Symasym - the next generation (supersym)

[pacificblue]

Originally posted by ostripper
Gave them PCB's to Danielwritesback

That's, why he became so silent.

[ostripper]

By Forr - My concern is that current flows through C8 because of the varying voltage at Q5 collector, but Q6 collector voltage being almost fixed at about +0.6 V above ground, current variations in C7 can only be very small. So I don't think we can consider that C7 and C8 load the LTP collectors equally.

You are correct , in the sim there is only a couple uA on C7 (green)
100's on C8 (red). I guess C7 can go , I'll try it. It does not seem to add another pole to the amp. If you replace the cascode with a resistor (22k) , it does.
I will have check whether removing C7 has any effect on THD, FFT , and loopgain response.

OS

[forr]

Hi Ostripper,
In fact, Q6 replaces a resistor in parallel with a capacitor of an initial design that was first published by Hitachi, I think. So at high frequencies, with this older scheme, C7 will continue to see almost no voltage variations, because alternatively coupled to the collector-base node of Q7.
The purpopse of common base Q6 or the old RC network is to maintain DC voltages at collectors of Q4 and Q5 roughly equal, getting the same thermal dissipation for them.

[Bigun]

OS,

The pcb explanation makes good sense now, I hadn't understood how you were doing it properly before.

The other question I had was bass 'slam' - is this just down to having a big caps on the input and feedback loop or is there more to it than that ?

[ostripper]

By bigun - The other question I had was bass 'slam' - is this just down to having a big caps on the input and feedback loop or is there more to it than that ?

Some , like mike chua of ampslab , say the metal can(TO-3) devices give better bass , others say it is the topology. They are both right,
as the ability of the OPS to handle transients is the key. Then , your assumption is also right , having more current and voltage does have a MAJOR impact. The 2 OP supersym's I gave to DWB did not have the "slam" that the new 4 pair boards do on the same PS. Conversely,when the 2 op pair boards were run on an 300VA EI, the bass was normal(not impressive). With the 1500VA and 100's of K uF , ULTIMATE scary bass.

So , with each improvement (2 to 4 pair , 300Va to 1500VA) a very noticeable bass improvement occurred. With the 2 pair OPS , I think
beta "droop" at high level , hard loads affected bass response.
OS

[anatech]

Hi Gareth,
You are really talking about the ability of a circuit to deliver high currents accurately. The ability of an amplifier to control a bass driver.

I think most well designed amplifiers can do this easily. Most of these will be solid state and be of a higher power. That way you don't run into protection circuits limiting the current, or a loss of gain in the output stage that allows the current output to drop.

Being a subjective thing using a wide variety of speakers and cables, this is really not a valuable term. There is no real definition and really only points to amplifiers that have limited power or current output.

In short, nothing to worry about.

-Chris

[taj]

Originally posted by ostripper
I have only gotten this far on the PCB , I whether a am wondering whether a 3 X 9" with opposed output pairs would be a better
design instead of "the long way" (Attached).
OS

My 2-bits for the PCB layout: I much prefer a long layout with single row of output devices when the amp is this powerful. It better suits the most common long-sided heatsink/chassis configuration, and leaves ample room in the center of the chassis for the power supply.


..Todd

[ostripper]

My 2-bits for the PCB layout: I much prefer a long layout with single row of output devices when the amp is this powerful. It better suits the most common long-sided heatsink/chassis configuration, and leaves ample room in the center of the chassis for the power supply.

That is what I propose , with the single row OPS like I have on a 3.5" X 9", mounting flat on a 5" heatsink will look real cool , leaving that room for psycho power supplies That is what I think we all want , the most universal layout.
The only reason mine is 5.5" X 8" is I made it for the stealth amp.
OS

[taj]

Hey Chris, this would make a nice 4B retrofit project wouldn't it?

..Todd

[taj]

Originally posted by ostripper


That is what I propose , with the single row OPS like I have on a 3.5" X 9", mounting flat on a 5" heatsink will look real cool , leaving that room for psycho power supplies That is what I think we all want , the most universal layout.
The only reason mine is 5.5" X 8" is I made it for the stealth amp.
OS

Yup. Perfect. In fact, it ain't too different from my DX HRII-55 layout. (Based loosely on Quasi's layouts.)

..Todd