It is a thread about the Nobrainer phono but also a simple power ampilfier.
I will look up the thread and find the schematic for the phono.
I will look up the thread and find the schematic for the phono.
I have been measuring and found:
2.57v between T5 and T6 bases (this relates to a 0.64v voltage drop over each T9 T10 T11 T12 .... coinciding with measured Vbe on those trannies)
2.57 / 2 = 1.285v (opening voltage of bc337 being 1.2v I believe the drivers are working in class B)
Over the emitter resistors R2 and R4 I have 0.8v so current on the mirrors might be around 8mA
So if I use two 100r resistors in series with the bias circuit I will add 2 x 0.8v = 1.6v
1.6v + 2.57v = 4.2v and this should be the diff between the bases of the drivers If I use these two 100ohm resistors.
This should increase bias current to a clear class AB..... but the question is... can I exaggerate and go to class A ?
can this circuit survive enough current to operate in class A ? (I have enough sinking area)
2.57v between T5 and T6 bases (this relates to a 0.64v voltage drop over each T9 T10 T11 T12 .... coinciding with measured Vbe on those trannies)
2.57 / 2 = 1.285v (opening voltage of bc337 being 1.2v I believe the drivers are working in class B)
Over the emitter resistors R2 and R4 I have 0.8v so current on the mirrors might be around 8mA
So if I use two 100r resistors in series with the bias circuit I will add 2 x 0.8v = 1.6v
1.6v + 2.57v = 4.2v and this should be the diff between the bases of the drivers If I use these two 100ohm resistors.
This should increase bias current to a clear class AB..... but the question is... can I exaggerate and go to class A ?
can this circuit survive enough current to operate in class A ? (I have enough sinking area)
Why not get the LTspice simulator and insert the circuit, then you can try, and try again. If this leads to problems/questions/unknowns then I will show enough interest (as requested 🙂) and I will help you with the simulations (is that a good deal?).
I found this. It is an alternative to circumvent the bias diodes, in our case the transdiodes. I do not know if that improves our particular circuit.
Ok will do the ltspice thing.....
Reading the doc I got the idea I can just replace the transdiodes by two suitably chosen resistors... am I right ?
Reading the doc I got the idea I can just replace the transdiodes by two suitably chosen resistors... am I right ?
Hi brianco.... homemade speakers using old B&O enclosures 🙂
Here it is the LTspice thing... having difficulties getting a correct current on the power trannies.
Here it is the LTspice thing... having difficulties getting a correct current on the power trannies.
Thanks RC.
Have you tried this amp [ and also your 103s] with a pair of reasonably high sensitivity speakers of a known maker? [I ask because the only time I have heard 103 amps sound reasonably good, if a bit too "Hi-Fi' ish, was way back in an all Meridian active system. I have heard them with quite decent speakers from other makers and they were far from being, IMHO, good.]
Have you tried this amp [ and also your 103s] with a pair of reasonably high sensitivity speakers of a known maker? [I ask because the only time I have heard 103 amps sound reasonably good, if a bit too "Hi-Fi' ish, was way back in an all Meridian active system. I have heard them with quite decent speakers from other makers and they were far from being, IMHO, good.]
My second amplification is a pair of denon poa 6600 optical class A monster monoblocks and I can tell you they are not far apart 🙂
Thanks RC. I was worried that your comparisons may have been less than accurate whilst using unknown speakers, but if they work well [speakers] with both of you other amps, then I accept that, other than that the speakers may not be happy with such a low power amp as your very nicely built Nobrainer.
As far as i understand the abc paper the diodes should still be there plus the resistors in parallel, signal in between the resistors.
I do not think so.... anyway it sims ok without the diodes.
Otherwise why the switc ?
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My speakers are quite sensitive and took me a while to finetune. I am used to listen to high end speakers and know when they sound just right..... These are ok IMO
No Ricardo, i think the diodes are stil there, even after switching. They are now parallel to the resistors.
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