Aleph J-X Amp Project

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#424
a.wayne said:
Hello,

Thanks and advice noted , i will give the other pass Amps a look ...



OK,
So the monster class A is out and while i do agree somewhat with your assessment on listening , 80 watts would be way 2 small , 160 @ 1 would be the min for good dynamics ..

Now ... Aleph J or F5 ?
Click to expand...

can I ask what amp you currently use and why you think you need so much power at 1 ohm?
The thing about diy is its a journey, try a couple of small amps and see if they work well, I would build a stock F5, probably more important is what is the speaker efficiency?
The worsst thing you can do is take on a project like you talking about and get disheartened, start simple.
Good luck.
 
#427
Well I have my Aleph-J playing music right now, just powered it up about 40 mins ago, still warming up. I have a few questions

1. I measured DC offset, 51mV on R channel, 44mV on left, that seem ok?

2. I looked at the Burning amp 2 article and decided to add the .0033 caps before and after the switch, along with CL-60 thermistors on the xformer primaries as shown on that PS schematic, rest of the PS is Peter's board.

The CL60's are extremely hot, is this normal? Also the transformer is physically buzzing and I get some slight motorboating that does not change with input level. Should I remove those CL60's and see what happens?

3. My rail voltages were both right around 25v unloaded, now they are 19.8 V+ and -21.2 on V-. Transformer is an Antek 400VA 18Vx2

Thanks for any advice!
Other than the transformer buzz it sounds very good :cloud9:
 
#428
Coreyk78 said:
1. I measured DC offset, 51mV on R channel, 44mV on left, that seem ok?

2. I looked at the Burning amp 2 article and decided to add the .0033 caps before and after the switch, along with CL-60 thermistors on the xformer primaries as shown on that PS schematic, rest of the PS is Peter's board.

The CL60's are extremely hot, is this normal? Also the transformer is physically buzzing and I get some slight motorboating that does not change with input level. Should I remove those CL60's and see what happens?

3. My rail voltages were both right around 25v unloaded, now they are 19.8 V+ and -21.2 on V-. Transformer is an Antek 400VA 18Vx2
Click to expand...

1. This is acceptable, if you used 2SJ74 for the inputs, possibly they're not tightly matched.

2. When you say thermistors, I assume you are using one on each primary? Only one is necessary, put it on L1. If you're sharing one trafo for the stereo amp, thats close to 4 amps constant draw, it will normally be pretty hot.

3. 400VA may be a bit too small for stereo use, maybe not. Maybe the rail mismatch is due to using two (assuming) thermistors. Remove the .0033 caps, use one thermistor, and see what you get.
 

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#429
MEGA-amp said:
1. This is acceptable, if you used 2SJ74 for the inputs, possibly they're not tightly matched.

2. When you say thermistors, I assume you are using one on each primary? Only one is necessary, put it on L1. If you're sharing one trafo for the stereo amp, thats close to 4 amps constant draw, it will normally be pretty hot.

3. 400VA may be a bit too small for stereo use, maybe not. Maybe the rail mismatch is due to using two (assuming) thermistors. Remove the .0033 caps, use one thermistor, and see what you get.
Click to expand...

Yes I am using one CL60 on each primary, its a dual primary transformer like the one shown in the Pass schematic, 120-0 + 120-0, I have a thermistor on the 120 end of one winding and the other on the 0 end of the other winding. Not sure if that makes sense when I try to type it out.

I will try removing the caps and one of the thermistors and post back, probably will have to wait until tomorrow. Thanks 🙂
 
#437
Bigger transformer is definitely the way to go. Measure voltages across source resistors R18, R19 (PD boards). Say one is 0.58V other is 0.59V, interpolate .58+.59 / 2 = .59. If you're using 0.47R source resistors, 0.59/.47 = 1.26. 1.26 * 2 = 2.52A. 2 is the number of outputs in the gain section, if you had three, it would be 1.26 * 3
 
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#438
OK, I'm using 2 pairs per channel, here are the measurements. I ended up using 0.51 Ohm 3W panasonics because digikey was out of stock on the 0.47, don't know if that would make a difference, Mosfets were purchased as matched quads from TechDIY.

Left channel
R16= 0.527
R17= 0.514
R18= 0.436
R19= 0.607

Right channel
R16= 0.523
R17= 0.530
R18= 0.533
R19= 0.517
 
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#439
Using 0.53/0.51 = 1.04A x 2 = 2.08A per channel
WIth +/-20 rails. that is about 80W of heat per channel.
Does you amp (transformer) buzz with nothing connected to it?
I mean absolutely nothing.
Keep it powered on of course.
 
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