I found the genelater of tek AM700 have DAC+bandpass filter. The service manual with schematic are available. Check it!
" Residual THD+N with the bandpass filter in place. These
specifications are baseline for sine waves generated in
the low-distortion mode.
Amplitudes less than –16 dBu are noise limited (22 kHz BW).
Load resistance ≥ 600 Over 22 kHz BW Over 80 kHz BW
100 Hz to 749 Hz
Amplitudes ≥+4 dBu to ≤+26 dBu
Typ. ≤0.001%
(–100 dB) "
Interestingly, this was designed by the same guys that later founded Audio Precision. They learned a lot!
Jan
Jan
That sounds like a good idea, and I would think quite do-able, but I never gave it any thought at the time. The auto null would probably work something like that in a THD analyzer. Just thinking off the top of my head, those circuits often want to have a quadrature version of the test signal available. That might require some more thought 🙂.
Cheers,
Bob
🙂 😎
Hope you/others can help on this. It would take a good idea and make it into a really nice polished project.
THx-RNMarsh
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Rules breaking posts and their collateral have been deleted, however be assured that this is not the end of the matter.
Does this give any ideas ref to auto-tuning for null with THD meter;
Proposed auto-tuning circuit, (a) architecture of the tuning scheme.... | Download Scientific Diagram
Design of 4-pole filter with auto-zero op amps | Download Scientific Diagram
null detector circuit - Google Search
THx-RNMarsh
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Unfortunately the only relevant reference is the auto-null for the HP. This problem is similar but not the same. The other references are not that helpful.
Because this deals with both phase and amplitude you do need a sine/cosine decoder to even know which parameter to adjust. You could lift the circuit from the HP 339A or even the 333/334. Probably would need some manual range controls. Or a raspberry PI and some software.
Because this deals with both phase and amplitude you do need a sine/cosine decoder to even know which parameter to adjust. You could lift the circuit from the HP 339A or even the 333/334. Probably would need some manual range controls. Or a raspberry PI and some software.
Demian, I shamelessly lifted the quadrature detector from Bob Cordell's 1984 THD analyzer article, and use that in my tracking notch. Works like a charm. I guess you have the documentation for that.
Jan
Jan
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Many of the circuits are just there for spurring new ideas.
The HP339A is an exact app. which could be lifted and mod values to fit the Cordell values. The LDR would be a challenge to find??
The 339A can be copied as well.... with simple changes... the internal osc can be easily improved and the analyzer part as welll without changing circuitry/topology. Or just use the analyzer portion only;
stock and mod;
Not SOTA but easy to do for THD+N meter (-120dbv.... better with a Victor osc)
THx-RNMarsh
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Damir,
I changed the amp to mono.... lowered the rail voltage and increased the idle current..... +/-35vdc @ 5A total for 24 devices.
Tests for max power output level is, for example (THD+N)/ 2 Ohm ---
Had to fix a HF osc..... RC at each FET.....
Over-all improved SOA.
THx-RNMarsh
I changed the amp to mono.... lowered the rail voltage and increased the idle current..... +/-35vdc @ 5A total for 24 devices.
Tests for max power output level is, for example (THD+N)/ 2 Ohm ---
Had to fix a HF osc..... RC at each FET.....
Over-all improved SOA.
THx-RNMarsh
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