02.01.2006, 09:25 PM
Alright, over the holidays I've been able to try out different topologies (UcD, SODFA, hys. osc.) and have acquainted myself with RightMark Audio Analyzer (RMAA) which allows for frequency reponse, THD, IMD, S/N, etc. measurements using your PC equipped with a good quality sound card.
I've started out with a UcD concept, which is pictured above on the perforated board. It worked, but needed some tweaking to get it to run half decent (R/C in the feedback loop). The SODFA ran beautifully without any tweaks and the same applies to the hys. self oscillator. All of these were modelled in LTspice prior to trying them out on the breadboard, the carrier frequency is ~400KHz for all topologies.
Below you'll find the RMAA plots for all topologies (optimized with LTspice) running at ~80-watts/8-ohm at 1KHz. Needless to say I made sure that the output was identical for all topologies so these results can be compared directly. A 160-VA 2x35V transformer was used with 40.000uF of BHC slitfoils. Voltage was +/-42V at the terminals. The right channel is the amplifier the left channel is the reference signal which is a loopback from the soundcard input to the output, so I can compare directly (soundcard is a Audigy 2 ZS).
SODFA frequency response
[Bild: 11721.gif]
SODFA THD results
[Bild: 11722.gif]
UcD frequency response
[Bild: 11723.gif]
UcD THD results
[Bild: 11724.gif]
Hys. osc. frequency response
[Bild: 11725.gif]
Hys. osc. THD results
[Bild: 11726.gif]
Obviously you'll need to substract the THD for the soundcard from the total THD which yields the following results:
SODFA THD+N(A) = 0.033%
UcD THD+N(A) = 0.030%
Hys. osc. THD+N(A) = 0.012%
What's obvious from these results is that my output filter has a high-Q which isn't compensated for by the SODFA and hys. osc. that have pre-filter feedback, the UcD (with post-filter feedback) does a good job of keeping the output filter in check. What's also clear is that THD results are respectable for a breadboard-amplifier, but that the SODFA and UcD have comparable THD results. The hys. osc. clearly has the advantage here.
Any feedback, comments or suggestions are most welcome!
Best regards,
Sander.
I've started out with a UcD concept, which is pictured above on the perforated board. It worked, but needed some tweaking to get it to run half decent (R/C in the feedback loop). The SODFA ran beautifully without any tweaks and the same applies to the hys. self oscillator. All of these were modelled in LTspice prior to trying them out on the breadboard, the carrier frequency is ~400KHz for all topologies.
Below you'll find the RMAA plots for all topologies (optimized with LTspice) running at ~80-watts/8-ohm at 1KHz. Needless to say I made sure that the output was identical for all topologies so these results can be compared directly. A 160-VA 2x35V transformer was used with 40.000uF of BHC slitfoils. Voltage was +/-42V at the terminals. The right channel is the amplifier the left channel is the reference signal which is a loopback from the soundcard input to the output, so I can compare directly (soundcard is a Audigy 2 ZS).
SODFA frequency response
[Bild: 11721.gif]
SODFA THD results
[Bild: 11722.gif]
UcD frequency response
[Bild: 11723.gif]
UcD THD results
[Bild: 11724.gif]
Hys. osc. frequency response
[Bild: 11725.gif]
Hys. osc. THD results
[Bild: 11726.gif]
Obviously you'll need to substract the THD for the soundcard from the total THD which yields the following results:
SODFA THD+N(A) = 0.033%
UcD THD+N(A) = 0.030%
Hys. osc. THD+N(A) = 0.012%
What's obvious from these results is that my output filter has a high-Q which isn't compensated for by the SODFA and hys. osc. that have pre-filter feedback, the UcD (with post-filter feedback) does a good job of keeping the output filter in check. What's also clear is that THD results are respectable for a breadboard-amplifier, but that the SODFA and UcD have comparable THD results. The hys. osc. clearly has the advantage here.
Any feedback, comments or suggestions are most welcome!
Best regards,
Sander.