Mosfet v transistors

palesha · 26th November 2001, 06:17 PM

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

GRollins · 26th November 2001, 06:40 PM

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

Geoff · 26th November 2001, 06:44 PM

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

kiwi_abroad · 26th November 2001, 07:57 PM

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

walker · 27th November 2001, 03:59 AM

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

Lisandro_P · 27th November 2001, 04:58 AM

If the dissipated power is not massive, i'll take bipolars in a heartbeat

there, discuss!

jduncan · 27th November 2001, 05:08 AM

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.

Kilowatt · 12th December 2001, 02:48 AM

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).

27th November 2001, 03:59 AM	#5
walker diyAudio Member Join Date: Nov 2001 Location: Perth West Australia	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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26th November 2001, 06:17 PM	#1
palesha diyAudio Member Join Date: Nov 2001 Location: Pune India	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

26th November 2001, 06:40 PM	#2
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	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

26th November 2001, 06:44 PM	#3
Geoff diyAudio Member Join Date: Apr 2001 Location: UK	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

26th November 2001, 07:57 PM	#4
kiwi_abroad diyAudio Member Join Date: Sep 2001 Location: Wellington, New Zealand	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

27th November 2001, 04:58 AM	#6
Lisandro_P diyAudio Member Join Date: Oct 2000 Location: Argentina	If the dissipated power is not massive, i'll take bipolars in a heartbeat there, discuss!

27th November 2001, 05:08 AM	#7
jduncan diyAudio Member Join Date: Nov 2001 Location: Boston, MA, USA	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.

12th December 2001, 02:48 AM	#8
Kilowatt diyAudio Member Join Date: Nov 2001 Location: Harlowton, MT, USA	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).