Sziklai input to increase gain
MJL3281A / MJL1302A output
Low distortion
TMC compensation
31.6 Watt max
Transformer 2x18VAC
MJL3281A / MJL1302A output
Low distortion
TMC compensation
31.6 Watt max
Transformer 2x18VAC
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Current through U5 and U6 is too low. Change R19 and R20 to at least 620 ohms, that will set the current through U5 and U6 at 1mA. This will increase will Ft. Ft goes up with collect current to a point then it will start going back down. Increase the tail current to 4mA to 5mA by changing R1 to 120-150 ohms.
The TO-92 transistors don't need be high voltage types especially U12 and U14. Low vce parts have better quasi-saturation.
U12 and U14 should have ballast resistors on the emitters.
If using R23 you will need to add about 470pF base to collector on U14 for stability. Without R23 the cap may not be needed because U13's collector current is low so Ft is low.
R24 should be 1kohm or less.
U4 and U10 don't need to be 4281/4302. These are high voltage transistors that have poor quasi-saturation. You only have +/-25V rails so there's no need for 350V parts.
Jeremy
The TO-92 transistors don't need be high voltage types especially U12 and U14. Low vce parts have better quasi-saturation.
U12 and U14 should have ballast resistors on the emitters.
If using R23 you will need to add about 470pF base to collector on U14 for stability. Without R23 the cap may not be needed because U13's collector current is low so Ft is low.
R24 should be 1kohm or less.
U4 and U10 don't need to be 4281/4302. These are high voltage transistors that have poor quasi-saturation. You only have +/-25V rails so there's no need for 350V parts.
Jeremy
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Correct. The 3281/1302 are better for rails up to +/-70V. Above that, switch to the 4281.
C2 is too big, it shouldn't be higher than 2pF however I normally use about 1pF with 30MHz outputs. If C2 is too big it can degrade gain/phase margin or push it into oscillation.
C6 and C7 can be lowered. The best ratio for TMC is about 5:1 (C7:C6).
TTC004B would be better for U16, much faster and lower cob
C6 and C7 can be lowered. The best ratio for TMC is about 5:1 (C7:C6).
TTC004B would be better for U16, much faster and lower cob
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In a similar vein, this was a very old project that I have experimented. Inspired actually by a Toshiba Aurex amp, the evolution made it to move further away from the original Aurex design. While the simmed results at 1KHz looks promising but at 20KHz the amp becomes 3rd harmonic dominant. The hard part was balancing the values of TMC, it counters the CFP scheme of the LTP. You increase the gain but TMC will limit it. I could only limit it to a lower ULGF to produce a fair amount of GM. However I'm using a cascode for the VAS. It may produce different results if using Lineup's VAS.
Albert
Albert
Attachments
I have done a lot of changes as per the suggestions.
Still low distortion.
Still low distortion.
Are you laying out a PCB? At those performance levels trace routing becomes critical. Traces can radiate, pick up emi and get amplified by amp itself.
