Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Amplifier Discussion => Topic started by: tpb03 on September 12, 2017, 08:52:34 PM

Title: EBay TDA2050 boards
Post by: tpb03 on September 12, 2017, 08:52:34 PM
A few years ago I started to make a small combo amp for practicing in my bedroom. Due to starting a family I ran out of time and abandoned the project, but not before building a nice pine cab based upon the Fender 5F1 combo.

I now want to complete the project as a 5W SS Champ style amp. I have ordered one of these cheap TDA2050 boards form ebay ( which from the TDA2050 datasheet will deliver about 5W into an 8 Ohm speaker  at 18V single supply (I have some old 18V 4A laptop power supplies). I don't really trust the claims of 12-24V 5W- 120W, but happy to be shown wrong!

Could this project be as simple as (input -> Fetzer valve -> TDA board -> speaker) or do I need to put a buffer in somewhere? Also when running a fetzer vale at 18V, do I bias the transistor at 9V? (I obviously need to do some homework).

Does anyone have any experience using these prefab boards?

Title: Re: EBay TDA2050 boards
Post by: J M Fahey on September 15, 2017, 08:35:42 PM
Seller claims are wild unbelievable, from 120W out (out of a max. +24Vdc supply) :loco  to being able to be powered from USB (lower voltage than minimum acceptable) to being powered from AC (I´d LOVE to see that).
That said, it *should* work like a plain TDA2050 single supply datasheet example, so "just trust the datashet, not the seller".

Post here the preamp schematic you want to use with it.

If powered from 9V, you can easily get them from your +18V supply, all it takes is a resistor, a 9V Zener and a 100uF x 25V cap.

Nice project, now you must hunt for a suitable speaker.

Link to some Aussie site selling speakers to help you choose one.

Basically light, thin paper cone, like those cheesy 6 x 9 speakers old Falcons used to carry as factory installed ones in the 70s; you do NOT want "woofer" anything which will be dull and inefficient with guitar.

Or hunt pawnshops or Aunt Edna´s attic for old "home console" speakers, killer sound with guitar.
Title: Re: EBay TDA2050 boards
Post by: tpb03 on September 17, 2017, 08:22:52 PM
Thanks J M.

I will treat it as per the datasheet single supply. I also have a TDA2030 board that is claimed 15W 6-12V single supply. As I have the TDA2030 board already, I will test it at 12V and then higher just playing music from my phone.

I have been searching for a preamp and found this schematic on the forum (post (
It is Runoffgroove's Fetzer Valve with a buffer. This should give me a good approximation of the Champ tone going into the power amp board. Its also setup for 18V, although I did have a look through my laptop supply collection and the nearest is 19V. I'll test them all with my multi-meter to work out true voltages as from experience laptop supplies and wall-worts can be +/- 2V either way.

I would like to modify the preamp for two inputs like the 5F1. I'll report back when I proto this, but I think I will need to change the 4.7K input resister to 2 resisters running in parallel like the champ input. I can then solder the 1 Meg resister from active to ground on the input jack rather than on the board.

As for speakers, I have an 8" 8 Ohm guitar speaker from an old Park G10.

I'll report back here to share my experience as I am bound to need to help along the way!

Title: Re: EBay TDA2050 boards
Post by: tarahall on September 19, 2017, 08:39:21 PM
That said, it *should* work like a plain TDA2050 single supply datasheet example, so "just trust the datashet, not the seller".

The data sheet clearly states that the TDA2050 is a 35W IC so the seller claim of 120w is obviously seller promo "BS".

Title: Re: EBay TDA2050 boards
Post by: tpb03 on October 11, 2017, 07:42:58 PM
Just a quick update - I have received the board and set that up and played audio via my iPhone through it. So I can conform that it is working in order.

I have layed out the schematic I posted above on my breadboard running at 20V. When I measure the drain voltage between R4 and the drain I am not seeing any voltage drop, it is measuring at 20V still - shouldn't I expect this to be half the supply voltage so 10V?

Am I measuring for the bias voltage in the right place? Do I need to run a signal (ie guitar) through the circuit to bias the JFET?
Title: SS 5f1 inspired amp - was EBay TDA2050 boards
Post by: tpb03 on April 30, 2019, 09:52:31 PM
An update - I finally finished this project. I ended up buying a bunch of cheap boards from EBay and after testing them all decided to abandon the TDA2050 board and use a 2x10W class D PAM8610 similar to this one ( ( It sounds a lot better with less noise than the TDA.

The power amp is running at 12V and I use an LM2596 based step down converter design for model aircraft to provide a 9V for a fetzer value circuit which is the preamp. I also have an output for the second channel so I can run another speaker for a total of 20W. Overall sounds good with tone that is faithful to the original fender 5f1. The speaker is an 8" from a Park G10.
Some Pics attached (or via links) - including a guts shot

Title: Re: EBay TDA2050 boards
Post by: edvard on May 04, 2019, 01:01:31 AM
Congrats, 2 years is a long time to take on a project, but I'm not one to talk (took me 2+ years to finish building my guitar...  :loco)

The reason your TDA2050s sounded so bad could be because they are cheap knock-offs; the TDA2050 has been discontinued for a few years now, and new ones are just as likely to be filled with wet sawdust as silicon.

Counterfeit VS. Authentic TDA2050 audio amplifier ic test
Counterfeit parts have been a problem for many years. Let's do a comparison test of the TDA2050 audio IC to see the difference in performance.

Glad to hear that your Class D amplifier sounds good.  I may be going that way eventually, but haven't taken the plunge yet.