Transistor equivalent

[audioguru]

In Canada and probably the same in the States the electric company gives us 240V with a grounded neutral center-tap. Only high power appliances like a stove and a clothes dryer use 240V. They recently replaced the transformers (they were 30 years old) that are on top of the ground. The transformer for my part of the street is 100kW and feeds 12 homes. The electrical wiring, telephone, natural gas, water, sewer and cable-TV/internet cables are all underground.

 

[spec]

That sounds like a good system having the option for 120V and 240V in your house. Is Canada 60Hz, the same as the States?

 

[spec]

Talking about mains supplies: I was on jury service for a week. One case was these two fellows who grew hash in two metal cabins that they had burried in the ground. It was quite a set-up. They tapped the power for the heating and lighting from a utility transformer, about 15 feet up a pole. There was mains cables streaking everywhere. The lights were computer controlled to simulate the natural marijuana growing season, as was the temperature. The irrigation was also computer controlled. We saw the photographs- talk about Day of the Triffids.

What I can't understand is that these two fellows had obviously worked hard at all this and must have been pretty resourceful- why the hell didn't they just start a legitamate business- they would probably have made just as much dosh (cash).

 

[MaxHeadRoom78]

That sounds like a good system having the option for 120V and 240V in your house. Is Canada 60Hz, the same as the States?

Canada is same as US.
At one installation in a residence in UK for the installation of peak storage heaters, the service co insisted on 3ph with the heaters spread across the three 240v to N phases for balance.
Max.

 

[spec]

Canada is same as US.
At one installation in a residence in UK for the installation of peak storage heaters, the service co insisted on 3ph with the heaters spread across the three 240v phases for balance.
Max.

Tks Max

 

[audioguru]

Guys in court charged with growing pot? Or charged with stealing electricity?
I haven't met Mary Wanna for about 50 years. When my parents visited my apartment they didn't know what those potted plants I was growing were called.

 

[spec]

Just pot. The electricity company would still be going through 'internal procedures' if they were going to press charges. The guys were real characters and spun so many stories about their activities. The main mover brought in a key witness who's sole evidence was that his friend was the nicest man in the world and gave the stuff away- he would never dream of charging for it- he was just that kinda guy. This same nice guy kept smiling at the jury- he was genuenly shocked when we found him guilty.

I always like to try things and asked a student to get me some skunky black- the creme de la creme in the ganja world, much powerfull too- cost me £10. It hung around the house for about a year, but one afternoon when the wife was shopping/hardressers/visiting friend/at beauticians/having lunch with her mates, I went out to our large back garden and fired up right in the middle. At the time I had a smoker's pipe and went through a whole bowl full. You have never smelled anything like it- like rotting sweet moalasus. As for me- didn't do a thing. The lady next-door later leaned over the garden wall and asked if I could small anything- I sid no. That was the total of my ganja adventures. Had to chuck the pipe in the end because missus complained about the 'funny smell' in the house.

 

[Nikolai Petrenko]

2SC1815 & 2SA1015 are good transistors with 60V VCE. The BC337 & BC327 are only 50V.
The only transistors that handle substantial current are the output transistors and their drivers.

The VAS transistor pair handle 12mA top (Q5) and 6mA bottom (Q7).
The emmiter follower (Q6) driving Q5 handles very little current, but needs to have as higher ft as possible and good at operating at low currents.
The two input transistors only handle 500uA.
Q10 is only a 1mA constant current generator but it needs to be a low capcitance, high frequency type.

The rest of the transistors are not critical and you can use what you want, within reason.

BC549 & BC559 are only 30V VCE which means you would need to reduce the amp supply lines to +-15V



No. The variable resistor sets Iq, the quiescent current (no signal) flowing thru the output transistors, Q1 & Q2. This is adjusted to around 30mA to minimise cross-over distortion. The amp voltage gain is set by resistors R13 & R14: A= 1+ (R14/R13)



Bit of an open-ended question; it depends on the transformer type and the core material. As a rule of thumb, I would say 1,600 sq mm. 1 turn per volt is fairly normal for that area core. An alternative way to judge is by the power rating of the transformer: 100W upwards should be fine

C core is the best:
(1) Lowest size
(2) Lowest stray signals
(3) Lowest output impedance
(4) Lowest weight

Any transformer type will do though, but with the other types be prepared for some work to reduce hum introduced both by inductive and electrostatic coupling.

PS: amp schematic has been updated to issue 2: only minor mods

I mean the L1, not transformer

 

[spec]

I mean the L1, not transformer

Oh! my bad.
Don't even think about L1: it's only a few turns of copper wire with no core- just air. I will post details later to explain.

 

[Nikolai Petrenko]

Don't even think about L1: it's only a few turns of copper wire with no core- just air. I will update this post later to explain.

Thanks, how many turns of this inductor?
What about 40w amp circuit?
Why shouldn't I use only 1 bridge rectifier in supply circuits like in many dual rail supply circuits but use 2 ones with 2 seperated coils instead of center tapped?

 

[spec]

Thanks, how many turns of this inductor?

10 turns of 18SWG (AWG) enamelled copper wire wound on a 1" (25mm) diameter rod. While wire is on rod glue wires together with a light application of epoxy resin. Leave to set and gently remove from rod. That is your inductor. 17SWG and 16 SWG wire will be better but not essential. Do not have anything inside inductor except air.

Do not mount the two inductors (right amp and left amp) near each other and II alignment bad, I- alignment good.

 

[spec]

What about 40w amp circuit?

Make amp supply lines +-30V. transformer secondary = 2x 23V RMS. No other changes required.

 

[Nikolai Petrenko]

Do not mount the two inductors (right amp and left amp) near each other and II alignment bad, I- alignment good.

magnetic field around one inductor can affect the other, right?

 

[KeepItSimpleStupid]

Why shouldn't I use only 1 bridge rectifier in supply circuits like in many dual rail supply circuits but use 2 ones with 2 seperated coils instead of center tapped?

Torroidal transformers are easy to wind bi-filar. They take 2 wires and wind as though it's one. It does make them closer to identical. The torroidal transformer makes it much easier to star ground the reference.

A "tracking" power supply is the best way to go. This isn't the same as a dual supply. Tracking will generally make sure a +-15V supply always has a symmetric center. If one rail briefly dropped to 14.5 V, the other would too. The symmetry has more priority than the actual value.

 

[spec]

Why shouldn't I use only 1 bridge rectifier in supply circuits like in many dual rail supply circuits but use 2 ones with 2 seperated coils instead of center tapped?

Don't understand.

Here are your PSU options:
(1) Two secondary windings, joined (centre tapped) and one bridge rectifier (the last PSU that I posted has this arrangement, but with separate diodes cofigured as a bridge rectifier. If that worries you and you would rather use a bridge that is fine. Fuctionally it is the same thing).

(2) Two separate secondary windings and two bridge rectifiers giving two, essentially, separate power supplies. This is the Rolls-Royce arrangement and is best for layout and other practical reasons, but no big deal. But if I were building this system with all the other work and expense involved, I would definately use this arrangement.

(3) One secondary winding and two rectifier diodes in a half wave rectifyer arrangement. This will work OK but you will need twice the size of reservoir capacitors. The regulation will also be poor and you will be taking huge gulps of current from the transformer, which reduces efficiency. For Hi Fi this is not advisable.

Those are the only arrangements I know off- what are you thinking of? Post a schematic?

 

[spec]

magnetic field around one inductor can affect the other, right?

Yes that is correct.

 

[spec]

Torroidal transformers are easy to wind bi-filar. They take 2 wires and wind as though it's one. It does make them closer to identical.

True. Toroids have other advantages too, as listed in a previous post.

The torroidal transformer makes it much easier to star ground the reference.

Why is that?

A "tracking" power supply is the best way to go. This isn't the same as a dual supply. Tracking will generally make sure a +-15V supply always has a symmetric centre. If one rail briefly dropped to 14.5 V, the other would too. The symmetry has more priority than the actual value.

True but not an issue with voltage regulators because they are accurate in absolute terms.

With modern amps, which make extensive use of constant current generators, the absolute supply voltage is not that important. The biggest problem, especially with class AB amps, is preventing the distorted and asymmetric currents from modulating the supply lines and infiltrating the whole amp, especially the front end. Good layout and decoupling, both LF and HF, is essential to reduce this.

 

[Nikolai Petrenko]

the 40w circuit use tip41-42 you posted without value of components in page 16. Can you post the values?

 

[KeepItSimpleStupid]

Tracking: **broken link removed**

Torroidal star grounding: You have two separate wires (the CT) that you can move to the star point. With a center-tapped transformer attached to the star point, the line running to the CT is influenced by what's being drawn on the other secondary. It's no longer a noise-free reference.

Now, you COULD try to make the center tap the star point.

 

[spec]

Tracking: **broken link removed**

Torroidal star grounding: You have two separate wires (the CT) that you can move to the star point. With a center-tapped transformer attached to the star point, the line running to the CT is influenced by what's being drawn on the other secondary. It's no longer a noise-free reference.

Now, you COULD try to make the center tap the star point.

Ah yes I get your point now. What you say is crucial to a good audio amp PSU design. The nasty gulps of current that the output transistor pair take in a class AB amp are nothing compared to the explosion of current when the rectifiers charge up say a 10mF capacitor in a few mili seconds. It has always intreged me how well the diode/capacitor arrangement works- the diode/inductor/capacitor arrangement is a much more civilised thing, but the inductor would be huge for a decent sized amp.

I have often thought that a switched mode PSUs would be ideal for audio amps. I know it sounds like herassy, but SMPSs have a lot going for them- much more design work than a standard PSU though. Chord over here make upmarket amps- they break two rules: MOSFET output stage and switch mode PSUs. The guy who does the design work at Chord is an ex millitary designer and knows the ropes- cost, what does that mean exactly?

It looks like class D is catching on, even for HiFi, so you could go the whole hog and break all the rules: class D, SMPS and MOSFET outputs. It is quite possible that that is the way things will end up- just thinking out loud.