if you look at the values in the circuits I have presented then the FB values are lov, gain bandwith also indicates CFA, in my book it is as much CFA as any of the CFA's on this site.
That's real cool, I'm sure we all learned and we are all happy that you succeeded, congratulations on succeeding, it's not easy.
Will do it tonight....
For learning purposes:
LTspice Tutorial: Part 6
http://ecee.colorado.edu/~mathys/ecen1400/pdf/scad3.pdf
http://eecs.oregonstate.edu/education/docs/tutorials/LT Spice_VarResistor.pdf
Here you have the actual setup:
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I still would like it if you checked Q2 out with a bit more of current 🙂 For example R16 at 220 Ohm (3mA) and maybe even 100 Ohm (6mA)?
Well.... now I am repairing a 300B amp that has no bias.... for now I will be listening to the assemblage as is.... after that I will do your mod and report back.
PS: If I lower R16, will I not be modifying the VAS bias state ?
PS: If I lower R16, will I not be modifying the VAS bias state ?
There will be a small change in Vbe of Q2 and that may translate into (I think) a tiny change (Mostly Harmless - Wikipedia, the free encyclopedia (I think))
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Hello Frans
After listening to the Assemblage for a while, I do consider it a very good amp with incredible bass dexterity providing a fast and detailed sound. (Particularly good on strings)
Anyway I am still searching for some more treble integrity and fluidity .... after fighting with the simulator trying to cascode the VAS and not being able to find the issue (cascoding seems to produce instable offset trimming), I decided to go your way.
Today I had time for this mod... I replaced the emitter resistor in the beta enhancement bjt by a 180r and so raised it's idling current to 4.5mA.
Now listening to it... first impressions are good... retaining the very good bas dexterity I seem to have now a better treble presentation also.
Must listen more before I can really determine the differences 🙂
Hi Ricardo,
Seems like there is a result 🙂 that is what we are here for test these things and then reject or keep them 🙂 Lets see what more listening is going to tell us.
Seems like there is a result 🙂 that is what we are here for test these things and then reject or keep them 🙂 Lets see what more listening is going to tell us.
Listening again and now it seems clear, I have got more fluidity in the treble (bass remains quite incisive) .... this proves the VAS to be one of the main points in a power amp.
I wonder if I should install drivers before the laterals .....
PS: How is your BIG amp doing ?
I wonder if I should install drivers before the laterals .....
PS: How is your BIG amp doing ?
It's doing fine 🙂 even more than very well 🙂 🙂 It now has it's own line-stage/amplifier-driver (see 3D and functional diagram). And I am working on a Remote-on-off/Soft-start/Mains-Monitor/Muting-controller (this one http://www.diyaudio.com/forums/soli...ssing-cycle-detector-off-mute-controller.html). Most people think/say it is 'over-done' and thus no one is cooperating in that thread, it was kind of a gift from me and it would be nice if I got some constructive input on functionality and functioning, I do know how to make it work and I am currently designing the PCB for it 🙂
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there are some way to improve the design, one is to remove the VBE and bias the laterals with diodes instead of resistors, if you set the bias to app 110 mA then you're at a plateau when there's no thermal drift in the laterals.
Another option is to remove the bias circuit (the mirrored floating CCS) and drive the laterals directly off the VAS. with the VBE or diodes as a spreader.
For better treble it's my experience that there must be a good cap over the VBE, like 10-47 uF film. (ooh saw its already there)
you can also reduce gate stoppers to a lower value, decrease down to maybe 47 ohm, (this is with caution as the gate stoppers also aid stability).
Another option is to remove the bias circuit (the mirrored floating CCS) and drive the laterals directly off the VAS. with the VBE or diodes as a spreader.
For better treble it's my experience that there must be a good cap over the VBE, like 10-47 uF film. (ooh saw its already there)
you can also reduce gate stoppers to a lower value, decrease down to maybe 47 ohm, (this is with caution as the gate stoppers also aid stability).
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