Recommedations for cheap DIY speaker amps?

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cyberspyder

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T-path amps:

-http://www.autocostruire.com/catalog/product_info.php?cPath=42&products_id=257
-http://diyparadise.com/shop/index.php?main_page=product_info&products_id=67

Chipamps:

-http://www.audiosector.com/lm3875.shtml
-http://www.audiosector.com/lm4780.shtml
-http://www.chipamp.com/lm3886.shtml
-http://www.chipamp.com/lm1875.shtml

What PSU designs should I be looking at?

Brendan
 
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pacificblue

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Your amplifier list includes very different types of amplifiers. First step is to decide, what you want.

The LM4780 is a stereo IC, while all others are mono.
The T-class amplifiers and the LM1875 can deliver up to 20 W, the others up to 60 W.

What are you after? Best sound? Smallest package? Lowest power consumption? Stereo amplifier? Active speakers?
 
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cyberspyder

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pacificblue said:
Your amplifier list includes very different types of amplifiers. First step is to decide, what you want.

The LM4780 is a stereo IC, while all others are mono.
The T-class amplifiers and the LM1875 can deliver up to 20 W, the others up to 60 W.

What are you after? Best sound? Smallest package? Lowest power consumption? Stereo amplifier? Active speakers?
Click to expand...

The best sound really, space isn't a big concern, but I don't want a huge amp either. Power consumption shouldn't be too much, but anything that takes up relatively little to moderate power is OK. And yes, has to be stereo as I have two speakers, but honestly, what's the advantage of putting two mono stages together vs. a stereo amp? Lastly, active speakers as in speakers without an active amp? If so, no, as I have a passive crossover.

Thanks, Brendan
 
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cyberspyder

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Is it a bad idea to have a 'do everything' amp? I want to be able to do the following in the same enclosure:

1) Speaker amp
2) Headphone amp
3) A 'bypass' feature

I know I can have a switch that'd allow me to switch inputs to either amp, but how would I do it with one pot? Also, how'd do that bypass feature? I plan to have a DAC that'll input into this amp, but I'd also like to have the capability to 'pass-through- the analog signal to another amp without resorting to unplugging cables.

Brendan
 
mikejennens

mikejennens

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pacificblue

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cyberspyder said:
1) Speaker amp
Click to expand...

Of course.

cyberspyder said:
2) Headphone amp
Click to expand...

You can do it like in commercial amplifiers. Use a headphone jack with two switches. Add two resistors to adapt the voltage to the headphone. Complete that with a few capacitors and inductors to suppress switching noises, when you plug the headphone in or out.

Or you can build a dedicated headphone amplifier and put that in the same housing. Then you can use switches to activate speakers or headphone. Or you can use the switches on the headphone jack to switch a relay, which in turn switches speakers or headphone like in the above version.

cyberspyder said:
3) A 'bypass' feature
Click to expand...

One way would be to just use a Y-adapter. If you want to use the amplifier, switch it on, otherwise switch it off and switch the other amplifier on.

More elegant, but also more complicated would be to use a switch (DPDT = double pole double take) and an additional pair of RCA connectors. The inputs go to the common connections of the switch one each. The outputs to the other amplifier go to the corresponding NC connections of the switch. And the input terminals on this amplifier go to the NO connections of the switch.

Or you can use a DPDT relay. Connections as above. If the relay works off your amplifiers power supply, then you will automatically get the correct connection by simply switching the amplifier on and off.
 
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cyberspyder

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After revising my layout abit, here's the final plan:

DAC > Switchbox > Speaker amp (w. PSU) > Headphone amp (w. PSU)

To conserve on space, maybe I should stick the DAC and Switchbox together? I really want to know how to get (find) the push button selector board outlined here (I don't want a selector pot on the DAC if possible), and a DPDT switch may not provide enough poles for more than two sources:

homecinema-fr.com • Afficher le sujet - Ampli Casque DIY AMB M³ SE

Pour plus de souplesse lors de l'utilisation de cet ampli-casque, trois commutateurs de sources par relais seront donc disponibles en face avant. But de la manœuvre : pouvoir placer l'ampli casque entre les sources et le préampli afin de pouvoir indiféremment écouter un CD, le iPod ou la FM sans brasser du câble.
Pour une écoute normale sans casque, il suffira d'éteindre le M3 pour qu'il soit totalement "bypassé".

Voici donc les trois commutateurs D6 avec leurs diodes rouges pour la face avant :

An externally hosted image should be here but it was not working when we last tested it.


Les trois entrées/sorties RCA avec leurs relais pour l'arrière :

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


Et les deux connectés : ça marche ! 8)

An externally hosted image should be here but it was not working when we last tested it.
Click to expand...
The rear panel would include this: hohodiy - Login

Brendan
 
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pacificblue

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The DPDT switch was supposed to switch amps after the input source selector.

What you posted from that French forum is a different, more complicated setup, where the headphone amplifier is used before the speaker amplifier. Each input is selected to be used either for the headphone or for the speaker amplifier. Then the speaker amplifier has another source selector. In short, you would need two input selector stages instead of one.

That PCB seems to be DIYed by Gilor. You could try to contact him through that French forum or you would have to copy it from the photos.
 
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cyberspyder

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After a hefty bit of rethinking (turns out I was on the wrong path to begin with), this is what I came up with:

An externally hosted image should be here but it was not working when we last tested it.


The speaker amp has a push button switch that'll either: A) Bypass the amp portion and pass the signal on, or B) run the signal through the amp, thus outputting to the binding posts. Now, I need a circuit that'd allow me to either break the circuit or connect the circuit (break would be amping the signal, and connected would be a short circuit that'd intercept the signal and loop it back out to the RCAs).

Brendan
 
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pacificblue

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And you are back to the DPDT switch. Or a pushbutton operated, remanent DPDT relay, if you like that better.

1640716.jpg
 
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cyberspyder

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Joined 2008
dangus said:
How about making the headphone amp part of the DAC? There's not an enormous difference between a good line driver and a headphone amp.
Click to expand...

Not enough space :(...hoping to fit a Toroidal along with the amp, and the DAC would need its own transformer.

Another thing, is there an advantage using metalized film polypropylene caps in place of the standard electrolytic caps in the chipamp kits? Probably going for one of them, since the kit from autocostruire is expensive due to shipping and other stuff.

Brendan
 
danielwritesbac

danielwritesbac

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Joined 2007
startfetch.com
Puffin said:
Someone on here (I think) bought one. Mmmmmm
Click to expand...

I bought several in order to study their tone control varieties--discrete, op amp, passive, and codebase.

On these products, the presence of a potentiometer with light gray plastic for the threads on front also corresponded to poor quality throughout the product. However, decent, sturdy, potentiometers (with metal threads) plus one or more blue resistors and better boards, also corresponded to a product with same or better performance than mass market offerings.
Coincidence? Or, does it indicate whether they cared or not?

Further exploration of the power amp sections reveal that the Toshiba chip amp offerings were unusable, with Toshiba at fault for this.

By and large the tone controls of many varieties did work and did provided good study. Due to the low price and the low voltage, there was reduced risk for experimenting.

While study of real electronics (those that are physically present) does need both a high and low reference. I think that the high reference won't be coming from E-bay's china-bargain vendors. None had a "complete picture" although the preamp-with-tone sections were mostly functional by themselves.
 
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pacificblue

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cyberspyder said:
Another thing, is there an advantage using metalized film polypropylene caps in place of the standard electrolytic caps in the chipamp kits? Probably going for one of them, since the kit from autocostruire is expensive due to shipping and other stuff.
Click to expand...

Usually electrolytics are used, where high capacity values are needed. Film capacitors are used, where low capacity values are needed. Film types would not fit into the same space, where an electrolytic is present.

Adding small film capacitors in parallel to electrolytics can sometimes improve the sound. Rule of thumb is that the film type should have around 1 % of the electrolytic value.
 
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