You don’t have to use Vishay CMF55’s - I have built several with regular 1/4w metal thin film (Yageo) 1% and they work fine. The critical ones are the big 3W source resistors and Aleph sense resistor. You must use Panasonic ERX metal thin film (light blue color) for best performance. Others will work but may not give good performance or even may blow out like a fuse and go open circuit with no warning (this often happens on bright blue Chinese no name 3w 1% metal thin film resistors). For the feedback resistor - use a carbon film for best performance.
My all Vishay CMF55 amp measured about 0.002% better than the no name ones. So don’t worry about it too much.
My all Vishay CMF55 amp measured about 0.002% better than the no name ones. So don’t worry about it too much.
Hi X and Alpha Fellas,
i have used several times KOA Speer MOSX3CR33J KOA Speer | Mouser Deutschland
2% Type:MOSX3CT631RR33G KOA Speer | Mouser Deutschland
, because Pan ERX not stocked:
ERX-3SJR33V Panasonic | Mouser Deutschland
i have used several times KOA Speer MOSX3CR33J KOA Speer | Mouser Deutschland
2% Type:MOSX3CT631RR33G KOA Speer | Mouser Deutschland
, because Pan ERX not stocked:
ERX-3SJR33V Panasonic | Mouser Deutschland
Finally getting my Alpha 20W into a real case. This years Christmas present. 
The 4U Deluxe has been a pleasure to assemble. The case work has been very minimal with the baseplate as well. I highly recommend.
The 4U Deluxe has been a pleasure to assemble. The case work has been very minimal with the baseplate as well. I highly recommend.Attachments
That looks great Jwjarch! Very neat and clean setup. We made these to be UMS compliant and I think you are the first besides myself to use it in one. Actually, I recall 6L6 was the one who asked for UMS. I don’t think he has gotten to building the Alpha yet because of the backlog of other Class A projects.
Is that a protection relay I see next to the CRC?
Is that a protection relay I see next to the CRC?
Thanks X! Yes, the UMS worked out great. I haven’t had to drill or tap a single hole so far. Thanks for thinking ahead and incorporating that into the design!
The board in between the CRC and transformer is the soft start board from the store. I’m going to see if the soft start is enough to let the Alphas ramp up slowly to avoid the excessive dc offset I was seeing at switch on. If it’s not, I have the diyaudio store speaker protection board ready to go as well, which should solve the issue for good. I was just hoping to avoid one more link in the signal chain.
The board in between the CRC and transformer is the soft start board from the store. I’m going to see if the soft start is enough to let the Alphas ramp up slowly to avoid the excessive dc offset I was seeing at switch on. If it’s not, I have the diyaudio store speaker protection board ready to go as well, which should solve the issue for good. I was just hoping to avoid one more link in the signal chain.
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Got the soft start board hooked up and one channel wired. At switch on the soft start did its job, unfortunately it did not limit the dc offset at the speaker terminals. It may have actually made it worse. I’m now measuring about a 19v spike after switch on. I think the best course of action at this point is to install the speaker protection board. Has anyone else been experiencing similar things with their Alpha 20w?
I think that the time has come for a new Class A PSU based on an active (ideal) bridge using an LT4320 combined with a small CRC after the ideal bridge then followed by a cap multiplier with a slow ramp up. This should be perfect for the Alpha’s. I am testing a single rail prototype of it now. But I have to shop off the current slew of GBs I have going on now before starting on this.
Thanks for the feedback Vunce. I assume you’re talking about the Simplified MrEvil CapMx you used for your BB build? I hadn’t seen a post from you about switching from a CRC to CapMx on your alpha 20.
So I was thinking about ordering up a batch of the MrEvil CapMx’s but I already have a run of the MJohnson boards from X’s post #3013. X, do think the MJohnson boards can handle the Alpha 20 current draw AND have a ramp up to handle the dc offset issue like the MrEvil boards?
And yes X, A Class A specific PSU would be great! Sign me up!
So I was thinking about ordering up a batch of the MrEvil CapMx’s but I already have a run of the MJohnson boards from X’s post #3013. X, do think the MJohnson boards can handle the Alpha 20 current draw AND have a ramp up to handle the dc offset issue like the MrEvil boards?
And yes X, A Class A specific PSU would be great! Sign me up!