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Old 7th June 2006, 05:10 PM   #11
Tenson is offline Tenson  United Kingdom
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No suggestions?

Is it possible to just add more caps to the PSU?

Any idea what op-amps would be a nice direct replacement for those ones?
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Old 7th June 2006, 05:15 PM   #12
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Hi, Tenson,

It's not clear what you want with this amp. You mentioned more power, it is difficult to do so, because power is related to rail voltages, this will change everything, need to recalculate heat dissipation etc.
You can try (with carefull monitoring) change opamps and caps. Sometimes changing these "not harmfull" things can lead to dangerous oscilation.
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Old 7th June 2006, 05:25 PM   #13
Tenson is offline Tenson  United Kingdom
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I don't want more output power, I just think that for an amp which is rated at 500watts RMS when bridged, that it doesn't have much of a literal power reserve in the PSU for large dynamics.
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Old 7th June 2006, 08:11 PM   #14
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well its a very standard amplifier, very much from the japanese design school of power amplifiers.

Triple emitter follower output stage with current limiting

Balanced input stages to eliminate 2nd harmonic distortions,

looking at things, its been quite well optimised with emitter degeneration on the input stage and good matching arrangements.

Made in the wei-phon electronics factory in china.

Nice big mains transformer, but....

troulbe is, doesn't sound so good to me now, I had one of these and a behringer.

Whilst they worked, the be was pretty poor,

the alesis less so.

Output power is closer to around 70 watts into 8 rather than 150.

Power supply clips very easily, and you can tell upon transients.

Whether bigger capacitors would cure this, who knows, but don't touch the mains tx, EL cores are superior to toroids in numerous ways.

watch you don't blow the bridge rectifier.

or wreck the boards which no doubt is quite easy.

Bridged, you are only incresing the voltage capability, and they won't like varying loads, only happy really with 8 ohms.

nice amps tho for the cash.

Better off with a big mosfet pa amp.

5532 opamps are very good indeed, low noise, they are hard to beat, I wouldn't bother as you can't really drop in opamps, without possible attention to some factors.

some opams are subject of great hype, don't believe a word of it.

The servo cancels out dc, instead of just a basic passive capacitor.

I am undecided which is best.

Evox caps are the best small ones, nichicons and panasonics, some elnas, and siemens go for the biggest you can get for the psu.

If musical fidelity use jamicon and naim and graham slee and tom evans use tantalums then they are good enough for anyone.
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Old 7th June 2006, 08:42 PM   #15
Tenson is offline Tenson  United Kingdom
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Thanks! You mean the bass wasn't very good?

So really the only thing you suggest is adding bigger PSU caps?

I am going to use PA amps for bass duties; these are more for upper bass/midrange and HF. That still needs a lot of power though.
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Old 7th June 2006, 10:11 PM   #16
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yes once you start splitting amps and using different ones for treble and mid duties it makes you realise that the current and power drawn by them isn't neglible, it makes a huge difference.

go for active tri amping, the only way to go.

even a phonostage can benefit from using 2 units instead of one.

I found contrary to my intuition that an amp for bass and treble is much better than 1 on each speaker, which previously I preferred.

this was in someone else's rig tho', it may or may not be speaker/amp dependant, only way is to try.

personally, I am past the modding phase, I only do what needs doing when it does, and just concentrate more on music now instead of gear.

after all that's all its for, isn't it?
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Old 3rd October 2006, 06:32 PM   #17
mikeks is offline mikeks  United Kingdom
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Thumbs up Great potential..

The potential upgrade options for this amp. are endless. The Mother of all bargains!
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Old 4th October 2006, 10:24 AM   #18
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by lt cdr data
looking at things, its been quite well optimised with emitter degeneration on the input stage and good matching arrangements.

Not quite: degeneration is insufficient with respect to the values of compensating caps. used.

The thing tends to oscillate if turned on after the source; this is heralded by the heatsinks running very hot for a short period.

Be that as it may, the modular nature of this design makes it amenable to sweeping changes in circuitry.
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Old 5th October 2006, 02:04 PM   #19
mikeks is offline mikeks  United Kingdom
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Default update..

Indeed, i suspect this oscillatory tendency is, at least in part, aggravated by the wanton misuse of wiring throughout this design.

However, at the price, the purchaser could strip out the all gain modules and start again, without incurring a significant financial penalty.
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Old 6th October 2006, 11:23 AM   #20
mikeks is offline mikeks  United Kingdom
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Grounding scheme is excreble!
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