It wouldn't be too difficult to build one up for someone so inclined.

 

[JohnRoberts]

These meters were somewhat obscure when in production. Now they are probably close to unobtainium.

I have the schematic for the 310 meter; It wouldn't be too difficult to build one up for someone so inclined.

Yes, a collectors item or museum piece... (I still have a NOS transamp module back in my lab).

I designed a relatively popular piece of test equipment back in the '80s and it's hard to mass produce accurate low noise test gear.

DIY is fine for relative bench measurements like made when designing gear (you just want to see if it's better or worse, absolute numbers can wait.. )

JR

 

[BYacey]

I don't think I would rely on it for absolute measurements, but for comparisons it's more than adequate.

I bought the one I have around 1993 or so, new.  It doesn't use the green production transamp module, but a yellow epoxy potted transistor array, with the opamps external.

I've used it often in the past tracking down noise sources. One incident that comes to mind was in Edmonton's then-new  Winspear  Center concert hall.  I was called in when the sound installation contractor was unable to rid the system of residual 60 Hz hum from the speaker clusters.

It turns out the power amps located in the fly tower had poor common mode rejection, and the 200+ foot input lines driven from the Apogee Xover processor located in the sound booth were picking up lots of noise. Simple solution was to locate the Xover upstairs next to the power amps. The common mode rejection on the Apogee processor was much better, by about -30db.

 

[BYacey]

I designed a relatively popular piece of test equipment back in the '80s and it's hard to mass produce accurate low noise test gear.

JR

Just out of curiosity, what test gear did you design? Is this product still on the market today?

Cheers,
Bill

 

[JohnRoberts]

I designed a relatively popular piece of test equipment back in the '80s and it's hard to mass produce accurate low noise test gear.

JR

Just out of curiosity, what test gear did you design? Is this product still on the market today?

Cheers,
Bill

Good question... I just checked and it is still being sold but for almost 3x what I (we) sold it for back in the '80s. I designed it in the early '80s and it contains an OK sine wave generator, a frequency counter, and digital dB meter.  It was never intended to replace big dog bench test equipment but designed to be useful audio troubleshooting gear. Adequate to bias up magnetic tape reorders and check recording studio path levels and frequency response , etc.

No I am not making a penny off units sold for the last several decades.  :'(

JR

PS: The picture above is of the later unit (Loftech TS-2?) with a fine frequency knob added. The original unit covered 15Hz to 30kHz in a single sweep, but when you hang a frequency counter off the output customers will drive themselves crazy trying to set the oscillator to exactly 1,000 Hz.  ;D

 

[BYacey]

Small world, so to speak. We used to have one of those at a company I worked for; I never used it because it resided on the bench the speaker reconer occupied.  In reality it was the only piece of test gear they owned. I don't recall if it had the fine frequency adjust.

I owned all my own test gear, so when I left, it all went with me.
For service work at that time I mostly used an old HP 204B - In fact I still use it to this day, albeit in my own shop.  For a quick and dirty signal source I use a Wavetek 180 function generator.