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Old 2nd December 2004, 05:24 AM   #61
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Question ???

Quote:
Originally posted by djk
QUACK!
Yes.....?
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Old 2nd December 2004, 06:58 AM   #62
Zen Mod is offline Zen Mod  Serbia
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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 ?
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.

I was servician (or technician or repairer , if you wish ) for years ;
during that time I stashed pile of various schematics ,but what I never do is making sort of "mail order" bussines ,where I sell something. now I'm techie in local radio station-for everything-from PCs to mix board........
what I usually do is to look at some (probably) good schmtc or project and collect ideas .
sometimes is more important figuring why some designer make particular compromise ,then figuring golden book value for some component.
besides-I'm from former Yu ,and just for evaluating purposes going through messy procedure of ordering pair of boards just for that is just silly.
do not act like having few boards is nuclear physic.
I pooged DH101 and DH200 15 yrs ago,even without net and even without knowing that somewhere in some magazine someone do the same .
making money is not always first thing for everyone
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Old 2nd December 2004, 01:23 PM   #63
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KarlDL,

Thanks for the thorough explanation of how you used the relay in your MC amplifier.

"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."

I believe I can speak for Tom. He an I both appreciate your help.
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Old 18th December 2004, 09:56 PM   #64
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Old 21st December 2004, 04:44 PM   #65
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Default DH 200

Hey:
I have a DH 500 modded by Musical Concepts that has an Inrush Limiter in series with the thermal switches that limits the current spike when turning the amp on. The Dynaco part number is RZ016. I cannot find a regular part number to correspond. Anyone?
This would of course work in any amp. It has a higher resistance when cold and goes to a low res. when warm. This works ok.
The amp sound as good as a Adcom GFA 7805 except that the volume is slightly lower and there is slightly less Bass. Just turn the vol up and the Bass up a little bit and the sound is similar. both are non fatuiging to listen to for long periods of time.
Hope this helps
Ed
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Old 29th January 2005, 08:09 AM   #66
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Default Hafler XL280 Upgrade

Hello,

I have a Hafler XL280 amp.

2 Questions

1. I want to upgrade to get the most out of the amp, the place I saw is:
http://www.musicaldesign.com/mc_amp_mods.htm

Does anybody know if they are a good place to upgrade with and what is worth upgrading.

2. I have a yamaha 600 CX Pre-amp, but want to get a Hafler 945 W/Tuner, is it a good pre-amp, and will the pre-ampmake a lot of difference?

Thanks
Mona979
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Old 29th January 2005, 08:26 AM   #67
djk is offline djk
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"I have a DH 500 modded by Musical Concepts that has an Inrush Limiter in series with the thermal switches that limits the current spike when turning the amp on. The Dynaco part number is RZ016. I cannot find a regular part number to correspond. Anyone?
This would of course work in any amp. It has a higher resistance when cold and goes to a low res. when warm. This works ok."

That came stock in later DH500s.

Switches and thermostats failed in those early amps after a period of time. If you beefed up the supply caps they failed even faster.

A better solution is to replace the two pole relay with a three pole type and the inrush limiter with the CL30 Keystone. The CL30 is 2R5 vs the CL100 being 0R5, it just doesn't do much.
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Old 29th January 2005, 01:25 PM   #68
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Default Reply to mone979

mona,

I have used almost all the older Hafler amps but currently am using two of them with the Musical Concepts PA-3B circuit card mods and power supply cap upgrades. The MC mods are great, come in kit form, and have excellent installation instructions.

About your pre-amp question. What do you need to pre amplify? Are you still spinning vinyl? Most CD players have sufficient output to directly drive most amps to full power. Many find that all they need is a passive stereo line control center. The main criteria for this device being successful are short low capacitance interconnects, a quality selector switch and a volume control potentiometer that leaves little sonic signature on the signal.

Hope this helps.
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Old 29th January 2005, 01:30 PM   #69
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Default Question for djk

djk,

I have a pair of devices that sure look like a thermistor. On each are the letters and numbers:

KKK
C30-18

and they measure 2-3 ohms resistance cold.

Are these the CL30 you and others recommend. Mine don't have the "L" in their description but I assume they are the same thing. Am I correct?

Thanks.....
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Old 29th January 2005, 01:41 PM   #70
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Default XL-280 transformer question

As long as we are doing some thread hijacking please permit me to ask a question about the XL-280 Hafler amp.

I have a pair of power supply transformers that were used in the Dynaco ST-150 and ST-300 amplifiers, both solid state amplifiers. They are a little larger than the stock XL-280 transformer and weigh a little more and info I read about them in an old Audio Amateur issue indicates they have an equal if not larger VA rating.

These Dynaco center tapped transformers have a booster winding to provide either 50 VDC or 70 VDC +/-.

I would like to make a dual mono pair of XL-280 mono amps and have the parts and chasses to do so. What I lack is the 2nd XL-280 transformer. How about using these Dynaco transformers? I can drive their circuit cards with 70 VDC but what happens if I drive the output MOSFETs with only 50 VDC?

Will I only just observe a reduction in power because of the reduction in voltage from 65 to 50 VDC? If so, I can accept this. But, will the differential between the designed 65 and my 50 VDC create a problem when working with the circuit card driven at 70 VDC?

Thanks for your help.
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