Roger that. I'll try it out on my build to get things up and running with the CPU coolers I'm using. Eventually I want to move the ALPHA 20 to a 4u or 5u with big passive heat sinks.
So I have a three of Project16/Prasi CRC boards fitted with four 22mF 35v caps and eight MUR880 diodes with the full complement of snubbers. Since Alpha has such good PSRR, maybe all I need to do is to get a pair of 400VA 25v trafos and I am all set for PSUs for the B.B.?
http://www.diyaudio.com/forums/grou...er-supply-class-amplifier-28.html#post5050668
This is what I have (3 of these actually):
I knew they would come in handy. I now don’t regret putting 35v rated caps on them
Now just add these:
http://www.diyaudio.com/forums/grou...er-supply-class-amplifier-28.html#post5050668
This is what I have (3 of these actually):
I knew they would come in handy. I now don’t regret putting 35v rated caps on them
Now just add these:
Last edited:
Resistor swap provided positive results
I originally had .33R and .12R resistors in R131 and R132 respectfully. After getting feedback from X and Hugh I changed the values to .47R and .22R and the results were indeed better in my situation.
I did not change anything with the power supply yet and the background noise was reduced to a faint hiss from the speakers. I’m using a 6 speed fan control which was on speed 4 previously, now I just need the slowest speed 1 to keep the cpu coolers at 40°C. Voltage across R131 is very stable now hovering around .604v, previously it would slowly dip to around .585v
I haven’t had enough music time, tomorrow is another day.
I originally had .33R and .12R resistors in R131 and R132 respectfully. After getting feedback from X and Hugh I changed the values to .47R and .22R and the results were indeed better in my situation.
I did not change anything with the power supply yet and the background noise was reduced to a faint hiss from the speakers. I’m using a 6 speed fan control which was on speed 4 previously, now I just need the slowest speed 1 to keep the cpu coolers at 40°C. Voltage across R131 is very stable now hovering around .604v, previously it would slowly dip to around .585v
I haven’t had enough music time, tomorrow is another day.
Resistor swap provided positive results
I originally had .33R and .12R resistors in R131 and R132 respectfully. After getting feedback from X and Hugh I changed the values to .47R and .22R and the results were indeed better in my situation.
I did not change anything with the power supply yet and the background noise was reduced to a faint hiss from the speakers. I’m using a 6 speed fan control which was on speed 4 previously, now I just need the slowest speed 1 to keep the cpu coolers at 40°C. Voltage across R131 is very stable now hovering around .604v, previously it would slowly dip to around .585v
I haven’t had enough music time, tomorrow is another day.
Awesome news. This sounds like good advice for future builds. Use 0.47R and 0,22R on R131, R132, respectively.
Thanks for trying it out so quickly. Going from fan speed 4 to 1 probably is a big difference in fan audibility too.
I cannot remember reading that in the thread: what is the minimal supply voltage for ALPHA? I understand less voltage means less output power but is there a limit where the amp will not work or SQ deteriorate?
Resistor swap provided positive results
I originally had .33R and .12R resistors in R131 and R132 respectfully. After getting feedback from X and Hugh I changed the values to .47R and .22R and the results were indeed better in my situation.
I did not change anything with the power supply yet and the background noise was reduced to a faint hiss from the speakers. I’m using a 6 speed fan control which was on speed 4 previously, now I just need the slowest speed 1 to keep the cpu coolers at 40°C. Voltage across R131 is very stable now hovering around .604v, previously it would slowly dip to around .585v
I haven’t had enough music time, tomorrow is another day.
With low voltage and 4 ohm speakers fan or fans was/were at lowest speed. Voltage remained a problem with transformer, still low, but now with 8 ohm load the fan needed speed 4. Ambient temperature much higher ???
We are talking about reducing bias current in the amp, not voltage. R131 of 0.47R sets bias at 1.35amp and R132 should be about half of R131 so that Aleph CCS action is double the current in the sense resistor R132. By running lower bias, heat generation went way down hence fans needed only slower speed 1.
I did an experiment last night and reduced R113 to 15k for a 23.5dB gain amp. This in combination with the Aksa Lender Preamp running with 6k8 feedback resistors in combination produced an unbelievably good sound. I was listening to a 1956-1957 recording of Ella Fitzgerald and Louis Armstrong, a CD I have had for many years, but now it is like WOW, the vocals clarity, dynamics, depth of realism, it was like they were there in my lab - singing live. The nuances and emotions of “Summertime” was something was not quite prepared to experience. Just wonderful - I almost slipped into staying up all night just to listen over my music collection but had some self control and stopped at 330AM Work today still has to get done despite my wishes to just enjoy my music.
This works because I am driving with a good preamp. If you don’t have a preamp, you should probably keep it at usual 27dB gain with R113 set at 22k.
I have asked Vunce to try same configuration to see if he experiences similar increase in SQ. So with experience we are seeing some fine points of the setup that might be customized depending on your application.
Work today still has to get done despite my wishes to just enjoy my music. This works because I am driving with a good preamp. If you don’t have a preamp, you should probably keep it at usual 27dB gain with R113 set at 22k.
I have asked Vunce to try same configuration to see if he experiences similar increase in SQ. So with experience we are seeing some fine points of the setup that might be customized depending on your application.
So in preparation for B.B. build I have four of these coming in a few weeks. Probably from China.
DEEPCOOL GAMMAXX 300 CPU Cooling Fan 3 Heatpipes 120mm PWM Fan INTEL/AMD AM4 Com | eBay
Next are 400VA 25V Trafos...
I may order a small run of Alpha 52W B.B. boards to beta test before committing to a large order.
This sucker is going to be epic.
DEEPCOOL GAMMAXX 300 CPU Cooling Fan 3 Heatpipes 120mm PWM Fan INTEL/AMD AM4 Com | eBay
Next are 400VA 25V Trafos...
I may order a small run of Alpha 52W B.B. boards to beta test before committing to a large order.
This sucker is going to be epic.
I did a test with Vishay Dale metal film 1% for R113 and it was not detrimental to harmonic distortion. So stay away from metal thick film, but metal thin film and carbon thin film appear to be ok.
It depends more on your PSU rail voltages and how much or little they sag under load. With the SMPS and step up booster I was able to dial a predictable voltage. For 1.3amps and with +/-25.0v rails I was able to get 23.5wrms into 8ohms before onset of clipping. For a +/-24.0v it would be 20.2wrms into 8ohms. If you have rail sag below 24v, it will be less. The 1.35amp bias current is more of an issue for low impedance loads.