[BUILD] 1176 Rev A - Back to the beginning...

[Brian Roth]

I am still confused. The primary (or secondary for that matter) doesn't have an inherent impedance.

For example, a 1:1 transformer with a 600 Ohms load on the secondary "reflects" 600 Ohms to the primary. A 60 Ohm secondary load will "reflect" 60 Ohms back to the primary. Thus, the amp driving the xfmr "sees" a load which is directly affected by the secondary load.

Or, does that particular xfmr have multiple secondary taps that you are selecting?

Bri

 

[Ilya]

It would be better to load the output not heavier than 600R and get the needed level with a voltage divider.

As for resistors valves, always check with the original schematic. IIRC sidechain is identical in rev A/B and D. Meter driver is different though. Frankly, I would’ve left meter driver circuit from later revisions because it’s much simpler.

 

[Potato Cakes]

The meter driver section itself is not changed. It is the voltage that feeds the Gain Reduction Controller Amp that is changed, which is why mnats put the optional trimmer on the ratio board. I was not concerned about what it looked like on the meter but the actual compression of the audio.

Thanks!

Paul

 

[Potato Cakes]

The frequency response does not seem to be affected. I will still see about changing it out with a U-Pad.

 

[Potato Cakes]

Just to be more electrically sound, I installed a U-Pad on the output to give me the same reduction (R1/2 = 150, R3 = 600). Frequency response is still the same. I would have liked messed with the the trimmer as I think the trimmer voltage divider for adjusting the overall threshold would have been a better solution than just adding more resistance before R78. Compared to the Rev D in the same box the compression and output levels appear to be pretty close. Once I close this up and put it back in the rack I won't think about it again. I hope.

Thanks!

Paul

 

[Potato Cakes]

It's an absolute mess in there. This was one of my very early builds before I converted it to a Rev A/D in the same box and I was focused on getting the boards swapped and putting back to work and not showing it off at this weekend's bake sale. Using some SMPS's and one of my capacitance multiplier boards to create +30/-10VDC. The additional caps for filtering wound up being unnecessary. I was getting about 0dBu of noise from somewhere I and I naturally thought it was from the power supplies. Turns out I did not have the ground connection for the XLR Pin 1 made on the hardwired bypass boards, so when I connected my bus powered interface I was getting noise injected into the output XLR which then showed up on the meters and also to the computer. I've discovered more than I wanted to find on a project that was supposed to take one day.

Thanks!

Paul