System synergy - or transparent tweaked WAD amp producing harshness

[buddam]

Thought some might be interested in this problem, particularly those familiar with KEL84 and those who heard mine at the Phono shoot-out in March. After thoroughly tweaking this amp for a couple of years I’ve produced an unexpected consequence. Vinyl now sounds a bit too aggressive and CD is worse still.

Neil (aka Acorn) found the same with his KEL84 - the increase in transparency and energy in the 3-5kHz region requires new value components in the cross-over.

In my case (Dave Berriman DBS7 kit from HFNRR in 1998) the 6.8uF tweeter cap can be brought down to perhaps 3.3uF. Depending on results then other values between these 2 can be tried. Wondered if others had experienced similar problems after ‘improving’ their amps.

I’ll post results when I’ve had time to get the caps. And if anyone wants to sell a couple of ICW or Arcotronics in appropriate values please PM me.

Cheers

Adrian

[NealG]

Can't help thinking Adrian you're treating the symptom and not the cause.

Can you re-trace your steps up to the point where you started to notice the affect?

[Rob042]

You beat to that Neal.

you could have over cooked the amp - too much plastic in the signal path (?)?

you could try replacing the decoupleing caps with pio's if you have plastic caps there.

Rob

[buddam]

Rob & Neal

the thought had occurred to me. The problem had started before the latest tweak (lowering feedback), while the previous mod of by-passing 4 resistors with 100pF silver micas shouldn't have too profound an effect. Same goes for improved diodes in PSU.

Rob, there's no plastic in there - all Jensen and AN PIOs.

In any case, swapping E80CFs from Telefunken to Mullard this morning has tamed the harshness and eveything is sweeter again - not sure why I hadn't tried these before - albeit that it could be sweeter still.

Nevertheless, there is a logic to Neil (Acorn's) suggestion. Speakers (high st or kit) are presumably tuned to 'average' amps, probably solid state. Very revealing amps, as mine now is, may well expose problems at the cross-over point.

[Gerry]

Adrian

That amp sounded fantastic at the phono shoot-out, I was really impressed with it.....but I think Neal & Rob might well have a point. Problem is that the upgrade may look good on paper, but with in the context of the system not work.
I'd back track first before messing with the xover.
..just my tuppence worth!

Regards

[Greg.]

I also agree

[Max N]

I agree also. You've changed the amp, it doesn't sound as good, and rather than undo the mod you're blaming the speakers. I've done the same thing myself, more than once. Its very understandable, but you have to put aside your pre-conception that the mods would work and be objective. The mods were an experiment, the result of the experiment was that the sound is worse.
I hope this doesn't come across as preachy, its not meant to be. But its easier to be objective from the outside, its harder when you are close to the problem. As I say, I've done this myself, went the wrong way with mods to my DAC, was convinced they must be better, wreaked havoc with the rest of my system trying to correct the sound, finally went back on the DAC and had to undo all the other mods to the system.
Cheers
Max

[steve s]

i thought the el84 was known for quite a bit of top end distortion, that distortion is used in guitar amps to good affect and results in a bright tone

a little of the right distortion sounds good, as it it thickens the music a touch,

if you remove many of filters and increase distortion in the amp ( ie better components and reducing feed back etc)... you may just start to realise the actual valve may be not quite what people rave and say about it ...

just my view....

steve

[Cobblers]

Originally Posted by Max N

I agree also. You've changed the amp, it doesn't sound as good, and rather than undo the mod you're blaming the speakers. I've done the same thing myself, more than once. Its very understandable, but you have to put aside your pre-conception that the mods would work and be objective. The mods were an experiment, the result of the experiment was that the sound is worse.
I hope this doesn't come across as preachy, its not meant to be. But its easier to be objective from the outside, its harder when you are close to the problem.
Max

I wrote something very similar to Max, which also made me feel preachy (so I deleted it) but he's right.
If you liked the sound better before then don't screw with another component in an attempt to rebalance the sound.
It is a really bad idea making the speaker sound more recessed to disguise issues with the amp, so that every recording will sound more distant with soft focus.
Coming from the World Audio stable I'm sure your amp's original spec was designed to sound as accurate in frequency response and most suitable for the large majority of loudspeaker designs.
If I were you I would retrace your steps to the point where you felt comfortable with the subjective balance, if that's possible.

[buddam]

Don't worry - I don't feel preached to. Points well made and well taken. I suppose that if you replaced your car tyres with well-reviewed super-duper ones and the handling deteriorated you wouldn't start resurfacing roads but revert to the old brand.

Nevertheless, it still seems to me that if amp and speakers form parts of a system it is legitimate to change x-o components to make the best of changes to the amp. Certtainly no harm done to experiment.

But, further thoughts. I noticed the touch of harshness after adding by-pass caps of 100pF across R16-19 (470K). These by-pass caps are MPR (metallised polyester?) and perhaps silver mica might help. I'll report when I've had chance to remove them.

Further thoughts still - I use particular test tracks. After changing the E80CF valves (see earlier post) and choosing different tracks, most of the harshness has gone. Could be partly due to poor recordings.

Also, can anyone recommend good EL84s? I've got Ei, which I've never cared for much, as I got a matched quad very cheap a while back after an accident involving the JJ EL84s.

Thanks for all the comments

Adrian