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Old 27th December 2008, 04:17 PM   #511
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by roender
It is possible to use other output voltages by putting other zener values but don't forget that this is a shunt PSU. You have to modify CCS current in order to keep at least 10-15mA through PSU output transistors (MJL15034/35).

Happy Holidays,
Mihai
Thanks Mihai. And Thanks to all for the pictures. Makes the build a little easier.

Best Wishes to All,

Sheldon
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Old 27th December 2008, 05:25 PM   #512
pooge is offline pooge  United States
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Quote:
Originally posted by roender
PSU

Roender,

Sorry if this was already discussed somewhere on this thread, but I noticed in your parts layout for the PSU, you didn't picture the required jumpers between the banded ends of D1 and D3, or across the pads next to the base and emitter of Q7. Anyone taking the care to build this should recognize this, but I just thought I've give a heads up.

Also, the labels for Q4 and Q5 could be clarified. I can't even see Q4 in there, and Q5 is unclear which transistor is intended.

Also, I got to wondering if you have any suggestion for mounting the PS board, since there are no mounting holes. At first I thought you mounted it via the vias under the heat sinks, since all those heat sink vias need to be connected to ground/each other. But then I understand the three ground busses are connected together via the heat sinks pins soldered to those vias.
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Old 27th December 2008, 06:01 PM   #513
roender is offline roender  Romania
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Hi Pooge,

You're wright, the PSU PCB need two jumpers in the positions you already mentioned.
At the moment when this PCB was constructed and tested I was unsure about mounting position, hence no holes.

Thanks,
Mihai
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Old 28th December 2008, 01:44 PM   #514
pooge is offline pooge  United States
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Roender,

You show a resistor to the left of the blue potentiometer in the picture of your completed board in Post #99. It appears to be in parallel with the pot from the circuit traces. However, I don't see any such resistor on your schematic.

Post #99
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Old 28th December 2008, 02:08 PM   #515
roender is offline roender  Romania
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I have plenty of 2k pots, which are to big as value for that position, so I create a place for a small value parallel resistor.
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Old 28th December 2008, 03:12 PM   #516
pooge is offline pooge  United States
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OK. Do you set it at maximum or minimum resistance when starting up for the first time to set bias?
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Old 28th December 2008, 05:19 PM   #517
roender is offline roender  Romania
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Quote:
Originally posted by pooge
OK. Do you set it at maximum or minimum resistance when starting up for the first time to set bias?
Put it at minimum when you'll first fire up the amp, then check the voltages over every output resistors. You should read something between 2 and 8mV. After that, slowly increase the voltage to 18-20mV and wait till heatsink will turn warm enough (one or two hours). Read again the bias level and readjust if necessary.

I must mention that heatsink should have at least 0.35 grdC/W in order to support such high level of power dissipation, around 37W per monoblock.
If you don't have a big enough radiator than increase all emitter resistors to 15 or 22mohm and keep the same bias voltage (18-20mV)

Happy building,

Mihai
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Old 29th December 2008, 01:30 AM   #518
pooge is offline pooge  United States
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Quote:
Originally posted by roender

Put it at minimum when you'll first fire up the amp, then check the voltages over every output resistors. You should read something between 2 and 8mV. After that, slowly increase the voltage to 18-20mV and wait till heatsink will turn warm enough (one or two hours). Read again the bias level and readjust if necessary.
Glad I asked! In the Leach amp you start at maximum resistance. Since the primary failure mode in pots is an open circuit, any problem with thermal runaway if this happens? If so, it would seem prudent to put in a parallel resistor as discussed previously to limit maximum safe resistance.


Quote:
Originally posted by roender
I must mention that heatsink should have at least 0.35 grdC/W in order to support such high level of power dissipation, around 37W per monoblock.
Can I make do with .375?


Quote:
Originally posted by roender
If you don't have a big enough radiator than increase all emitter resistors to 15 or 22mohm and keep the same bias voltage (18-20mV)
If it is no work on your part, can you estimate the class A range using 15 and 22mohm resistors?

Thanks.
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Old 29th December 2008, 02:53 AM   #519
pooge is offline pooge  United States
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Roender,

What .6w resistors do you use to fit 7.5mm hole spacing? Most of the .5w resistors I find go longer than that. I would assume that other than the 2w emittor resistors, .5w are fine for all the other locations.
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Old 29th December 2008, 03:46 AM   #520
andy_c is offline andy_c  United States
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Quote:
Originally posted by jcarr
To mention an alternative to batteries, you may like to try your hand at some type of "never-connected" power supply, similar to the circuit that I posted years ago, or the one that EC Designs has come up with recently for his DAC project. Based on personal experience (as well as listening feedback from dealers and customers), I can vouch that, in terms of sonic benefits, this is a worthwhile area for development effort - possibly more so than the amplifier circuit itself.
As one guy in Life of Brian said, "Follow the shoe!"
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