Transistor equivalent

[spec]

Hi AG and MrAl,

Thank you both for your posts. There is a lot to take in, but at a first glance I think all three of us are thinking along the same lines. I would be surprised if we were not! My head is spining with all this theory- I will recover after a good sleep.

UPDATE (2015_11_2015_07:39 am)

Recoverd now. Will do some work on Nikolia's project today, if I'm not shopping again that is!
Some really interesting points now that I have read both of your posts more thoroughly. Will reply soon.

 

[audioguru]

I agree that 1dB is a very small change in level and with a continuous tone I can hear it but not with music. 3dB (double or half the power) is a small change in level that anyone can hear. About 10 times the power (10dB) sounds twice as loud.

We forgot to talk about old fashioned electrostatic speakers. They sounded pretty good before they learned how to design good dome tweeters.
Vacuum tube amplifiers sounded pretty good before they learned how to design .... (you know).
Class-A amplifiers sounded pretty good before they learned how to eliminate .... (you know).

 

[Tony Stewart]

**broken link removed**

Low noise Tantalum alloy thin film & Metal Oxide power resistors where it counts for audio and rectifier filter, respectively.
Low Noise differential FET input and DC coupled 6FQ7 Tube output (Class A)
Soft start sequencer for Rectifier and boost pre-heater for tube.
To high impedance e-static Stax earspeakers.

Classy & sweet. (Class A) I can only imagine the linear response is spectacular.

 

[Tony Stewart]

You can easily hear a <0.5dB change in a 1kHz test tone just now in Audacity in a loop. But you have to pay attention.

 

[spec]

Hi Tony,

Post 243- wow! would love to hear that

 

[Nikolai Petrenko]

Oh, yes. You are too carefully, spec! I have learned 80% what you said at my "field" teacher, but your post still very very helpful.
I can buy 20 or 25 or even 35a bridge rectifiers
I plan to make capacitor input filter to make DC supply voltage smooth. so 100000uf not need, the biggest capacitor I can buy is 10000uf-63v. the inductor will be 10mH-30A.
If the power supply filter too big and heavy, I may voltage regulator to drive power transistor (create high power regulators)
Heat sink, not very difficult, I will collect a lot of drink can and melt it, then cast the heatsink, use knife and sand paper to make surface as smooth as I can
Mica always use as insulator, I have bought a tube of thermal paste.
The heatsink will be coooled by fan
I will collect computer power supply cases to put the amp in.
The tempurature inductor may not need, I just feel by hand (price of the temp. sensor pretty high)
I want do this project well but save money as much as possible.

 

[spec]

Hi Nikolai,

Nice what you say.
Good about bridge rectifier
I will have a think about 10mF (10,000uF) capacitor. The high ripple may make things difficult for you.
A regulator would be the way to go- Rolls Royce approach- and smaller, but once again, large heat-sink needed. More 2N3055s also required.
Mica washer and thermal paste good
You will make a heatsink by casting ally! wow! I hadn't thought of that. Dying to know how that turns out. You could do a fantastic design with that approach. Im thinking the whole rear part of the chassis as a heatsink. This opens up all sorts of possibilities. How do you melt the cans?
Cooling by fan- excellent! and no noise in practical terms, either.
Not sure about computer case; perhaps not substantial enough. I have some thoughts about your case now you mention casting. I will give that some further thought too.
Yes, your finger is a good judge of temperature. 70 deg C is getting uncomfortable. Lack of thermometer is not a show-stopper anyway.
Saving money is good. When I was younger that was always my aim- most stuff came from scrap: ex military, TVs, radios, junk yard, etc. I get a real sense of satisfaction by making something from nothing.
I wish you good fortune with your project and feel that, now we know your requirements, there is a clear way forward. I see no reason why you shouldn't make a high end amplifier that would not only sound good, but impress your audiophile friends too.
You remind me of me, only 50 years ago.

 

[Nikolai Petrenko]

Oh melting aluminium too easy because the melting point is 660°C. I have built a furnace when I was 12 years old, I tried to melt some aluminium and successed. But when I pour liquid aluminium into wet mould the alum spatter and hit my hand, deep and heavy burn . After this, I continue tried to melt copper and successed too.
The furnace is an old paint barrel with a thick layer of refractory material (very simple: mix of slaked lime and sand), fuel is charcoal of hard wood, and a bellow made from burlap bags, sometime I blow it by mouth, feel the taste of smoke very interesting.
Ok, turn back to our topics, you can say how many transistor will be use?
I will collect resistors and low capacitance capacitors from junk yard (hmm, my parents don't like me get them from scrap so I need to "cheat"). TVs is rich source of components (richer than any devices) but I can't get because people selled them to recycle factory, if I take it I am be a thief . I will try to collect transformer from microwave oven (do you know any other things have?)

 

[spec]

Oh melting aluminium too easy because the melting point is 660°C. I have built a furnace when I was 12 years old, I tried to melt some aluminium and successed. But when I pour liquid aluminium into wet mould the alum spatter and hit my hand, deep and heavy burn . After this, I continue tried to melt copper and successed too.
The furnace is an old paint barrel with a thick layer of refractory material (very simple: mix of slaked lime and sand), fuel is charcoal of hard wood, and a bellow made from burlap bags, sometime I blow it by mouth, feel the taste of smoke very interesting.
Ok, turn back to our topics, you can say how many transistor will be use?
I will collect resistors and low capacitance capacitors from junk yard (hmm, my parents don't like me get them from scrap so I need to "cheat"). TVs is rich source of components (richer than any devices) but I can't get because people selled them to recycle factory, if I take it I am be a thief . I will try to collect transformer from microwave oven (do you know any other things have?)

Hi Nikolai,

Amazing about furnace and all. Sorry to hear about burn- bet that was painfull . I was badly burnt in 2011- agony.

Best wait until I do a bit more work on the design before getting components, but definately go ahead with the microwave transformer.

Some questions for you. The answers will save me a lot of time:

(1) Are you going for just 1 class A stereo audio power amplifier, 40W into 8 Ohms (will drive 4 Ohms too)?

(2) Do you want a single power rail or + and - supply rails?

(3) In the attached block diagram below, which approach would you like (Approach 1 would be possible but it would mean a big case. Approach 3 is the best)?

​

 

[Nikolai Petrenko]

Here are my answers:
(1) I want make 2x20W class A to drive 2 speakers to make satellite systems
AND 4oW class A or AB to drive subwoofer
=> I need total 3 amp circuit , two 20W and one 40W
(2) Single rail make the circuit smaller, easier and safer but you can choose any will be best for audio quality
(3) yes the Approach 3 is the best, I can easy fix the problem or arrange circuit more compact

 

[spec]

Thanks Nikolia,

That is a great help.

In view of your information this is what I propose:

(1) Approach 3

(2) Split power supply rails. (my calculations show +- 30V @ 1.58A each amp. Must be stabilised. Calculations are only notional at the moment till checked fully)

(3) Three amps all the same ie 40W into 8 Ohm Class A (you can make any power lower simply by reducing the supply line voltage)

(4) It looks like only 2 of 2N3055s per amp will manage but it will be close. Again calcs not checked.

(5) It looks like the heatsink requirements are not as demanding as I thought.

(6) I suggest that the power transistors be mounted onto a block of ally without insulating washers. The ally block would then be bolted to the heatsink with an insulating mica sheet between it and the heatsink. Ally block say, 70mm x 70mm x 10mm. You say you have cast copper. That would be even better but not essential.

Power supply options

(1) One single power supply for all three amps. all in same case.

(2) One power supply for sub and one power supply for the two amps all in the same case

(3) One power supply for sub, One for left, & one for right, all in the same case.

(4) One supply for sub in own case. One single power supply for left and right in separate case.

(5) One supply for sub in own case. One power supply for left, one supply for right in same case.

In terms of performance and flexibility I would suggest that (5) above would be the best all round, but in terms of quality (3) is just as good.

I will work on (5) for now uuntil you tell me which way you want to go.

Where the supplies are in the same case, wether independent or not, there is no reason why a single transformer cannot be used. You will need a separate pair of winding on the transformer secondary for each supply.

Components for each power supply (assuming split rails)

This is notional at the moment but I give it to you so you will get an idea of what is likely

(1) 2 of transformer winding 28V RMS (to be defined exactly) 3A rating or above.

(2) 2 of bridge rec 10A or above

(3) 4 of 10mF or above caps 50V or above

(4) 2 off 2N3055 (this may change)

(5) 10 100nF or above ceramic capacitors 50V or above

Transformer

Each supply, (comprising +-rails) requires: 28V x 3A x 2=168W. (this is not the power used by an amp, which is 94W)

From that you can calulate the power of the transformer

For the sub it would be 168W up

For the two amps it would be 336W up

I think microwave transformers are around 1Kw but not sure. If so one transformer supplying all three PSUs in one case would be good.

 

[Nikolai Petrenko]

Thank you, (5) will be best, before you post, I calculated the supply +-35V and 2A
I think I will wind 2 primary coils, microwave oven must >1000W if no it doesn't effect.
Mica insulator for to-3 case are availlable. I have draw the supply circuit 1 week ago, I will post tomorrow.

 

[atferrari]

Hola Nikolai

I dare to post this which is actually derailing your thread but I find it will make sense if I do it here. Otherwise feel free to ask a moderator to split it to a fresh one. Gracias

Hi spec,

This is not a rant but a couple of questions.

You can find posts recurrently suggesting, instead of building, to use the latest audio amps, say, by National Semiconductors because they achieved a very low level of distorsion, very low level of noise with the added bonus of being much easier to implement if a proper PCB is implemented. On the other side, you and so many, dedicate uncountable time to build from scratch amplifiers that hopefully will achieve good (better?) performance if compared with the commercial ones.

I know there are the audiophools, audiophiles plus experienced DIYers and EEs that can handle the technical part of this.

Many times as well, I've read, mostly by Audioguru or maybe Nigel, saying things like: "... the XXXXX amp sports a 0,00002% distortion plus -xxx dB of noise, that anyway you will never could hear".

Is it all about people doing it just for the pleasure of reinventing the wheel, building is own wheel or just learning how to build one? After all, from all what I read, heard, talk and done, besides PSUs, audio, seems where most people started with when they knew nothing about electrons and what they could be used for.

Is there a real chance that a single soul could build something that corporate engineering cannot achieve? Probably not so often, isn't it?

In case you, Nikolai or anyone reading this will take this as a pejorative comment, please be aware that I am also involved in learning to build some wheels whether a DSP filter with a simple micro or, lately, a fully analog PID controller. My list is long.

Interested on your comments.

 

[MrAl]

Hi,

Some small replies...

Tony:
Wow, interesting amp. In my experience i have noticed that the biggest part of the sound comes from the choice of speaker. Good speakers sound amazing while not so good ones sound flat and lifeless. Interesting amp though with both transistors and tubes too.

Atferrari:
Quoting your paragraph:
"Is there a real chance that a single soul could build something that corporate engineering cannot achieve? Probably not so often, isn't it?"
Mainstream engineering has to worry about cost. The home guy worries about cost too, but since it is a one off they dont have to worry as much. When mainstream engineering adds a single transistor, they have to raise the price of the unit by 5 dollars and so after a few more the unit is suddenly into a new price category. The home guy can add five transistors for 5 bucks and love the outcome without worry. So there is a little quiet competition going on there: if the company wants to make a good unit it has to sell for a high price, but the home guy gets to build one for less, but usually only one because if they try to market then they end up with the same overhead as the main companies do.

 

[spec]

Hi Nikolia,
First rush of amp PSU below.
Is the LM350 a problem for for you . If so what voltage regulator can you get, if any?

 

[spec]

Thank you, (5) will be best, before you post, I calculated the supply +-35V and 2A
...
Mica insulator for to-3 case are availlable. I have draw the supply circuit 1 week ago, I will post tomorrow.

Hi Nikolai,

Our posts crossed. I just posted a PSU design for you to consider but if you have one sussed already that is fine. Just a couple of points though:

(1) my calculations show that for 40W @8 Ohms you need 3.16A peak. therefor the standing current in a class A amp will be 3.16A/2=1.58A

(2) from that you get the voltage= 3.16A * 8 Ohms =25.30V

(3) from that you get the supply rail voltage: allow 5V overhead (so the amp does not saturate) and you get 25.30V +5.00V= 30.30V. We are not going the fuss with 300mV so you get a round 30V. Thus the amp needs +- 30V rails, at a constant 1.58A.

(4) Each output transistor thus dissipates 30V * 1.58A= 47.4W, under static conditions.

(5) Knowing the maximum 2N3055 junction temerature of 200 deg C and the thermal resistance, juction/case, of 1.52 degC/W you can do the thermal budget to see if the 2N3055s can do the job. I recon with a heatsink of 0.92 degC/W or less it just will, but it will be tight.

I don't like to counter your good work but +-35V supply rails would be too much for 2N3055s: +-30 is max.

Sure mica washers are available for the TO3 case, but they introduce a thermal resistance of 0.7 DegC/W. If you do what I suggest and use an ally block you, could probably half that, which would give the transistor an easier time.

I think I will wind 2 primary coils, microwave oven must >1000W if no it doesn't effect.

I don't fully understand what you are saying here. Two primary windings will not be necessary, unless you are thinking of providing a tap for operation on 110V US supplies. Can't you leave the primary of the transformer as is. Just unwind the secondaries and rewind with the secondaries that you want. The thicker the wire you can use the better.

With approach (5) you will need two independent 28V RMS windings on one transformer for the sub and for the two amps you will need four independent 28V RMS windings on another transformer. If the microwave transformer is 1KW, you will have a fine pair of PSUs.

 

[audioguru]

I suspect that a 1kW microwave oven transformer might get very hot if operated continuously at only 600W because a microwave oven is not used long enough for it to get hot.
But these three amplifiers will not use anywhere near 600W so the transformer will be fine.

I never play my sound system continuously at full blast because I hate acid rock so my transformer can be de-rated.
Oh, I forgot, you are talking about class-A where the output transistors operate at full blast all the time even when the amplifier is not playing.

 

[spec]

Each amp effectively takes 125W from the rectified DC, So, ignoring the RMS thing with gulps of current thru the recs, the two amps in one case will use 250W contiuous and the sub will take 125W continuous. At least the class A amp will keep Nikolai warm in the winter, unlike the super efficient class D

What class is your amp? Is it a beast?

 

[audioguru]

Rod Elliot of Elliot Sound Products.com has some good articles and some good amplifiers. He says a class-A amplifier is usually only 25% efficient so a 40W RMS amplifier dissipates 120W of heat all the time!. He says the hfe of the output transistor drops as its current increases which causes more than 7% of even harmonics distortion with the 3rd harmonic not far behind and he says that valves (vacuum tubes) are worse and that their "linear" claims are unfounded.

 

[KeepItSimpleStupid]

Raise your power supply current requirements by 1/0.62 or 1.61.