dougi
Addicted to Fun and Learning
After recently discovering this forum (and others) I decided to start measuring my own system, with interesting results!
Given this is the amp forum I will focus on my TacT/Lyngdorf SDA-2175, a 13 year old switching amp, well regarded at the time but no measurements published. (there was one review with some on the SDAI2175 integrated but none on the power amp).
Quoted specs are in the attachment.
I constructed a 200W 8 ohm load last weekend which went well. I won't go into all the travails, but after measuring a class AB amp ok (Krell KAV-300i, 20 years old) trying to measuring an amp with common mode voltage on both speaker outputs was tricky. I ended up making an RCA to XLR cable using +ve and -ve only (no shield/ground) into my audio interface (Scarlett 2i2 gen2) from the test load sample point so it was differentially measured (with no connection to ground). This picked up a lot of 50Hz products. I added a (cheap) isolating transformer which improved things from a noise point of view, but ended up adding a lot of low frequency distortion. Anyone with how to measure with this common mode voltage present better I'm all ears!
I was mostly happy with the results though, using the 2i2 with REW with a 192kHz sampling rate. The amp driven directly from the 2i2 balanced output, and back into the balanced microphone input. To summarise results, single channel driven :
1kHz THD: 0.1W 0.015%, 1W 0.03%, 10W 0.06%, 100W 0.07%, 150W 0.08%, 200W 0.1%, 230W 1%. The load survived OK! Third harmonic dominated.
20kHz THD: 0.1W 0.08%, 1W 0.04%, 10W 0.04%, 100W, 0.07%, 150W, 0.13%, 200W 0.13%, 230W 0.14% (I ensured they included up to 96kHz)
CCIF IMD 19/20kHz: 1kHz difference tone 1W 0.0006%, 10W 0.0019%, 100W 0.023%, 130W 0.023%, amp started protecting itself after that! (Actually looked horrible on the plot at 100W with lots of products including above the band around 60kHz only 35dB down).
S/N ratio A weighted ref 200W: 100dB A weighted, (20 Hz to 20kHz filtered) but limited by the audio interface. (amp floor was about 1dB above interface noise floor so if you do the calcs the real S/N >105dB A weighted)
Frequency response into 8 ohms (measured without the isolating transformer which was not flat): wrt 1kHz, -0.2dB@20 Hz, +0.5dB @20kHz, -3.0dB @35 kHz.
Conclusions:
It certainly gets to the power spec, clipping >230W. Distortion somewhat higher (but measured differently), just OK and perhaps influenced by the isolation transformer used. Distortion is flat at least and less @ 20 kHz. S/N OK but limited by the other noise being picked up and of the 2i2. frequency response similar to spec . In practice it should sound quiet and clean, not edgy and never clip, under my listening conditions.
To compare with the older Krell KAV-300i 1kHz THD was as low as 0.017% at 1W, 0.023% @ 100W, 0.04% @ 150W, clipping @ ~200W. THD @20kHz @150W 0.5%. CCIF OK at low power but took off before 100W (0.02% @ 50W but 0.68% @100W). S/N about 105dB A weighted (20Hz to 20kHz limited) reference to 150W (nominal rating). This was the good channel, after rebiasing. The other got a bit bad when hot to around 0.15% at 1W @1kHz, despite rebiasing it.
Any feedback gratefully received! I enjoyed doing it and didn't blow anything up which is a good start. I did accidentally ground the speaker terminals once, but all was OK. I want to give it another go if I can work out a better way getting around the 35V on the terminals.
Given this is the amp forum I will focus on my TacT/Lyngdorf SDA-2175, a 13 year old switching amp, well regarded at the time but no measurements published. (there was one review with some on the SDAI2175 integrated but none on the power amp).
Quoted specs are in the attachment.
I constructed a 200W 8 ohm load last weekend which went well. I won't go into all the travails, but after measuring a class AB amp ok (Krell KAV-300i, 20 years old) trying to measuring an amp with common mode voltage on both speaker outputs was tricky. I ended up making an RCA to XLR cable using +ve and -ve only (no shield/ground) into my audio interface (Scarlett 2i2 gen2) from the test load sample point so it was differentially measured (with no connection to ground). This picked up a lot of 50Hz products. I added a (cheap) isolating transformer which improved things from a noise point of view, but ended up adding a lot of low frequency distortion. Anyone with how to measure with this common mode voltage present better I'm all ears!
I was mostly happy with the results though, using the 2i2 with REW with a 192kHz sampling rate. The amp driven directly from the 2i2 balanced output, and back into the balanced microphone input. To summarise results, single channel driven :
1kHz THD: 0.1W 0.015%, 1W 0.03%, 10W 0.06%, 100W 0.07%, 150W 0.08%, 200W 0.1%, 230W 1%. The load survived OK! Third harmonic dominated.
20kHz THD: 0.1W 0.08%, 1W 0.04%, 10W 0.04%, 100W, 0.07%, 150W, 0.13%, 200W 0.13%, 230W 0.14% (I ensured they included up to 96kHz)
CCIF IMD 19/20kHz: 1kHz difference tone 1W 0.0006%, 10W 0.0019%, 100W 0.023%, 130W 0.023%, amp started protecting itself after that! (Actually looked horrible on the plot at 100W with lots of products including above the band around 60kHz only 35dB down).
S/N ratio A weighted ref 200W: 100dB A weighted, (20 Hz to 20kHz filtered) but limited by the audio interface. (amp floor was about 1dB above interface noise floor so if you do the calcs the real S/N >105dB A weighted)
Frequency response into 8 ohms (measured without the isolating transformer which was not flat): wrt 1kHz, -0.2dB@20 Hz, +0.5dB @20kHz, -3.0dB @35 kHz.
Conclusions:
It certainly gets to the power spec, clipping >230W. Distortion somewhat higher (but measured differently), just OK and perhaps influenced by the isolation transformer used. Distortion is flat at least and less @ 20 kHz. S/N OK but limited by the other noise being picked up and of the 2i2. frequency response similar to spec . In practice it should sound quiet and clean, not edgy and never clip, under my listening conditions.
To compare with the older Krell KAV-300i 1kHz THD was as low as 0.017% at 1W, 0.023% @ 100W, 0.04% @ 150W, clipping @ ~200W. THD @20kHz @150W 0.5%. CCIF OK at low power but took off before 100W (0.02% @ 50W but 0.68% @100W). S/N about 105dB A weighted (20Hz to 20kHz limited) reference to 150W (nominal rating). This was the good channel, after rebiasing. The other got a bit bad when hot to around 0.15% at 1W @1kHz, despite rebiasing it.
Any feedback gratefully received! I enjoyed doing it and didn't blow anything up which is a good start. I did accidentally ground the speaker terminals once, but all was OK. I want to give it another go if I can work out a better way getting around the 35V on the terminals.
