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Old 10th October 2013, 09:54 PM   #11
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Quote:
Originally Posted by dadod View Post
What models did you use?
BR Damir
Just mainstream stuff. Sorry, I can't remember where I got from (it's a long time ago). Anyhow, these models were way too simplistic and didn't account for the sub-threshold trans-conduction.

Cheers, E.
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Old 11th October 2013, 04:06 AM   #12
danny92 is offline danny92  Portugal
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Hi everyone,

I've modified the astx's circuit present in the thread entitled "2stageEF high performance class AB power amp / 200W8R / 400W4R", and now I've lower THD20 characteristics [0.007% with 4 ohm (at maximum power), 0.006% with 8 ohm (at maximum power)], and those results are fine to me, but THD1 characteristics are a little high [0.0007% with 4 ohm (at maximum power), 0.0007% with 8 ohm (at maximum power)]. I've to thank to astx, that's a fine amp
What's the secret of this amp? It's the double EF? This circuit it's similar to my circuit. How I can get lower THD1 with this design, with my design I've higher THD20 characteristics (maximum 0.01%), but lower THD1 characteristics (maximum 0.00008 %). I can have an amp that can combine the THD1 characteristics from my amp with the good THD20 characteristics of the double EF amplifier by astx, is that possible?

Best regards,
Daniel
Attached Files
File Type: asc 2stageEF_class_AB_power_amplifier.asc (27.4 KB, 33 views)
File Type: txt Cordell Models.txt (19.2 KB, 10 views)
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Old 11th October 2013, 06:12 AM   #13
danny92 is offline danny92  Portugal
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Hi everyone,

I think that I finally hit it my objective, I've to thank you all, especially to astx and ostripper (Peter V), this amp is capable of perform 200W/4 ohm with THD20 of less than 0.005 % and 100W/8 ohm with THD20 of less than 0.004 %
THD1 remains bellow 0.0001 %, (4 Wrms into 8 ohm with 0.000004 % THD1 xD).
To achieve this I've removed the zobel networks (because they cause a huge phase lag) from the MOSFETs and EF, and than with more phase to spare, I can use lower TMC values to increase slew rate
The reverse of this improvement is less OPS stability, due to the absence of zobel networks, but I don't see another option, zobels kill the amps phase margin :P
Now the amp has 68 degrees PM, acceptable, right?
I'm a little concerned about OPS local stability while driving inductive and capacitive loads
Circuit diagram attached + models

Best regards,
Daniel
Attached Files
File Type: txt Cordell Models.txt (19.2 KB, 15 views)
File Type: asc Amp7_tmc_hb5.asc (16.0 KB, 23 views)

Last edited by danny92; 11th October 2013 at 06:16 AM.
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Old 11th October 2013, 01:36 PM   #14
astx is offline astx  Austria
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Dear Daniel,

you may try some of these steps:
  • try to use BC550C or BC337-40 for Q13/Q14/Q5
  • try to use BC560C or BC327-40 for Q4/Q7
  • try to use KSC1845 for Q11
  • split R6 into R6a and R6b and check when Q12 begins to limit current on maximum load or overload - it should not start current limiting of Q5 even if you are at or near clipping.
  • add 47 - 100R to Q17 base
  • add 47 - 100R to bases of Q15/Q16 and add a capacitor 22µ parallel to D5
  • replace D1-D4 by a green LED and add a parallel capacitor 22µ
Maybe this betters your THD values a bit - but don't look to much on simulated THD ppm - real world measurements are often totally different.
Run SOA tests to be sure your output drivers and power fets will survive.
And then it would be time to build a prototype to verify that your BUZ901/ BUZ906 do what you want.

Good luck, Toni
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Old 11th October 2013, 01:44 PM   #15
astx is offline astx  Austria
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Dear Daniel,

forgot to say: don't skip zobel and output coils. This helps to keep your amplifier and speaker running and avoids high frequency oscillation on complex load or EMI from outside. E.g. use split zobels:

amplifier output - 47nF/10R - 1µH coil ||10R - 47nF/10R - speaker output

I have done many measurements and hearing test - this filter doesn't kill your good THD values.

Br, Toni
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Old 11th October 2013, 04:50 PM   #16
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Add Hawksford?
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Old 11th October 2013, 09:57 PM   #17
danny92 is offline danny92  Portugal
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Hi everyone,

I've made some changes as astx suggested, the ones that I've seen that slightly lower THD, and I've added the capacitors. Now I'm concerned about a gain peaking appearing at the MHz region, I don't know if that's normal or it's some form of instability that should be avoided (vout bode plots with v1 influence and vin influence attached). After solving this problem, if it's necessary, I'm thinking in incorporating a simple output protection circuit, maybe similar to the one that astx used, how the values are calculated?
Do you think that I should use a Hawksford error correction circuit like bear suggested?
I don't know almost anything about error correction.
It seems that the problem that causes this peaking is in the IPS or VAS (TCS or TIS) because the amp7_tmc.asc circuit has a similar IPS-VAS topology and BJT output and the same happens. With NPN (IPS) and PNP (VAS) there's almost no peaking, like in circuit amp7_tmc_hb6.asc

PS (about amp7_tmc_hb5.asc): The amplifier has good square wave response, without overshoot.
The circuit's phase margin is 68 degrees.

Best regards,
Daniel
Attached Images
File Type: jpg amp7_tmc_hb5_vout_v1.jpg (242.5 KB, 382 views)
File Type: jpg amp7_tmc_hb5_vout_vin.jpg (263.5 KB, 376 views)
Attached Files
File Type: asc Amp7_tmc_hb5.asc (16.7 KB, 8 views)
File Type: txt Cordell Models.txt (19.2 KB, 1 views)
File Type: asc Amp7_tmc.asc (9.6 KB, 4 views)
File Type: asc Amp7_tmc_hb6.asc (23.3 KB, 5 views)

Last edited by danny92; 11th October 2013 at 10:19 PM.
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Old 12th October 2013, 02:42 AM   #18
danny92 is offline danny92  Portugal
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Hi everyone,

That peaking was caused because of the MJE340 on the VAS cascode, replaced VAS transistors with KSA1381/KSC3503, and know that's fine

Best regards,
Daniel
Attached Files
File Type: asc Amp7_tmc_hb5.asc (16.7 KB, 7 views)

Last edited by danny92; 12th October 2013 at 02:57 AM.
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Old 12th October 2013, 03:55 AM   #19
danny92 is offline danny92  Portugal
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Hi everyone,

That's right the KSC3503/KSA1381 pair does a good a job at the VAS, a small reduction in THD1, I still with 68º phase margin and 11 dB gain margin, there's no peakings on open and closed loop bode plots and now I can use 330 ohm for the N MOSFET gates and 220 ohm for the P MOSFET gates as suggested by Semelab to prevent local parasitic oscillations
I'm still interested on astx's simple VI limiter circuit, what I have to do to adapt it?

PS: I don't have the KSC1845 models for LTSpice, can you give them to me please?
The split resistors for Q15/Q16 are a good or a bad idea?
And as about adding the Hawksford error correction circuit, it's a good or bad idea?


Best regards,
Daniel
Attached Images
File Type: jpg amp7_tmc_hb5_s.jpg (159.0 KB, 362 views)
File Type: jpg amp7_tmc_hb5_s_clg.jpg (339.5 KB, 359 views)
Attached Files
File Type: asc Amp7_tmc_hb5_s.asc (16.8 KB, 8 views)
File Type: txt Cordell Models.txt (19.2 KB, 6 views)

Last edited by danny92; 12th October 2013 at 04:08 AM.
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Old 12th October 2013, 08:51 AM   #20
astx is offline astx  Austria
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Quote:
Originally Posted by danny92 View Post
...
I'm still interested on astx's simple VI limiter circuit, what I have to do to adapt it?
...
read the SOA parts in "2stageEF ..." thread. Build your own SOA curve for your BUZ90X's, e.g.: use step feature of LTSpice using low ohmic output load at full power to find the correct resistor values.
Maybe you want to experiment with single or dual slope VI limiter - ask Michael Kiwanuka (PM him @ michaelkiwanuka) for his excellent SOA paper.

Quote:
Originally Posted by danny92 View Post
...
PS: I don't have the KSC1845 models for LTSpice, can you give them to me please?
...
download "my_libs.lib" from my "2stageEF ..." thread

Quote:
Originally Posted by danny92 View Post
...
The split resistors for Q15/Q16 are a good or a bad idea?
...
EF's are prone to oscillation so I try to use them whenever possible.

BR, Toni
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