I never thought of this as an “amateur” Class A. But seeing as there are no adjustments really, it does seem rather low maintenance. I think all the trimpots can swapped for fixed resistors on the first try even.
One other thing: the parts are very inexpensive, or as Hugh says, “cheap as chips”.
The amateur was in relation to the fact that boards are available, parts are cheap and easy to source and as you noted, very little adjustment (if any) is needed to get it working, unlike the more "complex" dialing in the NP amps require. I still remember the first time i tried setting the bias on my F5 (more than a decade ago), and ended up with the SJ74 blowing up in the most catastrophic of fashions
Those Speedsters indeed look like a fun lively speaker to hear. Although only 80dB sensitive, it shows that this amp has the muscle to play with not only high efficiency speakers, by your usual multiway.
An externally hosted image should be here but it was not working when we last tested it.
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Hi X,
If you need another project to occupy yourself with, try these. You will be amazed at how full sounding such a small speaker can be. The ribbon tweeter is the key.
Even with only 22 V feeding the ALPHA, it was able to drive the Speedster’s to uncomfortably loud listening levels. This amp definitely has some muscle!!
If you need another project to occupy yourself with, try these. You will be amazed at how full sounding such a small speaker can be. The ribbon tweeter is the key.
Even with only 22 V feeding the ALPHA, it was able to drive the Speedster’s to uncomfortably loud listening levels. This amp definitely has some muscle!!
Piece by piece, slowly it's going to get it's PSU and frame ready. Too big toroid just for modeling it's upcoming place. Tomorrow I'll try to add lower platform for trafo and rectifiers (3mm alu). First test will be as "skeleton"-frame, if I get it work right then aluminium sheets all around and dreaming about BigBoy-version 
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Hi Vunce,
I have been looking for a good ribbon tweeter project. This looks perfect for an apartment. Can you believe there are college kids with these for their dorms? Man, wish I had anything his good for college dorm rooms. Great feedback to know you got it *loud* with Alpha 20 and a low 80dB sensitive speaker. I have a lot of speaker projects in the works. Currently testing out a new design with dual Beta 8 mid bass, and very nice (low cost) Peerless aluminum dome tweeter (DA25BG08-06) I am testing a new design, now verified that XO works and that it is a true 4pi 94dB (after -6dB baffle step loss) at 2.83v and 1m down to 55Hz (F3). Extension is well past 20kHz probably 30kHz according to specs. It sounds very nice.
With the Speedsters, the woofers are so small, are you running into cone travel issues or higher distortion issues due to the cone travel?
I have been looking for a good ribbon tweeter project. This looks perfect for an apartment. Can you believe there are college kids with these for their dorms? Man, wish I had anything his good for college dorm rooms. Great feedback to know you got it *loud* with Alpha 20 and a low 80dB sensitive speaker. I have a lot of speaker projects in the works. Currently testing out a new design with dual Beta 8 mid bass, and very nice (low cost) Peerless aluminum dome tweeter (DA25BG08-06) I am testing a new design, now verified that XO works and that it is a true 4pi 94dB (after -6dB baffle step loss) at 2.83v and 1m down to 55Hz (F3). Extension is well past 20kHz probably 30kHz according to specs. It sounds very nice.
With the Speedsters, the woofers are so small, are you running into cone travel issues or higher distortion issues due to the cone travel?
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Thanks X! This frame is for prototyping purposes only, so that's why there's only dots welded quickly. Final frame will be Tig welded all over, this is because I usually drill holes in wrong positions and change my mind on layout and stuff before it's finally done for example I was thinking external PSU at first. Then ditched that idea and made lower section for trafo. Of course it's lot of work to build working prototype first and then take everything apart for final frame
Sinks might be enough for BB-version, I used them Alpha 5 60w before. But I was thinking water-cooled BB?
for example I was thinking external PSU at first. Then ditched that idea and made lower section for trafo. Of course it's lot of work to build working prototype first and then take everything apart for final frame Sinks might be enough for BB-version, I used them Alpha 5 60w before. But I was thinking water-cooled BB
?
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Oh, you must been like in candy shop
it really is quite fun. My girlfriend is actually Tig-welder, so she will do weldings for final frame. I will try to find some stainless if I can.
That's fair point. Final frame will probably get some black paint though, I think that's enough insulation?
Maybe get the heatsinks black anodized? That will improve thermal efficiency as a radiator. The anodized surface effectively is a non-conductor. My DIYA store Dissipante case is steel with black anodized heatsinks and has no issues. The trick is getting electrical connection for the grounding to be effective. Either has to be via screw threads which are not anodized or use sandpaper to remove coating where ground connection goes.
I am fired up with stereo speakers!!
After messing around with the SMPS bricks some more without success, I scraped the plan.
I put together a traditional linear power supply with components on hand and fed both ALPHA boards 22vdc.
SUCCESS!! Sweet music from both channels. Even with my pieced together power supply you can get the feeling that this is a special amplifier.
Words of advice, do not skimp with heatsinking. Even at 22vdc the ALPHA gets warm/hot rapidly. I planned to use forced cooling with the cpu coolers anyway.
With the proper power supply treatment, this amplifier is going yo ROCK
I tend to agree with X, “no doubt it will be an enduring classic”.
Thank you Hugh and X for bringing the ALPHA to the DIYA forum
JPS64, your amazing layout/design and board quality is first rate!! Thanks.
Nice work Vunce! Congrats!
You have really nice looking original HUGE Class A amps - seems folks in Finland have really nice audio setups from what I have seen on this forum.
