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AlephJ Mimi! (Mini)
AlephJ Mimi! (Mini)
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Old 7th January 2017, 01:16 PM   #101
2 picoDumbs is offline 2 picoDumbs  Australia
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Very nice.
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Old 7th January 2017, 04:53 PM   #102
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AlephJ Mimi! (Mini)
Quote:
Originally Posted by lykkedk View Post
Hello.

I assume that this is the right procedure, when testing/powering up ::

Short -IN and +IN to GND

Plug in mains (Variac, lightbulb is only for Sissy )
PSU is +18 - "0" -18 VDC

Meassure voltagedrop across R16 (Source resistor Q5)
This is BIAS, but howto calculate this ???
I expect this voltage to be around 0.5V for Bias >1A ???

Bias is adjusted with R27 trimmer.

When everything is good, also adjust DC-offset with R7 trimmer.

Normal procedure after that, let amp. warm up and settle, then readjust and see if everything is stable and temperature is not to hot (>55C)

Jesper.
pretty much - yes

also , it helps if you have mosfets mounted on heatsink

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Old 8th January 2017, 12:33 PM   #103
lykkedk is offline lykkedk  Denmark
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Default Initial test success AlephJ_Mimi!

Hello.

I powered up our little AlephJ (Renamed to Alepj_Mimi!)
Accecdentily i renamed some pictures to _Mimi!, so hereby a new name... tadaa : AlephJ_Mimi! ... Cool yes ?

Some of the parts are slightly different from schematic, but not much; i will ofcause post that later on, when prober testing is done.

Bias is easily adjusted, up/down around 0.6V (1,27A Bias)... I figured out that voltage divided by sourceresistor (eg. 0.6/0.47 = 1.2A)... Silly me i should have know that before i asked that yesterday Sry...

After a short while, without prober heatsinking devices are heating up. DC-offset was a little jumpy for a start, but after 30sec. it was also good enough to adjust... So i guess circuit is working.

Next week i will try mounting heatsinks, and ofcause adjust the thing for good.

Thanks everybody for helping me, get this far by now.

Good sunday!

Jesper.
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File Type: jpg AlephJ_mimi_test_1.jpg (258.7 KB, 346 views)
File Type: jpg AlephJ_mimi_test_2.jpg (221.2 KB, 336 views)
File Type: jpg AlephJ_mimi_test_3.jpg (164.3 KB, 323 views)
File Type: png AlephJ_Mimi_ sch.png (43.7 KB, 320 views)
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Old 8th January 2017, 12:43 PM   #104
2 picoDumbs is offline 2 picoDumbs  Australia
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Congrats mate
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Old 9th January 2017, 07:31 AM   #105
lykkedk is offline lykkedk  Denmark
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Default Setting Bias

Morning.

I have mounted some heatsinks, which size should match the dissipation (i hope), for our MiniAmp. here.

Rail is with this PSU ~ -19 "0" +19 vdc.

I tried setting bias at 0.61 (~1.3A), but source resistors/mosfets are getting hot to the touch. Setting Bias around 0.51 (~1A) is much better.

I just remember, that i read somewhere Bias should be set to no less than 1.2A ? -Can't remember where i read this? -And why?

Can someone comment on this ?
- I mean, what is pros and cons ?

- Later today i will try listning to some recordings, to hear if Amp. is swinging enough watts for my setup!

Really exciting Looking forward to this test.

Jesper.
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File Type: jpg Bias1.jpg (204.9 KB, 292 views)
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Old 9th January 2017, 07:42 AM   #106
2 picoDumbs is offline 2 picoDumbs  Australia
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At 1.3 A, 0.47Ohm resistor is only dissipating 1.3 x 1.3 x 0.47 = 0.8Watts

Set at 1.3A and stop worrying about it.

This is a single ended amp (not push pull), you want as much bias current as the mosfets, and your heatsinks allow, so set at 1.3A and stop worrying about it.
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Old 9th January 2017, 10:14 AM   #107
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all Danes are having same heatsinks

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Old 9th January 2017, 10:37 AM   #108
lykkedk is offline lykkedk  Denmark
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Quote:
Originally Posted by Zen Mod View Post
all Danes are having same heatsinks

You allready know that ZM ...

I am lucky, that mine is partly, so i can use lower half, for making a lower chassis.

Jesper.
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Old 9th January 2017, 11:03 AM   #109
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AlephJ Mimi! (Mini)
aha

in spirit of the day , you can name it Aleph SissyJ

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Old 9th January 2017, 02:37 PM   #110
lykkedk is offline lykkedk  Denmark
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Quote:
Originally Posted by 2 picoDumbs View Post
At 1.3 A, 0.47Ohm resistor is only dissipating 1.3 x 1.3 x 0.47 = 0.8Watts

Set at 1.3A and stop worrying about it.

This is a single ended amp (not push pull), you want as much bias current as the mosfets, and your heatsinks allow, so set at 1.3A and stop worrying about it.
Hi.

I see the point here.
Running at 1.3A will give near 25w pro mosfet, and 100w for stereo, which is i think perfect.

I will start it up again and cranck bias to 0.6 now...

Too be continuied

Jesper.
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