Pro Audio Design Forum

Cross-posted from the Build thread for ULD-Nacho: I've assembled quite a few ULD_Nacho boards using value-matched resistors for the 15KΩ in the Wien bridge and the 10KΩ in the inverter. I've been installing Xicon or Yageo which appear to be identical and consistently get THD levels around -143 dBc o...

I've assembled quite a few ULD_Nacho boards using value-matched resistors for the 15KΩ in the Wien bridge and the 10KΩ in the inverter. I've been installing Xicon or Yageo which appear to be identical and consistently get THD levels around -143 dBc or -139 dBc with a 600Ω load. I decided to try the ...

A picture is worth a thousand words... For future reference I found this linear domain versus log domain filter comparison in Fred Floru's AES paper. https://proaudiodesignforum.com/images/jpg/Linear_Vs_Log_Domain_Filter.JPG Linear vs. log-domain filter The diodes in the final stage of the RMS detec...

IIRC both DBX and Paul Buff made wide range dB meters back in the day. Both probably used VCAs and companding inside to deliver wide dynamic range (my speculation). Sorry for yet another veer... ;) JR You sent me the data sheet for the Valley People meter I've been meaning to scan. I think I have a...

Thanks Jeffrey!

I found the companding RMS detector post: https://proaudiodesignforum.com/forum/php/viewtopic.php?p=17023&#p17023 With Ct doubled (due to 2:1 companding) the timing characteristics are identical to the THAT2252. Note that the input to the RMS detector from the VCA output has no resistor - both a...

The THAT300's rbb is 32Ω typical. I'm not sure I've ever seen the rbb spec for the CA3046 or CA3086. I'm currently using TL072B for the op amps. I don't need great low-level performance and I think it would be challenged if it were used in a compander. I need to find the post but I built a companded...

I lowered the value of Rin to 33K2 to give myself some additional trim range.
It varies slightly between channels but at the wiper I'm measuring about 260 mV (-9.5 dBu) for an input current of about 7.8 uA.

I saw Rt but discounted it. 8.3 uA x 49.5k is down a few dB from typical 0VU (around 0.4V) discounting the parallel junctions. Never mind... JR OK, got it. The normalized "0" is less than 0 dBu because there's a -6dB line receiver in the circuit it was taken from. The trim needs to offer ...

Wouldn't subtracting a reference 0VU current from the common emitters (Sym adj probe node) deliver a + and - voltage relative to 0VU threshold? It may need an offset subtracted to account for two pairs in parallel. JR Not sure I completely follow the question but an existing reference current sink ...