Bought this as not working and has been modified . Someone has had a go at fixing this but thats the only info i have . The mods consist of bigger supply caps changed from 4x 4,700uf to 22,000uf 😱 the rectifier package on the pcb has been removed and replaced by a another one attached to the heatsink
the fuses x4 where moved to the back of the pcb and most of the capacitors have been swapped out for panasonic fc then bypassed with film caps under the pcb .
the case alone is worth what i payed for it not to mention the Eichmann Cablepods on the back 🙂. On powering it up after a few seconds the relay for the speaker output clicked in so i connected my stunt speakers and although the source selector and volume control worked on the lcd display nothing from the speakers .
Checked the 2x big transformers all ok 2x 20v. the front display lcd and input selector relays are fed from a small transformer on the front panel pcb .
So the big transformers just power the output . Decided to remove the pcb to investigate further see pics . Removed the 4x supply caps and removed the output mosfets on the heatsink which all tested ok . removed the fuse holders and put them back on top of the pcb .
After studying the board i noticed a voltage regulator was missing i traced the tracks to a PGA2311 volume control chip on the back of the pcb after looking at the data sheet of the ic i found out it needs a +/- 5volt supply so i have replaced with new + and - 5v regs .
I have probed most of the components with my component tester on my Hameg hm605 oscilloscope and none where short all looks good .
I am hoping its just the supply to the PGA2311 and thats it 😉. What i would like to know is am i better to replace the main power supply caps with 4,700uf original caps as the 22,000uf wont fit now i have moved the fuse holders back didnt want to leave them under the pcb as it needs to be removed to replace fuses.
Looking at the build quality of the amp i dont think they used 4,700uf to save money ! Whats your thoughts on that ?
here are the pics....
the fuses x4 where moved to the back of the pcb and most of the capacitors have been swapped out for panasonic fc then bypassed with film caps under the pcb .
the case alone is worth what i payed for it not to mention the Eichmann Cablepods on the back 🙂. On powering it up after a few seconds the relay for the speaker output clicked in so i connected my stunt speakers and although the source selector and volume control worked on the lcd display nothing from the speakers .
Checked the 2x big transformers all ok 2x 20v. the front display lcd and input selector relays are fed from a small transformer on the front panel pcb .
So the big transformers just power the output . Decided to remove the pcb to investigate further see pics . Removed the 4x supply caps and removed the output mosfets on the heatsink which all tested ok . removed the fuse holders and put them back on top of the pcb .
After studying the board i noticed a voltage regulator was missing i traced the tracks to a PGA2311 volume control chip on the back of the pcb after looking at the data sheet of the ic i found out it needs a +/- 5volt supply so i have replaced with new + and - 5v regs .
I have probed most of the components with my component tester on my Hameg hm605 oscilloscope and none where short all looks good .
I am hoping its just the supply to the PGA2311 and thats it 😉. What i would like to know is am i better to replace the main power supply caps with 4,700uf original caps as the 22,000uf wont fit now i have moved the fuse holders back didnt want to leave them under the pcb as it needs to be removed to replace fuses.
Looking at the build quality of the amp i dont think they used 4,700uf to save money ! Whats your thoughts on that ?
here are the pics....
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
this is all i could find on google same amp but different bias setup
An externally hosted image should be here but it was not working when we last tested it.
You can't really go wrong by restoring the original spec. components though it may now be possible to use similar quality (check ripple current rating is higher) 10,000uF electrolytics that are small enough to fit in the same location, if that's what you want to do.
I would also test the power mosfets for proper function whilst they are out of circuit. Goodness knows how much damage unwise audiophool mods can do to amplifiers - often to parts that don't show any damage externally, like semis.
http://www.firstwatt.com/pdf/art_mos_test.pdf
I would also test the power mosfets for proper function whilst they are out of circuit. Goodness knows how much damage unwise audiophool mods can do to amplifiers - often to parts that don't show any damage externally, like semis.
http://www.firstwatt.com/pdf/art_mos_test.pdf
And take the opportunity to replace that bridge rectifier with a fresh one and use proper blade connectors rather than that messy soldering job!
Thought while i am waiting for my caps to be delivered i would check the mains wiring 😱 really glad i did the transformers have been shielded with copper foil tape and are connected to iec earth but i can live with that the blue cable supplies mains to the 3 transformers via the connector on the front panel pcb which turned out to be 3x 0.5mm silver wire individually insulated the spades just pulled of the ends 😕
also the transformer mains input wires black & white had gaffa tape wrapped around so i thought it was a cable join cut it off and it was just foil with a fiber backing under the gaffa tape no joins ! 😵 ( what kind of snake oil is this ) everything added has now been removed except the copper screening on the transformers will re wire with suitable cable .
also the transformer mains input wires black & white had gaffa tape wrapped around so i thought it was a cable join cut it off and it was just foil with a fiber backing under the gaffa tape no joins ! 😵 ( what kind of snake oil is this ) everything added has now been removed except the copper screening on the transformers will re wire with suitable cable .
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Sadly, that's the sort of mess of crazy audiophool ideas that many newbies are suckered into. You're on the right path to getting back to a safe, working state though. Thanks for the pics - they sure give us some appreciation of the problems.I just can't understand why people believe the upgrading nonsense they read on the 'net enough to pay money for snake oil parts and wires but screw up their amplifiers in the process due to lack of skills or at least some electronics savvy.
it would take a day to make a thread on all the snake oil products that we have come across in our lives, I think there is a way to laugh a lot.
@Glennjarrett
there is a cairn 4808 out of order for sale on an ad site in France (70 €) if you want, I pass you the link.
@Glennjarrett
there is a cairn 4808 out of order for sale on an ad site in France (70 €) if you want, I pass you the link.
Ended up changing the rectifier and the output devices just in case of any stress
as they where very tightly fixed 😱
first power on through a 100w light bulb got a qick glow then went out 😀
everything cool even the main heatsink
now listening to a bit of Dub Syndicate
to say its got 4x new power supply caps and output transistors it sounds bloody awsome through my stunt speakers
cant wait for it to bed in .
I have no idea what the bias should be set at and cant find any information on the web
is there a trick you can do to find out what it should be ?
as they where very tightly fixed 😱
first power on through a 100w light bulb got a qick glow then went out 😀
everything cool even the main heatsink
now listening to a bit of Dub Syndicate
to say its got 4x new power supply caps and output transistors it sounds bloody awsome through my stunt speakers
cant wait for it to bed in .
I have no idea what the bias should be set at and cant find any information on the web
is there a trick you can do to find out what it should be ?
An externally hosted image should be here but it was not working when we last tested it.
20190729_125148 by glenn jarrett, on Flickr
An externally hosted image should be here but it was not working when we last tested it.
20190729_135325 by glenn jarrett, on Flickr
I also have this amplifier model in not working condition (damaged output power devices - I think MOSFET's).
Unfortunately I don't find the schematic on the web.
I try to order it approximately 15 years ago without any reply.
short form datasheet is here:
Cairn • Ezo
Cairn • Ezo
The manufacturer don't longer exist or under an other naming
Who can upload the schematic ?
Please note - this amplifier don't use any DC speaker protection and runs very hot in cases of working condition.
Unfortunately I don't find the schematic on the web.
I try to order it approximately 15 years ago without any reply.
short form datasheet is here:
Cairn • Ezo
Cairn • Ezo
The manufacturer don't longer exist or under an other naming
Who can upload the schematic ?
Please note - this amplifier don't use any DC speaker protection and runs very hot in cases of working condition.
I had assumed this was a class AB amp by the size of the heatsink so even though the heatsink is substantial, in class A it would run quite hot with (lets assume from a rectified 20+20VAC supply) +/- 28VDC rails. That would probably permit 25W in classA and require about 3.5A bias to cover the peak current requirement. It would also need a much larger heatsink than we see in the images. About 0.15 degrees/watt would be more like it and that is a large heatsink, about 5 times what is now fitted.
I think instead, that this is a high bias class AB design and perhaps you could measure what the bias current actually is now, before adjustment, and post it if you wouldn't mind.
I was the primary, actually the only one, responsible for repairing these buggers in Norway.
Something like 15 years ago.
I have a comprehensive set of schematics.
They utilize IRFP150 / 9140 as output devices.
Regards
R
Something like 15 years ago.
I have a comprehensive set of schematics.
They utilize IRFP150 / 9140 as output devices.
Regards
R
Hi RM
you have the schematic
i cant find anything on the web about it apart from a few reviews
I would be very grateful if you could let me have a copy of the schematics or let me know what the correct bias should be
Kind regards Glenn
ps i will pm you my email address
you have the schematic
i cant find anything on the web about it apart from a few reviews
I would be very grateful if you could let me have a copy of the schematics or let me know what the correct bias should be
Kind regards Glenn
ps i will pm you my email address
Hello,
Because my cairn failed, I 'll be interested to get schematic from 4808 NF & A versions
Best regards
Trevyse
Because my cairn failed, I 'll be interested to get schematic from 4808 NF & A versions
Best regards
Trevyse
Hi, I bought cairn K2, and something happens to my cairn, do you have the schematic?, Can you send to my email guntech88@gmail.com?, Sorry for my english,Thank you
Hi RM, I would greatly appreciate if you send me the Cairn 4808 schematics. I have one but it is incorrect. Please send it to: m_cendoya@yahoo.com.
Regards,
Marcelo.
Ciao RM
Ho in riparazione un Cayrn
4808A di un mio amico,
potrest postarmi lo schema
e il valore di bias al mio indirizzo
carsol@alice.it
Ho in riparazione un Cayrn
4808A di un mio amico,
potrest postarmi lo schema
e il valore di bias al mio indirizzo
carsol@alice.it