Your opinion about this schematics?

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Please observe the current / capacitor relationship. The capacitor bank in your amp is ridiculously small.

No actually his cap bank is fine, because it is being supplied by a much higher frequency.

Self is correct in that the PSU caps are dealt with to an extent by the PSRR of the amp. And the PSU caps are in parallel to the transformer voltage source. However, an output capacitor is passing the signal directly through it, which is less good.
 
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Lumba,
I know capacitors can't pass a DC current.

Ripple voltage on the supply has no bearing on the low frequency response of the amp.

The load is not in series with the reservoir caps.

If it were, then an amplifiers response would always roll off toward DC... it doesn't.
 
richie00boy: Yes, in schematic resistors is 1/2 W,of course I put
most likely 4W(2X1 ohms in paralel,2W metal film resistors).
30mA shold be idle current through the output devices

tiefbassuebertr : I don't understand which J FET input you think?
In schematic don't have J-Fet inputs,only if I put that like alternative(changes in scematic).


I am concerned about the outdated(old) shematic, what will the sound be?
Good, bad or OK sound for such a concept schematic.


Later this schematic would built in bridge mode, so missing the need for output capacitor.

Best regards!
 
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The circuit will sound excellent... however it is NOT suitable for bridge use without being AC coupled as the mid point voltage is not precise enough... and even then I wouldn't entertain that idea... that's a recipe for disaster sound wise on something like this.
 
Yes,I can buy a kit.
Mooly,but in bridge mode how know, we can to put IC's, example TDA2030 or LM1875....etc
That IC's don't have AC coupled,yes that IC's have simetrical supplay,or can to work with single supplay,but they haven't AC coupled.
Maybe,for security I can put capacitor on output before the speaker,maybe on both of side on speaker(I'm talking about bridge mode) as prevention of AC, and DC coupled.
What dou you think about that?
 
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Yes,I can buy a kit.
Mooly,but in bridge mode how know, we can to put IC's, example TDA2030 or LM1875....etc
That IC's don't have AC coupled,yes that IC's have simetrical supplay,or can to work with single supplay,but they haven't AC coupled.
Maybe,for security I can put capacitor on output before the speaker,maybe on both of side on speaker(I'm talking about bridge mode) as prevention of AC, and DC coupled.
What dou you think about that?

Hi Pigy,
I don't quite follow you, you were asking about the circuit you posted and that's not suitable for bridge mode at all.
Using IC's is different and they can be bridged if run on a symetrical supply because the output can be guaranteed to be at zero volts DC. It's still something I would never do though... bridge mode has it's uses but not something I would ever consider for high quality audio.
Using a capacitor to couple the speaker is always a good safeguard but if you do this with a symetrical supply you need a non polarised cap as any fault could swing the output positive or negative. You can make one from two equal value caps "back to back" the totaly equivalent value would then be half the value of either cap.
 
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Why do you say the circuit is unsuitable for bridge?

I was thinking mainly of having to AC couple, and then there is the added complexity of a phase splitter to drive them, and the fact that the sonics won't be as good etc .... and how much "subjective" increase in volume will you get from all that. The power supply won't be rated for the increased output too.

Bridge use is fine for specific applications, say the limited supply available with a 12v battery etc... my opinion anyway :)

Keep it as it is I say.
 
Dear poynton, because I like to make stronger amplifier with bridge mode.
I know that can find on internet many similar shematic like that sheme,but stronger.
Problems is because that stronger sheme from internet I,m not sure that will work ok.
This sheme is checked.

Mooly, I understand that,I think that with ,,bipolar" capacitors not worth it.
Please,coud you tell me iff I can do my sheme in bridge mode with classic capacitor(output) because I've single supplay in sheme.
In bridge mode I need to single supplay same in single(classic) mode amplifier.
Second, I know that bridge amplifiers have more greater distortion than standard aplication.
I would like to do in bridge mode bacause that amplifier is more simple to build...
I need few parts for build....etc, but only problem is low power.
How I can solve the problem with 0 volts in coupled point?
Thank's!
 
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Pigy,
If you use the discrete amp circuit you posted at the start in bridge mode you need a suitable phase splitter (using opamps) to give you the two inputs to each amp. You understand that... a bridge amp MUST be fed with signals that are 180 degress out of phase.
If you can arrange that then you need only a single speaker coupling cap (bipolar... so that's two in series) cap of say 2200 mfd (two 4700's back to back)
There is no problem with the 0 (zero) point, the inputs are ground referenced, the speaker connected between the amp outputs.
 
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Can you please explain why you prefer to use an output coupling cap in bridge.

Because the circuit Pigy has posted has a mid point voltage (DC volts at amp output) that is not well defined and that will drift with temperature and rail variations. It's a non problem normally but DC coupling a speaker between two such amps will give an offset voltage of perhaps 2 to 3 volts or so, maybe more.

With an IC based design on split supplies that doesn't happen.

With an IC design on a single supply the problem can be better managed by using a precise DC reference to set the operating point of both amps. You can not do that for the discrete design however as it is "single ended" and prone to drift.
 
Because the circuit Pigy has posted has a mid point voltage (DC volts at amp output) that is not well defined and that will drift with temperature and rail variations. It's a non problem normally but DC coupling a speaker between two such amps will give an offset voltage of perhaps 2 to 3 volts or so, maybe more.

With an IC based design on split supplies that doesn't happen.

With an IC design on a single supply the problem can be better managed by using a precise DC reference to set the operating point of both amps. You can not do that for the discrete design however as it is "single ended" and prone to drift.

Some years ago I find on the web a German diy project, that have the same topology. Unfortunately this article is deleted. Because I have store this websites, I have make a pdf file (see botton). The same author has descript a possible of a bridged version about this topology - but unfortunately this article I haven't. Both article was release in the no longer available German diy magazine "ELRAD" (not "elector") between 1985 and 1990 - as I know.
You can ask Mr. Gerhard Haas about this article, title "Brücken-Teufel" (bridge devil) - Go to the weblink
EXPERIENCE electronics - Contact
to send an e-mail about this -
because about EXPERIENCE electronics - HiFi-Amplifiers 'Classic'-Series
this information presently not available
 

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It will take a bit of care to get the offsets to cancel, but it's possible. You need to bias from a common point and match the input stages. Use 1/2 the value of R3, double C2, and make this common for both halves. Match R2's and R1's, as well as T1's. A matched diff pair in a common can would be best for the input stage. Do this and the offset will be just fine, but if you go to this much trouble you may as well build a more advanced circuit.

The other thing you need is a phase splitter, which can be a separate outboard unit or just play with the feedback. One way is to add another resistor the same as R6 from the output of the first amp to the summing node of the second. The other way is to connect the feedback grounds (the R5 C3 ground connection) to each other instead of to ground.
 
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