PUNCH - 1W amplifier

[chptunes]

awesome look.. that big 'ole knob looks great right on top.. nice work.

-Corey

[kingswayguitar]

Ah, damn, it's mydiypedals.tumblr.com not .org

hey cool stuff

[nomorebetts]

This looks great!

Can't wait to get this on bread board and try it out.

Hey chromesphere, I just ordered a couple of the chips from your store.  I hope you have fast postage 

[chromesphere]

Hey man, thanks for the order! Well you just live around the corner so lets see if Australia Post can get off their asses and get it to you?  Will post out tomorrow, cheers
Paul

[nomorebetts]

The order arrived promptly, thanks Paul!

I bread boarded the schem on page 4 and couldn't believe my ears!    I plugged it into an entertainment system rear speaker which I picked up (literally off the side of the road) for free courtesy of hard rubbish collection... and boy oh boy it sounded sweet!  And way louder than I expected! My wife burst into the room telling me to turn it down or I would wake our son.  Haha! 

Below is a picture of it on bread with the speaker.  I am really surprised at the quality of the sound it produces.  I was expecting it to sound toyish and be a novelty item so was planning to marry it up with an 8 bit fuzz. 
Now I'm thinking a simple Over Drive circuit... any suggestions?  Preferably with low parts and knob count.

Cheers Tiago for a great little circuit!

[chromesphere]

Glad you got it quick!
Yeah its pretty amazing hah?  You should hear it through 2 x 12 inch fender twin speakers.   
Paul

[chptunes]

Glad you got good results.. I was initially surprised by it's sweet response with a dinky speaker too.. it's clean, but not cold.

[nomorebetts]

I was playing around with this again tonight and I get an audible "thump" when I power up the circuit.

Is anyone else experiencing this?  What can I do to avoid it?

Thanks in advance!

[chromesphere]

Hey David,
I just built one last night as well. I just break 9v with a spdt to turn the effect on and off.  I don't think I get a thump, although I might if the effect was up loud when I turn it on, but that's probably expected.
Paul

[PRR]

> I get an audible "thump" when I power up the circuit.

That's surely normal.

When you turn-on, various points have to rise-up from zero Volts to half of supply voltage.

The Power Stage tends to have low turn-on thump. It is two sides. If both come-up equally fast, there is no thump *across* the speaker. In practice the two sides aren't exact-equal, but thump may be small.

We usually need additional stages befor the Power stage. I forget which plan is current. The one at the top of the thread has a JFET buffer in front. This *must* come-up from zero to whatever its normal voltage is. As shown there, this may only be 1V or so. But the amp is designed to get loud with the part-Volt signal from guitar. So a 1V sudden rise will "thump" the speaker.

It is perhaps possible for this to "blow a speaker"; however a single thump can't do as much damage as playing LOUD for many minutes. Which is what we do. And if the speaker can't take it, we get a tougher speaker.

[chromesphere]

I built a 2nd punch amp and used a J201. I think I found a potential problem, but im no EE so im possing the problem here to see what you guys think.

For some reason this one distorts when the input is too high.  A high output guitar can make it distort.  if I put my EQ pedal infront of it and turn the level down on the EQ, the distortion goes away and I can compensate with the volume on the punch amp and not get any more distortion.  I didn't notice this with my first punch but will have to experiment to see if I can replicate the problem.

I thought the buffer was meant to circumvent this problem?  Is it the j201 perhaps?  If not, and this is normal behaviour, would a limiting pot on the front of the amp be a good idea to cut back the voltage on the input of the circuit?

Paul

[tca]

^ The J201 has -.8V pinch voltage... this is to low if you put a booster, or something that amplifies the signal, in front of it. The MPF102 has a -3V pinch voltage. The J201 is the cause of the distortion.

[chromesphere]

Ah k, I though any jfet worked with this buffer.  No problem I will replace it!  Thanks TCA!
Paul

[nomorebetts]

Thanks for the explaination PRR  - Your posts are always very informative!

[chromesphere]

I was thinking, for others that want to build this effect with a j201, would anyone know if you can sub the resistor values for the buffer to make the circuit behave with the j201?

[nomorebetts]

I still have my punch on breadboard and have paired it up with an Electra Distortion derivative.  My question is, should I put the buffer part before the distortion?  Right now I have it between the distortion and the punch.
Which would be better?  I see in TCA's 'Lux version he has the buffer before his OD.
Cheers

[tca]

The buffer ensures that the guitar signal sees a high impedance, preserving the highs. It depends of what you really want.

[chromesphere]

On a side note, my buffer (the non-j201 buffer) definitely doesn't preserve the highs and needs an eq pedal to boost them.  In fact this goes for my 2nd punch amp as well (the j201 version).

[tca]

^ If you are powering it with a battery you should decrease the coupling cap between the buffer and the IC, to less than 1u.

P.S.
I've written that in the PDF

[chromesphere]

Im using 470nf on the coupling cap after the jfet.  Is this still too much maybe?
Edit: so that's 470nf with dc power