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Old 27th June 2008, 12:12 AM   #51
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Quote:
Originally posted by mannycc
Hi Space,

just like you, Iím just a hobbyist and understand only a little bit of things. I previously built amps in the past and now beginning to dip my toes again (slowly).

b. regards,
mannycc

Audio amps are very interesting and cover a huge range of electronic disciplines.
I have been in electronics 30+ years and still dont understand every in and out of amplifiers.

Its fun learning tho !
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Old 27th June 2008, 02:36 PM   #52
mannycc is offline mannycc  Singapore
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QTE
Audio amps are very interesting and cover a huge range of electronic disciplines.
I have been in electronics 30+ years and still dont understand every in and out of amplifiers.

Its fun learning tho !
UNQTE

We are on the same boat, it's one of those sentiments you feel challenged and glad to face! Let's move on!

Regards.
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Old 27th June 2008, 02:43 PM   #53
mannycc is offline mannycc  Singapore
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Sure Space! Just donít remember the thread where I got this, Iíll post it here for everyone to see and would welcome the comments from the experts as well. To start with and because of the amps simplicity there are some ideas and possibilities I wish to explore;
1. The amp used series of opamp configured as current amplifier, my idea is to bypass and minimize the opamps to remove the distortion they may create.
2. The feedback opamp is configured as comparator (or maybe), so I will only know once I have a working amp.
3. The 1st opamp is designed for gain but instead can be substituted with active tone control or just design for preamp.
4. Lastly, the amp design is so simple and so Iím having a mixed thought because of this! The idea of less part means less distortion (or otherwise), but may also mean more unwanted unfiltered signal.

I really need to build this amp and proved my ideas wrong!

Regards.
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Old 27th June 2008, 04:41 PM   #54
Mooly is online now Mooly  United Kingdom
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Hi,
Well it's different ! The bias for the outputs, I guess you are thinking of a fixed bias scheme but those four diodes need reversing by the way or it will just turn the outputs hard on and pop something. The 12 k resistors will just turn both output pairs on together. You don't need all those OpAmps either the middle two can be ommited, just feed the output from the first into the final OpAmp AC coupled if needs be together with a suitable resistor to the non inverting input and ground as a DC reference. What does the pot do and don't say volume. It will not reduce the gain below 1.
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Old 6th July 2008, 06:29 AM   #55
EMX_125 is offline EMX_125  Philippines
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Hi.... Space2000

I See Your Amp you Used a sanken Power Transistors This is My Favorite Transistors Like My Amp so Can I See Your Schematic Diagram?

Thanks......
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Old 6th July 2008, 07:03 AM   #56
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Default There's a problem here Mannyc

The output does not amplify voltage.... the amplification into those darlingtons you have (those two transistors up, the driver and the output one is connected darlington mode) 2 units up and 2 units down.... each one using it's own supply polarity, is unitary...the gain is one.... and something multiplied by one result itself..... so...there's no voltage gain.

Because of that, voltage must be created, generated, produced, amplified, into earlier stages...in special the one is called Voltage Amplifier Stage (VAS).

In this schematic, this work is realized by the last chip stage, the last operational amplifier stage.... so... the maximum voltage produced will be the voltage you can measure in this stage reduced by the losses into base to emitter junction of your output transistors...... but this stage is limited by his own supply.

Amplification is made with the "manipulation" of the supply voltage tracked by the input signal...seems the output signal will be the same shape, alike a copy, but with HIGHER voltage.

You see the problem...how to manipulate a very big voltage when you have plus 15 volts and minus 15 volts into this "VAS" operational circuit.... cannot produce more than 15 plus 15 volts...cannot produce more than 30 volts peak to peak.

Imagine this operational amplifier, this one is working like a VAS send 30 volts peak to peak of audio to the output.... the output will use this 30 volts to produce current...the current amplification will be huge...but voltage will still the same.... the difference will be power.... and this is the result of multiplication of voltage by current.... before the output you had 30 volts peak to peak without power.... if this op amp could support the effort (it cannot) you could install a speaker into this operational amplifier output (this one working as VAS, this last stage before the output) and it could produce some sound.... in reality will not produce something good...has only voltage, but has not power... when you plug a low impedance... a speaker that needs power... the resistance is low... those 30 volts will drop to almost zero volts..this means has no power...has not condition to keep 30 volts, to maintain 30 volts over so low impedance load....BUT.... after the ouput.... those 30 volts, reduced by the base to emitter junction losses will appear and able to face the low impedance load represented by the speaker.

There's no way to increase this 30 volts in this circuit you have shown to us dear Mannyc....you can install thousand stages earlier to produce more voltage and will not result good..only distortions will be created and enormous sensitivity.... every magnetic disturbance will be captured by your chain of amplifier stages, operational amplifier stages you install into your power amplifier left side... the earlier stages of amplification, the ones must produce swing of voltage..... the limiting factor will be the supply voltage you have into your VAS, in this case this last operational amplifier connected to the output....

You can install high voltage into the output...you can put 100 volts, 200 volts....300 volts...but no way to have more than 30 volts peak to peak (reduced by losses, of course)

I hope i could help you to understand those things... wonderfull things into amplifier operation.... i love those things deeply.

regards,

Carlos
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Old 7th July 2008, 07:38 AM   #57
mannycc is offline mannycc  Singapore
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Hi Mooly,
Thanks for the thought, it seems to be that I may have no choice but to go for a more complicated but working amp circuits even if I donít feel like giving up so easily. I still have this nagging feeling though that amp with less part can offer less distortion once properly biased, although hi-end (expensive) amps show otherwise.

Regards
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Old 7th July 2008, 07:41 AM   #58
mannycc is offline mannycc  Singapore
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Hi Carlos,
Just the though of how those small combined parts give me a thrill and I donít know why, itís the beauty I cant explain to my wife who does not understand as well . Those parts so few may not cost much but the precious time could be saved if spent on something else and not on an amp thatís not working.

As i recall from electronic class you just describe how the emitter follower circuit behaves and one of the most common use of that circuit is for power supply voltage regulator (pls correct me if Iím wrong) however it will require reference voltage at the b-c junction. Just a thought, could the output tranny 2SC3281 be driven by BD139 voltage swing which happened to be the supply rails?

Regards,
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