John Curl's Blowtorch preamplifier part II

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> Except I know very litle about Circlotrons, so that will now be another Saturday afternoon in front of this PC !!!

I started here :

The Tube CAD Journal, Circlotron Relativity

Tubecad has published many versions of circlotron, including ones with MOSFETs.
Another info source is the Pass forum, where I have also published a few simplified circuits.
And many others also at the same forum from Circlomanen.


Happy reading,
Patrick

PS the reason why I use circlotron is because I only need N devices and they are by design balanced. You could also do the same (unity gain output stage) using the DAO with Taylor Current Source. Only thing you need to do is to run the LU1014s as in Zen V9 with higher bias and lower source degenration, and you need to change a few things around the Taylor current source to balance current modulation. See also Tubecad for the Taylor current source.
 
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i build versions with the LME49600 and also with the BUF634. The BUF worked without trouble but i got offset with the LME. I whould recommend a servo in the Opamp stage then.

I'm not sure how the output buffer could add offset that the input couldn't correct. Is it possible it was oscillating? With a 100 MHz power bandwidth it could oscillate at a very high frequency.

In many cases discrete circuits offer the ability to use currents not possible in an IC. Something like these buffers seem to be special cases where the internal currents are high. The biasing and matching are probably very good. That was why I was asking about the line between discrete and integrated design.
 
I have LME49600 working in my DA converter, i use a servo there. No problem with oscillation there.
Sofar i had no success using the LME49600 without servo but that does not mean it can not
be made to work without. Maybe it needs a stopper resistor, maybe something else.
John mentioned in another thread that a preamp should never leave class a.
Look at my headphone amp. It has an bias current ( new version ) of 70mA. The Buf634 has a maximum bias current of 15mA so it leaves class at loud volume on a low impedance, low sensitivity headphone. Is that one reason that my discrete circuit does work well with the demanding AKG 701 ?
 
is there a preferred bend radius for
leads, wires, traces
IPC-610-D "Acceptability of Electronic Assemblies" gives suitable recommendations in Table 4-1 for wires and as usual, the answer is "it depends".

Fixed coaxial cable - 5 x OD (outside diameter)
Flexible coaxial cable - 10x OD
Unshielded wires - 3xOD < AWG10, 5XOD >AWG10
Shielded wires/cables - 5x OD
Harness assembly - Bend radius equal to or greater than the minimum bend radius of any individual cable within the harness

And later on in Section 7 for through hole components, for those people still using this technology...

For components (where D = lead diameter or max thickness), minimum inside bend radius is:

D < 0.8mm - 1D
0.8mm < D < 1.2mm - 1.5D
D > 1.2mm - 2D
 
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