Building the ultimate DIY power amp

[Damon Hill]

K-amps:

At one time Motorola was going to supply a MJ1302/
MJ3281 in TO-3 cases, but evidently these never
went into general production. I've got a Motorola
bipolar power catalog from circa 1995 showing them and
they would have had most of the characteristics you
mention. I do wish they'd offer their Toshiba clones in
metal cases; they'd have higher SOA and wattage.

As we know, Nelson Pass likes to order in quantity for
that discount price. Hate to be the one paying taxes
for all that stock, though.

Special labling is common, and I'm not too surprised to
see that custom parts were/are done.

[K-amps]

Originally posted by Damon Hill
K-amps:

At one time Motorola was going to supply a MJ1302/
MJ3281 in TO-3 cases, but evidently these never
went into general production. I've got a Motorola
bipolar power catalog from circa 1995 showing them and
they would have had most of the characteristics you
mention. I do wish they'd offer their Toshiba clones in
metal cases; they'd have higher SOA and wattage.

As we know, Nelson Pass likes to order in quantity for
that discount price. Hate to be the one paying taxes
for all that stock, though.

Special labling is common, and I'm not too surprised to
see that custom parts were/are done.

Thats good info...however I have poor memory but for some reason the 250watt figure also comes to mind... thereby made me not think of the 1302/3281's... any thoughts on that?

K-

[tcpip]

Originally posted by Jennice
After reading about Civic's, Mark Levison's etc. for pages on end, I'll give my try to get back to more hands-on basics...
....
Just my 2 cents...
Now go and have fun. You'll probably be surprised to see how far you'll come with modest budget.

I found this post very well written and useful --- I learned a lot. Thanks.

[Jennice]

*comes creaping out of his bomb-shelter*

Huh...? No crazy attacks on my points of view!?

Thanks for your comment, itcpc.

I kmow it's kept pretty simple, but I'm pleased with the results I've achieved (well, mostly, except from the subject of interferring electronics when cramming 4 channels and 2 x 500 VA transformers into 1 case.) In my oppinion it took too much controlling circuits to power on/off and mute the 4 channels, which leads me to the thought of KISS and mono-blocks (or in this case 2 stereo-units in stead of 4ch in 1 unit.)

My next project still just in my mind, waiting for an excuse to get implemented (the W.A.F. issue, you know ).
It'll have the switch/mute controll circuits in a seperate chassis, along with the first voltage amplification stage. Also, this approach solves the problem with turning on(off poweramp(s) located away from the other gear - or rather... forgetting to turn it off.

This way, I will not have any low level signals near the large PSU section, and only the relays to power-on/off and output relays located in the power blocks. The controlling circuit resides in the controll box along with the voltage amplifier stage. All this is fairly low current stuff, so I'll avoid the magnetic radiation problems from nasty PSU transformers/rectifiers/cables.

Jennice

[tcpip]

Originally posted by Jennice
I kmow it's kept pretty simple, but I'm pleased with the results I've achieved (well, mostly, except from the subject of interferring electronics when cramming 4 channels and 2 x 500 VA transformers into 1 case.) In my oppinion it took too much controlling circuits to power on/off and mute the 4 channels, which leads me to the thought of KISS and mono-blocks (or in this case 2 stereo-units in stead of 4ch in 1 unit.)

This made me think. I'm thinking of embarking on a few speaker projects, starting with my current MTM-MM dream. All of these are active speakers. Eventually, I want to build speakers which will house the power transformer and PSU, active xo, and power amps all inside the speaker body (just like the Rushmore of Nelson Pass, but with Class B amps). What does one do to avoid all these shielding and interference problems? One thing one can do is use the full height of a floor-stander, I guess, and keep the transformer at the bottom and the signal-level electronics at the top. Is that enough? Secondly, do the speaker coils induce interference into the electronics?

Anyway, I guess this off-topic...

[Jennice]

Hi tcpip,
I've just mailed you directly - so we won't run too far off topic in here :-)

Jennice

[cbdb]

I have read (more than once) on two separate interviews where Dan D'Agostino made statements about how they had custom parts ordered from Motorola. In the same interview he also mentioned that Motorola was not entertaining the idea of the Part he describes 20A 250v and fT of 30Mhz custom made for Krell so they said they would not do it for less than 1 million pieces... Dan agreed and they went ahead with the order.

Some how I dont believe that Motorola(ON) can all of a sudden design and manufacture a better transistor just because some one asks for it.
If Motorola is the buisness of making audio power transistors, are they not already trying to make the best transistors they can? Sure they can tweak a parameter here and there or change the packaging, but they wont be able to double the Ft over night. This makes it hard to believe the custom transistor stories.

[Nelson Pass]

Originally posted by cbdb
This makes it hard to believe the custom transistor stories.

In the old days, if you did enough business to buy from the factory,
Motorola would mark them any way you liked, thus you see "Stasis"
on the TO-3 cases in Threshold's product, or McIntosh on their
transistors.

[scott wurcer]

Originally posted by cbdb

This makes it hard to believe the custom transistor stories.

Don't . It's wishful thinking and myth that somehow an extra dollar here or there can make a 30MHz transistor 60MHz. Power transistors are made at the limits of the respective processes. That is the only thing that makes competitive sense.

[traderbam]

Originally posted by cbdb


Some how I dont believe that Motorola(ON) can all of a sudden design and manufacture a better transistor just because some one asks for it.
If Motorola is the buisness of making audio power transistors, are they not already trying to make the best transistors they can? Sure they can tweak a parameter here and there or change the packaging, but they wont be able to double the Ft over night. This makes it hard to believe the custom transistor stories.

I doubt Motorola make transistors for audiophiles anyhow. They may market general purpose power transistors for audio use, but just how big a market is it? I'm not sure. Nor am I sure that Motorola know what an audio transistor needs to do anyhow (just look at the arguments in this forum).

There are more degrees of freedom than just the silicon wafer, such as thermal design, select-on-test (parametric selection), multiple wafers in the same package.

I know from Julian Vereker that Naim worked with their power transistor mfr to create a customized TO-3 package to enable higher power dissipation from the wafer - thus allowing the use of a faster wafer. Changes included using a copper pad beneath the wafer and improved internal wire bonds.

I would think that designing a custom wafer would cost millions. A lower cost could be incurred by customizing wafer fabrication parameters for a batch. The designer would have to be pretty savvy to know what to change. I imagine silicon wafer customization is beyond the financial means of most audiophile companies.