help wanted in this schematic

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Off set voltage and stand by current may be strange if you

have sligthly different voltages into the Integrated circuit...if your supply voltage is not controled by zener, not exactly the same voltage to the positive and negative rail voltages... both of them should be controled by zener diodes (+15 and -15 volts DC).... then.... if no zener exists (not sure if you're using them)...this will appear into the chip output... will result in strange off set and strange stand by bias current.

It is normal that transformers produces sligtly different voltage into positive rail compared to the negative rail.... this can produce strange voltages into the Integrated circuit output line too... as this chip amplifier output line controls the amplifier, any strange thing into the supply voltage will appear into the transistorized output.

Audio quality is because of this chip...if good it is because of this chip...if bad, also because of this chip.

I do not like chips.... we cannot make things..non tweakable black boxes.

This circuit seems to me to be very poor Sakis....i am glad it is working perfectly and stable, and also i am very surprised that you are wasting your time with this one....

Interesting... you was not satisfied with one of Bora's circuits, and this one cannot be compared to the Bora circuit you have tried... strange things happens too.

Enjoy!

Carlos
 
As you know Sakis... the power output depends from the supply voltage

With 80 volts rails... every amplifier can produce the power you have found.... and more than that sometimes.

So... the power is not because this one or other one.... it is because the supply voltage.

The amplifier can use all positive to negative swing or not to use, but it is not a sign of amplifier quality the production of power....better if does not use all voltage swing.... and this depends on the sensitivity.... and this is adjusted into the input feedback.

We must see how good is this power to your ears, and listening and comparing into A to B mode... or to instruments if you prefere and believe they show audio quality (I don't)... and how long time it will work, how stable it is while receiving complex signal into the input, when subjected to radio frequency interference, when submited to heat, to extreme audio high frequencies and when facing difficult speakers, difficult output crossovers, difficult loads.

I have made the fastest radio controled car in my place (into this scale..it was the slowest one... was transformed in super hiper turbo!)... i could win other boys alike me (i am a young kid internally)...but mine super powerfull car (over voltage into the motor) burned in a couple of minutes racing....not an advantage to be strong this way.

Power without reliability is not a very good idea.... do not know if this is your amplifier (if yours) sittuation or not....but i have strong suspections this one is not stable.

regards,

Carlos
 

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dear uncle charly !!!!

voltage of op amp is not a question comes of a fully regulated power supply from difefernt trafo to keep stabilty ( this is under investegation also )

it could be better that secondary psu off 15+15 volts is a separate trafo .....

tehn 5534 is very nice chip and almost famous of teh quality produces ....

then the quality produced of this amp is also given as a fact ...this is almost class B amplifier and you dont expect miaracles from it ....

but you expect it to be cheap to make powerfull like hell and stable with in the quality limits ....

its a minimalistic approach and can followed by the idea that les stages les places to be effected by any thing .....

hell awrong screw close to vas amplifier created so much capacitance and so much ocilation that was dc in the out any way ( mosfet amp ) in this amp there is no question that a thing like that might happen ....

when i am fivished with it i think is going to be solid rock

thanks though uncle charly .....seeing you here is an honour !!!!!!!
 
Re: Off set voltage and stand by current may be strange if you

destroyer X said:
Audio quality is because of this chip...
if good it is because of this chip...
if bad, also because of this chip. Carlos

Exactly, Carlos.
What op-amp you use will decide the overall performance.
> TL071 will have one quality.
> NE5534 will have a better quality.
> But NE5534 is not bad quality. Many like this op-amp.
:cool: Read forum topics!


However, if we use modern OPA627, AD797, LME49870
= Very High quality = better than NE5534.
But if works good with NE5534 & no problem with sound,
I would stay with NE5534.
Because we know not what will happen if we put some AD797 etc.
into this circuit :D :D
Maybe a big crash ..... :bawling:
 
Re: ok line up

sakis said:
fotios ...my friend !!!!

i think when you look at a target of a cheap made machine to produce arround 300w in a cheap way then 6 outputs is almost enough then one pair more may require base resistors which is ok but also may be possible to create ocilation ( quiet comon when you drive multiple outputs).and i will not be able to locate this easily ......

so far i think i ve been lucky cause even in this protoype ive made pp hand job ...all wave forms are very very clean ( compaired to how the tests were made with two seperate trafos and rails of 2.5 mm but almost 1 m long, no zobel, no inductor and generally a cable mess ) which normally "pick" up things on the way and then drive amp to oscilation ....well not in this case

even when my "board" and set up was very messy wave forms were very very clean .....

hell !!!! i produced almost 320w at full rail voltage almost 80v and i had a very clean sine wave on my scope while with the same messy set up a legend 4 mosfet amp with 40+40 volt rails and almost 100w power was oscilating cause it didnt like one earth loops created by the interconnects of power between my signal genarator and the scope ....amazing !!!!!

Saki, maybe you have missunderstand what i propossed. I don't disagree with the simplicity or CFP of your amp. This is your issue. Me, simply i propossed (from tose i have seen in your schematic there are two pairs of output transistors) in you to add one more pair so as the iddle current shared in three devices. Maybe this can drop down the temp. of heatsink. Only this.

Fotis
 
good morning macedonian !!!!

thanks for your help

first of all i allready added one more pair of outs any way since i thought only two pairs of outs in 75+75 is almost not enough .... that will probably share the idle ..... but idle was too much any way

to my understanding in this circuit in transistors Q1 and Q2 a bias is provided by R26 and R27 but since the amplifier was designed to work with other types of transistors this bias might not be proper for 2SA1943 and SC 5200

i am waiting for pcb now days and in this pcb i will expirament with 2x33K resistors in parallel to achive 16.5K which i think will do the job properly

where is all the guys that did me a math lesson some posts ago ??????

and aslo what i asked before about opinions on changing R26-27 and side effects ?????

any way ..... let us also not forget that this amplifier and the way its designed has efficiency of almost 70% so after all the extra pair is a luxury

regards Athenian
 
I am a big fan of simple amplifiers. This amplifier no doubt will sound good. I would be concerned for my speakers though since there is no thermal compensation. I am the last one to say to make a circuit more complicated, but, adding a better bias circuit would benifit this amp. Attached is a very good way of doing this with opamp input. Using mpsa06/56 as q1 and q3. This will give a way to adjust idle current for the output as well.
 

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Varying R26/27 will change the idle current through Q1/2 as well as Q3/4/5/6 ect.. It will also change the load presented to the opamp. This is also an advantage that the adjustable bias circuit has in that the load seen by the opamp will remain fairly constant. Unless you do beta matching so the bjts are the same for both channels these resistors can end up being different values for each channel to get the same idle current through the outputs. A very bothersome way to do things. Replacing R26/27 with current sources or bootstraps would further improve things as well as helping with power supply noise rejection.
 
thanks you very much

i am with you so far all the way just a couple of things .....

1-except the change of idle do you see any other side effects ????

2- do you have any opinion and or do you find critical the pcb design of this amp ???? one reason i can imagine is that the location of the op amp must be very critical since so much current flows all arround the device ( expected power >300 w)
 
Question 1: If these resistors are different between the channels there would be a slight difference in gain/feedback but probly not enough to make a difference.

Question 2: Just keep the high current traces away from the low current signal traces and there shouldn't be a problem.
 
jerluwoo said:

Attached is a very good way of doing this with opamp input. Using mpsa06/56 as q1 and q3.
This will give a way to adjust idle current for the output as well.

jerluwoo
your attached circuit to feed the output, via emitter input
is a way I often use for
VAS Output >>> Output Stage drive.

I could easily post you almost 10 amplifier schematics I have designed and tested in Simulation
using this nice idea.

Advantages:
You can drive the output from any source, not necessarily push-pull VAS stage.
Like from one Op-Amp output, as in your circuit.

After this we take feedback from Output
back to the Voltage Amplifier Stage

.... or back to These Emitters of the input (= power 'follower' with local negative feedback)


Regards Lineup
 
Please Jerluwoo, post a more complete schematic.

Your idea to substitute chips is very interesting...but the schematic is not complete...put supply voltages, filters, inform voltages and currents for us...a more detailed thing for us.... please.

I like... and very much.... the idea to substitute the input chip.. and in special if able to work into the same power amplifier voltage....not to have the audio swing limits resulted from the plus 15 and negative 15 volts DC supply.

Is this common base?.... strange way to connect the input.... but also very nice..... higher current together the input is very interesting.... having your input into the emitter, you can have more current "contribution" from the colector to emitter junction...this will change impedance.... interesting.

Please, if not asking too much...indicate the output current and voltage.... all transistor leads voltage and currents too.... say... the ones you suggest.... things you have made REAL world and listened...if made only into the simulator (untested real life) ...well.... this way will not be needed anymore, because i will not trust to try real life a sample of your circuit...i have simulator and i know the differences between them and real life.

Into your circuit, we will be able to introduce the off set control and bias control.

I know others have tried this...but i had not readed... i have enormous resistance to integrated circuits and everything connected to them...so i have not readed...but thinking once again into this subject, if we can make it discrete..will not be chip anymore and i feel better.

Since the day i found a dual transistor case... a chip case... two transistors into the same die.... 5 leads out... and i have measure the gain and found very different...them i said @&¨$%¨@%%@ to chips... what a hell.... cannot EVEN produce matched things?

regards,

Carlos
 
jerluwoo
your attached circuit to feed the output, via emitter input
is a way I often use for
VAS Output >>> Output Stage drive.

Hi

You will definitely want some sort of bias control that senses temperature, so mount these devices to the driver transistors for compensation. Replacing R26/27 with CCS's is a good improvement because if the line voltage fluctuates larger, the bias will remain constant.:up:



Hi Carlos

I have used monolithic transistor arrays and found them to be useless in positions requiring matched transistors. They also can crosstalk. It is just too convenient to be true.:rolleyes: You can buy matched transistor arrays that are really separate matched dies such as those from THAT corp. and there are others. But they are EXPENSIVE.:bigeyes:

Compare 40 cents to about 7-8 dollars!! ...if you buy 10 or more.:bawling: :smash:
 
Thanks CBS240, should have mentioned to mount them on the heatsink. I first saw this configuration used in an early 90's USAmps car amplifier. Opamp TL074 input into triple EF output. The amplifier was rated a mere 40 watts into 4 ohm but made about 270 watts bridged into 1 ohm, it trully was capable of some mad current output.
 
Ok .....

AFTER SUMMER VOCATION ......

pcb is going to be ready in just a couple of days and serious testing ....

The pcb is based on a piggy board idea ...so its actually one main board that includes the output devices, filters, zobel ,inductor ,power connectors ,output connectors ,ground and so on.

On the top of this will be one board of very small size that will include op amp local filters for the 15+15 volts and input connector .

The two boards are to be connected with a metal spacer of 3mm for the ground and three more leads from one board to the other ....

a generic picture can be found here http://www.diyaudio.com/forums/showthread.php?postid=1580163#post1580163
 
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