Best DIY TDA2050/ or other guitar amp

[R.G.]

There are two opinions on the issue of single versus dual power supplies. You have heard both of them. Both ways work, but have different secondary technical issues and details. Both are sufficient to and exceed your needs.

They take the same number of parts (i.e. two big filter caps) of about the same size and value. The decision must be made on secondary issues.

1. Thermal issues: the power amp chips generally have the metal tab attached to the most negative power supply pin. If you use a single supply, you can make the most negative power supply be ground, so the tab can be bolted directly to a grounded heat sink (always, always with heat sink compound between the two, always) and it doesn't matter if it makes electrical contact. Well, unless you have ground loop issues. But still, you can leave off the electrical isolating wafer and get marginally better heat transfer without it. Or, for the LM3886 and possibly the TDA7429(?) you could get the "f" version of the chip, which has an epoxy layer over the metal chip area and can also be bolted directly to the heat sink.  Or, for the ordinary, metal tab version of the chip amps, you can just order the insulating film wafer and use thermal compound on both sides. Or you can get a silicone rubber insulating wafer and not use thermal compounds. There is a slight thermal advantage to single supply here.

2. Speaker protection. Opinions are divided on this one, but the theory is that having a BFC (Big Freaking Capacitor) between the power amplifier and the speaker will protect the speaker from being destroyed if one or the other of the power transistors in the output stage short. This is true in most cases. The chip amps also tend to have much more effective monitoring of the output transistors on the chip, so they can tell the transistors to stop playing if the transistors get near dying, so they don't die as often, meaning the cap doesn't have nearly as much to protect against.

3. The dreaded **THUMP** at power on: When you turn a single-supply amp on, that series capacitor before the speaker needs to be charged up to 1/2 of the single power supply voltage, so there is a big **THUMP** when you turn it on if the speaker is connected. If the speaker is not connected, the cap doesn't charge. So you need to either live with the thump, or set up some kind of resistor pull-down on the output capacitor and also a relay to disconnect the speaker for some time to wait for the cap to charge up before connecting the speaker. Chip amps and modern-style differential-amplifier input power amps tend to be symmetrical around ground as dual power supplies ramp up evenly toward + and - , so there tends to be very, very quiet power ons. No thump. In addition, the LM3886 and possibly others have a "mute" pin, which can be held in the inactive position by a resistor/capacitor at power on to make power-on almost completely silent.

4. Esoterica about distortion: As bool mentioned, there are hifi tweako concerns about capacitor distortion mechanisms. These are pretty inaudible for musical instrument use and I'd ignore this.

For my opinion, I prefer to use dual supplies to get rid of the series capacitor issues and deal with the thermal needs directly, especially since using luxuriant heat sinks is a good idea for all chip amps.  I trust the built in protection for saving the speakers. Bool prefers the added security of the series cap. That's a valid opinion too.

It works either way. Either one will give clean, clear, loud and warm if you implement it right. Al the chip amps I know of will work with either single or dual supplies. I think that there is some practical advantage to you in that you're being confused by technical advice on more subtle things than your technical level is ready to cope with, so the existence of pre-existing PCBs for dual-supply LM3886 amplifiers may help simplify that. So will the availability of pre-existing PCBs for the dual-supply filter caps and rectifiers and vendors selling transformers for them.

But again, I want to emphasize that the work you're about to launch into is mostly mechanical, not electronic circuits. Don't mess about too much with the ideas about which circuit style you want until you know how you're going to build the box, mount the speakers, make a chassis, mount a heat sink, do the AC mains electrical work (which, by the way, can KILL you if you don't do it right). These are the big problems to solve first. Leave the small stuff about which chip and what power supply til you know your solution to the big problems.

[R.G.]

Go here:

http://www.ssguitar.com/index.php?board=2.0

[bool]

Mind you, I'm not "preferring" single-supply amps. My favorite designs were the "8-transistor" bipolar quasi-complementarys from the very beginning of the '80s (with zener faux-ccs in the ltp).

Onto the single-supply amps: If you design them right, they are much safer in use, esp. with chipamps that tend to blow-up often if something isn't "just right". Translated: when an inebriated player cranks them or shorts something etc etc etc. So read this again and again: there is only ONE fuse to blow in the PSU. (Bipolar suppply amps will usually have two fuses in PSU, meaning if one sides' fuse blows, you often get full rail voltage dumped at the output - no-good at all).

Often there is no need for an "output" (speaker) fuse with cap-coupled amps. So all in all, an external (mains) fuse and one internal, PCB-mounted (PSU rail) fuse - and you're ready to rock.

There are design tricks that make the "thump" at power-on a non-issue in practical application, even with the chipamps. (I wouldn't waste a LM chip in a guitar amp, they're for Hi-Fi, but that's only me). TDA's were designed for abuse from the get-go. May be an Euro thing, hey..

There is "losses" consideration with cap-coupled amps. Also there's a power-limit to where this approach is sane. Also, higher powered amps will require higher voltage rails, requiring bulky mucho macho big-buck reservoir cap(s), twice the nominal voltage compared to bipolar supply.

Up to 60W into 4 Ohm... imho.

[Crontox102098]

Mind you, I'm not "preferring" single-supply amps. My favorite designs were the "8-transistor" bipolar quasi-complementarys from the very beginning of the '80s (with zener faux-ccs in the ltp).

Onto the single-supply amps: If you design them right, they are much safer in use, esp. with chipamps that tend to blow-up often if something isn't "just right". Translated: when an inebriated player cranks them or shorts something etc etc etc. So read this again and again: there is only ONE fuse to blow in the PSU. (Bipolar suppply amps will usually have two fuses in PSU, meaning if one sides' fuse blows, you often get full rail voltage dumped at the output - no-good at all).

Often there is no need for an "output" (speaker) fuse with cap-coupled amps. So all in all, an external (mains) fuse and one internal, PCB-mounted (PSU rail) fuse - and you're ready to rock.

There are design tricks that make the "thump" at power-on a non-issue in practical application, even with the chipamps. (I wouldn't waste a LM chip in a guitar amp, they're for Hi-Fi, but that's only me). TDA's were designed for abuse from the get-go. May be an Euro thing, hey..

There is "losses" consideration with cap-coupled amps. Also there's a power-limit to where this approach is sane. Also, higher powered amps will require higher voltage rails, requiring bulky mucho macho big-buck reservoir cap(s), twice the nominal voltage compared to bipolar supply.

Up to 60W into 4 Ohm... imho.

I understand all but... which chip would you recommend for a guitar amp?

[R.G.]

I understand all but... which chip would you recommend for a guitar amp?

Use either one you can get. They're both OK within their power limits. Both can be run with dual or single power supplies.

Don't sweat the small stuff - and "which chip?" is the small stuff.

[Crontox102098]

I understand all but... which chip would you recommend for a guitar amp?

Use either one you can get. They're both OK within their power limits. Both can be run with dual or single power supplies.

Don't sweat the small stuff - and "which chip?" is the small stuff.

TDA2050 is it what i've got, so, i'll start.
Thanks guys, specially R.G's and bool. 

I'll put pics when it's done.

Thanks, and cheers.

[bool]

You asked for "which chip to use". If you need higher power, check out TDA7294. It has a "standby" function which you could use to mimic tube amp "knobs and switches". Www is full of schematics and info.

Since you have TDA2050, here's a hint, if you plan to use it with an output cap: Use the protection diodes like you would with the weaker TDA2030. Charging/discharging mechanisms are a bit different in single supply circuit, and this should add some more safety margin for the chip.

So use diodes like here, but with TDA2050: