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Old 8th January 2011, 06:07 PM   #1
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Default My latest project - 60w per channel amp (just pics)

After languishing in my project box for about 2 years, I finally got around to building this amp, based on two modules bought off that well known auction site.

My original intention was to make these into mono blocks, and I'm still undecided about doing that. As it stands here, it's built into a Cambridge A5 chassis that I had (amp was blown).

I still have some work to do, such as fitting some snubber caps across the rectifiers, and also some additional filtering on the PSU. I also have a set of four matched caps to replace the 'prototypes' you see here.

The sound is very good, which doesn't surprise me, as I believe these amps were based on a Musical Fidelity design.

I may also look at reducing the overall gain, as it currently seems a bit high when used with a preamp. This may or may not be a good thing..

All comments (bad or good!) welcome.
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File Type: jpg Power-Amp-Overall.jpg (775.8 KB, 583 views)
File Type: jpg Power-Amp-boards.jpg (686.7 KB, 519 views)
File Type: jpg MX50X2-02.jpg (39.1 KB, 533 views)
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Old 8th January 2011, 09:56 PM   #2
jaycee is offline jaycee  United Kingdom
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Looks good The problem with the Cambridge amps can be seen easily - that heatsink is rubbish and the Sanken SAP transistors used in the circuit blow up due to overheating.

I'd neaten up the power wiring a bit. The best thing to do is to twist together the +V, -V and GND wires and run them back to the psu. This keeps interference down. I'd use some screened cable for your signal inputs too.
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Old 8th January 2011, 10:49 PM   #3
Join Date: Jan 2005
Yes those heatsinks made from a thin aluminum plate and folded aluminum/steel sheet are the worst heatsinks you can find!! I HATE HATE HATE them!!
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Old 9th January 2011, 08:58 AM   #4
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Yes I had planned to tidy up the wiring. I used some quite thick 42 strand cable, and it's quite unmanageable really. I need to use something thinner I think.

And those heatsinks... yes, I know they are rubbish, and again I am looking to replace them. As I'm still undecided about whether or not to make this into monoblocks, I haven't yet decided which heatsinks to go for.
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Old 20th January 2013, 02:24 PM   #5
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Default Amp now has a new home.

As of this weekend, the project now has a new home.

A Rotel RB-956AX 6 channel amp gave up it's life for the cause

My first chassis (A Cambridge A5) used the Cambridge heat sinks which were grossly inadequate.

After some searching, I concluded that one of the Rotel power amps would have suitable heat sinks, and when the 956AX came up on Ebay at a good price, I bought it. After having listened through it for a few days, I decided it wouldn't be too much of a travesty if i used it for spares.

I had to bend the legs of the transistors to make them into the original Rotel heat sink holes, as I was reluctant to drill the heat sink - also the bolt holes in the transistors didn't line up with the spaces between the fins (so I would have needed to move the transistors anyway), so that was what prompted me to simply relocate the transistors. It doesn't look nice, but so what?

I also have 2 Cambridge A5 mains transformers that I was going to use for this - however, the Rotel has a rather large toroidal (24-0-24 Vac) which is pretty much perfect for these amps, given that my speakers are 4 ohms.

On our slightly high mains here, I'm seeing about 36-0-36 Vdc.

I also used the original Rotel rectifiers and smoothing caps (6800uF 50v Rubycon), which has kept the PSU nice and simple. There are 3 individual secondary windings (each 24-0-24) on the transformer, and the PSUs are completely separate from each other - so this is essentially 2 monoblocks in one box.

Even playing at relatively highish levels, the heat sinks now remain cold (perhaps too cold!).

So on to the pictures.
Attached Images
File Type: jpg P1010369.JPG (170.0 KB, 305 views)
File Type: jpg P1010371.JPG (149.4 KB, 257 views)
File Type: jpg P1010374.JPG (142.9 KB, 175 views)
File Type: jpg P1010375.JPG (149.9 KB, 148 views)
File Type: jpg P1010378.JPG (142.3 KB, 130 views)
File Type: jpg P1010379.JPG (99.3 KB, 118 views)
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