Hello you investigators
This is getting exciting
This NOS DAC with no Oversampling nor any filters, lets it output analogue "like" Square wave levels.
Everything is almost totally analog, but the form of the signal waves have steps in total Squares.
These things explains like Paul N notes, why the wide band I/V stage + wide band buffer gets into some trouble.
Square waves, or a analog level change that is in square form, really is a level change that is a Sine Wave
containing "all" frequencies. (The Flat part is 0Hz, the up is Infinite Hz)
Despite all these possible issues,
It seems that this is the absolute best way to obtain the most analog and natural sound from a digital source, if compared to any other way of doing this.
More bits, more Sampling, more filters, just anything will destroy the fantastic Naturalness of this NOS
I've been thinking of trying a Transistor 2N5416 and 2N3439 instead of the BC550/BC560/BC557B/BC547B.
Reason this is a good transistor is that it is supposed to be very linear and it has a rather low transition frequency. min=15MHz. I've seen these used in places where stability and linearity is essential.
They really are switching transistors, but performs flawlessly also in audio circuits because of their
This should, if it at all works in this circuit resolve the oscillation problems in this part of the Circuit.As I do not know if this transistor really is within working range with the Currents and voltages present here in this Gainstage circuit, maybe someone here can help out with this?
Maybe some values somewhere must be changed?
2C2547E in place of BC550 at Q3 and Q4, maybe these can be used with even more stability when the other transistors have a lower Transition Frequency?
Something else, As it is rather useful having a Grid/Gate resistor on the buffer stage, could it also be beneficial to do the same thing at the I/V stage Jfet 2N3819/BF245A??
OR Would it be possible to build a Constant current source with a lower bandwidth??
I do understand this was a lot of ideas in one post, but just want to hear what others think.
It is very possible all of these suggestions of mine are totally useless
Thanks you guy's for all the superior tips so far