300B solidstate?

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Forgive my intrusion in this Solid State temple.

I wonder if somebody can reccommend a very good sounding amplifier, solid state, 15W power output that can be compared to a 300B monoblock.

I'm searching for a class AB (classa A till 1W) , 15W output power on 8 ohm speaker (rule of thumbof twice the power of a 8W tube amplifier).

Low part conts, nice topology and cheapness preferable.

Thank You,
May be more near you than you can imagine.

Va molto benne, il uomo di tuo risercha e presenti...AKSA!

The man you search for is already present....but you will have to pay for it.

Lucky guy you are.


Carlos Danesi.... il Brasilianno medio tedesco, medio Itálico

Carlos, half European, German and Danish and half from Italy.

EPUPA....also extraordinary is reach the adress you offered to us...can you please check it again.


I'll surely follow the last Pavel Makura works.

A brief surfing bring to my attention a old Pavel's design : the Sinclair Z-30 . Very simple, chaep european transistor, i'm going to give it a try.
What about the power supply, is it conventional unregulated one?

Anyone has built this amplifier? How does it sound?
The last work of PMA is the V/I converter, but not much information about this piece. I think it should sounds very good.
My simulator (which is powered by 3 meals/day, not by 2.5Ghz processor:D) think that PMA's Error Correction is better than Hawksford Error Correction. How does it sounds? In DIY audio, you cannot rely on other's opinion, so you will have to build yourself and judge yourself:D
Hello guys,
several answers to your questions:
1) Z-30 is not my design, but Sinclair project from late sixties. Easy to build, but sound is nothing special - cross over distortion is apparently audible. On the other hand - can be compared to many designs seen here.
2) The error correction amplifier had been discussed here: http://www.diyaudio.com/forums/showthread.php?postid=469442#post469442
3) And here is the review from our forum member: http://www.diyaudio.com/forums/showthread.php?postid=482839#post482839
Thanks a lot PMA,

I'm intrigued by the Sinclar schematic. How was the power supply?

Do you think there is space for some improvement on this remarkably simple design, without added complexity, for example increasing the Iq and replacing the 2N3055 with some other more linear (MJ series?)
New sets of measurements were done since it had been discussed before. Here is the result of my FM method - firstly input signal.


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Hi Plovati,

Here is an explanation of the PMA-NP error correction mosfet output stage. It is brilliant design, one of the very best I've seen. It has efficiency, speed, local feedback only, very low output impedance, and need only be driven by a voltage source of moderate Zout.

Two diff pairs lie at the heart, with input drive to the left side emitters via diodes, and output error sense to the right side via diodes. The mosfet gates are driven from the top and bottom of the diff pair 'trees'. The right side has a resistor in its collector circuits, top and bottom, while the left side has no collector resistor.

Consider a positive going signal; we will look only at the top 'half' of the circuit. The bottom half is complementary, so the operation is identical.

If the output potential drops below the input because of gain droop in the output device, then the right side transistor of the diff pair turns on harder because the emitter potentials are no longer the same. Rather than sharing the current equally, the two diff pair transistors are now unbalanced, with more current passing through the collector of the right device.

This increased current drops more voltage in the right side (upper) collector resistor, which connects to the mosfet gate. The adjacent transistor on the left side passes less current, but this current does not pass through a collector resistor, so there is no voltage effect and it readily accommodates this increased potential since collector voltage is always flexible.

We now have more voltage dropped across the upper of the two resistors on the right side. The voltages across all other resistors are essentially constant as they are fixed by base bias currents, so now, addressing the entire circuit block, we have more voltage dropped from the mid-point error correction node on the right side to the top of the collector resistor on the right side - which of course is connected to the mosfet gate.

This means that voltage between input and upper mosfet gate has increased. Thus there is more voltage drive to the upper mosfet measured from left side input to upper mosfet gate, which immediately compensates the gain droop, and again raises the output potential to the input potential. At this point the diff pair currents again become equal, and the voltage drop across the upper (collector) resistor drops, and the cycle starts over, with continuous adjustment to ensure the output tracks the input.

Of course, the complementary operation takes place when the negative half cycle conducts, with explanation identical.

Top and bottom of the error correction circuitry is fed by constant current sources. Any spillover current finds its way harmlessly into the output via the error node, ensuring that minor differences in source and sink current do not halt proceedings.

The circuit is extremely fast because small signal devices around 150MHz are used and there are only parasitic capacitances. However, it requires appreciable operating voltage bias from gate to source of the output device - no problem on a hexfet, but rather tight on a double emitter follower. I've not built and tested it, but it is likely the operation is compromised to some extent with only 1.2V to 'fit' it in compared to a hexfet's 3.2V or so.


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