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Old 30th August 2006, 07:12 PM   #1
latala is offline latala  United Kingdom
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Default Cambridge amp

I have an Cambridge audio A1 made in 1995 this has blown the right channal.
The output devices are 2n3055/2955 has any one got a circuit of the power amp as a lot of reistors etc have burnt out!
As ever i like to have as much info as possible before I attempt a repair
Regards Trev
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Old 31st August 2006, 07:08 AM   #2
latala is offline latala  United Kingdom
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Well the amp has now been taken apart The output devices are shot 3055/2955 as well as the drivers ?/?. Can any one recommend replacement devices for both output and drivers.
Supply is +/- 30 volts .
I feel this is an opportunity to upgrade this amp !
In anticipation
Regards Trev
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Old 31st August 2006, 07:36 AM   #3
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If you search on here I'm 99.9% sure I have seen the schematic posted as well as do's and don't for upgrades on that exact amp. You could run into stability problems if you put 'upgraded' output devices in.
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Old 31st August 2006, 07:54 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
the 2n3055 come in different versions which have different characteristics.
Similarly, different suppliers (smaller companies & fakes) may not reach the published specs from the big reputable manufacturers.

The 3055 was a slow, low gain, low voltage output device. Take care to replicate these characteristics.
The gain is possibly the least sensitive of these. You may improve performance, very slightly, by selecting a higher gain device that maintains a more linear gain characteristic over a wider range of operating currents.
A higher voltage device could be substituted but high voltage is usually designed in at the expense of some other characteristic, be careful.
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Old 31st August 2006, 09:51 AM   #5
latala is offline latala  United Kingdom
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I have spent at least 30 mins on two occasions looking on the site for any thing that refers to this amp but I have found no info! So any help will be appreciated.
Mainly with regards to decent output and driver transistors as the amp is a reasonable simple affair.
I would like to know what are consisdered the best devices in the sub 50 watt 8ohm class of amp.
regards Trev
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Old 31st August 2006, 10:27 AM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
2n3055 will do the job.
Changing the specs raises the possibility of the amp going wrong.
Quote:
You could run into stability problems if you put 'upgraded' output devices in
Just check which TYPE of 3055 you currently have.
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Old 1st September 2006, 01:19 PM   #7
clem_o is offline clem_o  Philippines
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Yep, it would be hard to find modern transistors as slow as the '3055... getting modern, admittedly more linear devices may just open up the amp bandwidth - you could wind up blowing the outputs, or your loudspeaker's tweeters...

Cheers!
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Old 1st September 2006, 01:51 PM   #8
MikeW is offline MikeW  United States
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You should be able to get them fom On semi.
http://www.onsemi.com/PowerSolutions/home.do
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Old 1st September 2006, 10:21 PM   #9
latala is offline latala  United Kingdom
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The whole idea is to extend the amplifier bandwidth and linearity etc
I have full facilities ie oscillators ,scopes distortion analysers etc.
I have asked this question as I am not up to speed on the latest devices available ! I want to find what are the flavour of the month at this moment?
My idea is to modify the dead channel and then compare it with the existing channel.
So please give me your suggestions
Circuit topology seams to be an npn diff pair fed via a two transistor current source
the output is then fed into a PNP driver that has a two transistor constant current load
Output stage isa pair of fully complimentary emitter followers.
protection is the normal type of complimetary transistors that monitor the emitter current of the output devices and then divert the drive current if required
Regards Trev
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Old 1st September 2006, 11:52 PM   #10
clem_o is offline clem_o  Philippines
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Oh, then perhaps you can look at the outputs used on the SymAsym - several have tried this amp designed by MikeB, and like it:

http://www.lf-pro.net/mbittner/Sym5_...ymasym5_3.html


Several DIYrs have also tried other output transistors on the same amp, but you'll have to hunt it down in a rather long thread:

Explendid amplifier designed by Michael Bittner, our MikeB
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