"Punch" mini-amp with a 32 Ohm speaker?

[SeneX225]

Salut!

I want to make this tiny 1W desk amp (for quick on-hand testing of other guitar things):



However, I have this salvaged 32 Ohm 0.2W speaker lying around without any use, so I would like to use that instead of 8 Ohm one on the schematic, if possible. I have a notion that some tweaking is required to do it, yet completely clueless what exactly it would be.

As always, I'm humbly seeking your advice. Thanks a many in advance!

[ElectricDruid]

It'll work, but the amp chip won't be able to generate so much power into a larger speaker load.

The datasheet here gives figures for 8ohm and 16ohm:

https://www.nxp.com/docs/en/data-sheet/TDA7052A_AT.pdf

Basically, it halves the output power from 1W to 0.5W. So at 32ohm, you'll get 0.25W. Is that enough? I notice the datasheet also mentions that the supply voltage can be as high as 18V maximum, so you might do better getting the supply voltage up close to that if you're using a 32ohm speaker.

[Clint Eastwood]

If you have a junkbox with some transistors, you could build something simple like this:

https://www.homemade-circuits.com/wp-content/uploads/2020/06/tiny-two-transistor-amplifier.jpg

[SeneX225]

Basically, it halves the output power from 1W to 0.5W. So at 32ohm, you'll get 0.25W. Is that enough? I notice the datasheet also mentions that the supply voltage can be as high as 18V maximum, so you might do better getting the supply voltage up close to that if you're using a 32ohm speaker.

Then, perhaps, I should use another chip? I've found this page considering LM386, with something that looks like right up my alley:

LM386N-4

    Power output: 1W into 32 ohms at 10% 1kHz distortion with power supply 16V
    Gain: 26dB default, variable from 19dB to 46dB
    Power supply: 4V to 18V single supply

The page says it can me implemented in a guitar amp with the only change of volume pot:

VR1 and C1 are at the line level input. VR1 is a potentiometer and is ideally a 10k log (logarithmic) pot, but the value is not too critical and 22k or 4.7k will also work. For guitars, higher values are preferred such as around 100k.

They've even included schematics for both the amp itself and the entire system!





(By the way, is it safe to get rid of that inductor (L1) at power jack (J2) hot? The page says it's for stability only and I'm not advanced enough to make a coil yet, although I probably should learn how.)

If you have a junkbox with some transistors, you could build something simple like this:

https://www.homemade-circuits.com/wp-content/uploads/2020/06/tiny-two-transistor-amplifier.jpg

This is very neat, thank you!

Do I understand it correctly that since there's no chip, the power output to the speaker would be directly tied to over power input and therefore, if I use 12V it should be enough to drive 32 Ohm speaker?

[antonis]

Do I understand it correctly that since there's no chip, the power output to the speaker would be directly tied to over power input and therefore, if I use 12V it should be enough to drive 32 Ohm speaker?

It's a standard CE Class A amplifier..
https://www.electronics-tutorials.ws/amplifier/amp_5.html

The problem here is the relatively high output impedance (R2) in relation with load (32R)..
https://www.tutorialspoint.com/amplifiers/transistor_load_line_analysis.htm

You might need an output CC Amp (Emitter follower) driven by Q2 or turn Q2 itself into a CC amp..

P.S.
The above circuit proposed by Clint Eastwood is a tiny hearing aid amp ( https://www.homemade-circuits.com/mini-audio-amplifier-circuits/ ) and can't serve for your puprose for reasons other than "power"..
(e.g. it can't amplify anything of amplitude lower than +500mV, or so -  I let you guess why..)

[Steben]

Salut!

I want to make this tiny 1W desk amp (for quick on-hand testing of other guitar things):



However, I have this salvaged 32 Ohm 0.2W speaker lying around without any use, so I would like to use that instead of 8 Ohm one on the schematic, if possible. I have a notion that some tweaking is required to do it, yet completely clueless what exactly it would be.

As always, I'm humbly seeking your advice. Thanks a many in advance!

Hi.
What kind of speaker is this?
I ask because the speaker is perhaps more of influence on the character of your setup than the amp circuit.
Smallish speakers are not the best for discerning tonal differences between stompboxes 
Giving full 0.1 - 0.2 Watts to a efficient 10"-12" speaker is a more than present tone. 1 Watt in a 4" will sound meh.

[SeneX225]

Hi.
What kind of speaker is this?
I ask because the speaker is perhaps more of influence on the character of your setup than the amp circuit.
Smallish speakers are not the best for discerning tonal differences between stompboxes 

Hi!
I want to use a 32 Ohm 0.2W speaker like this:

[SeneX225]

Do I understand it correctly that since there's no chip, the power output to the speaker would be directly tied to over power input and therefore, if I use 12V it should be enough to drive 32 Ohm speaker?

It's a standard CE Class A amplifier..
https://www.electronics-tutorials.ws/amplifier/amp_5.html

The problem here is the relatively high output impedance (R2) in relation with load (32R)..
https://www.tutorialspoint.com/amplifiers/transistor_load_line_analysis.htm

You might need an output CC Amp (Emitter follower) driven by Q2 or turn Q2 itself into a CC amp..

P.S.
The above circuit proposed by Clint Eastwood is a tiny hearing aid amp ( https://www.homemade-circuits.com/mini-audio-amplifier-circuits/ ) and can't serve for your puprose for reasons other than "power"..
(e.g. it can't amplify anything of amplitude lower than +500mV, or so -  I let you guess why..)

I see, sort of. The amp would need a higher amplitude window to properly amplify guitar signal (what a mouthful!), correct?

Will LM386N-4 suffice, though?

[Mark Hammer]

Have you measured it?  Is it possible it's actually a 3.2R speaker and the decimal is not very visible (if at all)?
But higher-impedance speakers DO exist.  I made some mini-columns with a quartet of the 64R speakers that were used in early Macintosh computers.  A local surplus place was selling them cheap, so I bought a bunch.  With 4 in parallel, that makes each "cab" 16 ohms.  The original Macs had a surprisingly wide bandwidth for such a small speaker (with a very big magnet).

[Steben]

https://www.switchelectronics.co.uk/32-ohm-miniature-mylar-cone-1w-speaker-66mm-x-19mm

?

[SeneX225]

Have you measured it?  Is it possible it's actually a 3.2R speaker and the decimal is not very visible (if at all)?
But higher-impedance speakers DO exist.  I made some mini-columns with a quartet of the 64R speakers that were used in early Macintosh computers.  A local surplus place was selling them cheap, so I bought a bunch.  With 4 in parallel, that makes each "cab" 16 ohms.  The original Macs had a surprisingly wide bandwidth for such a small speaker (with a very big magnet).

Measurement reads around 30 Ohm, so it is a 32 Ohm speaker indeed.

Here's a picture:

https://www.switchelectronics.co.uk/32-ohm-miniature-mylar-cone-1w-speaker-66mm-x-19mm

?

Yes, but only 0.2W.

[rutabaga bob]

What about putting a 32 ohm, larger-wattage resistor across the speaker terminals?  That would bring it down to 16 ohms.  Or a 5.6 ohm resistor?  That would bring it down to just under 5 ohms.

Edit: I think that tiny of a speaker will sound like poo.

[Steben]

What about putting a 32 ohm, larger-wattage resistor across the speaker terminals?  That would bring it down to 16 ohms.  Or a 5.6 ohm resistor?  That would bring it down to just under 5 ohms.

But why exactly?

Edit: I think that tiny of a speaker will sound like poo.

Well, I kept it polite

[rutabaga bob]

Parallel resistances.

[SeneX225]

What about putting a 32 ohm, larger-wattage resistor across the speaker terminals?  That would bring it down to 16 ohms.  Or a 5.6 ohm resistor?  That would bring it down to just under 5 ohms.

Haven't thought of that! In this case I could put a 10 Ohm 2W resistor in parallel with the speaker, therefore turning it down to a bit under 8 Ohm and use the LM386 schematic. Would that work?

Edit: I think that tiny of a speaker will sound like poo.

I prefer the term "Lo-Fi garage aesthetic" thank you very much.

[Steben]

But I am not sure a higher impedance wouldnt work. It's not a tube amp.
Lm386 is used as small signal distortion device in some circuits. Loads > 1k .....

[antonis]

What about putting a 32 ohm, larger-wattage resistor across the speaker terminals?  That would bring it down to 16 ohms.

Bring down what exactly..??   

Spreaker resistance remains 32 Ohm and pure resistances don't produse sound..!!

[Matthew Sanford]

2 ¢: I've tried LM386 (not marked, likely-1) with a 25 Ohm speaker to no avail, but it might be good to try it on a breadboard and give the results here, these brilliant minds here (not me) work great with data

[Clint Eastwood]

2 ¢: I've tried LM386 (not marked, likely-1) with a 25 Ohm speaker to no avail

Why did it not work?

[SeneX225]

2 ¢: I've tried LM386 (not marked, likely-1) with a 25 Ohm speaker to no avail, but it might be good to try it on a breadboard and give the results here, these brilliant minds here (not me) work great with data

Sounds reasonable! I'll find a LM386N-4 and try it out.