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Old 26th November 2001, 06:17 PM   #1
palesha is offline palesha  India
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I have one circuit of Dicksmith amp 100W at 4 ohms. It has 2 x 2N 3055 & 2 x 2N 2955 parallel at the output. Can I replace it with mosfets? How about replacing it with IRF 540 & IRF 9540 just one pair at the output. Does Mosfets sound better then transistors?
Mahendra Palesha
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Old 26th November 2001, 06:40 PM   #2
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Mahendra,
Asking whether MOSFETs or bipolars sound better is likely to start a riot. As of a moment ago, I saw that Geoff was online...I expect that he'll post in favor of bipolars. Me? I've got bipolars, MOFETs, JFETs, and tubes, all coexisting happily in the same system.
That said, I suspect that the circuit is more-or-less optimized for the output devices you've got. You can substitute within reason, but may need to tweak the amp to take care of oscillations, etc. It's not going to be a good idea to simply drop in MOSFETs without being prepared to revise the rest of the circuit.

Grey
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Old 26th November 2001, 06:44 PM   #3
Geoff is offline Geoff  United Kingdom
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Grey

You 'expect' incorrectly. Yes I have a preference for bipolar, but it all depends on the application and I will readily accept that in certain circumstances MOSFETs are the best solution.

Geoff
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Old 26th November 2001, 07:57 PM   #4
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Hi Palesha,

If memory serve me correctly, those 100W amps are of quite an old design, although DSE has had considerable success with them. They have an odd output stage, and I wouldn't simply substitute in Mosfets.
If you have already brought the kit, then use the power transistors supplied, they will more than adequetely suffice. Otherwise, DSE, and other australian kit makers have other much more modern (and mosfet based) designs.

Cheers, Adrian
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Old 27th November 2001, 03:59 AM   #5
walker is offline walker  Australia
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I'm not trying to set the cat amongst the pigeons, but, has anyone played with IGBTS? I've got some real beauties, (EUPEC BSM200GB120DN2s, 1200V 290A 1400w), don't tell Kilowatt.
Thinking of using them in the output for a sub, but then again they're pretty fast.

Your thoughts / experience please gentlefolk?
Regards WALKER
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Old 27th November 2001, 04:58 AM   #6
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If the dissipated power is not massive, i'll take bipolars in a heartbeat there, discuss!
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Old 27th November 2001, 05:08 AM   #7
jduncan is offline jduncan  United States
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I'll take bipolars if I want class A/B stuff....if I want a serious Class A design I'll use mosfets purely because of their higher linearity at high bias.
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Old 12th December 2001, 02:48 AM   #8
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Uh oh, Walker. Paulb just included a link to this thread in a post on one of my threads, and I saw about that 1400W IGBT. Even if he hadn't, I frequently read the threads, so I would have found out. Anyway, a long time ago, long before I found DIYaudio.com (ah, those were the days for you guys, weren't they? ), I wanted to use IGBTs for my infamous big amp, but I was never able to find a P-channel one that was as massive as some of those N-channel jobs. I also found that IGBTs are not cost-effective for amps, at least not what I found. I even found a bipolar that was rated 2400W, but only NPN, there is no compliment. Power-Tech makes these for the military. I then decided on using lots of ordinary bipolars (or now, I plan on using MOSFETS).
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