Very simple quasi complimentary MOSFET amplifier

[xrk971]

FWIW, I am using Abletec 53v dual rail SMPS for my VHEX+ amp and the ripple is less than my linear 300VA toroid with lots of caps and LC filter bank with 25,000uF per rail. Ripple with no load was 0.2mV with a simple 4700uF x 4 CRC filter between SMPS and amp. Continuous current is not as high at only 4.5amps for 5 min and 9amps for 10ms. But for my purposes of a 95w amp - perfectly suitable.

 

[thimios]

Hi Eric,

I have examined this and my thoughts are the a few values could be changed to optimise the harmonic profile based on what people have experimented with and auditioned:

C4 feedback shunt cap 470uF SHOULD BE 1000uF (more bass)
Q2 VAS master 2N5551 SHOULD BE KSA1845 (more bandwidth, higher beta)
Q3 VAS buffer MJE350 SHOULD BE KSA3503 (more bandwidth)
D7 Voltage Reference Blue LED SHOULD BE 3.3 ZENER (better tempco and not bright!)
C9 Bax cap 20nF filmcap SHOULD BE 22nF (20nF is not a npv)
R20/R21 OPS source/emitter resistors 3W wirewound SHOULD BOTH BE 0.33R (extends the conduction angle of Q6 nmos and improves stability of OPS quiescent current)

These are my beliefs for this amp, I will be building this too, and my voltage rails will be 42V, the absolute maximum for IRFP240 and 2SC5200.

If you want more power, up to 62V rails which will give you 200W, I would suggest a FQA40N15 nmos and a 2SC3264 Sanken, 280W and 200W respectively.

Hugh

Q3 VAS buffer MJE350 SHOULD BE KSA3503 (more bandwidth)
You mean ksa1381(pnp).

 

[AKSA]

Ah Thimios,
Yes and No! A3503 is very similar to A1381, both pnp TO126 high voltage and low Cob. The idea was to give options but I personally don't like the slow MJE350 although to be honest it's used as a buffer, a fast configuration.

HD

 

[still4given]

It is KSC3503 (NPN), and KSA1381 (PNP)

 

[e_fortier]

Can we then assume that Q3 = Q5 = KSA1381 ?

I want to make sure before I order my components ;-)

TIA,
Eric

 

[Ranchu32]

Yes Eric, that is correct.

 

[AKSA]

My mistake very late night....
HD

 

[Algar_emi]

Hi ASKA. You recommend for +42V the FQA40N15 nmos. It seems very difficult to get. I think you recommended an other NMOS in some of the post?
You mentioned also possibly the IRFP250 instead of the IRFP240. Any suggestion?

Alos in some other post you mentioned the MJL3281AG instead of the Saiken. Again can we used either?

Thanks
SB

 

[AKSA]

SB,
Here are a few devices taken straight from Digikey.com using their parametric search. There are about 33 of these devices needed here. Select one then check with me. Essentially, it should be rated to 250-300W, up to 40A continuous, and TO3-P or TO247 package. Voltage rating should be 150 to 250. You are in North America, Digikey is rather closer to me, and you have huge resources to find good mosfets!

BTW, the MJL3281 is NOT a 200W npn bipolar. You need a npn at 200W rating, but only if you using 50V rails or higher. If you are using 42V rails, IRFP240/250 and 2SC5200/MJL3281 is just fine.

Ciao,

Hugh

STW40NF20 Datasheet STW40NF20 - STMicroelectronics 497-5807-5-ND

This part is RoHS compliant.
STW40NF20 STMicroelectronics MOSFET N-CH 200V 40A TO-247 680 - Immediate
3.58000 1 Tube? STripFET™ MOSFET N-Channel, Metal Oxide Standard 200V 40A (Tc) 45 mOhm @ 20A, 10V 4V @ 250µA 75nC @ 10V 2500pF @ 25V 160W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247-3
IRFP264PBF Datasheet IRFP264PBF - Vishay Siliconix IRFP264PBF-ND

This part is RoHS compliant.
IRFP264PBF Vishay Siliconix MOSFET N-CH 250V 38A TO-247AC 3,656 - Immediate
4.00000 1 Tube?
-
MOSFET N-Channel, Metal Oxide Standard 250V 38A (Tc) 75 mOhm @ 23A, 10V 4V @ 250µA 210nC @ 10V 5400pF @ 25V 280W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247-3
IXFH40N30 Datasheet IXFH40N30 - IXYS IXFH40N30-ND

This part is RoHS compliant.
IXFH40N30 IXYS MOSFET N-CH 300V 40A TO-247AD 494 - Immediate
9.95000 1 Tube? HiPerFET™ MOSFET N-Channel, Metal Oxide Standard 300V 40A (Tc) 85 mOhm @ 500mA, 10V 4V @ 4mA 200nC @ 10V 4800pF @ 25V 300W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247AD (IXFH)
FDA38N30 Datasheet FDA38N30 - Fairchild Semiconductor FDA38N30-ND

This part is RoHS compliant.
FDA38N30 Fairchild Semiconductor MOSFET N-CH 300V TO-3 802 - Immediate
29,700 - Factory Stock

3.45000 1 Tube? UniFET™ MOSFET N-Channel, Metal Oxide Standard 300V 38A (Tc) 85 mOhm @ 19A, 10V 5V @ 250µA 60nC @ 10V 2600pF @ 25V 312W -55°C ~ 150°C (TJ) Through Hole TO-3P-3, SC-65-3 TO-3PN
STW46NF30 Datasheet STW46NF30 - STMicroelectronics 497-13595-5-ND

This part is RoHS compliant.
STW46NF30 STMicroelectronics MOSFET N-CH 300V 42A TO247 1,001 - Immediate
6.20000 1 Tube? STripFET™ II MOSFET N-Channel, Metal Oxide Standard 300V 42A (Tc) 75 mOhm @ 17A, 10V 4V @ 250µA 90nC @ 10V 3200pF @ 25V 300W 175°C (TJ) Through Hole TO-247-3 TO-247
IXFH40N30Q Datasheet IXFH40N30Q - IXYS IXFH40N30Q-ND

This part is RoHS compliant.
IXFH40N30Q IXYS MOSFET N-CH 300V 40A TO-247AD 479 - Immediate
9.95000 1 Tube? HiPerFET™ MOSFET N-Channel, Metal Oxide Standard 300V 40A (Tc) 80 mOhm @ 500mA, 10V 4V @ 4mA 140nC @ 10V 3100pF @ 25V 300W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247AD (IXFH)
IXFH42N20 Datasheet IXFH42N20 - IXYS IXFH42N20-ND

This part is RoHS compliant.
IXFH42N20 IXYS MOSFET N-CH 200V 42A TO-247AD 1,948 - Immediate
12.00000 1 Tube? HiPerFET™ MOSFET N-Channel, Metal Oxide Standard 200V 42A (Tc) 60 mOhm @ 500mA, 10V 4V @ 4mA 220nC @ 10V 4400pF @ 25V 300W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247AD (IXFH)
IRFP3415PBF Datasheet IRFP3415PBF - Infineon Technologies IRFP3415PBF-ND

This part is RoHS compliant.
IRFP3415PBF Infineon Technologies MOSFET N-CH 150V 43A TO-247AC 6,238 - Immediate
2.69000 1 Bulk? HEXFET® MOSFET N-Channel, Metal Oxide Standard 150V 43A (Tc) 42 mOhm @ 22A, 10V 4V @ 250µA 200nC @ 10V 2400pF @ 25V 200W -55°C ~ 175°C (TJ) Through Hole TO-247-3 TO-247AC
FQA40N25 Datasheet FQA40N25 - Fairchild Semiconductor FQA40N25FS-ND

This part is RoHS compliant.
FQA40N25 Fairchild Semiconductor MOSFET N-CH 250V 40A TO-3P 234 - Immediate
6,750 - Factory Stock
?
3.28000 1 Tube? QFET® MOSFET N-Channel, Metal Oxide Standard 250V 40A (Tc) 70 mOhm @ 20A, 10V 5V @ 250µA 110nC @ 10V 4000pF @ 25V 280W -55°C ~ 150°C (TJ) Through Hole TO-3P-3, SC-65-3 TO-3PN
IRFP4229PBF Datasheet IRFP4229PBF - Infineon Technologies IRFP4229PBF-ND

This part is RoHS compliant.
IRFP4229PBF Infineon Technologies MOSFET N-CH 250V 44A TO-247AC 168 - Immediate
3.79000 1 Tube? HEXFET® MOSFET N-Channel, Metal Oxide Standard 250V 44A (Tc) 46 mOhm @ 26A, 10V 5V @ 250µA 110nC @ 10V 4560pF @ 25V 310W -40°C ~ 175°C (TJ) Through Hole TO-247-3 TO-247AC
IRFP4137PBF Datasheet IRFP4137PBF - Infineon Technologies IRFP4137PBF-ND

This part is RoHS compliant.
IRFP4137PBF Infineon Technologies MOSFET N-CH 300V 38A TO-247AC 1,006 - Immediate
5.07000 1 Tube? HEXFET® MOSFET N-Channel, Metal Oxide Standard 300V 38A (Tc) 69 mOhm @ 24A, 10V 5V @ 250µA 125nC @ 10V 5168pF @ 50V 341W -55°C ~ 175°C (TJ) Through Hole TO-247-3 TO-247AC
FQA44N30 Datasheet FQA44N30 - Fairchild Semiconductor FQA44N30-ND

This part is RoHS compliant.
FQA44N30 Fairchild Semiconductor MOSFET N-CH 300V 43.5A TO-3P 420 - Immediate
900 - Factory Stock
?
5.35000 1 Tube? QFET® MOSFET N-Channel, Metal Oxide Standard 300V 43.5A (Tc) 69 mOhm @ 21.75A, 10V 5V @ 250µA 150nC @ 10V 5600pF @ 25V 310W -55°C ~ 150°C (TJ) Through Hole TO-3P-3, SC-65-3 TO-3PN
IXTQ36N30P Datasheet IXTQ36N30P - IXYS IXTQ36N30P-ND

This part is RoHS compliant.
IXTQ36N30P IXYS MOSFET N-CH 300V 36A TO-3P 43 - Immediate
3.75000 1 Tube? PolarHT™ MOSFET N-Channel, Metal Oxide Standard 300V 36A (Tc) 110 mOhm @ 18A, 10V 5.5V @ 250µA 70nC @ 10V 2250pF @ 25V 300W -55°C ~ 150°C (TJ) Through Hole TO-3P-3, SC-65-3 TO-3P
IXTH40N30 Datasheet IXTH40N30 - IXYS IXTH40N30-ND

This part is RoHS compliant.
IXTH40N30 IXYS MOSFET N-CH 300V 40A TO-247AD 8 - Immediate
11.29000 1 Tube? MegaMOS™ MOSFET N-Channel, Metal Oxide Standard 300V 40A (Tc) 85 mOhm @ 500mA, 10V 4V @ 250µA 220nC @ 10V 4600pF @ 25V 300W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247 (IXTH)
AOK40N30L Datasheet AOK40N30L - Alpha & Omega Semiconductor Inc. 785-1447-5-ND

This part is RoHS compliant.
AOK40N30L Alpha & Omega Semiconductor Inc. MOSFET N-CH 300V 40A TO247 0
Standard Lead Time 12 Weeks
1.88000 480
Non-Stock
? Tube?
-
MOSFET N-Channel, Metal Oxide Standard 300V 40A (Tc) 85 mOhm @ 20A, 10V 4.1V @ 250µA 72nC @ 10V 3270pF @ 25V 357W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247

-
IXTH36N20T - IXYS IXTH36N20T-ND

This part is RoHS compliant.
IXTH36N20T IXYS MOSFET N-CH 200V 36A TO-247 0
2.49767 30
Non-Stock
? Tube?
-
MOSFET N-Channel, Metal Oxide Standard 200V 36A (Tc)


Through Hole TO-247-3 TO-247 (IXTH)
IXTQ42N25P Datasheet IXTQ42N25P - IXYS IXTQ42N25P-ND

This part is RoHS compliant.
IXTQ42N25P IXYS MOSFET N-CH 250V 42A TO-3P 0
Standard Lead Time 8 Weeks
3.01500 30
Non-Stock
? Tube? PolarHT™ MOSFET N-Channel, Metal Oxide Standard 250V 42A (Tc) 84 mOhm @ 500mA, 10V 5.5V @ 250µA 70nC @ 10V 2300pF @ 25V 300W -55°C ~ 150°C (TJ) Through Hole TO-3P-3, SC-65-3 TO-3P

-
IXTQ44N30T - IXYS IXTQ44N30T-ND

This part is RoHS compliant.
IXTQ44N30T IXYS MOSFET N-CH 300V 44A TO-3P 0
3.37500 30
Non-Stock
? Tube?
-
MOSFET N-Channel, Metal Oxide Standard 300V 44A (Tc)
-

Through Hole TO-3P-3, SC-65-3 TO-3P


IXTH44N30T - IXYS IXTH44N30T-ND

This part is RoHS compliant.
IXTH44N30T IXYS MOSFET N-CH 300V 44A TO-247 0
3.51000 30
Non-Stock
? Tube?
-
MOSFET N-Channel, Metal Oxide Standard 300V 44A (Tc)

-
Through Hole TO-247-3 TO-247 (IXTH)
FKP280A Datasheet Photo Not Available FKP280A-ND

This part is RoHS compliant.
FKP280A Sanken MOSFET N-CH 280V 40A TO-3PF 0
3.60450 1,500
Non-Stock
? Bulk?
-
MOSFET N-Channel, Metal Oxide Standard 280V 40A (Ta) 53 mOhm @ 20A, 10V 4.5V @ 1mA
-
3800pF @ 25V 85W 150°C (TJ) Through Hole TO-3P-3 Full Pack TO-3PF
RJK2009DPM-00#T0 Datasheet RJK2009DPM-00#T0 - Renesas Electronics America RJK2009DPM-00#T0-ND

This part is RoHS compliant.
RJK2009DPM-00#T0 Renesas Electronics America MOSFET N-CH 200V 40A TO3PFM 0
Standard Lead Time 16 Weeks
6.04000 1
Non-Stock
? Tube?
-
MOSFET N-Channel, Metal Oxide Standard 200V 40A (Ta) 36 mOhm @ 20A, 10V
-
72nC @ 10V 2900pF @ 25V 60W
-
Through Hole TO-3PFM, SC-93-3 TO-3PFM
IXTH41N25 Datasheet IXTH41N25 - IXYS IXTH41N25-ND

This part is RoHS compliant.
IXTH41N25 IXYS MOSFET N-CH 250V 41A TO-247A 0
6.19100 30
Non-Stock
? Tube?
-
MOSFET N-Channel, Metal Oxide Standard 250V 41A (Tc) 72 mOhm @ 15A, 10V 4V @ 250µA 110nC @ 10V 3200pF @ 25V 300W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247 (IXTH)
APT30M85BVRG Datasheet APT30M85BVRG - Microsemi Corporation APT30M85BVRG-ND

This part is RoHS compliant.
APT30M85BVRG Microsemi Corporation MOSFET N-CH 300V 40A TO-247 0
9.80958 48
Non-Stock
? Tube? POWER MOS V® MOSFET N-Channel, Metal Oxide Standard 300V 40A (Tc) 85 mOhm @ 500mA, 10V 4V @ 1mA 195nC @ 10V 4950pF @ 25V 300W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247
APT30M85BVFRG Datasheet APT30M85BVFRG - Microsemi Corporation APT30M85BVFRG-ND

This part is RoHS compliant.
APT30M85BVFRG Microsemi Corporation MOSFET N-CH 300V 40A TO-247 0
11.17357 42
Non-Stock
? Tube? POWER MOS V® MOSFET N-Channel, Metal Oxide Standard 300V 40A (Tc) 85 mOhm @ 500mA, 10V 4V @ 1mA 195nC @ 10V 4950pF @ 25V 300W -55°C ~ 150°C (TJ) Through Hole TO-247-3 TO-247
AUIRFP4409 Datasheet AUIRFP4409 - Infineon Technologies AUIRFP4409-ND

This part is RoHS compliant.
AUIRFP4409 Infineon Technologies MOSFET N-CH 300V 38A TO-247AC 0
Standard Lead Time 11 Weeks
3.79436 250
Non-Stock
? Tube? HEXFET® MOSFET N-Channel, Metal Oxide Standard 300V 38A (Tc) 69 mOhm @ 24A, 10V 5V @ 250µA 125nC @ 10V 5168pF @ 50

 

[Idefixes]

Nice liste Hugh, no reason to find the good one?

MJL3281A is a 15A/200W NPN (taken from onsemi datasheet)

Marc

 

[farjon]

can please verify electrolytics voltages?

Dacz, please look at Q1 in your schematic. The symbol at post #1122 should be PNP...

Rgds.

 

[Dacz]

thanks farjon well spotted.

 

[Zero D]

I think that including a cap in that position should help to prevent garbage from the Neg PS getting into the input. 100uf should be plenty, but more wouldn't hurt ! I realise there is C3/22uf but even so ....

Very interesting, & low component count circuit

 

[minek123]

thanks farjon well spotted.

Is it RACHU, or should be RANCHU on your diagram?
I guess that would be the LAST mistake

 

[AKSA]

Zero D,

Not required. I tested on another amp with low noise and there was no benefit and slowed the settle of the offset.

Hugh

 

[thiagomogi]

Hi Hugh,


I played a lot with my Quasi .
Now Q3 and Q5 is 2sa1538 - FT 400mhz - 2.1pF COB
Q2 must be high FT and low COB ?
R20 and R21 is 0R47
I want to go a little more the value of R20 and R21 ... what is the maximum ?
The sound is very good.
A little noise when not connected to the DAC .

Regards

Thiago

 

[AKSA]

Hi Thiago,

In my experience I have found that only Q2, the voltage amp, should be high Ft and low Cob. The buffer, Q3, is an emitter follower and this is a very fast configuration just about any device, even a BD140, is just fine here. The phase inverter, Q5, is operating like Q2, a common emitter with wide voltage range, and it needs to be fast device too so a A1381 or A1538, both with low Cob.

Now, R20/R21, the source/emitter resistors respectively are interesting. Since this amp has a global feedback around 31dB, say 38 times, theoretically increasing these resistors, particularly the source resistor, affects the Zout of the amp, which is already pretty low, though not the same with each half cycle. If you increase them, the sensitivity of the quiescent current decreases, but in either case, 0.33R up to about 2.2R setting the quiescent is not difficult. At 0.33R the upper device, the nmos, stays ON right through the waveform, meaning that it never turns off and the 'crossover' from this device is reduced, though this phenomenon is not strictly a problem for a quasi. The lower device, the npn, WILL turn on and off as the waveform passes into negative territory, but it's switching is very clean, a characteristic of bipolars in complementary configurations.

If you go higher for both resistors, to 0.47R and even to 1R, the quiescent current is more stable, and the upper device is harder throughout the signal, that is, it does not go very low, but no longer than about 40mA even at full clip. The penalty is the clip point; the amp will clip earlier, and furthermore the Zout will increase. With 1R R20 and R21, the nmos will dip down to 28mA at 105mA nmos quiescent for just under clip at 35.2V with 42V rails. Reduce them to 0.33R, and the conditions change to 13.5mA at 105mA nmos quiescent and just under clip at 37.2V with 42V rails.

I have not checked distortion, but I would think it would sound different, and you might like to experiment. Just be careful to ensure that you set the quiescent at the same current; I have used 105mA at the nmos, and around 97mA at the npn. Some people think that a higher Zout loosens the bass response; another way of saying this is that the bass has more decay. Some think that sounds better, in the same way as a tube amp delivers bass.

Cheers,

Hugh

 

[thiagomogi]

Hi Hugh .
Thanks again for this lot of information.
It's been really fun for me this amp .
I will try and report on MOD.

Regards

Thiago

 

[xrk971]

Hi Thiago,

In my experience I have found that only Q2, the voltage amp, should be high Ft and low Cob. The buffer, Q3, is an emitter follower and this is a very fast configuration just about any device, even a BD140, is just fine here. The phase inverter, Q5, is operating like Q2, a common emitter with wide voltage range, and it needs to be fast device too so a A1381 or A1538, both with low Cob.

Now, R20/R21, the source/emitter resistors respectively are interesting. Since this amp has a global feedback around 31dB, say 38 times, theoretically increasing these resistors, particularly the source resistor, affects the Zout of the amp, which is already pretty low, though not the same with each half cycle. If you increase them, the sensitivity of the quiescent current decreases, but in either case, 0.33R up to about 2.2R setting the quiescent is not difficult. At 0.33R the upper device, the nmos, stays ON right through the waveform, meaning that it never turns off and the 'crossover' from this device is reduced, though this phenomenon is not strictly a problem for a quasi. The lower device, the npn, WILL turn on and off as the waveform passes into negative territory, but it's switching is very clean, a characteristic of bipolars in complementary configurations.

If you go higher for both resistors, to 0.47R and even to 1R, the quiescent current is more stable, and the upper device is harder throughout the signal, that is, it does not go very low, but no longer than about 40mA even at full clip. The penalty is the clip point; the amp will clip earlier, and furthermore the Zout will increase. With 1R R20 and R21, the nmos will dip down to 28mA at 105mA nmos quiescent for just under clip at 35.2V with 42V rails. Reduce them to 0.33R, and the conditions change to 13.5mA at 105mA nmos quiescent and just under clip at 37.2V with 42V rails.

I have not checked distortion, but I would think it would sound different, and you might like to experiment. Just be careful to ensure that you set the quiescent at the same current; I have used 105mA at the nmos, and around 97mA at the npn. Some people think that a higher Zout loosens the bass response; another way of saying this is that the bass has more decay. Some think that sounds better, in the same way as a tube amp delivers bass.

Cheers,

Hugh

Hi Hugh,
A lot of neat things to try on tweaking this amp. Thanks for all the info.
It sounds like you built one of these amps. Can we see a photo of yours?
Thanks,
X

 

[AKSA]

X,

Thanks for the post; I built one of these three years ago with Richard in my home town in South Australia. He went on to sell it in Oz as the Quasimodo. We'd done the design together, so I'm passing aware of the details. BUT no, no amp just yet, I've asked Prasi to rejig one of my pcbs which went south when the Protel software screw a loose......

Since then, I've bought DipTrace, and so I'm starting the long, arduous learning curve. Right now I'm am filling orders for my new Maya and SAKSA, so the quasi will have to wait a bit longer.......

Cheers,

Hugh