The Alpha Big Boy with Buttah (ABBB) 52w Class A Amp GB

[gary s]

Wrong G - that would be Greg, X.

 

[maty tinman]

NF-A12x25 PWM

Rotational speed (+/- 10%) 2000 RPM
Rotational speed with L.N.A. (+/- 10%) 1700 RPM
Min. rotational speed (PWM, +/-20%) 450 RPM

Airflow 102,1 m³/h
Airflow with L.N.A. 84,5 m³/h
Acoustical noise 22,6 dB(A)
Acoustical noise with L.N.A. 18,8 dB(A)

Human ear begin to listen to about 19-21 dB. (A) -> measured at 1 meter.

 

[drpro]

X, do you have a pair of the ABBB pcbs in stock. I have yet to finish my BB Alpha V1 pair. Figured I could salvage those parts and add the new ones.
Having a combined board would certainly make life easier, plus a bit smaller amp.
Thanks
David

 

[xrk971]

Yes, plenty of ABBB’s left, just order in my shop.

 

[drpro]

Order placed!!

 

[xrk971]

Thanks, DrPro. Will go out first thing on Monday. The perfect amp to drive the new 10F/RS225 TL!

 

[drpro]

Received the boards today. All intact.
Thanks
David

 

[xrk971]

They are 2mm thick, 2oz, ENIG finish, I would hope they are intact! Glad they got there safely though.

 

[drpro]

Quick question for those that have built the ABBB. Parts arrived from Mouser and I thought I would build Cap Mx sections first. Is there a starting point setting on the adjustment pot? I realize there is no load yet.

 

[jhofland]

Not to steal X's thunder but the control isn't useful at no load. Setting it at midpoint is a fine place to start.

 

[drpro]

Thank you

 

[Vunce]

Is there a starting point setting on the adjustment pot? I realize there is no load yet.

Drpro,
Jan’s suggestion is spot on. But in case you forget to preadjust, there is only about 1V of adjustment to be had, so no fear of damaging anything.

Good luck with your build!

 

[drpro]

Quick question X, working on the ABBB just soldered the 47R and 220pf SMD parts on the mother board. Should I be placing them on the flying lead boards instead? If so then just leave the spaces on the MB empty?
Thanks
David
______

 

[xrk971]

Yes leave MB empty and place on snubber boards.

 

[drpro]

Thank you

 

[32y0]

How would the modushop/diyaudio store chassis fare in terms of heat dissipation?

It would make for a rather large amp, but the 5u heatsinks are rated as follows:
200 x 40 x 210 0.28 C/W
250 x 40 x 210 0.19 C/W

 

[xrk971]

+/36v rails = 72v total x 3 Amps = 216W per channel

216W x 0.19C/W for the 250mm x 40mm x 210mm heatsink is 41C rise.

Assume ambient temps are 20C to 25C, possibly 35C in some parts of the world in the summer with no A/C. Taking even the coolest A/C settings of 20C, we get 20C + 41C = 61C. This is 6C higher than the recommended 55C max (based on burning one's hands from touching the sink). So unless you are prepared to back off on the bias current and/or rail voltage, I don't think the 5U is big enough.

However, even a very low speed (silent) Noctua 120mm fan blowing against the outside of the heatsinks would bring the temperatures down significantly. However, if you will use a fan, may as well go with heatpipe CPU coolers and save tons on the chassis/heatsink.

 

[32y0]

Thanks for the answer!

The 5u chassis (with the heatsinks mentioned) actually have 2 of those heatsinks per side, so I guess it should work. However, like you mentioned the heatpipe CPU coolers will be the more compact and economical option.

 

[xrk971]

I could be wrong - but I think that rating is for the combined total heatsink, two are used to form the one with this rating. I don’t recall any Modushop 5U that could take 400W per side.

 

[32y0]

I could be wrong - but I think that rating is for the combined total heatsink, two are used to form the one with this rating. I don’t recall any Modushop 5U that could take 400W per side.

I could be wrong too, but I think it's per heatsink. The diyaudio store states this:

"The 5U Deluxe (400mm Deep) contains four heatsinks and each is rated at 0.28 C/W" (40mm Heatsink Information – diyAudio Store)

At modushop you can order a single heatsink and they say:

"Used for the 5U container 500mm deep, coefficient 0.19 C ° / W" (Dissipatore 250 X 40 H 210 mm)