TSSA - The Simplest Symmetrical Amplifier

[Lazy Cat]

IRF matching, very simple, but it will take you some time hehe

Do not try to find or make a selection of IRF610 and IRF9610 according to Vgs voltage. That is not important. Usually they differentiate for 0,5 V but that is OK as offset setting eliminates this.

Transconductance curves of each type have to be parallel as much as possible. That you will get from three sets of measurements for each type of mosfet. Mark each mosfet with number. Start with 1 by IRF610 and the same with IRF9610.

IRF610 step 1
- take first IRF610 and set potentiometer that you read 100 ohm, read out Vgs and record the value as Vgs-initial-610
- leave potentiometer as it is and measure all other IRF610
- for each numbered IRF610 put a measured resistance value at initial Vgs in a table chart

IRF610 step 2
- take first IRF610 and set potentiometer that you read 50 ohm, read out Vgs and record the value as Vgs-medium-610
- leave potentiometer as it is and measure all other IRF610
- for each numbered IRF610 put a measured resistance value at medium Vgs in a table chart

IRF610 step 3
- take first IRF610 and set potentiometer that you read 10 ohm, read out Vgs and record the value as Vgs-maximum-610
- leave potentiometer as it is and measure all other IRF610
- for each numbered IRF610 put a measured resistance value at maximum Vgs in a table chart


IRF9610 step 1
- take first IRF9610 and set potentiometer that you read 100 ohm, read out Vgs and record the value as Vgs-initial-9610
- leave potentiometer as it is and measure all other IRF6910
- for each numbered IRF9610 put a measured resistance value at initial Vgs in a table chart

IRF9610 step 2 (attention)
- take first IRF9610 and set potentiometer to Vgs-medium-9610= Vgs-initial-9610 + (Vgs-medium-610 - Vgs-initial-610), read out and record resitance value in a table chart
- leave potentiometer as it is and measure all other IRF6910
- for each numbered IRF9610 put a measured resistance value at medium Vgs in a table chart

IRF9610 step 3 (attention)
- take first IRF9610 and set potentiometer to Vgs-maximum-9610= Vgs-medium-9610 + (Vgs-maximum-610 - Vgs-medium-610), read out and record resitance value in a table chart
- leave potentiometer as it is and measure all other IRF6910
- for each numbered IRF9610 put a measured resistance value at maximum Vgs in a table chart

From IRF610 and IRF9610 table charts you can select the first pair from the ones that have most similar resistance values at all three Vgs voltages. In this way transconductance curves of the first pair are closely parallel-matched. Second pair is the second most matching combination from all three Vgs measurements, etc.

[Jay]

I lost track as of why IRF matching is discussed in this thread. Anyway, I have been waiting for anyone to mention about TSSA-HEXFET. TSSA-HEXFET is very different with other versions of TSSA/SSA. It is very cooperative (and very useful) and the performance is more like the F5 topology than the other SSA versions.

[Lazy Cat]

I'm just helping to select mosfet driver for BIGBT which is useful for anyone who will try this kind of output.

Hey Jay which specific hexfet are you interested in?

I didn't have time to work more on a TSSA basic, since I was ocupied with SSA upgrade but I promise I will. If you read the thread you can see that Sonnya and Gerhard already made it.

[Idefixes]

Hi LC new issue : Mouser have different grade for vas : E(hfe 100-200) for KSA and D(hfe 60-120) for KSC....that not top for PNP/NPN matching....

[Lazy Cat]

Originally Posted by Idefixes

Hi LC new issue : Mouser have different grade for vas : E(hfe 100-200) for KSA and D(hfe 60-120) for KSC....that not top for PNP/NPN matching....

Yes it is really not the best starting position, but first we have to know few things about (driven) cascodes here. KSA/KSC cascode BJT's hFE in TSSA can hardly influence only to initial DC offset (different voltage drop on R8, R9 as a result of their base current difference), which is in any case calibrated to zero with trimmers.

hFE of KSA/KSC doesn't influence the open loop gain value nor the linearity of TSSA amplifier. Their main job as cascodes is to maintain Vce of VAS gain transistor constant, that results in a reduced power dissipation (stable hFE), constant and smaller Cob (bandwidth extension) of VAS gain BJT. Cascode BJT role is mostly supporting one, main (gain) job here is still on VAS gain transistors (BC550/560C), which have to be matched to be complementary equal.

[Lazy Cat]

Nice supporting circuits you have Idefixes. In a soft-start circuit you could replace R4-R7 with this one.

[Idefixes]

So the main point lay in BC560C/550C matching. We have more room on KSA/KSC as when can calibrate initial DC offset with trimmer, the goal is to not have KSA and KSC at oposite hfe range (60 and 200) but to try to maintain they closed possible to the area 100-120. Have you a cross reference for KSA/KSC maybe 2SC3423/2SA1360 could do the job?

Marc

[Idefixes]

Originally Posted by Lazy Cat

Nice supporting circuits you have Idefixes. In a soft-start circuit you could replace R4-R7 with this one.

That's a good idee as it save a huge place. This could be used to build the speaker protection in the same board as softstart=> results in wiring simplification.

Marc

[Lazy Cat]

To resume IRF matching described in post #261 in short.

IRF matching is reduced to a form similar like finding the most equal "potentiometers", where mechanical scale is set to a certain position by accu & P, at which Ohm-meter readout is recorded for comparison.

[Idefixes]

Originally Posted by Lazy Cat

To resume IRF matching described in post #261 in short.

IRF matching is reduced to a form similar like finding the most equal "potentiometers", where mechanical scale is set to a certain position by accu & P, at which Ohm-meter readout is recorded for comparison.

Yes LC that was i have understanding from your process description. It's quite clear.

Marc