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..... 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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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.
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).
An externally hosted image should be here but it was not working when we last tested it.
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).
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
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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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.
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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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
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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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.
Using Graeme's circuit as a guide, I arranged the ZTX550's and the 2SJ74's on a small sub-board.
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.
And finally, here is a circuit diagram that I drew up that might be helpful for others to follow.
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
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.
An externally hosted image should be here but it was not working when we last tested it.
Using Graeme's circuit as a guide, I arranged the ZTX550's and the 2SJ74's on a small sub-board.
An externally hosted image should be here but it was not working when we last tested it.
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.
An externally hosted image should be here but it was not working when we last tested it.
And finally, here is a circuit diagram that I drew up that might be helpful for others to follow.
An externally hosted image should be here but it was not working when we last tested it.
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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Zen: Looking again at the photo, I'm wondering if I just took the picture from a poor angle. All of my wires to the daughter board are less than 3" in length. The brown and white twisted pair that runs from the bottom foreground of the image to the top is the extension for the VR2 trimpot for offset adjustment. The daughter board is mounted just behind where the original 9610 pair were.
Here are some before and after comparisons with the JFET front end.
Original 9610 differential (technical details of images are in the image headers):
8 ohm output = 73w, bandwidth = 210kHz
4 ohm output = 90w, bandwidth = 140kHz.
New JFET differential (technical details of images are in the image headers):
8 ohm output = 66w, bandwidth = 95kHz
4 ohm output = 62w, bandwidth = 120kHz
The traces with the JFET front end look more rounded with more overshoot on the leading edge. This doesn't make sense to me. It looks like increasing the value of the feedback caps would "fix" the overshoot on the leading edge of the square wave, but would also decrease bandwidth... Grabbing the feedback caps with my fingers confirms a reduced overshoot on the leading edge.
JFET Sine Wave:
This one has me more baffled: the sine wave is not symmetric, it leans to the right. Sine wave from the 9610 looks perfectly symmetric (no image).
The top and bottom of the traces with the JFET differential look thicker than with the 9610. Is this oscillation? I don't understand the "messier" output and reduced power with the JFET differential. I was expecting cleaner output than from the 9610 differential. Any insights?
Here are some before and after comparisons with the JFET front end.
Original 9610 differential (technical details of images are in the image headers):
An externally hosted image should be here but it was not working when we last tested it.
8 ohm output = 73w, bandwidth = 210kHz
4 ohm output = 90w, bandwidth = 140kHz.
New JFET differential (technical details of images are in the image headers):
An externally hosted image should be here but it was not working when we last tested it.
8 ohm output = 66w, bandwidth = 95kHz
4 ohm output = 62w, bandwidth = 120kHz
The traces with the JFET front end look more rounded with more overshoot on the leading edge. This doesn't make sense to me. It looks like increasing the value of the feedback caps would "fix" the overshoot on the leading edge of the square wave, but would also decrease bandwidth... Grabbing the feedback caps with my fingers confirms a reduced overshoot on the leading edge.
JFET Sine Wave:
An externally hosted image should be here but it was not working when we last tested it.
This one has me more baffled: the sine wave is not symmetric, it leans to the right. Sine wave from the 9610 looks perfectly symmetric (no image).
The top and bottom of the traces with the JFET differential look thicker than with the 9610. Is this oscillation? I don't understand the "messier" output and reduced power with the JFET differential. I was expecting cleaner output than from the 9610 differential. Any insights?
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Subjectively on my main speakers, the JFET front end seems to be coaxing a bit more sparkle out of the tweeters and perhaps a pinch less weight or "tubby-ness" out of the midrange drivers. I would characterize these as positive improvements.
I'm also getting a bit more hum out of the speaker now, too... Perhaps it is time to work on shortening those wires to the daughter board. This will be a bit of a challenge as it will leave me with little room to work with the wires. I wanted to keep the daughter board from overlapping the main PCB so I could tweak the resistor values.
I'm also getting a bit more hum out of the speaker now, too... Perhaps it is time to work on shortening those wires to the daughter board. This will be a bit of a challenge as it will leave me with little room to work with the wires. I wanted to keep the daughter board from overlapping the main PCB so I could tweak the resistor values.
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Graeme's JFET Schematic
I only changed out the transistors, removed the diodes, and removed the gate stoppers for the 9610. I didn't change any resistors - I figured one step at a time. My resistor values for the input front end are listed a few posts up.
The JFETs are nicely matched (from Spencer), but I did not make any effort to match the ZTX550 transistors.
I only changed out the transistors, removed the diodes, and removed the gate stoppers for the 9610. I didn't change any resistors - I figured one step at a time. My resistor values for the input front end are listed a few posts up.
The JFETs are nicely matched (from Spencer), but I did not make any effort to match the ZTX550 transistors.
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looking at pointed schm , I can think of few things :
- for voltage bias of cascodes - put them to 12V , changing D3 to 12V ; nice cap - 2u2 will do , is fine to put across diode
that's where , at least to my experience , Jfets are somewhat happier than on under 9
DZ - you can put plain 1N4148 in series , cathode pointing down of course - it will somewhat null tempco of DZ itself , but dunno for overall CCS tempco ..... I'm used to use two-bjt- CCS ( Widlar ) which is having somewhat better Tempco than sole mosfet CCS
regarding other things - you're pretty much there on your own in your own physical layout , to fiddle with drain resistor (at LTP) values and current through LTP , to achieve best performance , sound wise and CRO wise
- for voltage bias of cascodes - put them to 12V , changing D3 to 12V ; nice cap - 2u2 will do , is fine to put across diode
that's where , at least to my experience , Jfets are somewhat happier than on under 9
DZ - you can put plain 1N4148 in series , cathode pointing down of course - it will somewhat null tempco of DZ itself , but dunno for overall CCS tempco ..... I'm used to use two-bjt- CCS ( Widlar ) which is having somewhat better Tempco than sole mosfet CCS
regarding other things - you're pretty much there on your own in your own physical layout , to fiddle with drain resistor (at LTP) values and current through LTP , to achieve best performance , sound wise and CRO wise
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