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Old 22nd February 2013, 08:27 PM   #2281
Eric is offline Eric  United States
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Quote:
Originally Posted by Zen Mod View Post
..... here's one for you
Quite a nice build!

I do have some extra aluminum and copper sheets hanging around. I guess I'll give it a try and see what happens. It will be interesting to see if this reduces some of the speaker noise. It's not very much at all, but I'd prefer for it not to be there.
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Old 3rd March 2013, 04:14 PM   #2282
Eric is offline Eric  United States
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I reworked my power supply as an actual start ground and it eliminated the small amounts of DC across the ground terminals for the power supply caps.

Click the image to open in full size.

The overall output is somewhat more quiet now, measuring across the output terminals on this amp shows 0.2mVAC and 2.2mVDC. Previously, I was getting 0.4-0.5mVAC across the output terminals. I can still hear a small buzz at the speaker if my ear is within a foot (30cm) of the tweeter, but it has improved.

Now that the configuration is different, the ripple levels that I had previously measured on the power supply caps for this have not really changed. Now that I have a star ground, I measured AC voltages between the star ground point and the ground terminal for each of the power supply caps:

Positive Rail: 5.8mVAC on first cap, 6.2mVAC on second cap, Resistor, 0.1mVAC on final cap
Negative Rail: 12.3mVAC on first cap, 0.1mVAC on second cap, Resistor, and 0.3mVAC on final cap

Is it "normal" to find AC voltages in this manner ? I've never measured it before (and can't measure on my other amp that still has a "circular" ground wiring pattern across the caps).
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Old 3rd March 2013, 05:26 PM   #2283
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Hi Eric,

it is as long as there is a bit of resistance and some current. Did you solder the cables?

William
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Old 3rd March 2013, 05:27 PM   #2284
Zen Mod is offline Zen Mod  Serbia
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naah

just chill - everything is fine

even these differences between adjacent caps in two rails are logical , considering that caps aren't exactly brand new

edit - off course - I agree with W. - all connection must be soldered , but I presume that you made it already
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Old 3rd March 2013, 05:33 PM   #2285
oiphy is offline oiphy  Norway
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I measured AC voltages between the star ground point and the ground terminal for each of the power supply caps:

Positive Rail: 5.8mVAC on first cap, 6.2mVAC on second cap, Resistor, 0.1mVAC on final cap
Negative Rail: 12.3mVAC on first cap, 0.1mVAC on second cap, Resistor, and 0.3mVAC on final cap


is this ripple? trying to learn here so bear with me.

thanks gentlemen

stig
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Old 3rd March 2013, 07:24 PM   #2286
Eric is offline Eric  United States
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William and Choky - no, I didn't solder the wires just a tight crimp. I'll have to remove the plastic tabs and solder the crimps to see if that makes any difference. Thanks for your input - I keep learning what seems to be basic stuff...

Stig - no, as described, this is not a measure of power supply ripple. I was measuring AC ripple within my grounding scheme. To measure power supply ripple voltage, set your meter to AC and put the probes across the terminals of a single power supply cap.

The thermistor at the star ground goes to chassis and AC Mains ground. Jumpering the legs of the thermistor makes no difference in output noise level. I'm just about to order parts for the JFETs upgrade to the input differential, so I'll report on that shortly.
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Last edited by Eric; 3rd March 2013 at 07:28 PM.
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Old 5th March 2013, 08:43 PM   #2287
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Hi all.
There have been a few discussions online about replacing the 9610 mosfets that comprise the front-end input differential pair with JFETs that have more linear behavior characteristics. I want to update my Aleph-x 100w with the 2SJ109. I have them already and wat to use them in near future.Is there any good exactly schematics how to do it in my case ?
Gr.
Robert
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Old 5th March 2013, 10:00 PM   #2288
Zen Mod is offline Zen Mod  Serbia
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floating all around

search for cascoded input Aleph 60 - same approach

or - I'm lazy- post exact schm , say what PSU voltages are and I'll Paint it
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Old 5th March 2013, 11:32 PM   #2289
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Quote:
Originally Posted by slowikpl View Post
Hi all.
There have been a few discussions online about replacing the 9610 mosfets that comprise the front-end input differential pair with JFETs that have more linear behavior characteristics. I want to update my Aleph-x 100w with the 2SJ109. I have them already and wat to use them in near future.Is there any good exactly schematics how to do it in my case ?
Gr.
Robert
Post #2219 earlier in this thread has a link to what you want.

Graeme
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Old 15th March 2013, 12:49 PM   #2290
Eric is offline Eric  United States
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Smile JFET upgrade

I have upgraded one of my Aleph-X amps to a JFET front end. It seems to work and makes nice music, but I'm seeing some intermittent variations in Absolute DC Offset (for example, it jumps from 12v to 2v to 6v to something else) if I touch any of the wires that connect my sub-board to the main PCB. Is it possible that this is a capacitance issue with my body, or is it just a lo0se solder joint somewhere? I'm double checking things now.

R46/R47 (McMillan Resistors) are 10K
R16/R30 (Feedback) are 100k
R19/29 (input ground resistors) are 10K
R18/R28 (input resistors) are 10k
I lifted one leg of both D3 and D5 (input static protection zeners)
I removed and jumpered R22/R27 (9610 gate stoppers)
I also removed VR2 (offset adjust pot) and put it on an extension wire so I can play with the KTY-81 trick in a little while.

It was a real pain to remove VR2 and the 9610 from the circuit board as I didn't really design my configuration for ease of maintenance...

The schematic I am using is here.

I thermally coupled my JFET pairs to one another with a copper strip and plastic wire ties. I'm not sure if this is really necessary, but I thought it would be worth a try.
Click the image to open in full size.

Using Graeme's circuit as a guide, I arranged the ZTX550's and the 2SJ74's on a small sub-board.
Click the image to open in full size.

Here is the sub-board in place in the amp. I had a tough time trying to figure out how to secure it in my chassis.
Click the image to open in full size.

And finally, here is a circuit diagram that I drew up that might be helpful for others to follow.
Click the image to open in full size.

The ground for the JFET sub-board is connected to R49 on the main PCB which is just a wire jumper, not an actual resistor.

The negative power supply for the sub-board is connected to the left leg of R23 on the main PCB.

Relative DC Offset seems to float between 20-40mV (was about 3-5mV with the 9610's in place). The JFET pairs that I used were matched at 10.63mV & 10.65mV and 10.64mV & 10.64mV.

Absolute DC Offset starts much higher and decreases more slowly now. I presume this is why William increased the value of the McMillan resistors.
0 mins: 16.5v
5 mins: 11.9v
10 mins: 9.8v
15 mins: 9.3v
20 mins: 9.2v
25 mins: 9.0v
30 mins: 8.5v
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