Cambridge Audio A3i Relay

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BradNad

Member
Joined 2006
The output relay on my Cambridge A3i is on its way out. It lies at the back of the power amp board near the speaker outputs.

It has Cambridge Audio on it. Does anyone know which relay would work? It looks to have four soldering tails and switches both left and right channel on and off and forms part of the muting and speaker protection circuit.
 
O

OXAUDIO

Member
Joined 2006
Relay in Cambridge Audio A3i

The relay coil has a DC resistance of ca. 1000 Ohms(in an A3i that I'm in process of repairing at least) and is a DPCO type. Most Component suppliers should stock a suitable device, although I haven't checked, and it will probably cost less from the likes of RS, CPC, Maplin, Radio Shack, etc., than the 'official' spare part from Cambridge Audio(if it's still available from them!) A Maplin store near to where you live may stock a suitable relay.
 
x-pro

x-pro

Member
Joined 2003
ant-audio.co.uk
BradNad said:
However, the amp got very hot and went bang a few months ago, and does not even power up anymore.

I have owned 2 A3i's, and both of them ended up doing this.
Click to expand...

Unfortunately, the build and some components quality were really poor, plus the original circuit was designed to be 40 W amplifier and than by a management decision was promoted to 60W just by increasing the supply voltage. Two things combined made for a poor reliability. I can supply you the circuit diagrams for A3i plus some suggestions how to improve it - in a little while. I've purchased an old A3i from ebay recently to rebuild and modify it, so I could publish an update guide on the web. The circuit in that amp is quite capable and uniquie, so I thought that I should do this update for my old design.

Cheers

Alex
 
O

OXAUDIO

Member
Joined 2006
x-pro said:


Unfortunately, the build and some components quality were really poor, plus the original circuit was designed to be 40 W amplifier and than by a management decision was promoted to 60W just by increasing the supply voltage. Two things combined made for a poor reliability. I can supply you the circuit diagrams for A3i plus some suggestions how to improve it - in a little while. I've purchased an old A3i from ebay recently to rebuild and modify it, so I could publish an update guide on the web. The circuit in that amp is quite capable and uniquie, so I thought that I should do this update for my old design.

Cheers

Alex
Click to expand...

21/04/08 4.06PM GMT

Alex,
Would you mind supplying me with a circuit diagram, and any other useful information on the A3i. I am in the process of repairing one in which Q14(2SA1216) had failed(Base/Collector s/c). Having replaced both O/P Transistors in that channel, and checked other components, I find that, after a few minutes, the relay trips out, the centre rail rises to ca. +26v, and LED2 goes out. Would I be correct in thinking that Q7 & Q8 are at fault, and, if so, with what should I relpace Q7? The type No. looks like ZVB330 to me, and that's not in any Data Book I have.
Incidentally on all the PCBs in the A3i which I have it states 'Copyright Michael Creek, 1996'
 
x-pro

x-pro

Member
Joined 2003
ant-audio.co.uk
OXAUDIO said:


21/04/08 4.06PM GMT

Alex,
Would you mind supplying me with a circuit diagram, and any other useful information on the A3i. I am in the process of repairing one in which Q14(2SA1216) had failed(Base/Collector s/c). Having replaced both O/P Transistors in that channel, and checked other components, I find that, after a few minutes, the relay trips out, the centre rail rises to ca. +26v, and LED2 goes out. Would I be correct in thinking that Q7 & Q8 are at fault, and, if so, with what should I relpace Q7? The type No. looks like ZVB330 to me, and that's not in any Data Book I have.
Click to expand...

Hi,

I've emailed you through the forum and on reply will send you the diagrams. Most likely the LED2 itself is at fault - just replace it first with a good quality green LED, lifting it at least 15 mm of the PCB. Mind the polarity! If it is the transistor (also possible, thought less likely) the correct type is ZVP3306A from Zetex, available from Farnell:

http://uk.farnell.com/9524851/semiconductors/product.us0?sku=ZETEX-ZVP3306A

OXAUDIO said:
Incidentally on all the PCBs in the A3i which I have it states 'Copyright Michael Creek, 1996'
Click to expand...

In 1996 I was working for Creek Audio and Michael was my boss :) . That does not change the fact that I've designed all electronics in that amp, including the PCB layout.

Cheers

Alex
 
O

OXAUDIO

Member
Joined 2006
Cambridge Audio A3i Schematics

Alex.
Thanks for your prompt reply and the info. re Q7. I have now downloaded the diagrams, which, with your advice, should help me to get the amp. working again. It seems, from reading other posts on this forum, that these amps have been prone to failure, due mainly to poor build quality and (sometimes) poor components, so I will recheck everything carefully.
Michael('OXAUDIO')
 
homemodder

homemodder

Disabled Account
Joined 2006
Hi X-pro

Ive seen your thread on the mosfet vas, and played around in it with in lt spice. Very interesting topology with good results congrats. i dont have much experience with spice yet( learning now) and would like to ask if you have spice models on the mosfets(zvp3306 or zvp3310). I tried using the models from zetex but they dont seem to work with lt spice.

Thanks
Alexandre (also call me Alex)
 
O

OXAUDIO

Member
Joined 2006
x-pro said:


Hi,

I've emailed you through the forum and on reply will send you the diagrams. Most likely the LED2 itself is at fault - just replace it first with a good quality green LED, lifting it at least 15 mm of the PCB. Mind the polarity! If it is the transistor (also possible, thought less likely) the correct type is ZVP3306A from Zetex, available from Farnell:

http://uk.farnell.com/9524851/semiconductors/product.us0?sku=ZETEX-ZVP3306A



In 1996 I was working for Creek Audio and Michael was my boss :) . That does not change the fact that I've designed all electronics in that amp, including the PCB layout.

Cheers

Alex
Click to expand...

I have now completed the repair to the A3i. LED2 was indeed faulty, and, having replaced it(with an orange LED incidentally- I didn't have any suitable green ones to hand), set the bias so that there is ca -1.2v at the collector of Q10, then test run the amp., first with no signal applied, for maybe 30 to 40 minutes, then for 2 or 3 hours continuously playing music of various types and at varoius volume settings, without any further problems.
Forgive my possible ignorance, but does the LED HAVE to be green? The orange one seems, so far, to be OK.
 
x-pro

x-pro

Member
Joined 2003
ant-audio.co.uk
homemodder said:
Hi X-pro

I would like to ask if you have spice models on the mosfets(zvp3306 or zvp3310). I tried using the models from zetex but they dont seem to work with lt spice.
Click to expand...

Sorry, no, I don't have these models.


OXAUDIO said:
Forgive my possible ignorance, but does the LED HAVE to be green? The orange one seems, so far, to be OK.
Click to expand...

Good to know that the amp works. Green colour is important only because of the voltage drop on the LED. For green it is about 2V. On an orange LED the drop could be a bit less. Measure the difference - if it is only 100-150 mV than you probably can get away with this.

Cheers

Alex
 
G

gigimagnat

Member
Joined 2015
hello dear friends
i am new here and i don t write english very well so excuse me if i make mistakes
i am from hungary and i buils a lot of hifi audio kit
and for the moment i buy from a car boot sale an cambridge a3i with a lot off faults
one channel works perfect
one channel give a hum like tunning radio stations
volume button doesen t close the volume totaly
on the pre board with the input connectors is a small green LED .it should be on?or off
here in this amplifier is off
i found the led 2 unsolder on the power board
i fix it ..still radio noise in speaker but the amplifier works loud but not clear and after 1 min or 30 sec relay click off and after on after 10 sec random
i change the capacitors with some denon 12000 up 63 volts
it s ok
what i should change there?
or somebody have time to fix it?
change all the components with good new components
contact me if someone is interested
here is my first amplifier build in 1987
very simple and sound greatif you make the voltage higher 50 volts you can get 80 watts per channel
simply great
thanks
waiting for an answer or solution
 
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