Zener Limiter Build

[Ó Draighnáin]

Boards are finished, lets hope the layout is ok. Circuit breaks up pretty well into input, output and side chain. Power supply will be remote. Only a couple of slight component changes over the original circuit - have adjusted the HF boost and the pad at the input. Chassis arrived yesterday but the wings/ears were bent during shipping.

 

[thomasdf]

Impressive ! What transformers are these ? Keep us posted

 

[Ó Draighnáin]

Thanks!

Input transformers are BBC LG/61ASC (1.75:1). It doesn't look like they were Sowter manufactured, might be Gardners. Not sure what to expect here. They were used on the AM6/3 limiter and as a valve (line to grid) input transformer.

Output transformers are model number 31740, manufactured in the USA by Leightner Electronics, which came from an Autogram IC-10 broadcast console. Can be wired 1:2. They look really well made.

 

[Ó Draighnáin]

It looks like Brian Sowter wrote the following on another forum:

"An LG/61ASC is not in my stores catalogue, however an LG/60 is

1:2.68 ratio, 600:1600 Impedance, 10.6 henries primary Inductance, internal cost in 1980 £3.75

An LG/63 had a ratio of 1:2.78 so the 61 is likely to be similar."

 

[thomasdf]

Thanks ! Interesting
What schematic did you follow ?

 

[Ó Draighnáin]

I used the original schematic (the transformerless version). The difference I implemented is with the 9db pad and HF boost at the front end. I tuned the pad and the HF boost to take into account the voltage drop from the input transformer windings to still maintain a drop of about 9dB. Nothing very scientific, just spending some time plugging different resistor capacitor combinations into a spice model.

I rhe read somewhere that the input transformer I am using is designed for a secondary of 4k3? This seems like a good match.

I read that when using 1N5231 diodes there is about a 6dB signal drop, so that is why I went I:2 on the output.

Otherwise, the hold, recovery and switching is all going to follow the original. I am not trying to build a distortion box. Looks like it will take some time to tune.

 

[alphasnk]

Impressive! I built two zeners from Friphom's pcbs with 1:2 api output transformers, they work great. Let us know how the tuning goes!

 

[Script]

That must have taken some time
Inspiring. Thanks for posting.
Hope it all works on first fire up.

 

[thomasdf]

I used the original schematic (the transformerless version). The difference I implemented is with the 9db pad and HF boost at the front end. I tuned the pad and the HF boost to take into account the voltage drop from the input transformer windings to still maintain a drop of about 9dB. Nothing very scientific, just spending some time plugging different resistor capacitor combinations into a spice model.

I rhe read somewhere that the input transformer I am using is designed for a secondary of 4k3? This seems like a good match.

I read that when using 1N5231 diodes there is about a 6dB signal drop, so that is why I went I:2 on the output.

Otherwise, the hold, recovery and switching is all going to follow the original. I am not trying to build a distortion box. Looks like it will take some time to tune.

Amazing ! Can't wait to see the rest of it Keep us posted !

 

[slipperyflax]

@Ó Draighnáin Any progress?

 

[Ó Draighnáin]

Hi, I've been side tracked by progressing a couple of diy U67-type mics (I posted elsewhere about these). I finished the first mic only yesterday. I am wavering between finishing the second mic while I am in that zone or taking a break to progress the zener. I need to finish them all off relatively soon though. These mics and the limiter might well be my last builds before I transition completely to just building acoustic guitars.

Next big job on the zener is metal work. Once the chassis is cut and drilled (and external power supply for this one) it all seems to feel more downwind sailing.

I have all the components at hand for the limiter and I will certainly put up a progress pic after all the chassis cutting and drilling has subsided, and the boards, meters and controls are in place (before the final wire up).

Cheers.