Hi Roclite ,
This is regarding about my previous question about the relay on this board, I forgot that the original version of this does not have relay.
My version of this amp have 2 relays connected in parallel and when I power up the amp , there is about 5 second delay until the replay is engaged .
I think my version of this amp have built in DC speaker protection too. But I can't confirm it. ANd I ODn't wanna test it , It is running fine right now , Except that I have to replace the 2 separate cheap small EI transformer that I added for the protection circuit with a small toroidal transformer , Because they are making mechanical noise . This is DIY audio life 🙂
Thanks
This is regarding about my previous question about the relay on this board, I forgot that the original version of this does not have relay.
My version of this amp have 2 relays connected in parallel and when I power up the amp , there is about 5 second delay until the replay is engaged .
I think my version of this amp have built in DC speaker protection too. But I can't confirm it. ANd I ODn't wanna test it , It is running fine right now , Except that I have to replace the 2 separate cheap small EI transformer that I added for the protection circuit with a small toroidal transformer , Because they are making mechanical noise . This is DIY audio life 🙂
Thanks
Hi Marchel, your later version of the board will have DC and short-circuit protection with its on-board relays. The circuit diagram here is only for first version of PR800. Hope the transformer change goes well and the amplifier sounds great.
Here, almost finished. It was left in the case to install ...
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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.
Pr-800 bias settings help
I don't know why I built this amplifier. Have many much better more exspensive. I am a bit afraid of using it. There is no bias at all. Can anybody tell me if I should turn potentiometer clockwise or anticlockwise to raise bias? Thought this could be used as subwoofer amplifier. Should I add series capacitors at output? In that case how many uf and volt?
I built a pair of monoblocks with these and they're great. I didn't use an output cap but i did use a speaker protection board ust to be sure. I biassed mine by using a multimeter on the +ve rail, trimming the pot untiul it drew 36ma with no input and speakers disconnected. Be careful with the input, mine went straight to a transistor base and needed a tantalum capacitor on the input.
I will add a Muse at the input then. I think the low voltage I use for it 2x56 vdc is the culprit why there is no bias.
What do you mean by 'no bias'?
I used + / - 55v with mine with no trouble. You need to add a 2nd supply for the bias / protection circuit. it's +12v off the negative supply which can be a problem when you also need +12v off the 0v rail too for your speaker protection board. So my power supply gave -55v, -43v, 0v, +12v, +55v. The -43v went to the bias / protection rail (+12v from the -ve supply).
Cheapest option for me was to buy 2 x the chaepest 12v switch mode ($5) psu and use them to power the bias rail (ov tied to -ve rail of main psu) and the speaker protection board (0V tied to main PSU rail).
If you avoid earth loops it sounds sweet.
I used + / - 55v with mine with no trouble. You need to add a 2nd supply for the bias / protection circuit. it's +12v off the negative supply which can be a problem when you also need +12v off the 0v rail too for your speaker protection board. So my power supply gave -55v, -43v, 0v, +12v, +55v. The -43v went to the bias / protection rail (+12v from the -ve supply).
Cheapest option for me was to buy 2 x the chaepest 12v switch mode ($5) psu and use them to power the bias rail (ov tied to -ve rail of main psu) and the speaker protection board (0V tied to main PSU rail).
If you avoid earth loops it sounds sweet.
I have12 vac for each PR 800 allready. What I mean by bias is that the amp is totally cold and does not draw any Question current . I have tried to turn up the bias at the potentiometer.
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Had to have seperate transformers for each channel. Common ground did not work. Now I use 2x 50 vac transformer and it works. Had to turn the potentiometer almost totally clockwise to get bias. Waiting for transformer for other channel to arrive in 2 weeks from Toroidy.
I'm really interested in your reply, i have maybe been running mine 'cold' all along. They're a great amp but they didn't sound as loud as they should have. I didn't have an issue with common ground as i built mine as monoblocks. How did you measure the bias or did you do it by ear / temperature?