A&R MC60 Moving Coil Pre-Amp (KiCAD)

[PigletsDad]

This is what puzzles me - if you look at say https://www.onsemi.com/pub/Collateral/BC550-D.pdf on page 3, the top left hand graph shows collector current versus Vce for different base currents. For Vce near zero, the lines all collapse together - in other words, you get no gain! So I don't understand how the circuit works as drawn.

 

[graham-r]

This is what puzzles me - if you look at say https://www.onsemi.com/pub/Collateral/BC550-D.pdf on page 3, the top left hand graph shows collector current versus Vce for different base currents. For Vce near zero, the lines all collapse together - in other words, you get no gain! So I don't understand how the circuit works as drawn.

Yes, on closer inspection it is a strange circuit, I've only had a cursory glance but it differs from most complementary pairs in that the emitters are connected to +/- Vcc in reverse mode - that is the PNP has +4.8v at it's emitter and the NPN has -4.8v and the output is taken from the combined collectors. I'm sure there is a name for this configuration but I can't think of it right now !

I have double checked and the schematic above is the same as the original A&R version - hopefully that is right.....

 

[graham-r]

Been delayed for various reasons, I hope to finish this in the not too distant future.

 

[davidsrsb]

The Quad 34 MC buffer had a similar circuit, with small but non zero Vce
Vce=0.65V
Cob will be high and Hfe will be low in these conditions

 

[Geof-P]

To graham-r
I have been wondering you you have a spare PCB you might be interested in selling?

I have just picked up an A60 as a Christmas gift for my son and noticed he will need this preamplifier.

Many thanks

 

[berni13]

Been delayed for various reasons, I hope to finish this in the not too distant future.

Hello Sir.

We are a few owners in France of A60 without the MC60 module, difficult to find. We follow and admire your development work with attention;-)
What would be the modalities for sending at our expense for your fully assembled DIY module?
Thank you for your understanding.
Sincerely.
Bernard.

 

[grahamdocman]

Hi Graham

On a different note, I've tried sending you a PM's since,your original thread, but that option seems blocked.

KiCAD: Velleman K4700 DC Offset Detection PCB - updated

OK, so I wanted to use a Velleman K4700 DC Offset Detection PCB to protect speakers when using my aging Crimson Elektric CS1500 Power amp...... But there was no way the Velleman PCB would fit in the remaing space in the CS1500 as it was too long (approx 125 x 55mm). So, once again having...

pinkfishmedia.net

I'm really interested in your single chqnnel (mono) speaker protection modules, as in the tread above you launched.

I'd love to build some - did you ever complete the design.
Feel free to PM me,

Regards,
Graham