PUNCH - 1W amplifier

[chromesphere]

So ive spent more time with the punch amp.

I left out the 8 ohm resistor on the speaker load but then started to worry if that might damage my fender twins speakers.  I added it in, and it might be my imagination, but I think its even louder!?  Would that actually happen?  more resistance = more voltage?

Also I found adding me GE7 eq at the front of it made it sound even better, to the point that I would have trouble telling the difference between this thing and a store bought amp.  When I finished playing it tonight I reached behind my fender twin to turn it off! lol An eq is essential if you ask me.  Also tweaking an eq can give you even more volume on the output to the point that I cant turn it over 1/3 volume before it starts to get uncomfortable to sit directly infront of the amp!

I'm still totally shocked at how awesome an amp you can build with 6 components. 

Huge success!  If your reading the thread thinking about building one (your first amp perhaps?) do it!  Just have a good set of speakers or speaker in a cabinet and an eq ready and you will get the full potential out of this little puppy

Paul

[tca]

^ I'm glad you like it. Has you said, the speaker has an enormous influence on the final tone. Your entries made me  think that I should do an upgrade to the PUNCH by adding a volume and tone control. Nothing fancy. Using the TDA7052 but with a Tweed Princeton-style single tone control and current feedback to increase the output impedance of the amp.

Cheers.

[chromesphere]

Pretty sure the (A) suffix of TDA7052A is the volume control option and is really easy to implement.  CHPTunes on page 4 has a schematic with it on it already.

A tone control is essential.  I've recorded a video of this little beast for my YouTube channel twice now, each time I finalise it I discover something that improves the sound further.  The EQ is the next 'upgrade'.  The amp sounds a bit dull / flat without it.  Increasing the top end with my GE7 makes this thing sound deceptively like a real store bought amp.  its amazing....!  I've only ever built a ruby and this amp so I'm no expert on these small scale / 9v amps but I have a pretty good ear, and I think it sounds incredibly good....and that's not even taking into account this thing costs under 10 dollars and consists of about 8 components!

So yeah, if your going to implement a tone control, one that can boost the treble is what you'd want imo!  It sounds out of this world when you brighten it up!

Paul

[tca]

The EQ is the next 'upgrade'.  The amp sounds a bit dull / flat without it.  
(...)
So yeah, if your going to implement a tone control, one that can boost the treble is what you'd want imo!  It sounds out of this world when you brighten it up!

The current feedback will take care of that dullness!

Cheers.

[artifus]

The current feedback will take care of that dullness!

to a degree - dependent on speaker response? and input, of course.

[chromesphere]

Question.  What's current Feedback?

[tca]

Question.  What's current Feedback?

See http://www.thatraymond.com/downloads/solidstate_guitar_amplifiers_teemu_kyttala_v1.0.pdf pg.87

[chromesphere]

Question.  What's current Feedback?

See http://www.thatraymond.com/downloads/solidstate_guitar_amplifiers_teemu_kyttala_v1.0.pdf pg.87

I was hoping for an answer in 10 words or less Thanks for the link.  Looks like an interesting read!
Paul

[artifus]

I was hoping for an answer in 10 words or less

resistor from speaker output goes to feedback input.

how's eight?

[artifus]

^ that's ten 

[chromesphere]

Well done artifus!  Now all I have to do is understand it
Paul

[artifus]

http://www.current-drive.info/9

[chromesphere]

Had a very BRIEF read of both links, thank you both.

So would adding a negative feedback resistor somewhere help brighten things up?  Probably totally misreading this.

Paul

[PRR]

> I left out the 8 ohm resistor on the speaker load but then started to worry if that might damage my fender twins speakers.

No way it can hurt a Twin's beefy speakers.

> I added it in, and it might be my imagination, but I think its even louder!?  Would that actually happen?  more resistance = more voltage?

If the speaker were a pure 8 ohm resistance, with-resistor puts half-voltage and quarter-power to the speaker.

However an "8 ohm" speaker is 40+ ohms near your lowest note, 16++ ohms above your highest fret-note (in string harmonics). So while you may have less overall, you get full volume in two important areas: thump and zizz. This may impress the ear more.

Also: connected straight the amplifier damps-out some of the stray flaps and cone-tone of the speaker. With 8 ohms in series, the damping is much less. Do drummers still put their wallet on a too-busy snare drum head? The amplifier can do a similar thing; with extra resistance, it does it less. Good Twin speakers are designed/selected for "interesting" cone-tones. You may like it better with less damping.

FWIW, the classic older Fenders had output resistance similar to speaker impedance.

Some old tube amps had no feedback. With pentodes (6L6 EL84 etc) the output resistance could be 5X or 10X the speaker nominal impedance. I had such a VT40 with some lively speakers in a combo-cab designed for this amp, and I never had an urge to change that sound.

> current feedback to increase the output impedance of the amp.

That works too. And avoids the power loss in a build-out resistor.

At the 20W level, that lost power is significant. Some chip-based commercial amps use current feedback to raise output resistance and reduce damping. However designing a STABLE current-feedback loop can be difficult.

At the 1 Watt level, it isn't a big deal. We over-build the amp a bit, add a 25 cent resistor, it's un-damped and no heavy thinking needed.

[Rock_on]

Hey sir! Can you make A Super Punch?

Hahaha i mean make it 2-3W to rock thy neighbors \m/

[chromesphere]

Forgot to respond!  Thank you PRR for your detailed explanation.  It seems that RL was really doing nothing interesting but decreasing the output so i removed it.

@Rock_on - If your punch amp is set up anything like mine (EQ -> punch -> twin 2 x 12's) you wont need a super punch.  Seriously this thing is loud enough with this particular set up to annoy the neighbours at half volume.  No i dont live in an apartment.  Its mental loud for what it is!

The only complaint with the punch that i have is gain pedals.  It just doesnt seem to reproduce them well.  As far as clean goes, i would use this any day of the week!  Outstanding clean tone for something so simple.  I have a few videos in the upload queue i will upload soon.

So glad i revisited this one!
Cheers,
Paul

[tca]

^ The only complaint with the punch that i have is gain pedals.  It just doesnt seem to reproduce them well.

Yes  and no...  the biggest  problem with  this  type of  chip amps  is the  low
amplitude input voltage that it can take (can't find that value on the datasheet
for the TDA7052). If  you feed the amp with a hot signal  it will start to clip,
and  it does  not sound  good. This  is a  case where  a passive  volume control
(between  the buffer  and  the amp)  would improve  that.  This is  not a  PUNCH
specific problem it will happen with any amp, but specially with chip amps.

For instance, the LM380 has an input voltage limited to +-0.5V, the only way of
making it full proof is to put some schottky diodes to ground at the
input. Otherwise you have to adjust the amplitude of your input signal.

> have a few videos in the upload queue i will upload soon.


Cheers.

P.S.
My strat can give up to 200mV with a chord, and 50mV to 100mV for a single note
(depending on the string). Gain is limited to 2.5 for the LM380! This is the
reason why you can take almost any chip add a buffer and make a guitar amp!

P.P.S.
Can you explain that: "It just doesnt seem to reproduce them well." in more
detail?

Is it clipping or freq response?

[chptunes]

i'm still reading along.. love my Punch amps.

[chromesphere]

Hey TCA.

I think you explained the problem.  Could be the input limit of the TDA7052?  It sounds a bit broken up..sort of...Gain pedals just don't sound clear or as good as clean (which sounds freaking superb!).  It could be clipping.  Do you guys noticed any issues with distortions / fuzzes etc?

Paul

[Gurner]

...  the biggest  problem with  this  type of  chip amps  is the  low
amplitude input voltage that it can take (can't find that value on the datasheet
for the TDA7052). If  you feed the amp with a hot signal  it will start to clip,
and  it does  not sound  good.

You can work sort of work backwards, the TDA7052 datasheet gives the voltage gain in db (39db), which is about 90x.

On a 9V supply, the largest signal you can reasonably expect to get out of the amp is about 7.5V peak to peak.

Therefore 7.5V/90 means that anything over (approx) 83mV will start clipping ....which isn't particularly hot at all!  (though it probably won't sound objectionable until the signal gets hotter, resulting in more 'squaring').

If you use two 9V batteries in series to give an 18V supply (which the TDA7052 can run at), you'll be able to run a lot cleaner signal through before clipping kicks in ...but the IC will get nuclear hot if you feed to hot a signal into it! (& you'll spend most of you salary on PP3 batteries!)

In my opinion a TDA7052A is a better choice as it has a DC vol control which reigns in the gain & will allow a far cleaner signal through. As an aside, using two 8 ohm speakers in series, will result in less heat stress on the IC (which being BTL can get darned hot at 8 ohms) & much longer battery life (but less power output). I used to be quite keen on the TDA7052A (& indeed it's a far better chip than the over used LM386), but comparing the scoped output to a fully differential input audio AMP IC ...sees the TDA7052A a fair bit noisier on the trace (like for like)...of course whether you can hear this scoped noise is debatable.....