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Old 29th November 2004, 11:10 AM   #51
slydwz is offline slydwz  United States
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You can get the CDE 12K/80V from Apex Jr. for $4.95 each.
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Old 30th November 2004, 07:04 AM   #52
KarlDL is offline KarlDL  United States
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Attached is the schematic for the Hafler step-start.

Basically, the 120VAC interlock circuit through the thermostats is opened, with the wire removed from the thermostat attaching to one of the relay contacts, the other contact is jumpered to the thermostat lug where the wire was removed, and the 5 Ohm resistor is connected across the relay contacts. So there's 5 Ohms in series with that interlock loop, shorted out when the step relay closes.

Sorry that there's not a comprehensive schematic & instructions. I did take a number of photos during the modification effort, showing how all this gets assembled. But, being a road warrior, I've not had time to write/package all of it up.

Hope this helps,

Karl
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File Type: pdf visio-hafler step.pdf (23.8 KB, 786 views)
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Old 30th November 2004, 01:25 PM   #53
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mebbe this is just old barking ,but I must ask again-it is possible to someone send me just PA3B schematic ?
I'm interested just for evaluating and I really have no need to build it ,in case that someone sez smthng about intelectuall property etc.........
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Old 30th November 2004, 02:57 PM   #54
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Default Hafler delay circuit

KarlDL,

Thanks for posting the schematic. Now, it raises more questions.

Is the relay's coil you are using run by 110VAC or DC? Your schematic shows the relay coil with + and - symbols.

Your diagram about how to wire up the series power resistor is clear but what is the relay coil attached to, 110VAC or the power supply's DC?

Thanks


"Basically, the 120VAC interlock circuit through the thermostats is opened, with the wire removed from the thermostat attaching to one of the relay contacts, the other contact is jumpered to the thermostat lug where the wire was removed, and the 5 Ohm resistor is connected across the relay contacts. So there's 5 Ohms in series with that interlock loop, shorted out when the step relay closes."
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Old 30th November 2004, 03:07 PM   #55
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Default Hafler Delay Circuit

KarlDL,

Aha. Now that I read the fine print I see you are using a 110 VDC relay.

Now, if it is connected across the two secondaries is their combined voltage too high for the relay's coil. We know the amp has rails of +/- 65VDC, depending on initial VAC level. If we add 65+65 we get 130. Is this a safe voltage for the relay's coil?

Do the 2K resistor in series with the relay coil and the coil's resistance make a voltage divider which reduces the 130VDC to a lower level?

Thanks for helping to educate us.
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Old 1st December 2004, 06:44 AM   #56
KarlDL is offline KarlDL  United States
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Dick asked whether the 110V relay used in my step-start circuit is AC or DC, and how that coexists with the 130V total PS voltage (rail-to-rail).

The rated current for this DC coil is approximately 10mA. The 2K series resistor drops approx 20V at that current, hence the coil voltage is approx 110VDC under normal operating conditions.

There's an argument for using a larger-valued voltage-limiting resistor, based on the rated pull-in voltage of the relay. But I'm happy with the results obtained at 2K. Also note that the drop-out voltage rating for the relay is much lower than its pull-in rating, so the PS caps have to discharge significantly before the step-start relay releases.

Choky asked if anyone has reverse-engineered the Musical Concepts PA-3B driver board. I have done so, but I believe that there are errors in my original schematic trace; the apparent circuit topology doesn't seem fully logical. I will take another look at the board after the holidays end. It is a much simpler circuit than the original Hafler design.

Karl
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Old 1st December 2004, 08:41 AM   #57
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Quote:
Originally posted by KarlDL

Choky asked if anyone has reverse-engineered the Musical Concepts PA-3B driver board. I have done so, but I believe that there are errors in my original schematic trace; the apparent circuit topology doesn't seem fully logical. I will take another look at the board after the holidays end. It is a much simpler circuit than the original Hafler design.

Karl

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Old 1st December 2004, 11:05 AM   #58
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"mebbe this is just old barking ,but I must ask again-it is possible to someone send me just PA3B schematic ?
I'm interested just for evaluating and I really have no need to build it ,in case that someone sez smthng about intelectuall property etc........."

If you just want to rip them off, order a pair of boards. By the time you reverse engineer them and sell 10 sets you will have made a pile of money.

Your baloney about 'evaluating' doesn't wash. They describe the topology in great detail, and even show the board layout with the traces.

Figure 2N540X/2N555X for the small plastic types and MJE340/350 for the larger pair.

Calculating the resistors is left as a design exercise.

If you're actually going to build one, the Miller cap (C11) and VAS feedback cap (C4) are best adjusted with a 'scope.
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Old 1st December 2004, 11:43 AM   #59
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Question Schematic PA3B

Quote:
Originally posted by djk
"mebbe this is just old barking ,but I must ask again-it is possible to someone send me just PA3B schematic ?
May I have the schematic too?
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Old 2nd December 2004, 01:03 AM   #60
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QUACK!
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