best way of applying amplifier protection for both power supply and speaker's ?? - Page 1
Forum section: electronics / beginners

author: paulflan79
author_rank: Newbie
timestamp: November 16, 2018, 12:17:35 am
content: In the true spirit of reusing salvaged part's on a budget project I've stripped down a non working Onkyo TX-875 with a dead HDMI board plus other issues due to the regulator's set to high and the heat from the amplifier cooking the small capacitor's, So i've salvaged the power supply and power amplifier module as a hole unit to reuse removing all the logic control board's and everything else to hopefully use with another preamp as a multi-channel power amp,I've got it now working for testing purposes, It's got the main's input for the transformer and then 2 pairs of relay's for the two secondary winding's for B+/B- that go's onto power the amplifier, I've also found and checked the 7 line level input's with another preamp and also the 7 speaker output's and it all work's fineAnd here come's the bit i need help, support and guidance with....here's a link to the full service manual however i'm only really using the part's shown on pages 14 to 19 and removed everything else that was just to complex for me to work with just leaving me with the power supply and main power amplifier which is quite a beast,https://www.manualslib.com/manual/1064234/Onkyo-Tx-Sr875.html?page=15#manualthe amplifier is made up of 7 identical driver board's, one for each channel driving 2 2sa1962 and 2 2sc5242 providing 140W RMS into 8 ohm's each so that's 28 genuine Toshiba output transistor's and a huge high current power supply with 2 separate B+/B- secondary winding's and appear's to be easily salvaged and reused as i've already got it working under basic test conditions just powering the main transformer and a couple of relay's however now it has no protection circuit what so ever just a bunch of 12v relay's i need to control for power and speaker output's,So that's my challenge to make this beast of an amplifier safe to use,there are sense lines on each channel called IPRO (current sensing ?) VPRO (voltage sensing ?) and VOLH however im unsure of how to make use of them hence me asking hearhere you will find pic's of the amplifier stages taken from the service manual showing you the circuit layout of each channel as there just duplicated 7 times across the huge heat sinkhere's the driver board..https://www.dropbox.com/s/ngkt81vhy2gphu1/Onkyo%20TX-875%20Amp%20Driver%20Board.png?dl=0here's how the main output transistor circuit is laid outhttps://www.dropbox.com/s/l758lcp3dedfnl9/Onkyo%20TX-875%20Power%20Amp%20transistors%202SC5242%20%26%202SA1962%20layout%20board.png?dl=0and here's two more showing where the IPRO, VPRO and VOLH sense lines goto before leaving the board and going to the microprocessor with no longer exist's in the circuit,https://www.dropbox.com/s/wrcdfp5bx1lj0y0/Onkyo%20TX-875%20Power%20Supply%20and%20protection%20board%201.png?dl=0https://www.dropbox.com/s/amml26symaoumpf/Onkyo%20TX-875%20protection%20IPRO%2C%20VPRO%20%26%20VOLH.png?dl=0Now is there anyway i can reuse them sense lines and relay's to implement my own effective protection circuit for the power supply and speaker's controlling the 12v relay's already present in the amplifier please ??This is just as much about learning and personal development and setting myself a challenge as it is about finding a solution, eBay is full of cheap Chinese board's for speaker protection and there's already fuses in the main's plug and on each secondary winding of the power supply,one last thing, do you think one driver board would drive two channel's of main output transistor's (4 pair's of 2sa1962 / 2sc5242) in parallel for more current for driving 4 ohm's load please as i want to modify 2 channel's to drive a single 4 ohm 500W RMS subwooferso please any help, support and guidance to better understand how to best apply the protection circuit and possibly modify this beast would be gratefully received,Cheer's

author: paulflan79
author_rank: Newbie
timestamp: November 16, 2018, 01:25:09 pm
content: Think i'm just going to settle for fuses in the power supply and standard DC speaker protection board's you get cheap from china in order to use it safely, seem's to work well for some of the biggest names in amplifiers and it get's the job done,is there any boards out there that are better than other's worth getting over the rest or are they pretty much all the same please ?