Transistor equivalent

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Hmm, I just realized that dual rail supply will be better than single ones. Why? You said that the circuits can be improved by increase the supply voltage and change some resistors. Now supply volt for subwoofer is 60V, while maximum volt of filter capacitors is 63V. So if I improve the amp in the future, capacitors will explode. If I use dual rail supply, only above 30V on each caps
 
Capacitor ratings of 1.5 to 2x the supply is good. I put ZNR's across the main filter caps to eliminate surges. (50 V nominal supply). My main supply caps (about 10,000 uf) were computer grade with Some V + some V surge. I don't remember the numbers.

I initially used 100 uf caps at 50 V on the board and they blew up.
 
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No problems Nikolai,

Why not learn how to do it in Eagle. A bright chap like you should have no problem. You can then use the printout to make a PCB by hand. The only reason I can't do a layout is that I simply do not have the time to learn and do the job, as I said, much as I would like to.

I have been spoilt; when I was at work someone else always did the job for me. I have never laid out a PCB with ECAD- done plenty by hand using trace black tape though.
 

Dual rails are much better for a number of reasons, but the main one is that you do not have the nasty class B switching currents rushing through the earth line and causing distortion. The physical layout of the PCB and PSU are also much less critical.

The other thing is that the 10mF capacitor between the amplifier output and the speaker is very undesirable. Not only is it big and expensive, but it also generates bad type distortion which the feedback does not correct. Also, when the capacitor impedence goes up as the frequency goes down, the amp loses control of the loudspeaker, which is bad news.
 
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PS: I meant to say that if you go for dual supplies without the big output coupling capacitor, you will not be able to use the latest 20W and 40W amp designs. You will need to have a long-tailed front end to get a low output offset. As a result you would be moving over to voltage frredback rather than current feedback. Current feedback is best but with good circuit design voltage feedback can be made just as good, in practical terms.
 
Wow, you said that you have been hang up your soldering iron, so you busy because of children or extra works? I just ask because I am to curiously .
I am also a spoilt child, too stupid. Now I still don't have anything about Eagle in my brain. I don't know how to put components from library to the draw page, my version of Eagle is 7.5.
 
Of course! I was wanted to ask you sth. about the output coupling caps but you have answered before I asked. I have thought that OCL circuits amp will be cheaper and better because they don't have output coupling caps. Electrolytic cap isn't linear, I have tried it in my LA4440 amp, I know that DC current can harm my speaker but when I remove output cap, the sound better
 
I agree to use new circuits. This project is one of my very very few projects that I decide to spent a lot of money (I am not make money appreciably yet) so I want it as good as my condiction can allow.
I want some suggests about resistors and caps:
- what type of resistors I should use? I found some stores sell vishay, dale, koa,... resistors, those resistor have 5 colours strips and blue paint coated so I think they are metal film. I am not found stores that sell carbon composite resistors yet. Carbon composite have lowest capacitance and inductance while metal film have lowest noise (some friends said that carbon composite provide more nature and warm sound).
- I know input capacitors can affect the sound quality a lot so their characteristics must be linear. Not just run to the market and ask for 10uF electrolytic caps but ask for 10uF polypropylene caps as you said. Is it necessary to buy polypropylene caps for other caps like 100nF and 22uF...
 

Hi Nikolai,

I hope you don't spend too much money.

Can I say that if you are spending money it would be cheaper and simpler to buy a kit of parts for a ready designed and tested amp. There are many on the net that would suit your needs.

Also, please do not spend any of your hard-earned cash until you have the case, power supply, and heatsinking designed, built and working- this is most important

General
People often think that a resistor is a resistor and a capacitor is a capacitor, and all the talk about differnt sounds is an illusion. As an engineer that was exactly my view, but I had a rude awakening when I built my first serious audio amp using ceramic capacitors. The next rude awakening was when I heard a good commercial amp with matching quality speakers and audio source.

The other thing is that, if you have ordinary speakers and average signal source you won't notice the different sounds of components. But if, for example, you have a pair of speakers that are revealing analytical and dynamic you certainly will hear a difference. Sometimes it is not imediately obvious but you just get the vague feeling that something is not right. The other point is that you can get listener fatiuge after a couple of hours of continuous listening- not so if you listen to the same music live.

Resistors
Metal foil resistors are the best type for high quality audio work. (inductance and capacitance are not too important). Metal film are the next best and far less expensive than metal foil.

The next quality resistor is tin oxide, but they do not sound as good as metal foil and film. Tin oxide are very stable and rugged and are best for general electronic projects. Because they are so reliable and stable, they are the military's preferred type- they are all I used at work.

Carbon composition resistors are liked by the valve boys, but I have not found them to be brilliant for solid state amps. I think it is because valve circuits have low currents and high voltage, while solid state is the other way around. Carbon film have very little going for them and are best avoided for all work.

There are also wire wound and ceramic composition power resistors (1W upwards). Special low inductance wire wounds will be required for the two low value resistors in the output transistor emitters.

Capacitors
Yes, polypropylene caps are what you want for the solid caps. Polycarbonate are the best, but they are not made anymore. In practical terms polypropylene are just as good

Electrolytic capacitors should be a good quality aluminium type, established as sounding nice, Rubicon and Alps for example.

Cetain tantalum capacitors don't sound bad but, for some reason, not the latest generation of high-value digital decoupling tants. Bead tantalums are quite good and have a sweet pleasing sound, but not as pure as polypropolene.

Don't put ceramic capacitors anywhere near the audio signal path or you will get a brittle disturbing sound. The first half-decent amp I built had ceramics- it sounded awful.

Having said that, there is absolutely no reason why you could not use ceramics to get the amps going. Later you can fit what you want.

Polystyrene also sound good, but you only get them in low capacitance values. Silver mica are very nice, but expensive and also not available in high values

Most run-of-the-mill solid capacitors are polyester. They are cheap and easy to get. They do not sound too bad either. My advice would be to use those if you find polyprops are too expensive or hard to get. Later you can upgrade. Polyester caps are not good for decoupling though.

In the dual-supply version of the amp, only the input capacitor is directly in the audio signal path, so that is the capacitor to concentrate on the most.

Once again- do the case, PSU and heatsinks before you spend any money elsewhere. If you like I will do a sketch to show how I think the case should be, or I can just leave it up to you- it is your choice.
 
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Nikolai Petrenko said:
Or can you send me all schematic files .sch? then my older-friends will have me turn they into PCB layouts
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Will send files if necessary when final design is sorted. Just one thing, the scematics will need to be connected properly and the correct component cases called up from the libraries. I haven't bothered to do the scematics for a layout
 
Nikolai Petrenko said:
Wow, you said that you have been hang up your soldering iron, so you busy because of children or extra works? I just ask because I am to curiously .
Click to expand...

This is going to be long: Wife and son but he is 45 and lives 25 miles away. The other things that take my time are: major house referbishment, gardening, plumbing, electrics, electronic design consultancy- I have a company, but only me. Woodwork, metalwork, car maintenance, fix TV , toaster etc when they go wrong. Writing, mainly on Wikipeadia these days, but also some technical documents. Photography, reading- mainly technical. Investing in stock market. Music have 2 guitars and some amps. Computing: Word, Excel, Autocad, and so on. Some light C# programing and web site design.


Nikolai Petrenko said:
Now I still don't have anything about Eagle in my brain. I don't know how to put components from library to the draw page, my version of Eagle is 7.5.
Click to expand...

You are not trying. Eagle is the simplest ECAD package that I have used. I listed how to insert a component. Just follow that and you will be there. Eagle version 7.5 is the latest and easiest to use.
 
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Thanks. I want schematic and make the pcb myself. Kits are more expensive than discrete ones
 
An audio amp from scratch is a really tough project. I did some looking ans found this: **broken link removed**

Let's have spec rip it **broken link removed** apart design wise.

My initial comments are
1. The bias regulator can be improved more mechanically than anything else.
2. Independent supplies is another.

I would like to see 3 diodes rather than two for easier mounting. And the diodes mounted direct to the heatsink.

The cost seems cheap until you add case/power supply etc.

We/spec can offer suggestions that can make the amp better.

A Variac or variable auto-transformer is indispensable when working on amplifiers. AN isolated variac is better.

This **broken link removed** company has always intrigued me.

I will repeat that The Leach Amp is fantastic.
 

Nice work Keep. Have had a look at circuit and without going into details quite a few mods would be required to make the amp sound high end- good basic amp all the same.

KeepItSimpleStupid said:
This **broken link removed** company has always intrigued me.
Click to expand...

Yes me too- they make some good stuff

KeepItSimpleStupid said:
I will repeat that The Leach Amp is fantastic.
Click to expand...

And then some- do you fancy building another one for me?

I have been examining the Leach amp for a couple of weeks now and comparing its design with what is known today about audio amp quality. All I can say is that the Leach amp ticks all the boxes. It was way ahead of it's time. I'm not surprised 'it still sounds good now'. I am planning to do a post about my findings... time permitting.

But for Nicolai it would be to much for a first amp build.
 

eeek. I always stand well back when turning on a high power PSU for the first time. Elecdtrolytics are much better made these days. A good design rule I would suggest is to run them at 2/3 of their rated voltage. That keeps the film nicely formed and does not stress the insulation. If really essential , I also find that 90% is OK.

A well designed big torodial transformer has more or less no leakage inductance and zero coil resistance which are all good things for PSU performance, but this means practically unlimited current capability. At turn on this can cause problems as the reservour capacitors will be at OV, so a destructive current can flow. Normally this is reduced by fitting an NTC thermistor in series with the primary. I don't think Nikolai will be able to get a toroid though.
 
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The first power supply I used was a 20 A 70 V c.t. Constant Voltage Transformer. The sound was really nice. The amp was "open frame" constructed like the original article. No case, just a chassis. Me, not knowing any better just used 50 V electrolytic which were local to the board. The main caps were 9600 uf computer grade stuff. So, one day, the cap blew up! Only one rail fuse blew and the 3 A AGX series speaker fuse and it sat there cooking stuff.

So, that's when I decided to flatten the amp to fit in a 2 RU 19" home made case with the top being a finely perforated aluminum. probably like the PA040116, here: http://www.metalsdepot.com/products/alum2.phtml?page=Perforated Aluminum Sheet

I ordered a custom 4 x 35 VAC x 3 Amp torroidal transformer and I now had about 40,000 uf of capacitance to tame. I didn't want the lights to dim or to stress stuff. Initially I set up some optocouplers and a zener diode to get the BJT on at 2/3 of 50 V. I strung the BJT''s in series to get an and gate. I used an LM324? quad op amp set up as a comparitor. That result shorts out the flameproof resistor int the line. So now, everything is "protected" EXCEPT the resistor.
There needs to be a power-up timer (AC applied) started and if the caps are not > 2/3 Vcc the amps should go into protect and "stay there" until reset. e.g. magnetic latching relay. Way more complicated.

The amp doesn't have a power switch. It's actually controlled by a "fancy timer" which uses a triac that was in radio Electronics, I believe. Some options are a 0-2 hr timer for say bedtime listening and a 30 sec to 20 min turn off after the audio stopped. So, a cassette deck or turntable that stopped resulted in the system turning off. The timer knob had two ranges and 1 hr for timed mode coincided with 10 minutes for auto mode. Worked for me.

The timer used Norton LM3900 amps so it could accept speaker or low level inputs. For another part of the system, I had to add an interface that created a pulse on power up for a (power up signal) and another signal for (A pulse on power down). The later was harder.

This is also tied to an optocoupler in the signal path and the speaker relay. Instead of just turning on the optocoupler, I decided to drive it with the voltage across a charging capacitor, so I now have an exponential increase in volume over about 10 seconds, The preamp turns on at about 5 sec, so you get the tail end. Still nice.

The design had one flaw: The optos burnt out. I added ZNRs across the caps and we're good.
 
Wow, you certainly have been sorting things out with your Leach amp. The most I have done is to use an NTC thermistor, colapse both the supply rails if one fails, and ensure that the power output stage turns on slowly to elliminate the thrump when you first turn on. I generally avoid current limiting because I wan't the amp to produce short bursts of infinite current at times.

Because of my much-stated speaker burning experiences, I started designing a zero distortion speaker protection circuit, but it fell by the wayside and I never did developed it.

Never used ZNRs or know much about them- can you post a link to a data sheet? Are they like zeners?
 
ZNR's: **broken link removed**

Zero distortion: Mine qualifies. The amp does not have a power limiter.

Inconvenient: Yes. The fuse basically protects overdriving. The AGX http://www.cooperindustries.com/con...t-datasheets-b/Bus_Ele_DS_2041_AGX_Series.pdf blows quite fast. The output transistors are rated for 30A. They won''t blow to protect the fuse. One of Murfys electronic laws. The AGX is accessible.

That's why a clipping indicator can be useful. I actually did design a cool clipping indicator for an I-V converter that I built for a custom instrument at work that was really cool. It did use fixed +-10V levels. It detected the "clip", determined the sign and extended the time to 1 second. It activated a two-color LED red for +clip, green for -clip and yellow for both clips. So, really cool.

Ideas for a clipping indicator involve monitoring Vce which probably can get messy. There might be better choices now than in the 80's. Then there is the idea of monitoring the difference of the input and output waveform. Possibly use a Norton OP amp.

I burnt tweeters where they "didn't sound right". They overheated and you got distorted output, eventually forever.

Some of these:

Klipstein's Laws of General Engineering and Production:

Any wire cut to length will be too short.
A fail-safe circuit will destroy others.
A transistor protected by a fast-acting fuse will protect the fuse by blowing first.
A failure will not appear until a unit has passed final inspection.
After an access cover has been secured by sixteen hold-down screws, it will be discovered that the gasket has been omitted.
After an instrument has been assembled, extra components will be found on the bench.

(some of) The Recommended Practices Committee of the International Society of Philosophical Engineer's Universal Laws for Naive Engineers:

Any device requiring service or adjustment will be least accessible.
Interchangeable parts won't.
Manufacturer's specifications of performance should be multiplied by a factor of 0.5.
Salespeople's claims for performance should be multiplied by a factor of 0.25.
 
I am curious now, do I able to make dual-rail supply amp? I said despite I not have much money but I will spend money for sound quality. Usually one times for several years I have a big project so I won't afraid so much about spending.
 
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