Jensen Twin Servo 500: Preliminary Information

[John Hardy]

I have finished the design for the Jensen Twin Servo 500, a variation of the original Jensen Twin Servo 990 Mic Preamp for the Lunchbox/500-series format. Here is the link to the pdf with preliminary information:

http://www.johnhardyco.com/pdf/JensenTwinServo500Preliminary.pdf

I have not ordered circuit boards yet, but will do so when I return from the Audio Engineering Society convention after October 12th.

Thanks to all of you for your patience. If you have any questions, please let me know.

John Hardy
The John Hardy Co.
www.johnhardyco.com

[pan60]

sweet!!!!!!

[bendymusic]

Looks promising.. any ideas on pricing? ;)

&e

[John Hardy]

Looks promising.. any ideas on pricing?
Thank you. The price is tentatively the same as a channel card for the original Jensen Twin Servo 990 Mic Preamp: $895.

John Hardy

[bendymusic]

Beautiful, a big fan of your work over here. My first job when I was 16 was helping to build a combine network for a film transfer bay, the summing amps were 990's. Sounded incredible, those were the clear potted ones BTW..

Thanks for bringing these to the 500 format!!

[John Hardy]

Andy;

Thanks for the story. The clear ones were fun, but a challenge to make. The newer packaging with an aluminum potting shell and silicone encapsulant is a better performing package, just not as fun to look at.

John

[bendymusic]

Lol, yup, those looked awesome. Was it a heat issue? I think I remember one of them burning up. Wonder if I have a picture somewhere.

&e

[John Hardy]

Was it a heat issue? I think I remember one of them burning up.
The clear epoxy package worked well, and it was a good conversation piece. But the newer packaging with an aluminum potting shell is better. The two output transistors, which produce almost all of the heat, are bonded directly to the wall of the shell for maximum heat sinking and heat dissipation. The soft silicone encapsulant greatly reduces the stress on the components due to the difference in the "thermal coefficient of expansion" between the encapsulant and the components. The clear epoxy was fairly hard. Its higher expansion rate compared to the components as things heated up put stress on things. The silicone actually expands at a higher rate than the epoxy, but it is so much softer that the stress is greatly reduced.

John