yannluaudio wrote: ↑Fri Nov 22, 2024 5:42 am
Hi there,
What is the specified maximum output level of this design ?
I measured only ca. 16dBu at the output of IC9 (ca.22dBu at the output of IC7) with +/-16V supply.
FYI I put some equivalent INA134 instead of the THAT1240.
Thanks for joining us and your question.
Where are your jumpers set for Mid encode and Mid decode gain/attenuation? (And also side?)
Where are you inputting signal? (Encode with loop-through or directly into decode?)
What is the actual input level?
Are both channels being driven?
Are you using INA137 for the 1246 or did you use 1246 where they are required? (You mention the substitution of INA134 for 1240s which should be fine.)
With those details I can give you a better answer.
Here is a summary that may help:
Clipping points:
The single-ended outputs and internal nodes of the 1240/1246 clip at about +21 dBu with +/-15V supplies. The 1246 inputs accept up to +27 dBu before their output clips at +21. The 1646 balanced outputs clip at +27 dBu or +21 dBu single-ended.
If the Mid decode output at the 1646 is connected single-ended it will clip at +21 and the maximum level you'll be able to produce at IC9 will be +16 dBu before the 1646 clips because there is +6 dB gain in the 1646. If however the balanced output of the 1646 is used, IC9 will be able to produce about +21 dBu before the 1646 clips.
Gain structure:
The Mid encode level can be set to -6dB to prevent a +6dB mid build-up when both channels are driven.
The Side encode level can be either 0 dB or 6 dB depending on whether a 1240 or 1246 is installed. (In this configuration the 1246 provides 6dB gain rather than attenuation.)
The Mid decode gain can be either 0 dB or +6 dB. The +6 dB gain is to compensate for when, and only when, the Mid encode is set to -6 dB.
The Side decode gain can be either 0 dB or -6 dB. The -6 dB attenuation is to compensate for when, and only when, the Side encode is set to +6 dB.
If you let me know where you are inputting signal, on how many channels and where your jumpers are set I should be able to give you a better answer.