About make an audio power amplifier.

[spec]

Thank a lot about your teaching!
So Q1 and Q2 must be near perfect good (has the nearest parameter to the other)?

No probs Nicolai,

Yes, the better Q1 and Q2 are matched the lower the distortion and the lower the overall power amplifier DC offset voltage.

There are two types of matching involved:
(1) Intrinsic
(1.1) hFE at operating IC, in the case of your schematic, 1mA
(1.2) VBE at operating VCE and IC

(2) Design
Q1 and Q2 should operate under identical conditions in the amplifier circuit: VCE and IC are the main parameters, but also the source resistance at each base should be identical. In the Elliot amp there is no provision for keeping the collector currents the same, and the tail current is ill defined, but you can always adjust it by changing Q3 emitter resistor (once the audio amp quiescent current is set) so that, at operating temperature, both Q1 and Q2 collector currents are the same.

One advantage of closely matching Q1 and Q2 is that it may be possible to eliminate the electrolytic capacitor in the feedback loop- it could not be in a worse place as far as distortion is concerned.

Transistor pairs in one pack with matched hFE and VBE are available cheaply (£0.50 UK), but the first two in the following list (SSM2220 & SSM2212) are more expensive (£5 UK) superior matched NBJT pairs designed for low noise, low distortion audio applications- probably overkill for this amplifier though. Also the SSM2220 is end of life. Other super match transistor pairs are about three times more expensive than these two.

Analog Devices SSM2220
https://www.farnell.com/datasheets/1793788.pdf
https://uk.farnell.com/analog-devices/ssm2220pz/transistor-matched-pair-pnp-2220/dp/9605096
https://www.mouser.co.uk/Search/Refine.aspx?Keyword=SSM2220

Analog Devices SSM2212
https://www.mouser.com/ds/2/609/SSM2212-879641.pdf

NXP BCM846
https://www.mouser.co.uk/ProductDetail/NXP/BCM846BSX/?qs=/ha2pyFaduia%2bDeCoCW6NobPbqHUuDuy612yZ0XLlf2iGIcolvpeIQ==

NXP BCM847
https://www.mouser.co.uk/Search/Refine.aspx?Keyword=NXP+BCM847

spec

 

[Nikolai Petrenko]

Thank, I will buy a bunch of BC546 and test to choose the best. Those luxury transistor seem be overkill.

 

[Nikolai Petrenko]

Please give a suggest about my previous question:

Ah, I have a question (may be not clear):
What kind of solder should I use? 63/37 or silver lead-free?

 

[spec]

Thank, I will buy a bunch of BC546 and test to choose the best. Those luxury transistor seem be overkill.

Why have all the hassle of matching when the BCM846 and BCM847 are dirt cheap and, besides, they would be much better matched and also, being in one pack, would thermally track much better- a win win situation.

By the way, in terms of chips, I think that:
(1) (NBJT) BCM846 [SOT363] = BC546 [TO92] = BC846 [SOT23]
(2) (NBJT) BCM857 [SOT363] = BC547 [TO92] = BC847 [SOT23]
(3) (PBJT) BCM856 [SOT363] = BC556 [TO92] = BC856 [SOT23]

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[spec]

Please give a suggest about my previous question:

Don't mess with lead-free solder- it is junk.

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[Nikolai Petrenko]

Don't mess with lead-free solder- it is junk.

spec

I also think like you but not sure. I have try lead-free only one time, in my opinion, it has very nasty bad wetting action and sometime pop so flux scattering all the PCB.

 

[spec]

I also think like you but not sure. I have try lead-free only one time, in my opinion, it has very nasty bad wetting action and sometime pop so flux scattering all the PCB.

The joints are also less desirable electrically and do not last well, in my experience anyway.

spec

(bad wetting and 'poping' may be due to your soldering iron bit being too hot)

 

[Nikolai Petrenko]

(bad wetting and 'poping' may be due to your soldering iron bit being too hot)

I don't think so, my soldering iron just no-brand buy at the market but I have made a temperature controller for it (using TRIAC). I also use it with leaded solder and no problems, but these problems appear when I tried lead-free solder. Lead-free has much much higher surface tension and not an eutectic alloy.

 

[Nikolai Petrenko]

Update:

 

[spec]

Update:

Nice job.

(1) Still no separate line for speaker 0V ie, 0V (OUTPUT)
(2) All signal designations should have different identities, unless they are the same.
(2.1) OV at input should read, 0V (INPUT)
(2.2) Present OV at output should read, 0V (PSU)

As a general point, for maximum clarity, main text, identities etc, should be in upper case only on engineering drawings. Auxiliary information- notes etc- can be in normal case.

While there is nothing wrong with the present 0V connection to the base circuit to the long tailed pair constant current generator, it is not necessary to take it back to the main star point. Just take it to a local 0V as on my circuit.

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[spec]

I don't think so, my soldering iron just no-brand buy at the market but I have made a temperature controller for it (using TRIAC). I also use it with leaded solder and no problems, but these problems appear when I tried lead-free solder. Lead-free has much much higher surface tension and not an eutectic alloy.

Oh I see.

You made a temperature controller for your iron- that is impressive. Out of interest, how did you do the bit temperature sensing?

Good point about lead-free solder being non-eutectic. I didn't know that. I just keep away from the stuff anyway!

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[Nikolai Petrenko]

Still no separate line for speaker 0V ie, 0V (OUTPUT)

No problem, in fact I never forget 0V wire for speaker.

Oh I see.

You made a temperature controller for your iron- that is impressive. Out of interest, how did you do the bit temperature sensing?

spec

No temperature sensor because I don't have sensor and display screen. I adjusted the knob from low to high temp. very slowly, until the soldering iron melt specific materials like PP, pure tin, pure lead........ (of course I know they melting points). Finally mark all temperature on the knob background like below:

 

[Nikolai Petrenko]

Good point about lead-free solder being non-eutectic. I didn't know that. I just keep away from the stuff anyway!

One of my friend tell me that he using lead-free solder just because heath reason, many "eutectic lead-free solder" just not really eutectic, just like common 60/40.

 

[audioguru]

A light dimmer circuit on a soldering iron is not a temperature controller. Sitting, the temperature gets hotter and hotter then when you begin soldering the temperature gets lower and lower. My soldering iron has temperature control so it is always at the correct temperature. It turns on and off as it senses the tip temperature.

 

[Nikolai Petrenko]

A light dimmer circuit on a soldering iron is not a temperature controller. Sitting, the temperature gets hotter and hotter then when you begin soldering the temperature gets lower and lower. My soldering iron has temperature control so it is always at the correct temperature. It turns on and off as it senses the tip temperature.

Though this fearture is very good, I don't need it. After solder a large junction, I guess the temperature drop about 50°C. Wait for 5sec and the temperature get stable again. My soldering iron is a big one (not really for solder surface mount and through hole) so it has big heat capacity.
I fell no problem with my el-cheapo stuffs.

 

[Nikolai Petrenko]

Cooler speed controller using NTC-MF52AT 10K:

 

[audioguru]

Your cooler speed control is backwards. It turns OFF the transistors and fan when the NTC thermistor gets hot.

The tip of my Weller temperature controlled soldering iron has a ferro-metallic part of the tip attract a magnet attached to a switch inside the pencil when it is cool which turns it on. When the tip reaches the desired temperature then the ferro-metallic part no longer attracts the magnet (Curie Method) and a spring turns pulls the switch which turns off the heater. When it cools a little then it turns on again.

 

[Nikolai Petrenko]

Your cooler speed control is backwards. It turns OFF the transistors and fan when the NTC thermistor gets hot.

The tip of my Weller temperature controlled soldering iron has a ferro-metallic part of the tip attract a magnet attached to a switch inside the pencil when it is cool which turns it on. When the tip reaches the desired temperature then the ferro-metallic part no longer attracts the magnet (Curie Method) and a spring turns pulls the switch which turns off the heater. When it cools a little then it turns on again.

I want to say about cooler for amp. What will happen if the amp reach Curie temperature (about 1000K for my normal steel)???

 

[Nikolai Petrenko]

I have done almost necessary schematic in eagle but only in the begin of convert into pcb layout. I need some basic skills and knowledges.
Here is my first, hope you see and correct any mistakes: (Cooler speed controller)

 

[KeepItSimpleStupid]

Comments:
The pads to the external world don't look evenly spaced. May not allow a connector to be used. The pads may be too small.

If this was a commercial board ans even if it wasn't, it's hard to tell which resistor is R5 and R6.

So, move the silk screen stuff a bit:
Center NTC with respect to R2
Move the labels R5 and R6 so you can tell which is which.
The BC557 is way out in right field.
Center R3 and R?
You can move the labels Q2 and TIP41C
I'd use a square PAD on one of the legs of C1 (I can't remember what the common convention is), probably negative. That's the striped side,

I think, "T" corners should be avoided. I think that's an etching issue.

If your etching this yourself, put some sort of label on the component side in copper, so you know what side is up. You don't want to etch a mirror image, Trust me.

One leg of R4 doesn't go anywhere?

Last, but not least. There are no mounting holes.