tips on refining an amp

[cressy]

Hi guys, I was wondering if there are any tips on refining the sound of an amp.
for example, if on wanted to reduce a slight bloom to the bass, or increase the soundstage, or refine a slightly grainy top end.
The reason i ask is that its sometimes difficult to know where to start if you want to attack a particular aspect of the amps performance.
I seem to have got mine to a stage I am happy with almost by accident.

the way I started to attack the problem was to put the amp back to the the original design, then listen to it and make a note if what I did and didnt like.
I then gave some thought to the component values, particularly cap values and corner frequencies for the coupling and bypass caps. I recalculated these based on a 3hz figure.

I then measured the actual ht voltages and currents on the driver and power stages and rebiased them based on actual figures rather than the original circuit. It turned out that they were actually quite a way out, alot more than 10% in the case of the driver

rebiasing was done first and then I listened again for changes, making notes again.

I then stuck a meter on the psu and checked its output while playing music to see if it was staying pretty constant, which it wasnt. Not knowing quite what to do, I stuck an extra 150uf cap in and checked voltages again, which were almost exactly the same.
Rechecing it, it was still dipping a little but not enough to be a problem at this stage. The psu will want looking at still to make it better, which is the next thing on the agenda.

after the psu, what else should I be looking at? Perhaps matching components across the channels or something?
cheers ant
ps, I'll put up the circuit when ive redrawn it

[Nick]

Well, in my book, you have started to do what I would suggest. Measure and understand whats going on. I would now suggest more measurement, but then more kit is needed.

"reduce a slight bloom to the bass,", check frequency response of amp, check dynamic behaviour of all the parts of the power supplies

"increase the soundstage". measure distortion, do the above, check cross talk, see how isolateded the power supplies are across channels.

"slightly grainy top end", look at distortion against frequency, if any feedback, see what it does to the spectra, if push pull, look at phase splitter. Look for RF getting in.

"after the psu, what else should I be looking at", the psu.

[Cressy Snr]

"after the psu, what else should I be looking at", the psu.

Amen to that.
The biggest improvements to my listening pleasure have happened during the past year, and it is no coincidence that in said past year, I have concentrated most of my efforts on power supplies.
They don't have to be complex, eg full of regulators, but if you are not going to regulate, then your PSUs ought to be BIG brute force buggers. It's either one or the other. The old weedy stuff from 50 years ago, won't cut it, if you want the best sound you can get.

[ed]

Hi Ant

I immediately latched onto 'slight bloom to the bass'

Just a thought...

In the last 10 years of messing with this stuff I have come to the firm conclusion that many of the problems in this area are to do with amp-speaker match.

every(almost) speaker alignment that I have conceived that has minimal mechanical damping has been very poor when connected to amps with low damping factor...i.e most valve amps, but much better with SS and PP valves with more feedback.

contrarywise, ever speaker design with higher loading and better mechanical damping has sounded much better with single ended valves and very constrained with SS and higher damping factor amps.....

I have come to MY conclusion that a lot of criticism for specific amps or specific speakers(other forums and hifi press) is uninformed with regard to the above......

Synergy...synergy....and then there's room compatibility

[Mike H]

^ I concur!

[pre65]

every(almost) speaker alignment that I have conceived that has minimal mechanical damping has been very poor when connected to amps with low damping factor...i.e most valve amps, but much better with SS and PP valves with more feedback.

contrarywise, ever speaker design with higher loading and better mechanical damping has sounded much better with single ended valves and very constrained with SS and higher damping factor amps.....

Thanks Ed, so how does one determine the optimum alignment for valve amps ?

[ed]

Thanks Ed, so how does one determine the optimum alignment for valve amps ?

which valve amp, which alignment, which speaker type

many variables
lots of info out there if you ask the right/specific question
lots of calculating software out there as well

[pre65]

Thanks Ed, so how does one determine the optimum alignment for valve amps ?

which valve amp, which alignment, which speaker type

many variables
lots of info out there if you ask the right/specific question
lots of calculating software out there as well

OK, can you point me to somewhere to get started please ?


*

[ed]

deleted...I was unable to answer so tried to be humorous.....

big mistake..apologies

perhaps Scott might have some recommendations

[pre65]

google
bing
yahoo
ask
...........

Thanks Ed.

[cressy]

Cheers for the replies, I'll get the circuit drawn out so folks can have a look and see if tjere are any glaring foulups with it
Cheers ant

[Paul Barker]

I attended a special discussion on M.E. as a student nurse. Each specialist got up and had his half an hour of self importance.

After each one had spoken you knew the cause of M.E. was from within each of their disciplines. One at a time. You left the lecture uninformed as ever.

You have to as you say Ant watch out for the glaringly obvious and then check you haven't fallen into the trap Ed talked about (which is outside my knowledge base).

To assume we don't have the same problems as you would be a mistake. you may be asking a cure of something we could all do with the antidote to.

We settle for a sound we like, which might not satisfy the objectives you are specifying.

[cressy]

This is the circuit, having drawn it I note there are no grid stoppers, methinks there should be.
When I looked at the choke it says 4h 10v, wether this means that it israted at 4h at 10v I dont know but I think it could do with replacing with a 10 h unit
The output transformers are 5k toroids and the mains is rated at 200ma which I missed off the drawing.
I also think that the kt88 could do with rebiasing again for 70ma rather than 60 to put it back on the 5k loadline

[ed]

signal into G2?

[cressy]

Cockup on the drawing, its supposed to be to the g1