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Old 22nd March 2005, 10:19 PM   #1
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Default My Amp Project (pictures for all to see)

So far I have only used these pages to search for info I have needed or to ask questions. So I thought I would post info on some of my current (no pun intended) amp project.

I managed to get 2 faulty Cambridge Audio A1 amps from Ebay for not a lot of money. Both had faults that were very simple to fix. One had a transformer with a blown primary and I already had a 300VA transformer scrapped from some telecoms equipment. The other had blown output transistors on one channel. These were 3055 and 2955 transistors which I bought new ones for about 80 pence each.

I removed the preamp sections from the amps and just used the poweramp boards which I modified to suit a split PSU so all 4 seperate rails (+ & - for each channel) had there own 4700uf caps. These were fed by 2 more 4700uf caps through 0.22 ohm resistors to form low pass filters. As you can see I made the bridge rectifier myself and bypassed the diodes with 100nf caps.
The whole PSU performs very well as these are 50W amps they did not need huge OTT PSU's. They are for use in my living room which is not huge so there is plenty of power to fill the room wih comfortable music.

I made a small mod the the amp circuit which was a current mirror on the LTP s it is now balanced. I cant believe that the original LTP was unbalanced. So much for ex-spurts and their conventional wisdom! The rest of the circuit seemed OK so I left it alone.

All in all it was a simple project but I think that I have 2 power amps that are very good for a very low cost. I could probably take the mods further but the amps work very well and any further improvements would be mostly improvements in terms of engineering but no difference in musical enjoyment.

Heres some pics the case in not finished yet but looks good enough for now. That 1/2 bottle of red wine is really starting to work now so i'm ging to stop!!
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Old 22nd March 2005, 10:21 PM   #2
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Heres another pic of the LTP current mirror mod which was very simple
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Old 22nd March 2005, 10:22 PM   #3
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Sorry the last pic was the new front of the amp. Here's the LTP mod
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Old 22nd March 2005, 10:24 PM   #4
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I apologise for the last pic. for some reason the trasistors on the current mirror haved seemed to have disapeared. Trust me they are there
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Old 23rd March 2005, 01:39 AM   #5
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Why is transformer is located near the input section of the PCB instead of block by a heatsink???
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Old 23rd March 2005, 08:01 AM   #6
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The amp was designed that way originally. I did have some problems with noise from the transformer getting into the input section of the amp. I put in a metal shield and this cut the noise completly. I did'nt bother moving the insides of the amp around as I needed to make 2 power amps quite quickly.

I used to have an ESP P3A which I made and spent a few years modifing. However it did not have any speaker protection and one day I went out and left the amp on. My wife decided to move the speakers and disconnected and shorted the banana plugs.

When I got home I discoved the amp did not work and the speakers had been moved. When questioned about it my wife said she wondered why the amp begun to smell funny for a while
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