No problem at all. It was recommended that I should use R24: I felt it was needless and far too low, but I followed their advice and didn't act to delete it. In practice I wouldn't bother with a resistor there. The relatively large capacitors C11, C12, and C13 were calculated and modeled to reduce the phase shift as much as practical, not for bass extension. R20 and R21 form a potential divider, and this could be substituted for a fixed value to set the gain for a solid state amplifier and it should be padded. R22 is just used to keep the output referenced to ground, and R23 represents the final load. What you pointed out about the grid and a 220k resistor- thank you, it slipped by me when I made that first diagram. I changed the schematic since then and I likely hadn't noticed this older one contained that omission. Most of the updates are obvious values for a more linear phase, and some improved B+ filtering.
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Johan Potgieter, in your opinion, how would you go about reducing the high frequency phase back near 0 degrees? Right now it is about -12 degrees with tone set flat.
I found a solution. The new version blows the old one (and the two in the first post of this thread) right out of the water. With the tone set flat, the distortion and phase are comparable to the preamp without any tone stack or output stage at all.
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Marantz 7 line stage with tone controls
Here's Marantz 7's way of doing tone controls with simplified schematic with output gain control bypassed. One channel shown.
Here's Marantz 7's way of doing tone controls with simplified schematic with output gain control bypassed. One channel shown.
An externally hosted image should be here but it was not working when we last tested it.
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😱😱😱😱
SORRY!
For some reason (not after-Christmas effect) I have missed this request. I am also at present unable to open the last diagram you have posted. Further, you appear to have solved the problem to your satisfaction.
If still of any relevance: I strongly suspect that the -12° phase shift you got had to do with potentiometer inaccuracy. Dual log pots are notorious firstly for poor tracking, often differing by a quite audible degree somewhere at the middle setting. Secondly, they often do not have an exact logarithmic 'division' when in mid-position. (Meaning that for a 470K pot one will have exactly 47K to one side and 423K to the other.) There are also capacitor tolerances. My apparently flippant advice would be: set the pots until you do get near 0° phase shift! That would in fact simply mean that at such a setting you are closer to the mathematically correct ratio than at mid travel of the spindle.
This might be partly bourne out by the improvement experienced with the Marantz circuit. Those taps are exact to the degree of capacitor/resistor tolerance, probably a whole lot better than with a pot setting. Also (might be old hat) usually one finds better tracking/accuracy with linear law pots than with log. In that sense the Baxandall type circuit is more satisfactory.
Hopefully I am now back in 2014.
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