I remember many years back I built a buffer for a passive pre-amp I was building. The construction was from a Danish HiFi magazine called "High Fidelity". I searched the web to see if I was able to find the schematics as I recall from that time that the buffer was working quite well. A later revision was with 2SA970/2SC2240 transistors which I think is still available. I often see ZTX450/550 in constructions here on this site. So I wonder if these could be used also. These seems to be good all purpose transistors with low noise?
What I also had in mind was if such a buffer could be a candidate for M2X input board sometime in the future. Apart from that it is just to show a construction from the past which some may find fun til play with. I remember the two pairs of transistors which are faced together on the PCB was glued together with araldite so they was "thermal connected" for better stability.
A "high-light" from that time was that the buffer was without "negative feedback". It was from a time where all kind of negative feedback was bad!!
What I also had in mind was if such a buffer could be a candidate for M2X input board sometime in the future. Apart from that it is just to show a construction from the past which some may find fun til play with. I remember the two pairs of transistors which are faced together on the PCB was glued together with araldite so they was "thermal connected" for better stability.
A "high-light" from that time was that the buffer was without "negative feedback". It was from a time where all kind of negative feedback was bad!!
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I love that PCB layout with it’s smooth, almost random shapes which in reality were carefully designed, something that modern PCB software has replaced with strictly geometric shapes
It is from a time where you used the photoresist etching method when making PCB's. It was quite fun. Everything was slower…….
The schematic has some similarities with M2X Austin......but not as symmetrical as Austin....by first "eye catch". But maybe it is a diamond buffer variant......as suggested.
The schematic has some similarities with M2X Austin......but not as symmetrical as Austin....by first "eye catch". But maybe it is a diamond buffer variant......as suggested.
Ok.....now I understand why Nelson has so many parts in his cellar.
The 2SA970/2240 was used for all transistors so also instead of the Rohm's which are much longer gone…..I assume.
Maybe ZTX450/550 would work?
Think I will buy some of those next time I order parts......
The 2SA970/2240 was used for all transistors so also instead of the Rohm's which are much longer gone…..I assume.
Maybe ZTX450/550 would work?
Think I will buy some of those next time I order parts......
2SA970/2SC2240, not the original Toshiba but from CDIL, maybe they are good enough:
SA 970: Bipolartransistor, PNP, 120V, 0,1A, 0,3W, TO-92 bei reichelt elektronik
SC 2240: Bipolartransistor, NPN, 120V, 0,1A, 0,3W, TO-92 bei reichelt elektronik
SA 970: Bipolartransistor, PNP, 120V, 0,1A, 0,3W, TO-92 bei reichelt elektronik
SC 2240: Bipolartransistor, NPN, 120V, 0,1A, 0,3W, TO-92 bei reichelt elektronik
Quite a few members here on diyAudio strongly believe that the Active Production devices 2SA1312 / 2SC3324 are the exact same transistor dice as 2SA970 / 2SC2240 --- just delivered in new, modern packages
Download the datasheets and compare for yourself.
(By the way, the schematic in post #1 is more or less the exact same circuit as the M2x "Austin" input stage. Compare them side by side.)
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Semiconductor Manufacturing Company | Continental Device India Ltd (CDIL)
Neither SA 970 nor SC 2240 are listed on CDIL's website.
Neither SA 970 nor SC 2240 are listed on CDIL's website.
The High Fidelity Super Buffer is a lot older than M2x "Austin". I have a pair of these Super Buffers with the original transistors. I also have some 2SA970/2SC2240 that I wanted to try back then. I have kept these over the years and maybe I put them into use again.
It is more or less a copy of an article in "The Audio Amateur" from the start/mid 80'es...
In the post #1 schematic, bias current varies with supply voltage. Replacing R2 and R4 by approx. constant voltage sources (zener diodes, LM285 reference ICs, 1N4148 pairs, etc) transforms it into an approx. constant bias current, independent of supply voltage.
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