DIY amplifier

Originally Posted by Stereodude 

Mouser

Getting parts rated for more power or voltage is okay assuming they're equivalent. For example, replacing a 6.3V 1000uF low ESR electrolytic cap with a 35V 1000uF electrolytic is not a good substitution. I'd be pretty surprised if you couldn't find the right parts at Mouser and needed to make substitutions.

Originally Posted by zora 

Unless you really want to source all the parts, solder them on the PCB, and learn - why not buy a module/transformer/box and assemble one?

http://classdaudio.com/

I've got a couple of their modules I used for testing if you are interested.

JP

Originally Posted by Bill Fitzmaurice 

You may, the question is why? It won't work any better. The only justification is if you have a pile of components lying about.

Originally Posted by cookieattk 

you also need to take into account lead spacing for caps and resistors

Originally Posted by Bushi 

On the link you posted you can see an image of an assembled amp. In the picture it looks like they have 4 heatsinks on 4 transistors. Most likely the output stage. That is why most of those transistors have that little metal tabs with a hole in it, for attaching heatsinks.

Originally Posted by MarkHotchkiss 

Hi Wag,

To do it right, you need a single heat-sink that will hold five transistors: Not just the four power transistors Q11, Q12, Q13 and Q14, but also Q6, as it needs to track the temperature of the four power transistors.

Also, the heat-sink in that last Mouser link looks pretty anemic for a 200 watt amplifier, but I can't say for sure. My suggestion would be to use a Wakefield 435AAAA, which can hold all four TO-3 transistors. You may need to drill an extra hole for Q6.

Here is the datasheet.
Here is a source.

Originally Posted by cookieattk 

try ebay

Originally Posted by MarkHotchkiss 

That's a good question. I was simply echoing what the author said on page 2, under "Vbe Multiplier".

In general, junction voltages drop with increasing temperature in bipolar transistors. So it looks to me that, as Q6 is heated by the power transistors, it's lowered junction voltage reduces the bias voltage to the driver transistors, compensating for the power transistor's reduced junction voltage. That's just what it seems at first glance, and I would need to run a spice simulation to know for sure.

As far a those eBay links, I'm really surprised at such a large selection for some great prices. I will have to stop bashing eBay now. I also noticed the lack of hard data, but when you need to fit four TO-3s on a heat-sink, it gets large enough to not worry too much.
That looks like the winner to me. I would use the center spot for Q6.

Originally Posted by MarkHotchkiss 

Hi Wag,
You're welcome.
I don't mind at all.
Right.

If you are building a single amp, like for a sub, then what is shown is what you need. However, if you are building multiple amps, like for a stereo or surround system, then a larger, single power-supply would be more cost-effective. I suspect that is why he has the power-supply separated from the amp.
If you are running on 117 volts AC, then I would use at least a 200 volt cap. If you need to also run up to 240 volts, then I would use a 400 volt cap.
I doubt that they are any better. If they were close to the same price, then I might consider the "audio" versions just to impress the layman. But price would be my main criteria.
Do you mean BR1? yes, it's a bridge. The rating should be at least 60 volts and 10 amps
I would use a circuit-breaker, myself. 250va divided by 110 volts would say a minimum of 2.3 amps. Probably a 2.5 amp slo-blo would be best. A fast-blow fuse would probably blow on power-up with the surge that fills the filter-caps.
SW1 is the main power switch.

Originally Posted by MarkHotchkiss 

Yes, you can go with four diodes, but a bridge would be simpler and cheaper. Something like this.

You don't need switching diodes. Switching diodes respond in nanoseconds, whereas a power-supply rectifier can respond over milliseconds. The important specs are only the current and voltage.


The fact that the transformer is capable of 320va is not as relevant as the amount of power that the amplifier will actually draw, which would still be only 250va. It means that it wouldn't hurt to use a 3 amp fuse, but a 2.5 amp would also work.

I don't really know how long "slo-blo" is. I just know that fuses are listed as fast or slow. A circuit breaker is typically better, as it is slow for currents marginally above the trip-point, and fast for direct shorts. Personally, I like combining the switch with the breaker, something like this.