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Pcb group buy Symasym, AAK modell

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#283
If it would be possible to make a third run I am strongly interested to have 4 boards !!!

Also if anybody would like to resale 4 boards – I am also interested to buy - send me just an email please 🙂 I have already some MJL1302A / MJL3281A from ONSemi and other parts left and I can just exchange for SymAsym PCBs 🙂
 
#291
Hi,
how does the second stage mirror work when the LTP is offset to maximum, trying to follow a high input signal?

I can see that at no input signal both halves of the LTP pass about 1.45mA. At maximum input signal all the tail current will pass down one half of the LTP, about 2.9mA down one side and near zero current down the other side.
What happens to the next stage? Q4 and Q12 have substantially different voltages on their bases but the mirror loads them up so that they pass the same current. How do you calculate the voltage across r10 and what current passes q4?

The reason I ask is that I am setting up a ccs and shunt regulator to feed the Vamp stages. I need to pass the maximum current for the Vamp through the CCS to ensure the reg continues to maintain rail voltage when worst case currents flow in the supply rails. I think it's about 25mA but have little confidence in this value.
 
#292
Hi Andrew,
I suspect that only the feedback side would saturate. The amp will be clipping before the input signal becomes high enough to saturate the input side.

I must admit I've never tested, looking for input currents, an amplifier in this (common) condition.

-Chris
 
#293
Hi Anatech,
if the mirror was the other way around, then a positive input would put the non-inverting side (Q1) into high current and this would drive the VAS (Q12) to high current and this in turn would match that same current into the cascoded side (Q4).
But since the mirror is using the left side (Q9 as diode) as the fixed current.
Then it takes a negative input to pull the inverting side (Q2) to maximum current and that forces the cascoded side (Q4) to maximum current. The VAS side (Q12) then has to pass the same current due to the mirror action.

My problem is that the voltage drop over the 68r (R10) goes from a quiescent 350mV to about 1330mV and this passes about 20mA.
I guess both sides of the second stage pass the same current i.e. about 10mA each, but I cannot get my head around to understanding how a transistor with the Vbe at near zero, or reversed, can pass 10mA.
That's why I have no confidence in my analysis.
The total Vamp current is I68r (R10)+I680r (R6) ~=25mA. But, is it?
 
#294
Sorry for the - perhaps stupid - question, but there were some posts in the "sequel" thread that confused me a little. As far as I understood is your board Al a realisation of Mike's schematic or are there any differences (that I did not find)? In my opinion, it is possible to build "Mike's amp" with your board - except for the size of some parts. Am I right?

Sorry but the length of the thread in one piece confused me a little.

Best regards

Floric
 
#295
Mkie B and AAK symasym

I am reading a lot of threads about members trying different parts in the symasym and varying the sound. Is there any pin base which you can buy like the ones used for op amps that will allow you to plug and unplug transistors and passive devices so as not the destroy the pcb with constant unsoldering and resoldering of parts? It seems this amp design is a fabulous test bed for different configurations. Job well done MikeB and AAK. Tad
 
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