1 Watt amplifier from ETI - 6V, 2 speakers, 0 opamps

[GibsonGM]

Yes, I found a bigger (better) 8 ohm spkr out of an old police scanner, and this sounds much better  The fuzz went away...    With some tweaking you could make it into a portable amp, or "desktop" unit for pedal testing or other purposes.    

I'm going to put one together on some perf, with a FET preamp....maybe add some clipping, ha ha...

*edit*   With a better speaker, heatsinking IS required

[tca]

I've breadboard it again a few moments ago, so that I could remember how it sounded. A very good sounded amplifier with very few parts! I've used six AA 1.5V batteries and works perfectly!

Cheers.

[GibsonGM]

Now, how do we make it louder? 

Any way to parallel the IRF?? 

[samhay]

@tca - did I see your "non-burning speaker amplifier" diagram somewhere recently? you know the one, with the audio coupling transformer in place of the loudspeaker.

this?
http://www.diystompboxes.com/smfforum/index.php?topic=100343.msg882961#msg882961
or
http://www.diystompboxes.com/smfforum/index.php?topic=103236.msg919214#msg919214

[tca]

@tca - did I see your "non-burning speaker amplifier" diagram somewhere recently? you know the one, with the audio coupling transformer in place of the loudspeaker.

Sorry for not answering your question. I think it is the mosfet version of Escobedo's amp.

Now, how do we make it louder?  
Any way to parallel the IRF??  

Without compromising the simplicity of the amp I only see 3 ways:

1. The way to make it louder is to increase power. Instead of batteries use a cellphone charger (6V, 400mA).
2. Add another speaker in parallel to get 4 Ohm; you will get a total of 6dB increase, 3db for halving the load of the mosfet and another 3dB by doubling the area of the speaker.
3. Do 1 and 2.

You can always parallel several devices but the distortion you get when overdriven changes, gets more fizz and bzzz...

Cheers.

[GibsonGM]

Well, I have this on my power supply, not batteries, so that is already covered.

I think I'll try a 2nd speaker in parallel, now that I have the mosfet on a heat sink.   6dB is a nice increase! 

Have to work, so I'll mess with this later.    If I can get it just a little louder, it will have potential as a practice amp.

[duck_arse]

@sam - no, I was thinking of this one ..... http://www.diystompboxes.com/smfforum/index.php?topic=107379.0 the one tca linked to ^ the hyperdrive. (the link showed this end as undecorated text, so I nearly reposted.)

I see some differences.

[tca]

The hyperdrive is simply a mosfet version of Escobedo's amp. It has an amazing .01W, it will not sound louder than your electric guitar when not connected to an amplifier! Just a fun circuit to play with, although you can use it as a booster as sam did.

[GibsonGM]

Yeah, putting another spkr in parallel really gained quite a bit of volume!   I'm surprised, but then, I shouldn't be.   We use this principle all the time with regular guitar cabs, so of course it works here....

[tca]

Hi Mike, judging from the "Read 752 times" score, I guess simple amps do get some attention.

Your persistence on this simple amp made me think about making a small useful amp out of this... I've been reading my notebook and there is a simple mosfet booster than could be added before the amp and a little mod that would make a good definitive version of this project. Do you have some written schematic of your tries?

Cheers.

[GibsonGM]

Do you have some written schematic of your tries?

Not really, Tiago...I tend to mod things and then just use the parts on the board when I make something permanent.  Lack of good record keeping is a personal flaw of mine!  The only changes I have to your schema on my IRF amp are the use of a 2.2u input cap, and a directly grounded source...

I am using a built-as-drawn AMZ Mosfet Boost in front of mine, and it sounds great!  Just the one stage right now.  I'm thinking of adding clipping diodes at the output and a recovery stage, for a 'distortion' feature.    Here is the link to Jack's site, with the schematic I use: http://www.muzique.com/schem/mosfet.htm      I love this booster!  I use it for solos when gigging.    

I don't know why I think this little thing is really cool, ha ha.  I've built tube amps and tons and tons of effects, but never played with transistor amps.   For such a simple thing, it DOES sound good!   It really depends on the speakers, though, and I feel the mosfet boost is doing quite a bit towards the 'rich' sound, too.  

PS - this sucker gets HOT with 2 in parallel!   I measure 150F on my heatsink right by the chip, which is 71C.   That is after playing through it for 20 minutes.  The data sheet says we're ok to 150C, though! 

[tca]

this sucker gets HOT with 2 in parallel!   I measure 150F on my heatsink right by the chip, which is 71C.   That is after playing through it for 20 minutes.  The data sheet says we're ok to 150C, though!  

Speakers or mosfets? I'm guessing you are using 2 mosfets in parallel (and speakers). I'm on the metric system, 150F~66C that seems ok, coffee drinking temperature.

P.S.
You should also find that the sound/distortion characteristics of the amp changes as temperature rises due to the variations of the mosfet parameters with  temperature. Nothing very drastic, but noticeable nevertheless.

[GibsonGM]

I'm only using one IRF510, with two 8R speakers in parallel (4 ohms).    Thinking of 66C as 'coffee temperature' is a good rule of thumb, thank you!    So the increase in heat is both expected, and normal, of course.

I have noticed that it seems to become 'warmer' as it heats up, a bit like a tube circuit.  This does sound pretty good for bedroom practicing!   Esp. with single coils, as on my Telecaster.  I could record with this amp, ha ha.