small amplifier options?

Cyber-Mav

Cyber-Mav

Cyber-Mav

Soldato
Joined
30 Jul 2005
Posts
19,821
Location
Midlands
hello all, i got a bar top arcade that iv been sorting out and now coming to sort the sound system out in it. its got a real ghetto job of an amp hooked up in it so was looking to replace it for a more safer option. iv attached pics which should explain it all really. the amp gets signal from pc mobo audio and then powers 2 speakers.
in the pic the transformer iv put a red box around runs fairly hot hence why i think its best to see if i can replace this setup with a much more cleaner and safer option. something more powerful is on the cards but depends on price want this to something cheapo but not as cheap as whats already in place lol.
is there some ready made micro amps that are made to do this sort of stuff?

amp1.jpg

amp2.jpg
 
That looks like a simple class b amp.

if the transformer is that hot then i’d look to replace it if you replace the amp - it’s clearly not up to the task (4ohm sucks more current so may be overloading the transformer). There doesn't seem to be much in the way of power supply regulation or capacitor filtering.

you could go class D - most are capable (but check) of driving 4ohms and will be cool as a cucumber compared the class b or a amps. There are some good Texas instrument class d chips out there.

you could also look at replacing the speakers - 4ohm 7W full range (for a small speaker - Mark Audio CHN-50).


From sound perspective that fan is acting like a speaker reflex port and so with both drivers in the same box they will be acting on each other.

https://www.audiophonics.fr/en/amplifier-boards-c-415.html

plenty of 4ohm capable modules.
 
Last edited:
the speakers sound decent but they are on the back of the cabinet hence why they loose some loudness. when i change position and stand to the side of the cabinet there is a lot more output. due to this just being a bartop cab it lacks the space to mount speakers at the front. i suspect the ones i got would be more than up to the job if front mounted. still though loudness is not the real issue i got, worrying about that ghetto amp is the issue. its not actually blown up or caused a issue for the previous owner of the cab but its not up to my standards lol.

now i regret giving away that creative labs 2.1 setup which i thought i had no more use for lol then this cab turns up. hahah.
 
Last edited:
Cyber-Mav said:
the speakers sound decent but they are on the back of the cabinet hence why they loose some loudness. when i change position and stand to the side of the cabinet there is a lot more output. due to this just being a bartop cab it lacks the space to mount speakers at the front. i suspect the ones i got would be more than up to the job if front mounted. still though loudness is not the real issue i got, worrying about that ghetto amp is the issue. its not actually blown up or caused a issue for the previous owner of the cab but its not up to my standards lol.

now i regret giving away that creative labs 2.1 setup which i thought i had no more use for lol then this cab turns up. hahah.
Click to expand...

Lol no worries - i would replace that transformer when you replace the amp. If it’s getting toasty then it’s running close, if not over, its limits.

In that link is plenty of class a/b, b or d amp modules so anything 10-15W would be fine, if they take DC then you could DC-DC or AC-DC. Even an efficient SMPS module or adaptor block would work.
 
Last edited:
Cyber-Mav said:
cool, the one that @Firestar_3x linked to seems to be perfect for the job and price seems decent too at 12 quid. wondering if a small car amp would do the job since its also 12v ?
Click to expand...

pretty much any car amp would work - most cars run 4ohms. Just need to find one that’s not a bajillion watts. The key point is a car amp needs 12Vdc and not 12Vac.

that red boxed component is a step down transformer - i assume from 240Vac to 12Vac. Careful that the amp board you have also has a AC rectifier circuit to give 12Vdc on it plus a cap for ripple filtering. You can’t plug an amp expecting 12Vdc into a 12Vac supply without AC-DC conversion.

if you have a 12Vdc supply with enough current capacity in the box already then that’s a option.
 
there is a pc power supply in the cab that has molex connectors so can easily wire up the amd @Firestar_3x linked me to.
yea that transformer getting hot is the whole reason i want to ditch the existing setup that came with the cab. ditched the hacked up keyboard encoder long ago and went with arduino for the joysticks and buttons.
 
Cyber-Mav said:
Brilliant. The speakers i got in it are 5w each so this looks like its gonna be perfect. How is it quality wise?
Click to expand...

Not got that exact one as my cab is full size so bigger amp, but it will sound OK. A cheap car amp would probably be better quality but then you have small speaker and it would pull more amps so just watch the PSU.
 
Cyber-Mav said:
Anyone got an idea on how much power my current amp makes from just looking at the amp board? Rough ballpark figure?
Click to expand...

Speakers are 5W 4ohm loads. Also no idea what frequency range they are either so I assume a 'full range' which is typically a mid-higher range with speakers that small. It looks like it's mono feed onto the amp?

Without seeing what the transistor/chip is it's almost impossible to say. Another way is - what amp do I need for 5W? I have a 18W/ch amp with 7-8W 4 ohm speakers. So basically any 20-30W/ch amp should be fine and will not be running too close to the edge (because distortion increases).

You may even be running a 3 W amp with 5W speakers..

You could put a multi-meter in current mode to find the current it's drawing. My little amp was drawing about 250-300mA from a 19Vdc supply during normal play but that could be increased depending on the CPU (it's a PI hat).

If you're looking for more bass - that's a different problem to how loud.
 
havent bought anything yet but was wondering if im gonna spend the cash i may as well put in a bit extra and get some quality bit of kit that has decent sound quality and power.
anyone got any recommendations for a very small footprint amp thats good build quality and decent sound quality too?
 
This is a rabbit hole :D There's a lot of complexity - so ignoring the perfect ideas and design concepts..

When you say decent sound the obvious step is trying to understand how good the source is - what is the amp plugged into? Does the source have a digital out?

You could change the speaker driver - typically they have design parameters that require a certain amount of airspace in litres etc. So you're probably still wanting something small with a low litre requirement. The fan hole is an untuned speaker port - if tuned with the design it could improve sound. How big is the hole that you have drilled?
You can use internal linings to dampen the reverb and sound within the box itself (I assume the box is a wood/ply construction?). You'd want ones that are fireproof due to the electronics.

I have a small RPI4+hat that's would fit but the hat takes digital. In that link there are plenty of amp boards that would fit your requirement and would probably be far better than the simple power supply+amp you have in there on that board at the moment. The power supply I'm using is over sized - it's a 90W 19Vdc medical power supply for two reasons - the mrs wants to use it in the bathroom on the odd occasion (so the 240V sits outside the bathroom), it's isolated and it's quiet for a SMPS power supply.

The problem with components in module form is that you can spend £30+ on the module and then £15-40 on the power supply, add 10-50+ for speaker drivers.. so it's probably a good idea to see what the source is, then go from there.

I'm assuming you're not handy with a soldering iron or with electrical components?
 
Last edited:
Im ok with soldering stuff and electronics.
The arcade cab has a pc in it so sound source is motherboard audio out via 3.5mm jack. Its a pentium 4 mobo if that matters.

Just wondering if spending 12 quid on a cheapo amp is there something thats gonna be solid in reliability for long term use if i raise budget up to say 35 quid?
Iv also got access to a server power supply i modded to act as a 12v psu with around 40amps current output.was used to test car stereos and amps with.
Also have access to a smd-dd1 distortion detector too which i use for amp installs in cars.
 
Cyber-Mav said:
Im ok with soldering stuff and electronics.
The arcade cab has a pc in it so sound source is motherboard audio out via 3.5mm jack. Its a pentium 4 mobo if that matters.

Just wondering if spending 12 quid on a cheapo amp is there something thats gonna be solid in reliability for long term use if i raise budget up to say 35 quid?
Iv also got access to a server power supply i modded to act as a 12v psu with around 40amps current output.was used to test car stereos and amps with.
Also have access to a smd-dd1 distortion detector too which i use for amp installs in cars.
Click to expand...

I was wondering if you had a SPDIF style optical connection or coaxial digital out. If you had you could use a power DAC instead (which is basically what I use).

If it's the audio out jack then you have a choice of amps, however given the speakers and the box I'd probably just update it with a class D amp capable of 4 ohms. Low power, low heat and use a rebuilt module for simplicity. Then just sort out the power and it's done.

You could go with a class AB2 amp but it would be hot and the output would be wasted given the speakers. My class AB2 get hot enough to fry eggs on the heatsink and that's 50W/ch!

You could change the speakers - no idea what you have (I couldn't find examples googling the codes on the back of the speaker). That may improve the sound with a new amp too.
 
Well finally getting around to sort this out, iv got a few amplifier boards on order. An XH-A232 and a XH-M543. Combined total of £7.50p all in delivered.
Will test these out and see which one i go with
 
forgot to add, i went with these options since they seem to be cheapo and from this review i read they are not bad especially for the money:

Dual-channel audio power amplifier XH-M543 (2x50W) class D chip TPA3116D2 - test and user review

Characteristics, waveforms, application, advantages and disadvantages of the TPA3116D2 amplifier
smartpuls.ru
and

Усилитель мощности звуковой частоты на микросхеме TPA3110 класса D - подробный обзор

Характеристики, осциллограммы, применение, достоинства и недостатки усилителя XH-A232 на микросхеме TPA3110 (TPA3110D2)
smartpuls.ru

will see how they work out at 12v before i slap in a higher voltage psu.
 
You must log in or register to reply here.
Back
Top Bottom