diyAudio (
-   Solid State (
-   -   Class A amp (

kro5998 5th December 2004 07:28 AM

Class A amp
Hi, has anyone build or has expierience with the class A amps designed by Knutt Nygaard?
I was considdering building the current feedback design.Any comments would be welcome.

jacco vermeulen 5th December 2004 03:52 PM

Hé Mènneke,

at 25 watt it is laid out for Tj= 80 C.

The powersupply and heatsink cost a bundle: add two more 1216/2922 and the bias can go a lot higher with heatsink temperature at 55 C instead of 45 C., Tj =75 C.

4 times 2SA1216 or 2SC2922 go for 17 Euro at Schuro.
With a few alterations the PCB layout of the elektor LMA50 can be used for 4 output transistors.

Replace the wirewound by MPC71, at Schuro for 0.62 Euro or at Speaker en Co.:clown:

AndrewT 6th December 2004 07:49 AM

tell us more about MPC71. Advantages? Is Schuro the make or supplier?
regards Andrew T.

jacco vermeulen 6th December 2004 09:15 AM

2 Attachment(s)
Hi Andrew.

MPC71 is the name of the white block emitter resistor you see in japanese amplifiers for decades.

It is a metalband resistor with low self inductance, unlike wirewound resistors.
Not completely inductance free, resistors that are supposed to be are 10 times the price.
MPC71 has a 5watt rating, MPC72 is 10 watt, made by Motorola.
There is also a dual version, the MPC725, if space is limited.

Like ring emitter transistors, MPC's are easilly available nowadays for $ 0.50 a piece, a DIY bloke like me had to travel half of Europe to buy them for five times as much in my early college days.
I used to scavange broken japanese amps for these parts.
(still do actually, the MPC725 i call Double Dutch :clown: )

Nygaard also uses ceramic caps in his designs.
The ceramic caps i swapped for low cost styroflex capacitors.
(i cherish my precious Siemens styroflex's )
I havent got a clue why some still use ceramic caps, other than that they are cheap caps in the pF range.
Steve Bench did tests on capacitors, check out the curve for ceramic's.

All times are GMT. The time now is 01:46 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 18.75%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio