MF E300 improvements..?

[raymondo]

Hi

I recently repaired the above Musical Fidelity power amp with the help of a few people here. So thanks again:-)
It wasn't quite sounding right initially but after replacing all the electrolytics its sounding quite good again.

The amp uses (per channel) a ne5532 at the input followed by a 5534 , then on to the discrete stages.

The op amps run off 16V rails which are rather crudely derived from the main supply of 50V via couple of resistors, so are obviously unregulated.

Im sure there is room for improvement with this arrangment, with better op amps for a start (which I have many to choose from opa627s,lm4562's, ad797,847 - got lots of these lying around from previous job :-) and possibly improving the psu , maybe putting a regulated supply in for the op amps?

Laughably, the amp has XLR inputs as well as phonos but two pins are grounded so they dont actually operate balanced. Im sure the 5532 op amp is there for an un-implemented balanced to single convertor stage that was maybe fitted on another model.

Im wondering if maybe I could omit that...most MF amps use one op amp followed by a discrete stage, seems odd this one uses two ., hence my theory that the 5532 might not be needed ...Roar if you read this maybe you could throw some light on this :-)

I realise buying a new amp would probably be best, but quite frankly i havent the money and have access to components and a soldering iron. and its more fun.

I did a quick swap of the op amps and the sound certainly changed for the better in some respects.

Any advice greatly welcome .

Thanks people

Ben

[raymondo]

tried some lm4562 /797. definite change in sound.
but now the amp picks up my mobile phone if near it! looking at it, there are no psu bypass caps near the op amps?!
when i worked it pro audio, it was a given to fit 4 caps right next to each op amp, ie 4u7/0.1uf for each rail.
or something similar......
looks like the 5534 is the feedback loop of the amp too.....
any thoughts anyone ?!

[jaycee]

To be honest MF designs are never that good. I honestly wouldn't bother putting something better than the NE5532 in it.

The mobile phone pickup most likely means that the amp has no RF stopping components on it's input.

If there's no bypass parts near the opamp, then it's likely that the LM4562 is just going to oscillate.

[raymondo]

thanks for the reply. i realise the amp isnt amazing, but im pretty sure that the 5532 input stage isnt required , only the 5534 after it. so i will have a tinker. whether MF design sound any good is a hotly debated subject. its badly engineered , that for sure. it was full of underated components which ive replaced .(ie 50v psu caps running at 50V+).
ive not got the cash to justify buying another amp,so i will probably build one.
i could always use the chassis and xformer :-)
any amp designs you would recommend here? i have a pair of sd acoustic sd5 spkrs, very sensitive, and i love the sound of them.