TBA820M as guitar amp?

mattusmattus · February 09, 2009, 08:24:07 AM

Been looking into possible cheaper chip candidates for ue in a ruby style project. Built up a few rubys/little gems in the past to make use of old hifi speakers I've got my hands on and the LM386 drives very nicely for guitar use. I've found a cheap supplier of TBA820's and this morning built an amp from the datasheet which is driving a 4ohm speaker, unfortunately it sounds pretty poor, kind of misbiased sounding (probably misbiased then?). The chip has a gain control which i've tried at full whack and its looouuuudd. As a distortion amp its ok, although the clipping isnt very musical.

Anyway, is it possible to get a good clean tone out of this thing? Mark Hammer seems to be a keen proponent of this chip so it must have potential! any ideas?

petemoore · February 09, 2009, 09:06:16 AM

The chip should be able to reproduce pretty cleanly whatever is 'reasonable' input.
^That said, assuming it's the kind of chip I think were talking about, amplifier chip, I haven't looked at the data sheet.

Mark Hammer · February 09, 2009, 09:49:27 AM

How are you powering it? This is NOT a 9v-battery-lasts-for-ages-if-you-use-it-for-headphones chip. It wants a nice hefty supply, on the order of something like a extet or octate of AA cells.

mattusmattus · February 09, 2009, 10:19:12 AM

Thanks for replying, been using a 9v battery and whilst debugging had noticed that there was a slight difference between the batteries I tried - I put that down to the quality of the battery (recently "splashed out" £1 on three 9v's from poundland). I forgot to mention that I had not been using the ripple rejection pin, will i need this if I use a 9v adapter?

Also is it possible that the ohmage of the speaker may have a buzzy effect? With my very best 9v battery i can get a relatively clean tone after adjusting the gain setting (too little gain means the sound is quiet and gated, too much and its raspy fuzz, and somewhere in between I get clean with a fuzz in the background).
I'll try a different power supply in the meantime.

Mark Hammer · February 09, 2009, 11:08:46 AM

I think that if you provide it more current (8 C-cells would be optimal), you'll be very pleased with its performance.

JMV · February 09, 2009, 09:56:27 PM

I built a small amp (from the datasheet) using this chip with a fetzer valve deluxe as a preamp, it sounds great! It's powered from eight AA batteries along with a Jensen 10" speaker in a open back enclosure. It has good bedroom clean volume, fully cranked it's loud, and has a decent rock sounding breakup, think Led Zeppelin, Heartbreaker. It sounds really good with my Ge Fuzz Face clone.

BTW, this is my first post. I really learned a lot from the greats here.

Joe Vernice

mac · February 10, 2009, 11:17:47 AM

QuoteBTW, this is my first post. I really learned a lot from the greats here.

Welcome!

I recently downloded the datasheet but for car use. If I find one I'll give it a try as a guitar amp.

mac

waltk · February 14, 2009, 10:19:03 AM

QuoteI built a small amp (from the datasheet) using this chip with a fetzer valve deluxe as a preamp, it sounds great! It's powered from eight AA batteries along with a Jensen 10" speaker in a open back enclosure. It has good bedroom clean volume, fully cranked it's loud, and has a decent rock sounding breakup, think Led Zeppelin, Heartbreaker. It sounds really good with my Ge Fuzz Face clone.

Hi JMV,

I built a small amp with a TBA820M with a Fetzer valve preamp exactly as you did - but mine doesn't sound that great. It could be that I'm just using a 9-volt battery (I noticed that a fresh battery works better than an old one), or it could be the cheesey speaker and enclosure I used. Would you be willing to share your schematic so I can compare it with mine?

- Walt

Mark Hammer · February 14, 2009, 10:43:04 AM

Trust me, it's the 9v battery.

JMV · February 14, 2009, 12:27:58 PM

waltk,

I used the figure 2 schematic from the datasheet and wired it just like the fetzer-ruby located on the runoffgroove FAQ http://www.runoffgroove.com/faq.html. I used a MPF-102 in the fetzer deluxe, it sounded a little brighter. Like I said before, it has a 10" Jensen and runs on eight AA batteries. I rigged a gain control (Rf) using a 1k pot. I don't have a schematic otherwise, I just used a breadboard, then built the final circuit on veroboard.

Joe

waltk · February 16, 2009, 11:56:59 AM

Thanks for the info. I'll have to revisit the design, bump the voltage, and re-bias the JFET when I get a chance. If anyone's interested, here's a schematic...
http://www.aronnelson.com/gallery/main.php/v/waltk/Schematics/Fetzer-TBA820+amp+schematic.jpg.html

mattusmattus · February 22, 2009, 12:50:16 PM

Just to update, I've finally got round to testing the amp at 12v, and its very loud, not quite as nice sounding as my similar lm386 effort but with some modification it could be improved. Still got a noticeable buzz on clean settings but I'm putting this down the low ohmage (and quality) of the speaker I'm using. Just wish this chip would come off better with a 9v battery.

meffcio · August 29, 2012, 07:12:54 AM

Sorry for digging an ancient mine, but here's something maybe worth trying.
http://www.mediafire.com/?ev580185gena4pi
It's simply a marriage of Noisy Cricket MKII with TBA820M chip. Only a little more components, and 2W output power at 12V into 8 ohms!
I didn't include the grit mod. And I'm not sure about the pot values. Would be nice if somebody checked how the thing goes.

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TBA820M as guitar amp?