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Post by Deleted on Feb 15, 2018 9:20:08 GMT
The last few days I have been testing and repairing a Magnum Pre-Amp and Power amp I designed for Etude in Belgium now nearly 40yrs ago. I was surprised to see that I had used my long forgotten Patented (now out of date) MC head amp. Even more surprised when testing it that the noise flour was a few dB lower than I expected when one considerer the new device we have today. I thought some of you Techy Buffs would like to see the circuit so here is the basic concept, Have fun.  Whoops spelling again wee = we |
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Post by Deleted on Feb 15, 2018 10:09:17 GMT
I did using a transistor and a green LED but the transistor had a low Rbe which helps so the limiting factor was the HFE, two of the circuit was used and the ref voltage the green LED was common giving me a random noise and a 3dB cut. There are 1000s of these circuit in Magnum's working well, at the time LM741 was the class act op-amp and NE5532 series was to be honest shit.
The worst source of noise was the PSU, but since that is my design skill set and I had to work on PSU with 10nV noise floor at lees than 1Hz no real problem. And some at 55V 100,000Amps (battery charger not for mobile phones) using transistors and thyristors and transformers at 7 English tons, tiny 1mA PSU's are easy.
Fun days and big bits no real SMD and pebble glasses to wear, now I am 65 they seem to be getting thicker every month, or are they cheating and making them smaller ?
Oh I used spice in this case only to act a simply drawing package, in real life there are 2 NPN and 2 PNP transistors in each stereo pair of constant current source on the same substrate and the design has been working for 40yrs, oh when I took it to Rotterdam I had the response by the Prof this can't work, oh dear I took the prototype out of my briefcase and guess what it works.
So Spice was not used and at the time there was no Spice only in Curry. he he
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Post by MartinT on Feb 15, 2018 11:10:46 GMT
Very elegant, Colin, and the transistor/LED current source works well. Are green LEDs quieter than red?
I always disliked the NE5532 op-amp but at least it could be easily upgraded.
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Post by dsjr on Feb 15, 2018 15:30:33 GMT
What's wrong with a 5532? It's output sounds just like its input to me and they're used all over in much good gear too I think...
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Post by MartinT on Feb 15, 2018 15:44:20 GMT
I've found 5532s to sound pretty meh in general, Dave. They're general purpose dual op-amps and can be upgraded to good sonic effect, like an OPA627.
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Post by Deleted on Feb 15, 2018 16:57:20 GMT
On testing lots of ref diode I found LED Green at 1mA to be at least 10dB lower in noise then a standard diode and 5dB lower than RED, now these were old LED's so max current would only have been say 50mA then poof smoke.
I bought my first blue LED then at £5.00 and a max current of a massive 10mA , you could just see it in a black room.
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