Another quasi-complementary design

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#162
Just don't forget to inspect the actual frequency curves for op amp PSRR. Some can have an impressive PSRR but with a very low frequency pole. For instance LT1028 has a positive PSRR of 140 dB, but is down to 90 dB already at 100 Hz!!! Also note that there can be quite a difference between the positive and negative PSRR in many cases, which may matter for decoupling. Once again time to recommend this app note
www.analog.com/UploadedFiles/Application_Notes/135208865AN-202.pdf
(it seems the link was broken for the moment, but hopefully that's just a temporary problem).
 
#164
Hi , QUASI

I see something has happened a lot .
Also I see nice job.
- explain me how you managed to mount DRIVER -PCB
- how to mount 2x irf9610 & BD 139, because BD 139 mast be on main heatsink( output tr.s )
- what do you think & how to put 2N3773 instead IRFP 240, because I, have 253 pcs original MOTOROLA (new)
- and for last how you spend christmas & others holydays

HI WHO DARES WINS
 
#165
Hey Zeonrider,

Holidays were very nice thankyou. Had my wifes family over at our house for Christmas lunch (too much food and drink). We saw my family later that day (more food and drink).

Earlier in this thread I posted PDF files showing a two PCB layout showing how the devices are mounted. The driver board can be mounted in line and close to the output board.

The other design "power amp under development" can be modified to use 2N3773s but will require very strong driver transistors to handle the drive current.

I'll try and post a schematic in the next week or so.

Ciao
 
#168
Re: Hi Quasi again !

zeonrider said:
I forgot to ask you ,
how you made +Vcc + 10v?, sorry, dont forget 2N3773.


HI WHO DARES WINS

CAO to YOU !
Click to expand...


The rail +10 voltage is provided by another winding on the transformer and the voltage is not that important (10-20 is okay). It can be 25-35 turns* added to one of the secondary windings to give at least another 8v. This and the centre tap is then rectified with a seperate diode bridge with the negative going to ground.

Use a 470uF 150v capacitor plus a 0.1uF (150v) to smooth the DC.

*dependant on the transformer.

Cheers
 
#169
MikeB said:
Lumanauw, your word "can benefit" was way to harmless, in fact high PSRR is one of the keys to a good sounding amp... High PSRR is mandatory. An amp with low PSRR connected to weak powersupply will distort as hell with odd harmonics, no matter of how much feedback it uses.

Mike
Click to expand...


Christer said:
Just don't forget to inspect the actual frequency curves for op amp PSRR. Some can have an impressive PSRR but with a very low frequency pole. For instance LT1028 has a positive PSRR of 140 dB, but is down to 90 dB already at 100 Hz!!! Also note that there can be quite a difference between the positive and negative PSRR in many cases, which may matter for decoupling. Once again time to recommend this app note
www.analog.com/UploadedFiles/Application_Notes/135208865AN-202.pdf
(it seems the link was broken for the moment, but hopefully that's just a temporary problem).
Click to expand...


High PSRR is a good factor.
Christer also tells that PSRR is most often strongly frequency dependant.

How important is PSRR?

As MikeB say it:
An amp with low PSRR connected to weak powersupply will distort as hell with odd harmonics, no matter of how much feedback it uses.

In a weak or normal power supply, it means a lot!
If your amplifier does not in it self have good rejection ratio,
you need to make your power supply very clean.
Maybe use regulation or extreme filtering.
Maybe use 2-3 different regulatad power supplies - one for each stage.


So by making a simple amplifier - with lower PSRR
you might need to build a power supply that is way more complicated than your amplifier.
And it will work good.

We can say that good OP-amps have built in regulation, its own internal power supply, with current sources.
This makes them less sensitive to a bad external supply.
 
#175
Quasi:


I would like to build your amp design, but I am looking at implementing an audio-tracking supply. (continuously variable SMPS with a Vmin of 10V and Vmax of 75V).

It is understood that a floating 10V supply will also be provided, which will be anchored to the V+ supply rail, to generate MOSFET enhancement bias.

This means the front end will experiance a bumpy ride with its V+ jumping around between 20V and 85V.

Can the front end accomodate this?

For simplicity's sake, assume for a moment the supply is not continuously variable, but just a single-step, with a VCC( lo) of 20V and VCC(hi) of 75V. Would that cause a problem at the front end?

thanks
Andy
 
#177
The second positive rail is not really a floating supply. It is simply another rail 10v higher than the output positive rail. So if the output rail is 80v then tha front end supply is 90v. Both of these are tied to ground.

Resistor R7 (27k) is there to take voltage away from the ccs T2. The resistor drops 49 volts so the negative rail must not go below about 53 volts or so, otherwise the ccs stops working.

So I have specified the amp as workable for a voltage range of 60 - 90v and these voltages must remain reasonably constant.

Cheers
 
#178
lineup:

I think that keeping the rails of the small signal stages always at its maximum value is advantageous, particularly in terms of PSRR and switching regulator ripple rejection. Furthermore, the increase in dissipation is very small.
 
#180
Thanks Hugh,

The two board design became too hard. With the second stage transistors placed on the PCB edge I couldn't find room to lay the surrounding components and tracks, so I went back to the board mounted small heatsink. This allowed me to use the space under the heatsink.

It's possible I'll be in Melbourne in the next 2-3 weeks to attend a seminar there. I'll let you know when dates are set.

For more sensible constructors here is a more compact 6 FET PCB. This is the one I will be building as the prototype.

Cheers
 

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