need help for NAD 3020a

[vubkevin]

hi, I want to replace my NAD3020's output transistors (MJ2955/2N3055) with modern transistors, is there are any options? how about MJ15003 / MJ15004 , or 2N5631 / 2N6031 ?
can I simply replace it?

[anatech]

Hi vubkevin,
You should be able to use 2N5631 / 2N6031 or MJ21193 / MJ21194. You want a device that isn't the fastest. You may need to add some small C-B capacitance. Don't use ceramic caps for this.

-Chris

[vubkevin]

thx for your reply, can I simply replace it with MJ21193 / MJ21194? don't need to adjust anything else?
and did u mean to replace all the ceramic caps with CBB caps?

[anatech]

Hi vubkevin,

can I simply replace it with MJ21193 / MJ21194?

Possibly. They are a little faster than the original devices. These should have lower distortion.

and did u mean to replace all the ceramic caps with CBB caps?

u=you?
No, just if you need to add any caps. Don't use ceramic. Eliminating all other ceramic caps in the amplifier stages will improve the sound quality. It is subtle but worthwhile. Use mica, teflon or polystyrene if you can.

-Chris

[John88]

Hello,

I found this forum searching the internet for replacing tranisistors in my Nad 3020a. these transistors you are talking about (MJ21193 / MJ21194)...what improvements will they give to the perfomance of my nad. Im really looking for more power and weight to the performance. My Friend has a Pioneer SA-8500 amp and he replaced his transistors with the best of the same sort that were all ready in the amp, and when we heard the new transistors it was awesome, so much more bass n control. Anyway any help will b appriciated, bearing in mind im 17 and can't rework circuits, but i think replacing the transistors will be simple as they seemed to just be blted down..

Thanks

[anatech]

Hi John,
Replacing transistors will not give you more power. Sorry.

Replacing transistors will not give you much improved sound. Unless the originals were broken.

but i think replacing the transistors will be simple as they seemed to just be blted down..

Not even close! Those transistors have thermal compound applied on both sides of a fragile mica insulator. You must clean everything completely without cracking the insulator. You also need to apply fresh (=new) thermal compound and the mounting hardware must be torqued down to the correct pressure. It's not much. Too much grease and you may crack the die inside the transistors, not enough and it bakes.

After all this, the bias current must be set (properly). Then you have to make sure it's not oscillating. So you need an oscilloscope and a good DVM - minimum.

My Friend has a Pioneer SA-8500 amp and he replaced his transistors with the best of the same sort that were all ready in the amp, and when we heard the new transistors it was awesome, so much more bass n control.

People should do some research before they dive into these things. Unless your friend is a properly trained technician, he just rolled the dice.

-Chris

[John88]

hi

ok thanks for that and yea i would assum it needed special torque and thermal compound. And yes my friends dad is a technician and modified the transistors slightly.

Ok so what would i have to do in order to get more 'Ooompth' from my nad??

Regards

John

[anatech]

Hi John,
You really can't. A new amp needs to be designed from scratch. It may be possible to gain a couple watts, or improve the sound of the existing amp. It's not worth the effort.

What is required is a larger power supply in both voltage and current with a matching redesign of the amplifier itself. Heatsinks will also need to be enlarged to handle the extra heat. In other words, a completely new amplifier. Doubling the power will only gain you 3 dB. You may possibly notice this - just.

-Chris

[John88]

Chris,

Aaaa all right that sounds fair haha Thanks Chris... Spose i will have to buy 2 Mordaunt Short 309i subs then :P that should give me the low end im looking for, as i had the original verson (which i melted) and that was aweseome...

Cheers

John

[planet10]

Somewhere buried deep in my email, i have some suggestions for improved output devices for the 3020. A tech in Montreal spent sometime pouring over data books to come up with some that would just pop in. The NPN parts will also sub in a Quad 303. I'll see if i can dig up that info.

dave