GB 2 for Alpha 20:
Danibosn - 2 sets
Yoaudio - 1 set
We need at least 12 sets for the next GB to start manufacture.
Danibosn - 2 sets
Yoaudio - 1 set
We need at least 12 sets for the next GB to start manufacture.
It’s set up nominally for 26.8dB gain but that can be reduced a bit, if you prefer. It is set by the 22k resistor that is specified as carbon film. The carbon film seems to give good harmonic distortion profile whereas metal oxide (thick film) here is not good. Lately I just tested a Vishay Dale 0.5w 22k 1% metal film and it measures just fine. Getting 0.0058%THD at 2.75vrms into 8ohms. Second harmonic is 6x greater than 3rd harmonic and no higher orders.
I also tested some Vishay Dale 3W 0.33R and Vishay Sfernice (wirewound) 0.15R and I got abnormally high distortion (0.05%) and higher 3rd order than 2nd. Switched to usual Panasonic metal oxide 3W light blue ones and seems fine now.
I also tested some Vishay Dale 3W 0.33R and Vishay Sfernice (wirewound) 0.15R and I got abnormally high distortion (0.05%) and higher 3rd order than 2nd. Switched to usual Panasonic metal oxide 3W light blue ones and seems fine now.
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Board's arrived today!! Very Nice..
Many Thank's To XRK,HUGH,JPS.
Hugh I have a pair of MF35-151.5 heatsinks from Julian (Conrad) will these be ok for the Alpha 20w version.
Steve.
Many Thank's To XRK,HUGH,JPS.
Hugh I have a pair of MF35-151.5 heatsinks from Julian (Conrad) will these be ok for the Alpha 20w version.
Steve.
After testing my second set of Alpha 20 amps I see that the topology with the LTP with Aksa Lender is pure genius. The DC offset is absolutely zero. It is zero mV when cold startup and tracks to 0mV when hot and everywhere in between. It’s like it has a zero offset opamp tracking it (and maybe it does in a way?). All Alpha amps so far have required ZERO adjustments. There’s no need for any pots anywhere. If you replace the pot above the LTP with a 1050ohm resistor - the amp would be happy as a clam.
Hi X,
My ALPHA20 has been in constant use the past two days. I’ve got to say, this amp is impressive! Andrea Bocelli’s voice in CANTO DELLA TERRA sounds so powerful, it’s amazing. Everything I’ve thrown at the ALPHA, classical, pop music, Slayer, Heavy Metal it has handled no problem.
I think I’m going to increase my source resistor to the .39R value Hugh mentioned and parallel two of them for R132. And remove the capMx in favor of a traditional CRC or CLC. After those changes, maybe I can still use the 400va trafo because of the slightly less current drain.
My ALPHA20 has been in constant use the past two days. I’ve got to say, this amp is impressive! Andrea Bocelli’s voice in CANTO DELLA TERRA sounds so powerful, it’s amazing. Everything I’ve thrown at the ALPHA, classical, pop music, Slayer, Heavy Metal it has handled no problem.
I think I’m going to increase my source resistor to the .39R value Hugh mentioned and parallel two of them for R132. And remove the capMx in favor of a traditional CRC or CLC. After those changes, maybe I can still use the 400va trafo because of the slightly less current drain.
Congratulations, Vunce! You meet an obstacle, but based on your experiences we can safely say that this amp needs a 400VA transformer with two 18Vac secondaries. Quiet, any ripple you can hear? And what is the offset at the output wrt ground at idle?
What sort of speakers are you using, what is the sensitivity, and how big is your room?
It's only 20W, but based on X's comments, it sounds very large in a small room.
Cheers,
Hugh
What sort of speakers are you using, what is the sensitivity, and how big is your room?
It's only 20W, but based on X's comments, it sounds very large in a small room.
Cheers,
Hugh
Thanks Hugh,
I’m using Klipsch Forte speakers with 99dB sensitivity and 8R, pretty easy to drive to rock concert sound levels 😀
Room size is 20x12x8 and offset is 10mV.
I do hear a noise at idle, that is why I will totally change the power supply, again. In your opinion, should I use a choke based filter instead of paralleled resistors?
Thank you again for sharing your ideas with all of us!
Regards,
Vunce
I’m using Klipsch Forte speakers with 99dB sensitivity and 8R, pretty easy to drive to rock concert sound levels 😀
Room size is 20x12x8 and offset is 10mV.
I do hear a noise at idle, that is why I will totally change the power supply, again. In your opinion, should I use a choke based filter instead of paralleled resistors?
Thank you again for sharing your ideas with all of us!
Regards,
Vunce
Didn't realize there was another Slayer / heavy metal fan on the thread. Once my amp is up and running, look forward to how Dave Lombardo's drumming sounds with the ALPHA20. 😀
But you have big speakers too - that helps with metal. As they say, there's no replacement for displacement. 🙂
Enjoy!
Right on!!
I never thought I’d be listening to the relentless drumming onslaught or massively distorted guitars with low power class A amplifiers and enjoy it so much!!
Dave Lombardo=MetalGod 😀
Congratulations, Vunce. You might consider running 1.35amp bias like I am now as that will draw even less current and minimize hum noise to negligible with 400VA 18v trafo. I am using Antek - probably same one you have. I am using 0.47R on R131 and tried both 0.22R on R132 or doubled 0.47R on R132 and works same. Here is latest measurements on amp board I built using all Vishay Dale resistors except R131 & R132 which are Panasonic. It is plenty of quiescent bias at 1.35amps for your 99dB Fortes.
I agree that any genre thrown at a good amp sounds excellent. But if you have not tried some Classical it can change your perception of some
recordings which were only so-so. Now they come alive with depth of sound stage.
Alpha 20 Premium Build
Here is the latest ALPHA 20 build using all Vishay Dale 0.5W 1% metal thin film resistors except for the 3W R131/132 which are Panasonic ERX series), and single R125 which is a Yageo 1% 1/4W metal thin film. It is the best measuring Alpha amp so far. The amp was measured sitting next to other equipment on equipment stand, so some mains EMI was picked up onto the measurement rig by radiation. THD is now about 0.006% on average and harmonic profile shows H2 is 6 times H3 and not much else. A very nice result. Listening to it now. This amp has perfect DC offset tracking with 0mV to 1mV at cold startup all the way to fully warm operation. Channel balance is also perfect with same 2.74/2.75vrms out for same DAC setting input.
FFT Ch 1:
FFT Ch 2:
Here is the latest ALPHA 20 build using all Vishay Dale 0.5W 1% metal thin film resistors except for the 3W R131/132 which are Panasonic ERX series), and single R125 which is a Yageo 1% 1/4W metal thin film. It is the best measuring Alpha amp so far. The amp was measured sitting next to other equipment on equipment stand, so some mains EMI was picked up onto the measurement rig by radiation. THD is now about 0.006% on average and harmonic profile shows H2 is 6 times H3 and not much else. A very nice result. Listening to it now. This amp has perfect DC offset tracking with 0mV to 1mV at cold startup all the way to fully warm operation. Channel balance is also perfect with same 2.74/2.75vrms out for same DAC setting input.
FFT Ch 1:
FFT Ch 2:
Attachments
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[Polish review] AUDIO RESEARCH GSi75 about €20,000THD is now about 0.006% on average and harmonic profile shows H2 is 6 times H3 and not much else. A very nice result...
Wzmacniacze stereo - testy
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Dominant 3rd order typical of standard LTP input stages but I would have expected lower THD and the preponderance of odd harmonic higher orders looks a bit unsettling. What power is that tested at? You can see why the ALPHA is a superb design.
ACCUPHASE E-470
I know, they are not class A amps but the harmonic profile...
ACCUPHASE E-470
Wzmacniacze stereo - testy
I know, they are not class A amps but the harmonic profile...
ACCUPHASE E-470
Wzmacniacze stereo - testy
