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Old 24th September 2005, 08:36 PM   #41
Stabist is offline Stabist  Slovenia
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Aleph L finished (it's done on the older version of AL schematic)

Measurments showed:
(btw - there isn't pot at the output right now but 10k resistor from out+ to GND)


Output PSU voltage: 53,1V (secondaries were only 1x50V)
- drop on R111:
L ch: 0,633V
R ch: 0,637V
- drop on Q103:
L ch: 4,2V
R ch: 4,2V
- drop on R107:
L ch: 4,2V
R ch: 4,2V
- drop on common Drain to GND: 33V

Hmm - all other measurment are pretty close to original schematic - excpet the last one - considering +53V PSU voltage - I would more expect something like 27V ...

Btw - the fets have around 45-50C surface temperature - too much or not to worry about?

There are two changes to original schematic - one is lower PSU voltage and other one value of c104 - instead of 680pF 1000pF ...
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Old 24th September 2005, 08:43 PM   #42
Stabist is offline Stabist  Slovenia
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Hi Chip,

thanks again for this explanation ...

Btw - about those source resistors measurments - I was refering to this post by wuffwaff

Quote:
Hi Kirc,

2.1A with 50% ac-current-gain should give around 50 watts 8 ohm (voltage limited) and 35 watts 4 ohm (current limited). (4.2A peak current)

25 watts 4 ohms means only 3.5A paek current or 1-2.1/3.5 = 40% ac-current-gain

To get 90 watts 4 ohms (if you want that) you must raise peak current to 6.7A. With 2.1A bias this means around 68% ac-current gain. .

To get this you must lower R21 until 68% of the ac current flow through the upper source resistors and 32% through the lower source resistors (at 10 watt 8 ohms for example)
Try something like 390 ohms for R21.

William
That can be found here:
A5 behaves strangely
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Old 24th September 2005, 08:46 PM   #43
Stabist is offline Stabist  Slovenia
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Aleph L is very compact sized

And build in two floors ...
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Old 24th September 2005, 09:18 PM   #44
Stabist is offline Stabist  Slovenia
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It will get a bit crowded at the back of the chassis ...

Trannie is "classical": EI; 120VA/2x12V + 40VA/2x25V

At around 1,35-1,4A bias/channel it works perfectly, doesn't produce hum, hasn't got any temp rises that would be worth to mention, etc ... With few words: EXCELLENT TRANNIE!!!

So now I'm not worried for bigger brother - A30 - for which I intend to use 2 pcs 160VA trannies from same manufacturer ...

I must still find a way to mount attenuator and selector switch somehow somewhere there at the back ...

Ofcourse - gretz bridge will NOT have his own heatsink but will be mounted directly to bottom ... So I will get some more place for capacitors placement and all ...
I'm still thinkig of a possibillitiy to use 4 of them instead od 2 - but then it will be REALLY crowdy
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Old 26th September 2005, 11:26 PM   #45
Stabist is offline Stabist  Slovenia
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Default AlephL Q

Any comments on my measurments of AlephL? Particullary about that Voltage at the output where it should be around 1/2 of PSU voltage but in my case the ratio is quite different ..
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Old 2nd November 2005, 09:29 PM   #46
Stabist is offline Stabist  Slovenia
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Gee ...

Tryin' different versions before make final cuts and holes in chassis ...

So first operational version of my MiniA (but without AlephL) looked like this:
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Old 2nd November 2005, 09:34 PM   #47
Stabist is offline Stabist  Slovenia
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It worked and played but annoying buzz was there - and I've tried many different GND connections versions - but no significant succes ...
So obviously it was AC ripple ...

So I added another pair of capacitors + 0R16 resistance and so formed CRC filter ... (I will try to lower down resistance to somewhere around 0R1 - cause now I have almost 0,5V drop ... - but I haven't got enough resistors at hand right now)

AND it works without hum )))))
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Old 2nd November 2005, 09:46 PM   #48
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BUT now I have a bit higher bias current flowing through power resistor in "lower" half (between Source of the mosfet and -V) - on the "upper" one I can measure around 0,490V and on the "lower" one 0,536V (resisitors are 0R33) ... (same for both channels) ...

The voltage on PSU caps is same for (+) and (-) and completely simetrical ...

Also measured Voltage drop between (+V) and sense vs voltage from sense to (-V) differs for around 0,16V ... Before it was completely identical ...

What does that mean? Why suddenly thid change?

I also find DC offset a bit higher than before - before it was like 40 and 50mV - now it is like 60 and 70mV ...
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Old 2nd November 2005, 11:27 PM   #49
Stabist is offline Stabist  Slovenia
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Hehe ... "problem" solved

The thing was - because of hard acces to some parts of circuitry - I measured the voltage between one side of the resistor and -V on PSU capacitor - and after trying a bit harder I've manage to measure the votlage drop on both sides of the resistor after all - and YEP - now everything is OK )))

BUT then again - now I'm not quite satisfied while I have quite some voltage drop on the power supply cabling itself ... And hence that difference ...

Well, it's fun to giving a birth to that little chap ))

Btw - it sings very nice Altough my ears says (but not mesaured yet) it starts to degrade the highs with raising the volume ... I guess I'll have to fidle a little with AC current gain a bit ... (that was allready in my plan before listening session) ...
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Old 2nd November 2005, 11:31 PM   #50
jleaman is offline jleaman  Belgium
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Heh i have 4 mini a's running the 2nd pair still running right now breaking in. i was going to build aleph 30's but heh 15watts is plenty for me ive had it up pretty loud and wel its loud. .. no need for more than 15 watts ..

j'
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