Seems more sensible to test the electronics rather than the aluminium
Hi Andrew.
I only gave a hint for people testing amps with a too small sink at medium power .
The electronics will not function right without the heatsink.....
So a powertest without a heatsink has no sense. So the sink is included in a (longer term) test is my idea.
I have repared cooked amplifiers with big enough sinks because people used them in a closed furniture during a party...
Loek
Hi Andrew.
I only gave a hint for people testing amps with a too small sink at medium power .
The electronics will not function right without the heatsink.....
So a powertest without a heatsink has no sense. So the sink is included in a (longer term) test is my idea.
I have repared cooked amplifiers with big enough sinks because people used them in a closed furniture during a party...
Loek
Hi,
just plugged in my fully assembled stereo Leach based on the clone PCBs.
Hum! Why, there is no hum when assembled out of the case?
After finding that the chassis ground/safety earth is directly connected to the audio ground for both channels
I completely dismantled the amp to search out the short.
Well it's obvious and I should have noticed earlier.
The PCB mounting holes are all connected to power ground.
F**k!!!!
I could drill all the holes oversize and fit tophat insulators to both sides of the PCB, twelve holes to drill and 24 insulators to fit, but I don't have any and that seems an overkill method.
or insulate the heatsink from the chassis (it's close coupled).
How have the rest of you secured the PCB to the heatsink so that the output device leads do not carry the weight of the board?
just plugged in my fully assembled stereo Leach based on the clone PCBs.
Hum! Why, there is no hum when assembled out of the case?
After finding that the chassis ground/safety earth is directly connected to the audio ground for both channels
I completely dismantled the amp to search out the short.Well it's obvious and I should have noticed earlier.
The PCB mounting holes are all connected to power ground.
F**k!!!!I could drill all the holes oversize and fit tophat insulators to both sides of the PCB, twelve holes to drill and 24 insulators to fit, but I don't have any and that seems an overkill method.
or insulate the heatsink from the chassis (it's close coupled).
How have the rest of you secured the PCB to the heatsink so that the output device leads do not carry the weight of the board?
I'm an aficinado of flexible spring/mass mounted pcb's for the microphonic influence thingy, in line with manufacturers such as Goldmund and DartZ.
Rubber damping and insulating ring incorporating pcb mounting studs can be ordered from several electronic stores.
The calculated damping can be obtained by making incisions in the rings or adding damping material in the core, depending on the weight of pcb and components.
Rubber damping and insulating ring incorporating pcb mounting studs can be ordered from several electronic stores.
The calculated damping can be obtained by making incisions in the rings or adding damping material in the core, depending on the weight of pcb and components.
I usually mount my Leach boards on plastic standoffs; in the case of Brian Bell's Leach variation, the output device leads are the mechanical support on one side of the board.
Don't recall a hum when I had an earlier version mounted with grounded supports, but I went to full isolation with all ground returns through the wiring and that worked well, as it should and was reflected in the low THD readings.
]
It just seems weird to have everything laid out on the bench and working well without benefit of a chassis...
Don't recall a hum when I had an earlier version mounted with grounded supports, but I went to full isolation with all ground returns through the wiring and that worked well, as it should and was reflected in the low THD readings.
]
It just seems weird to have everything laid out on the bench and working well without benefit of a chassis...
I'm having trouble understanding your post, but if you use isolated RCA jacks and the resistor from the gnd of the RCA to chassis, yoou really should not have a problem.
Make sure that there is some resistace from the GND of the RCA to chassis. I'm too lazy to look at the schematic for the value. It might be something like 4.7 ohms.
The output devices should already be insulated from the heatsink.
My heatsink and board are both mounted flat in my chassis.
Your suggested method of isolating seems a little odd. You should only need 6 nylon step collars and 6 washers and 6 spacers for 6 attachment points. A source of parts is www.smallparts.com.
Use:
nut, regular washer, step collar, board, nylon washer, thru hole spacer, chassis, screw
-or, for better asthetics:
screw, optional lock washer, regular washer, step collar, board, nylon washer, threaded spacer, chassis, optional lock washer, screw
Make sure that there is some resistace from the GND of the RCA to chassis. I'm too lazy to look at the schematic for the value. It might be something like 4.7 ohms.
The output devices should already be insulated from the heatsink.
My heatsink and board are both mounted flat in my chassis.
Your suggested method of isolating seems a little odd. You should only need 6 nylon step collars and 6 washers and 6 spacers for 6 attachment points. A source of parts is www.smallparts.com.
Use:
nut, regular washer, step collar, board, nylon washer, thru hole spacer, chassis, screw
-or, for better asthetics:
screw, optional lock washer, regular washer, step collar, board, nylon washer, threaded spacer, chassis, optional lock washer, screw
I have found that Rapid sell M3 nylon nuts and set screws.
Looks like I will need to buy again.
The problems are the 6 plated through holes for fixing the PCB to a structure, in this case due to the design of the PCB that structure is the heatsink.
They are all connected to the PCB ground and make 6 very effective earth connections to the chassis (=6 earth loops).
Looks like I will need to buy again.
The problems are the 6 plated through holes for fixing the PCB to a structure, in this case due to the design of the PCB that structure is the heatsink.
They are all connected to the PCB ground and make 6 very effective earth connections to the chassis (=6 earth loops).
Screw, e.g. M3
Nylon Step collar, e.g. M3 clearnce - Insulates screw from top surface and edge of hole (both top and bottom since the screw is kept from touching the side of the hole. The collar portion has to be less than or equal to the thickness of the board.
Board
Nylon Washer - e.g. M3 - Insulates spacer from bottom of board
Threaded spacer- e.g M3 - provides nut for screw
Chassis
Screw, e.g M3
Lock washers and regular washers as needed. Lock washers prevent loosening. The regular washer would prevent distorion on the screw on the nylon face of the step collar. (Not shown).
Nylon Step collar, e.g. M3 clearnce - Insulates screw from top surface and edge of hole (both top and bottom since the screw is kept from touching the side of the hole. The collar portion has to be less than or equal to the thickness of the board.
Board
Nylon Washer - e.g. M3 - Insulates spacer from bottom of board
Threaded spacer- e.g M3 - provides nut for screw
Chassis
Screw, e.g M3
Lock washers and regular washers as needed. Lock washers prevent loosening. The regular washer would prevent distorion on the screw on the nylon face of the step collar. (Not shown).
Power Output Transister
Hi All,
I'm in the process of gathering parts for my Leach Amp project. I've found from various posts that it can use many output transister to replace MJ15003,15004.
Can I use Toshiba 2SC5200, 2SA1943 as output transistor? Is there any pros and cons? It has 230V and 15A maximum.
Thanks, Kittikun
Hi All,
I'm in the process of gathering parts for my Leach Amp project. I've found from various posts that it can use many output transister to replace MJ15003,15004.
Can I use Toshiba 2SC5200, 2SA1943 as output transistor? Is there any pros and cons? It has 230V and 15A maximum.
Thanks, Kittikun
Andrew,
Are you sure the hum is coming from the power supply loops. These are not connected to signal ground on the board, so I'm wondering how the loops are coupled to signal.
You say that your amp is a stereo amp. Could the hum be due to a loop from one input back to your preamp to the other input?
Leach has a fix for this on his web page, and the fix helped solve the problem for another constructor.
Are you sure the hum is coming from the power supply loops. These are not connected to signal ground on the board, so I'm wondering how the loops are coupled to signal.
You say that your amp is a stereo amp. Could the hum be due to a loop from one input back to your preamp to the other input?
Leach has a fix for this on his web page, and the fix helped solve the problem for another constructor.
Hi Jacco,
thank you.
I "see".
Unfortunately they take up too much distance. The PCB sandwiches the output devices to the heatsink with just a tiny gap from PCB to the face of the package. The gap that needs screwing is 8.5mm.
I think I'll just repeat my existing steel screw fixing with nylon. Achieves the insulation required and goes a little way towards your compliant suspension system.
Thanks again.
thank you.
I "see".
Unfortunately they take up too much distance. The PCB sandwiches the output devices to the heatsink with just a tiny gap from PCB to the face of the package. The gap that needs screwing is 8.5mm.
I think I'll just repeat my existing steel screw fixing with nylon. Achieves the insulation required and goes a little way towards your compliant suspension system.
Thanks again.
Hi.
1943/5200 have a poor high voltage SOAR.
3pair give 450W with a 150degC package.
2pair of 15003/4 give 500W with a 200degC package.
One cannot extract as much power out of these devices at low voltage and it gets worse as the sink gets hotter or the voltage gets higher.
Go back and look at the Leach clone thread. It's all in there.
1943/5200 have a poor high voltage SOAR.
3pair give 450W with a 150degC package.
2pair of 15003/4 give 500W with a 200degC package.
One cannot extract as much power out of these devices at low voltage and it gets worse as the sink gets hotter or the voltage gets higher.
Go back and look at the Leach clone thread. It's all in there.
pooge said:
I know exactly why it hums.
Each of the audio grounds are shorted to chassis.
I am annoyed with myself for not noticing earlier and doing my best to stay calm regarding the stupid design decision to incorporate the mounting holes into the power ground plane.
Look at Leach or any power amp and somewhere the power ground is connected to the signal ground. The Leach is of the design where these two grounds are connected twice. Once on board by a low inductance route using a hum busting 10r resistor and once using longish wire leads (=high inductance and low resistance) through the audio ground.
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