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PR-800 ClassA/AB Amplifier Kit
PR-800 ClassA/AB Amplifier Kit
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Old 13th August 2017, 01:41 AM   #51
xextriz is offline xextriz  United States
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Join Date: Aug 2017
Hi,

I'm very interested in building an amplifier for a sound system I'm going to put together the next couple months or so. Would you be willing to provide a parts list of what is needed in addition to the PR-800? i'll be doing the same set up, a pair for 2 channels to 2 speakers. Thanks!
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Old 1st September 2017, 07:21 PM   #52
SwitchDoctor is offline SwitchDoctor
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Join Date: Apr 2017
Default Additional components

In addition to the amplifier modules themselves (one per channel);
You'll need a +- 55v power supply.
Speaker protection boards (ebay <5)
Output capacitors 10,000 uf 300v (one per channel)
A 12v power supply for the bias input


For the power supplies i used:
35-0 35-0 torroid 300VA
2 x bridge rectifier
2 x 10,000 uf 100v capacitors for smoothing
4 x 4uf capacitors for smoothinh
2 x 100nf capacitors for smoothing

12-0 12-0 torroid 15w for the bias and speaker protection
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Old 5th October 2017, 12:11 PM   #53
MusicSeeker is offline MusicSeeker  France
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Join Date: Jul 2010
Hello guys

Thank you Roclite for the schematics. I was also pissed off by the need of this extra transformer. After checking your schematic, I decided to add a resistor between GND and the anode of D5. Any value in the 1 to 10 Kohm does the result : the amp now works with its normal +V/GND/V- supply only. Is what I have done is correct and safe in the long run ?

Thanks
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Old 15th October 2017, 12:20 PM   #54
SwitchDoctor is offline SwitchDoctor
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I would advise using a separate bias supply. It only needs to be a small VA transformer and i used the 2nd winding from a 12-0-12 bias transformer to power my speaker protection circuit. That way the speakers shut off quickly without waiting for the main rail with it's huge smoothing caps to colapse.
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Old 8th March 2018, 09:55 PM   #55
marchel is offline marchel
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Join Date: Nov 2007
Hi , I just finished building a retrofit of this amp into an old amplifier chassis that has dual power transformer , I read that this have a over current protection. My Questions are :

1. Does this also have output short circuit protection?

2. Do the relay with it's corresponding circuit offer DC speaker protection in case of amplifier failure?

Thanks
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Old 9th March 2018, 04:10 PM   #56
roclite is offline roclite  United Kingdom
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Join Date: Dec 2011
Location: Middlesex
PR-800 ClassA/AB Amplifier Kit
Hi Marchel,
If you check the published schematic in previous post, PR800 has an output stage current detection circuit around PRO+/PRO- connected to an SCR latch U1. When the SCR is latched by an over-current condition, Q7 CCS is turned off and the amplifier shuts down until power is reset. This circuit has proven to be problematic for some users. I still don't see the need for the separate transformer power supply and a simple resistor bias circuit as described by musicseeker would probably be ok. I think the existing circuit is much more about ripple reduction for the CCS as the main power supply capacitors will remain charged regardless of how the SCR is tripped, discharging when the amplifier is in fault condition. Any additional speaker protection relay circuit should provide full speaker protection as it is normally tripped by DC detection on the amplifier outputs.
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Old 10th March 2018, 09:26 AM   #57
marchel is offline marchel
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HI roclite ,
Thank you for your reply , But I'm still not sure whether this amp have a short circuit protection , Meaning if I accidentally shorted the output wires , The Amp won't burn , That's what I wanted to know without learning the hard way

BTW , This is my amplifier , It is an updated version with 2 x 10,000uf elna caps. instead of the 4 caps in the original version of the pr-800 board, I use my old Onkyo M504 chassis and transformers , I just finished it and playing some tunes in my test music system as of this writing.

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Old 10th March 2018, 09:51 AM   #58
roclite is offline roclite  United Kingdom
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Location: Middlesex
PR-800 ClassA/AB Amplifier Kit
Hi Marchel,
Great job on your amp!.The PR800 on-board over-current detection should protect the amplifier from output short-circuit but I have never tested it or even powered up the amplifier. Hopefully, someone can confirm that the circuit works effectively, having tested or experienced this on their own amplifier.
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Old 10th March 2018, 09:58 AM   #59
marchel is offline marchel
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Hi , Finally you said it that it should have a short circuit protection ,But I will not test it though Thanks
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Old 10th March 2018, 12:03 PM   #60
andrewlebon is offline andrewlebon  India
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Hello roclite
greetings is it possible to share the over current detection schematic part

warm regards
Andrew
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"It's Better to try and fail than to never know and always wonder"
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