Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: shooter on August 14, 2019, 07:26:34 pm

Title: datasheetdelema
Post by: shooter on August 14, 2019, 07:26:34 pm

Getting ready to upgrade D.cavers 5ch A/B amp but I got one annoyance left from original build
2.jpg reads normal to me
3.jpg annoys me

I’m under the “working assumption” that if my speaker ohms goes up, my power comes down.  If rail volts go up, power goes up (all assumptions assume normal range:)
11.jpg – is this the reasonable explanation?  Somehow it holds power constant regardless of speaker or normal range B+

Thanks

Dave

Title: Re: datasheetdelema
Post by: PRR on August 15, 2019, 12:35:27 am

The cite speaks of "poor supply regulation". If it is 38V when loaded with 8 Ohms, but 29V when loaded with 4 Ohms, the outputs will both be similar.

I have heard this chip is very difficult to work with. Best left to factories with large development resources.

Title: Re: datasheetdelema
Post by: shooter on August 15, 2019, 08:37:11 am

mine came with a Chimade pcb + parts for the datasheets "typical application" circuit.
works fine at ~~ 25% stated spec  :think1:
I'll be scoping soon, but not using it to "upgrade", will be relegated to rear ch from front.

I'll just chalk up the bothersome to an inability to communicate  :icon_biggrin:

Title: Re: datasheetdelema
Post by: shooter on August 16, 2019, 04:07:22 pm

took the time to put a scope on one of the chips, even more underwhelmed!
started with 10ohm DL (R)
1.9Wrms max clean.  took 1.5vacrms in to get there

switched to 4ohm DL (R)
chip became unstable at about 2Vacrms out!

PS @ +/- 31vdc (+/- ~ .2vdc)
noise spikes ~ 200mV ballpark high kHz

I'll be back for the other chip and a better exam of PS @ chip unstable

Title: Re: datasheetdelema
Post by: sluckey on August 16, 2019, 04:56:02 pm

Suitable heatsink?

Title: Re: datasheetdelema
Post by: shooter on August 16, 2019, 05:32:11 pm

I believe so, although I didn't figure sqft or thermal dissipation yet  :laugh:
the main HS is ~ 1.5" X 1" X 8" finned and bolted to an "open-topped" aluminum box ~ 3" X 6" X 8" 1/8" thick

It appears to hit max I and the shortcircuit protection kicks in and clamps out to ~ 2vac from 14 - 17vac @4ohms
with 2 chips running clean the unit is warm, skin directly on chips will leave a mark

in previous post should be 1.5vac P-P input, reflected in scope shot.

Title: Re: datasheetdelema
Post by: shooter on August 16, 2019, 08:54:14 pm

put it back to music
both sides distort ~ same vol level ~ same way

at 1# dial down from clip after ~ 1hr hard listening the heatsink was ~ 60C
ranged between 40 - 60C clean listening
(temp measured with a fine instrument grade German glass "bulb" thermometer:)
the F one is keeping the camper fridge honest  :icon_biggrin:

listening as a stereo it's about 80% of my max
bring in the other 3ch and it's about 110% my max over 1 hr
I just don't have the heart to tell the neighbor, um, but it's only 2Watts  :icon_biggrin: