The MONGREL (supersym II)

[keantoken]

I suspect that D4 and D5 are important here... Why not replace them with resistors and look at the effect on distortion?

- keantoken

[keantoken]

Shouldn't the C6 bootstrap be referenced to the negative rail instead?

OLUG doesn't usually have to be smaller for higher OLG amps, but the OLG -3db point does. This is true for most designs, if OLG is increased being careful not to unwittingly lose BW.

PS: I like that design, I never liked cascaded differentials but the implementation here is growing on me.

- keantoken

[ostripper]

Originally Posted by keantoken

I suspect that D4 and D5 are important here... Why not replace them with resistors and look at the effect on distortion?

- keantoken

Changed R20/21/25 to 820R... removed D4-6. I suspect these were used to set the operating points for the voltage stage trannies.

Doing as you suggested decreased the distortion by half from what it was , BUT you had to choose your resistor wisely ... luckily 820 was about right. With the diodes in, 220/270/330 .. even 470R worked well without any simulator "hangup" (no operating point , Tseed messages).

Keen , I still have your address , on the first .. do you want 2 PB60's and the 2 Blameless's (AX)?? I will throw most of the parts in the box along with it. I figured you would want the "New" and not the "old" .. these are better anyways.
OS

[ostripper]

Thanks for catching that bootstrap error (C6) , haven't made a LED CCS in a long while.

I might ditch those diodes ... with them I had to use lead compensation to pull the phase up at unity gain. Without them I had a big bump at my UG point. remove the lead comp... perfect phase at 950khz without 4 more components. I like that!! (pix1 - no diodes-820R / pix 2 - remove C5)

last pix is the reference (M-90) as you can see I gave the poor amp a little better environment to work in.

OS

[ostripper]

PIX 1= updated PX

PIX 2= Boards that will find a new home ,made totally out of recycled parts.. are these acceptable? keen? (I will run the snot out of these in my PB250 tommorrow)
OS

[keantoken]

I calculated 340 ohms to match the VAS quiescent, 2mA through 340=.68V, to keep other factors as close as possible without skewing the measurements.

I was planning on using those older boards to experiment, and they so happen to have silver-mica caps on them, no? With the original boards I can use the existing components without worrying about a sub-optimal testbed, having to use NP0 ceramics (I don't have any SM's, my headphone amp is using what I hope are C0G ceramics). But the PB60's are also really nice for prototyping, I can airscuplture any frontend I want on to them. I am happy with the AX's, but the SM caps are important to me, will they be included?

I have done lots of simulations with this type of compensation. Here is my approach:

1: Make phase lead 5pF default (or whatever you prefer)
2: Make C103 10uF.
3: Adjust R115 for best phase margin/stability.
4: Decrease C103 until phase margin begins to worsen, back off until satisifed.
5: Change phase lead cap if the results do not satisfy.
6: If desired, repeat 3 and 4 to tweak OL BW, until OLUG is under the "phase hump". However, this may have negative effects on stability into capacitive loads.

This way, I don't believe it is necessary to change the phase lead comp, and I like to keep it low (say 5pF) to avoid excessive phase shift at 100KHz (but that's just me).

- keantoken

[keantoken]

Those boards are entirely acceptable, OS!

- keantoken

[ostripper]

Originally Posted by keantoken

Those boards are entirely acceptable, OS!

- keantoken

I will give you the other 2 68PF SM's , 4-6 NJW0281/0302's ,2 pair MJE15032/33, all sorts of caps .. most of my "junk plate" from the supersyms(I stripped them). You might have to spring for some .22-.27R emitters and the PS caps/ trafo.
My next round of Voltage boards will be 4 each of AX's/GX's/ and 2 PX's !! )

I give you these AX's not because they are defective .. But I am perfectionist and will update the AX as soon as these are tested. (I only accept the latest revisions. The PB60's I will update before I make my next 6 (2 are yours - I get 6 per 8" X 10" FR-4).

OS

[keantoken]

Thanks for everything, OS.

- keantoken

[ostripper]

Originally Posted by keantoken

Thanks for everything, OS.

- keantoken

Stay tuned for tomorrow's test , may be subjective but I am not too old (real good ears - and new tweeters)
OS