Connectors are a must - you'll regret direct wires (no - they are not highest reliability) when you need to service the amplifer. Take a look a my Leach clone - I used Molex Minifit-Jr connectors. They are polarized and locking. I always like to use unique connectors for my designs so that one can never accidentally plug any cable the wrong way or to the wrong connector.
As for grounding, yup - it's a wiring nightmare, especially when you have stereo amp boards sharing a common power supply. I kept all of my grounds on-board. Take a look at the attached picture - all you have is a short input cable, power cable and output cable. This is my method of implementing a multi-channel amplifier - by keeping each channel as a mono unit.
BTW, I never understood the need for tiny PCB's when the required heatsink is so much larger.
As for grounding, yup - it's a wiring nightmare, especially when you have stereo amp boards sharing a common power supply. I kept all of my grounds on-board. Take a look at the attached picture - all you have is a short input cable, power cable and output cable. This is my method of implementing a multi-channel amplifier - by keeping each channel as a mono unit.
BTW, I never understood the need for tiny PCB's when the required heatsink is so much larger.
Attachments
Finally making headway!!!
Can anyone help?
I am about to sort out the values of R41,R42,R43,R60,R61,R62,R28 and R30. Also R26,R34,R68 and R69.
I will be using MJL4302 and MJL4281 outputs when they finally get here.
The rails will be 56volts for outputs and regulated 58volts for front end.
Emitter resistors will be 0.47ohm.
R28,R30 will be 270ohm.
According to previous post with 3281 and 1302's R41,2,3 and R60,1,2 will be 1.2kohm.
R26,R34 will be 4.3kohm.
Can someone advise if these values will work with my outputs and what value will the value of R68,R69 be?
Also will they all be 0.6 watt or some other power ratings.
Regards
Loboone
Can anyone help?
I am about to sort out the values of R41,R42,R43,R60,R61,R62,R28 and R30. Also R26,R34,R68 and R69.
I will be using MJL4302 and MJL4281 outputs when they finally get here.
The rails will be 56volts for outputs and regulated 58volts for front end.
Emitter resistors will be 0.47ohm.
R28,R30 will be 270ohm.
According to previous post with 3281 and 1302's R41,2,3 and R60,1,2 will be 1.2kohm.
R26,R34 will be 4.3kohm.
Can someone advise if these values will work with my outputs and what value will the value of R68,R69 be?
Also will they all be 0.6 watt or some other power ratings.
Regards
Loboone
Hi Lo,
using your values of 270r, 1k2, 4k3, 0r47 and adding 33k for R68
gives a short circuit current of about 6A.
This current is quite low and is only just clear of the 8ohm load line. It only uses 110W of transistor capacity and your 4302/4281 have about 200W capacity until the sink starts to heat up. Then the fuses should blow
I am trying a different set of values (not tested yet) 200r, 1k3, 11k, 22k, 0r337 and give 8.8A into a short and use 160W of capacity.
For your chosen 0r47 emitter resistor the set would be:-
180r, 1k6, 8k1, 24k, 0r47 these give about 8.4A using 152W into a short and allow full use into any 8ohm load and 4ohm to about 45deg phase angle when full limiting is on.
But C17 & C18 allow higher short term peak currents if you can work out a suitable time constant. I am planning to try 10nF to 1uF
using your values of 270r, 1k2, 4k3, 0r47 and adding 33k for R68
gives a short circuit current of about 6A.
This current is quite low and is only just clear of the 8ohm load line. It only uses 110W of transistor capacity and your 4302/4281 have about 200W capacity until the sink starts to heat up. Then the fuses should blow
I am trying a different set of values (not tested yet) 200r, 1k3, 11k, 22k, 0r337 and give 8.8A into a short and use 160W of capacity.
For your chosen 0r47 emitter resistor the set would be:-
180r, 1k6, 8k1, 24k, 0r47 these give about 8.4A using 152W into a short and allow full use into any 8ohm load and 4ohm to about 45deg phase angle when full limiting is on.
But C17 & C18 allow higher short term peak currents if you can work out a suitable time constant. I am planning to try 10nF to 1uF
Thanks for that Andrew.
So just to recap and confirm.
R28/30 (180R)
R41/2/3 and R60/1/2 (1.6k)
R26/34 (8.1k)
R68/69 (24K)
Emitter resistors 0.47R
Sorry if i seem a bit thick with this but I just want to make sure we don't go bang after all this time.
Regards
Ian
So just to recap and confirm.
R28/30 (180R)
R41/2/3 and R60/1/2 (1.6k)
R26/34 (8.1k)
R68/69 (24K)
Emitter resistors 0.47R
Sorry if i seem a bit thick with this but I just want to make sure we don't go bang after all this time.
Regards
Ian
Hi,
yes, you have interpreted the numbers correctly.
The protection, even if wrongly scaled, will not cause your Leach clone to go bang. It is what you are doing to the amp that might cause it to go bang. eg. shorted output, overheated output stage, signal overload, excessive phase angle.
The protection is an attempt to stop the amp going bang, and will sound horrible while it is triggered.
If scaled correctly it will never limit on any valid signal into any valid load. This implies it will never be audible.
The difficulty is scaling the component values so that it provides effective protection for all likely failure senarios and is also inaudible. That's why I said untested.
I tried to extract from our fellow contributors a method of testing the protection circuit without risking destroying the output stage but to no avail.
My method of analysis depends heavily on the triggering transistor Vbe. Small changes in the Vbe make significant changes in the pass currents and that in turn either allows excess current to pass (risky) or too little current to pass (audible at the extremes of the SOAR curve).
Small changes in Vbe can be compensated for by adjusting r28/30 and this might be an area for experiment with a working circuit IF you can find a way to actually carry out the test and give sensible measurements before you overheat or destroy the outputs. A way to achieve this would be to use r28/30 @110% and parallel it with a ten to twenty times pot (i.e. 220r and 4k7) to enable trimming to 100% value then test either side of set point, for audibility and/or excess current into a shorted load.
BTW. make as good a job as you can of matching your 0r47s you need 12 for a stereo pair and this will allow grouping into threes for each half stage. String them in series, using terminal strip and pass a fixed (or regulated) 500mA to 1A through them. Monitor the volts drop across each.
Hope this helps, good designing (not luck)
yes, you have interpreted the numbers correctly.
The protection, even if wrongly scaled, will not cause your Leach clone to go bang. It is what you are doing to the amp that might cause it to go bang. eg. shorted output, overheated output stage, signal overload, excessive phase angle.
The protection is an attempt to stop the amp going bang, and will sound horrible while it is triggered.
If scaled correctly it will never limit on any valid signal into any valid load. This implies it will never be audible.
The difficulty is scaling the component values so that it provides effective protection for all likely failure senarios and is also inaudible. That's why I said untested.
I tried to extract from our fellow contributors a method of testing the protection circuit without risking destroying the output stage but to no avail.
My method of analysis depends heavily on the triggering transistor Vbe. Small changes in the Vbe make significant changes in the pass currents and that in turn either allows excess current to pass (risky) or too little current to pass (audible at the extremes of the SOAR curve).
Small changes in Vbe can be compensated for by adjusting r28/30 and this might be an area for experiment with a working circuit IF you can find a way to actually carry out the test and give sensible measurements before you overheat or destroy the outputs. A way to achieve this would be to use r28/30 @110% and parallel it with a ten to twenty times pot (i.e. 220r and 4k7) to enable trimming to 100% value then test either side of set point, for audibility and/or excess current into a shorted load.
BTW. make as good a job as you can of matching your 0r47s you need 12 for a stereo pair and this will allow grouping into threes for each half stage. String them in series, using terminal strip and pass a fixed (or regulated) 500mA to 1A through them. Monitor the volts drop across each.
Hope this helps, good designing (not luck)
BTW. make as good a job as you can of matching your 0r47s you need 12 for a stereo pa
Hi , i did this and found that those resistors are (of course) a little temperature dependent and so the reading is taking some time to stabilise.....
good luck with the job.
Hi , i did this and found that those resistors are (of course) a little temperature dependent and so the reading is taking some time to stabilise.....
good luck with the job.
troubleshooting
Hi,
My second clone won't power up.
Tried the usual light bulb and it stayed lit.
Tried a Variac and the PSU voltage came up to +-12Vdc but the dropper resistors across the open fuse holders became very hot and only +-1.1V was across the output stage.
Disconnected R1 & R23 and powered up the front end via Vc and Vs. Front end seems OK.
With front end still disconnected, tried powering the output end again via Vcc & Vss with F4A fuses in place.
With +-1.8Vdc on the rails (Variac set at 10%) there is 1A flowing through each emitter resistor (3A in total = 11W so nothing appears to get warm).
What voltages will help find the problem? output offset sits @ -200mV.
I have had the board off it's sink and examined both sides very carefully for shorts, none found.
Hi,
My second clone won't power up.
Tried the usual light bulb and it stayed lit.
Tried a Variac and the PSU voltage came up to +-12Vdc but the dropper resistors across the open fuse holders became very hot and only +-1.1V was across the output stage.
Disconnected R1 & R23 and powered up the front end via Vc and Vs. Front end seems OK.
With front end still disconnected, tried powering the output end again via Vcc & Vss with F4A fuses in place.
With +-1.8Vdc on the rails (Variac set at 10%) there is 1A flowing through each emitter resistor (3A in total = 11W so nothing appears to get warm).
What voltages will help find the problem? output offset sits @ -200mV.
I have had the board off it's sink and examined both sides very carefully for shorts, none found.
Andrew,
The board is designed for MPSA type small signal transistors, if you use BC types (BC546) you must reverse the part as the pinout of these are mirrored. I expect you know this as you have one channel running.
Do you have the BIAS diodes in place, and are they connected corectly?
Is there a shortcircuit to the heatsink (gnd??) from the biasdiodes?
\Jens
The board is designed for MPSA type small signal transistors, if you use BC types (BC546) you must reverse the part as the pinout of these are mirrored. I expect you know this as you have one channel running.
Do you have the BIAS diodes in place, and are they connected corectly?
Is there a shortcircuit to the heatsink (gnd??) from the biasdiodes?
\Jens
Hi,
I have checked P & N types for VAS, Predriver and outputs. Not checked Drivers (need to dismantle and rebend legs to see and bend legs again to reassemble).
BC5xx all OK (both PCBs the same as Jens already commented).
The first working version has the melf diodes lying on top of a piece of sticky tape to electrically insulate and then the diodes are smothered in thermal paste to transfer heat as efficiently as possible.
The second, faulty board, has leaded diodes placed in direct contact with the sink. They are insulated by the package, aren't they?
But, with the front end on zero supply voltage, the VAS and Vbe multiplier are disabled. I think they should have no effect.
The drivers have 1.95V between their emitters and 2.98V (PSU voltage) between their collectors and 1.39V between the bases.
Should there be zero or near zero Iq when the front end is disconnected?
BTW. the working version has 0.0mVdc between the sink and ground, but measures 6Vac between sink and ground. Where should the sink be grounded to? Do I use zero ohm link or low ohms link or capacitor link?
I have checked P & N types for VAS, Predriver and outputs. Not checked Drivers (need to dismantle and rebend legs to see and bend legs again to reassemble).
BC5xx all OK (both PCBs the same as Jens already commented).
The first working version has the melf diodes lying on top of a piece of sticky tape to electrically insulate and then the diodes are smothered in thermal paste to transfer heat as efficiently as possible.
The second, faulty board, has leaded diodes placed in direct contact with the sink. They are insulated by the package, aren't they?
But, with the front end on zero supply voltage, the VAS and Vbe multiplier are disabled. I think they should have no effect.
The drivers have 1.95V between their emitters and 2.98V (PSU voltage) between their collectors and 1.39V between the bases.
Should there be zero or near zero Iq when the front end is disconnected?
BTW. the working version has 0.0mVdc between the sink and ground, but measures 6Vac between sink and ground. Where should the sink be grounded to? Do I use zero ohm link or low ohms link or capacitor link?
AndrewT said:
You have insulated the C of the drivers towards the heatsink right?
The leaded diodes are mounted on the bottom of the PCB I suspect? You did turn everything the right way round for this (No turning required IFAKT)
If you short T11 (Bias transistor) from C to E you must have zero current through the driver and output stage! If not then you found a problem!
\Jens
Hi,
the drivers are To126, so are turned name side to PCB with the sink facing up on the component side, so no insulation required.
The diodes are bolted under the middle of the group of outputs (not below the two access holes in the PCB) on black and red wires 1 to1 and 2 to 2, so no mistakes there either.
I have access to top side so just tried setting DMM to ammeter and probed D13 +ve to TH pin2, effectively shorting link across T11. No change to DMM reading volts across output emitter resistor.
Looks like I will have to dismantle the drivers and check them. Unless there is a way to interogate them without dismantling?
What is the symptom if T21 & T22 are transposed? Does it show on voltage readings?
the drivers are To126, so are turned name side to PCB with the sink facing up on the component side, so no insulation required.
The diodes are bolted under the middle of the group of outputs (not below the two access holes in the PCB) on black and red wires 1 to1 and 2 to 2, so no mistakes there either.
I have access to top side so just tried setting DMM to ammeter and probed D13 +ve to TH pin2, effectively shorting link across T11. No change to DMM reading volts across output emitter resistor.
Looks like I will have to dismantle the drivers and check them. Unless there is a way to interogate them without dismantling?
What is the symptom if T21 & T22 are transposed? Does it show on voltage readings?
To126 has the C pin on the casing..... did you insulate the screw???
I think you will find an error in the output stage, that is as close as I can get from here.
\Jens
I think you will find an error in the output stage, that is as close as I can get from here.
\Jens
Hi Jens,
the screw holes for T21 & T22 are plated through but the plating is isolated from the rest of the PCB. So the answer is, none of the To126 screws are insulated on the working PCB or the faulty one.
Thanks for your continued efforts.
Can someone give me a clue to what kind of fault I am looking for?
the screw holes for T21 & T22 are plated through but the plating is isolated from the rest of the PCB. So the answer is, none of the To126 screws are insulated on the working PCB or the faulty one.
Thanks for your continued efforts.
Can someone give me a clue to what kind of fault I am looking for?
soldering through the green lacquer?
Hi,
is there a way to effectively clean off a small patch of the green lacquer on our GB PCBs to allow good soldering of a wire inserted through to the ground plane?
I only have big and tall caps for C21 & C27. 15mF blows F1 & F2 on start up. So I want to use some (two or three in //) 1mFs in the same locality. Cant' find a cheap low profile alternative in the 3m3 to 4m7 range.
Hi,
is there a way to effectively clean off a small patch of the green lacquer on our GB PCBs to allow good soldering of a wire inserted through to the ground plane?
I only have big and tall caps for C21 & C27. 15mF blows F1 & F2 on start up. So I want to use some (two or three in //) 1mFs in the same locality. Cant' find a cheap low profile alternative in the 3m3 to 4m7 range.
Andrew
What voltage are you using, I have tons of 10.000µF 63V caps that will fit the board. Let me know if you need any and I will send some over.
I use a sharp knife (scapel) to remove the solder resist... the tin it and you are ready to go.
\Jens
What voltage are you using, I have tons of 10.000µF 63V caps that will fit the board. Let me know if you need any and I will send some over.
I use a sharp knife (scapel) to remove the solder resist... the tin it and you are ready to go.
\Jens
Hi Jens,
thanks for the offer. I have a few 10mF as well as many 15mF.
I was hoping that on board capacitance could let me get away with smaller PSU smoothing but the current spike at start up is just a bit big. So I plan to cut by a factor of 3 to 5 to ensure the fuses have a margin. I want to use F3.1A for 8ohm duty but I'm using F4A just now and it starts OK with 3mF on board.
I tried the simple scrape and tin, keeping in mind the heat sinking effect of the large ground plain, but it did not tin evenly, to put it mildly. Could be temperature or lack of adequate scraping. Will try again.
Anybody else listening?
Come back on my bad board - please.
thanks for the offer. I have a few 10mF as well as many 15mF.
I was hoping that on board capacitance could let me get away with smaller PSU smoothing but the current spike at start up is just a bit big. So I plan to cut by a factor of 3 to 5 to ensure the fuses have a margin. I want to use F3.1A for 8ohm duty but I'm using F4A just now and it starts OK with 3mF on board.
I tried the simple scrape and tin, keeping in mind the heat sinking effect of the large ground plain, but it did not tin evenly, to put it mildly. Could be temperature or lack of adequate scraping. Will try again.
Anybody else listening?
Come back on my bad board - please.
JensRasmussen said:
Could I buy a few? Or could you point me at someone charging less than Farnell prices?
cheers
Chris
The worst ones to get into to examine the types inserted.
- Status
- Not open for further replies.