Download PUNCH – 1 W guitar amplifier

PUNCH – 1 W guitar amplifier
© Tiago Charters de Azevedo Creative Commons license Attribution-ShareAlike 2.5.
18/Oct/2012
I've started this project as an alternative to well known LM386 guitar amplifiers, e.g., the
infamous ROG's Ruby amp. I built a few LM386's amps but I didn't like the frequency
response of them. So before anything else here is the schematic.
As you see it shares with the Ruby the same topology: a buffer and a chip amp. It uses a
JFET buffer with a MPF102 and the 1W TDA7052 chip. It is a clean amp and it reacts very
well with any pedal in front of it. I don't use a lot of distortion so this little amp suits all my
needs. It doesn't have a volume and tone control because I wanted a plug-in-and-play amp. If
you want an amp with a volume control try the TDA7052A, it has a volume voltage control pin
that works perfectly (simple pot), this chip has the advantage that the volume pot is not on the
signal path.
Of course the PUNCH also works with batteries, a 9v battery or with six 1.5V batteries in
series. For small voltages and currents the sound could become distorted or to muddy, if so
decrease the 1u cap to 470n or smaller.
Speakers?
What about the speaker? The guys from ROG say
What speakers do you recommend for use with your mini-amp circuits? While
the Ruby, Little Gem, and Little Gem MkII practice amps can be used with any
speakers, best results are achieved with full-size speakers intended for use with guitar
amps. The amps will work well with an total impedance of 4, 8, or 16 ohms. We've tried
hi-fi speakers, clock-radio speakers, and auto speakers - they just can't cut it. For me,
using anything other than a speaker designed for the frequencies of an electric guitar
produced sounds more like a toy than an actual amp. However, you may want to ask at
Aron's Stompbox Forum. Many of the members have built one of the aforementioned
amps and may be able to suggest a decent-sounding small speaker.
This is only in part true. One thing they are right is that clock-radio speakers and small radio
speakers won't work! But the same is not true for hi-fi speakers and auto speakers. Let me be
more precise about it.
I've tested the PUNCH and the Ruby with some 6'' auto speakers and they work great,
specially with the PUNCH. This Fonestar UT528 speaker of 5.25''=13.3cm with a frequency
response of 50-12.000 Hz and a sensitivity of 90 dB - 1 W/1 m works great.
Fonestar speaker UT336
Fonestar speaker UT528
I've also test it with a smaller one, the Fonestar 3''=7.5cm speaker (20-14.000 Hz, 8 Ω, 89 dB
- 1 W/1 m) and also has a great sound. I plan to finish the cabinet soon and post some pics.
Bill of Materials
Resistors (1/4 watt rating)
1 – 1M
1 – 3k9
1 – 10k
Transistors
1 – MPF102 JFET
Capacitors (minimum 16 volt rating)
1 – 220u aluminum electrolytic
1 – 1u
IC
1 – TDA7052
Other stuff
1 – 3PDT or DPDT heavy duty foot switch (bypass)
1 – mono quarter inch jack
1 – stereo quarter inch jack
9v battery snaps & holder and/or DC jack,
wire and a nice enclosure
Cabinet
Cabinet for the PUNCH with a 3'' Fonstar speaker and using a IKEA wooden box. The rear
photo shows the 9V battery enclosure.
PCB (3 x 2.5 cm^2)