Stereo speakers + amplifier for an old Commodore 1084 monitor stereo mod.

[ltpitt]

Hi all,

I have decided to join this board and discuss about my current little project after I've read this amazing thread:

https://www.edaboard.com/threads/help-me-debug-what-is-wrong-with-my-commodore-1084s-p-crt-monitor.393932/page-5

This place seems to be filled with adventurers and experienced, kind and caring people.
Impossible to resist

In my case I have a kind of small audio need: I own an old computer monitor from the past (Commodore 1804) but unfortunately it is mono.
I would like to mod it and put inside a small amplifier and two speakers (at the moment the speaker inside, if this can be helpful, is: 3", 1 watt, 16 ohm and imho very weak and just... poor sound. Zero definition, only medium frequencies, etc).

I would assume, given space and not incredible budget, that getting amazing results is out of my scope but having respectable sound should be something achievable.
As very nice to have I would like to have a volume control knob and a headphones jack that will disconnect normal speaker output when I connect headphones.

I am far from an expert when it comes to electronics so in order not to destroy my beloved 1084 I'd prefer building something that is totally separated from it except, if possible safely, take the needed voltage to let the amplifier / speakers work.
In a dream scenario I'd be able to use the same headphone input / volume knob of the tv but it sounds very scary to me and the risk of ruining the monitor scares me more than a bit.

I thought about disassembling an old pc speaker set like Logitech S-120 (or countless others) and put it in the monitor...

In the past I had very nice experience with small Visaton speakers for example but on the amplifier side I have total ignorance I have found this one for example (that unfortunately does not have headphones out):

DollaTek PAM8406 Audioversterker-board, digitaal vermogensversterker, 5 W + 5 W immersie-gouden stereoversterker 2,0 tweekanaals mini-klasse D-DC5V versterken de doe-het-zelf-schakelmodule : Amazon.nl: Elektronica

DollaTek PAM8406 Audioversterker-board, digitaal vermogensversterker, 5 W + 5 W immersie-gouden stereoversterker 2,0 tweekanaals mini-klasse D-DC5V versterken de doe-het-zelf-schakelmodule : Amazon.nl: Elektronica

www.amazon.nl

And choose the best speaker for it among those two:
https://www.visaton.de/sites/default/files/dd_product/SC 5_9 ND.pdf

https://www.visaton.de/sites/default/files/dd_product/FR%207_0.pdf

Do you have any suggestion / hints / tips / does /donts for me?

Thanks for your help, time and patience.

 

[KlausST]

Hi,

Some questions:
* where does your (stereo) audio signal come from?
* how does it come? Via audio cable, USB, Bluetooth...
* what power supply is available?

Do you have the skills and the knowledge about safety (close to mains voltage) to install the amplifier inside the monitor case?

There are many small amplifier boards (similar than the one in your link) available.
Many of them are build in "bridge tied load" (BTL), but this is problematic when driving headphones. Try to avoid BTL amplifiers.

Many modern amplifiers are digital ones. To drive a headphone you may install a resistive voltage divider combined with a low pass filter.

Klaus

 

[Audioguru]

The weak PAM8406 amplifier shown from Amazon has BTL outputs that are awkward to drive headphones. The output power is fairly low, only 1.3W into 8 ohms or 2.5W into 4 ohms per channel at low distortion.
Both tiny speakers produce no bass sounds.

I think the audio parts of the original Commodore computer will match its poor sounding little speaker.

 

[ltpitt]

Thanks to both of you for your precious input!

First things first: I am 100% aware of the very serious risks of working with a CRT and I am doing my homework well: watching endless videos about how to discharge a tube, wearing serious gloves, etc.
This part should be ok given the fact that I am scared to death and that is indeed a good start.
I will not touch it, not even with a wooden stick, if I am not 300% sure that all is fine.

About the questions coming from @KlausST
1 & 2) My stereo signal will come from retro computers (c64 and similar) and retro consoles (super nintendo and similar) via SCART but I will break it out from the scart using something similar:

SpeaKa Professional SP-1300864 SCART / Cinch / S-Video Y-adapter [1x SCART-stekker - 3x Cinch-koppeling, SCART-bus, S-vi kopen ? Conrad Electronic

Uw SpeaKa Professional SP-1300864 SCART / Cinch / S-Video Y-adapter [1x SCART-stekker - 3x Cinch-koppeling, SCART-bus, S-vi koopt u bij Conrad Electronic. ✓ Altijd originele producten ✓ Gratis retourneren ✓ 30 dagen bedenktijd

www.conrad.nl

So I will have two nice RCA cables with left and right audio.

2) Power supply available: any power supply we need.
I am happy to simply bring in the monitor another DC voltage (or AC) using an extra cable but I'd be happier to avoid that and tap into the voltage already available in the monitor (if that doesn't risk ruining it).

@Audioguru
You are perfectly right and you underlined my current biggest challenge: can I find a small amplifier that supports stereo, headphone connection, sounds respectably good and doesn't break the bank?

Just to give a rough idea of what I consider already a decent audio output (I am indeed not picky in this specific case):
The amplifier provided in this little device:

YX5200 (origineel) DFPlayer Mini MP3 module met MicroSD kaartslot

Een kleine maar krachtige MP3 module voor het afspelen van geluidsfragmenten of muziek in MP3 of WAV formaat.Dit is de originele DF Player mini met de YX5200 chip. Deze worden helaas sinds maart 2021 niet meer geproduceerd en zijn hierdoor moeilijk verkrijgbaar en is de prijs fors gestegen.Als...

www.otronic.nl

Plus two Visaton BF32:

https://www.visaton.de/sites/default/files/dd_product/BF%2032.pdf

I have another small project using this setup and the result is quite surprisingly not too bad.

In this installation I have more room so I'd hope to achieve even better.

Deeply thanks for your help on this.

Ps
Also yestday I was searching and I found this:

12.59US $ 16% OFF|AU 10X NE5532 Stereo Muziek Audio Signaal Voorversterker Amp Hoofdtelefoon Versterker Board Gain 20db Rca 3.5 Mm Volumeregeling tone|Hoofdtelefoon Versterker| - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

nl.aliexpress.com

Also horrible?

 

[Audioguru]

You show another tiny little speaker that produces no bass. In open air it resonates at 280Hz but in a needed enclosure the resonance will be higher at maybe 340Hz like a bongo drum with 4 low frequency audio octaves missing!

You did not say the impedance of your headphones and AliExpress does not say the recommended headphones impedance needed for their no-name-brand preamp. But the old NE5532 dual opamp used has a minimum output load of 600 ohms. If the impedance of your headphones is much less than 600 ohms then they will produce low level sound without any bass.

 

[ltpitt]

You show another tiny little speaker that produces no bass. In open air it resonates at 280Hz but in a needed enclosure the resonance will be higher at maybe 340Hz like a bongo drum with 4 low frequency audio octaves missing!

You did not say the impedance of your headphones and AliExpress does not say the recommended headphones impedance needed for their no-name-brand preamp. But the old NE5532 dual opamp used has a minimum output load of 600 ohms. If the impedance of your headphones is much less than 600 ohms then they will produce low level sound without any bass.

You show another tiny little speaker that produces no bass. In open air it resonates at 280Hz but in a needed enclosure the resonance will be higher at maybe 340Hz like a bongo drum with 4 low frequency audio octaves missing!

You did not say the impedance of your headphones and AliExpress does not say the recommended headphones impedance needed for their no-name-brand preamp. But the old NE5532 dual opamp used has a minimum output load of 600 ohms. If the impedance of your headphones is much less than 600 ohms then they will produce low level sound without any bass.

Hello there,

As you can imagine my knowledge in the field is quite laughable.
What I can say is that the tiny speakers I've linked sound a lot better than the speaker currently available on the monitor.

I use common home headphones, like the ones coming with smartphones.

Given my lack of knowledge and ability to choose...
Can you help me picking up something that will be better?
I think the real limiter is the size because more than 3" (and somewhat not too tall) will not fit in the unit.

Thanks for your time!

 

[KlausST]

Hi,

Visaton speakers usually are quite good.
For sure size matters. Due to physics the lower cutoff frequency is limited.

Klaus

 

[ltpitt]

Hi,

Visaton speakers usually are quite good.
For sure size matters. Due to physics the lower cutoff frequency is limited.

Klaus

Hi Klaus!

I fully agree: for such a small project Visaton is indeed a nice product.
Do you have any idea / suggestion about the amp?
I really have no clue.

Thanks!

 

[D.A.(Tony)Stewart]

To upgrade the sound, the monitor box will compromise even the best attempts.

I suggest you put your Logitech's and sub-woofer well hidden behind and under.

I use Yamaha's I got for $9 behind my ears on the couch from Value Village (recycling) and a sub-woofer for the same price hidden in a drawer slightly open . driven by a Win 7 tower to watch a 56" Hitachi just past my feet to feel like a big theatre any movie or TV.

 

[ltpitt]

To upgrade the sound, the monitor box will compromise even the best attempts.

I suggest you put your Logitech's and sub-woofer well hidden behind and under.

I use Yamaha's I got for $9 behind my ears on the couch from Value Village (recycling) and a sub-woofer for the same price hidden in a drawer slightly open . driven by a Win 7 tower to watch a 56" Hitachi just past my feet to feel like a big theatre any movie or TV.

Thanks for your contribution!

Please keep in mind that the focus of this project is not building the perfect hifi audio system but just turning a mono monitor into speaker and upgrading, even a bit, its audio quality at the same time.
The fact that the monitor should look original and have internal speakers is important for the sake of this project.

 

[D.A.(Tony)Stewart]

Thanks for your contribution!

Please keep in mind that the focus of this project is not building the perfect hifi audio system but just turning a mono monitor into speaker and upgrading, even a bit, its audio quality at the same time.
The fact that the monitor should look original and have internal speakers is important for the sake of this project.

In that case (pun intended) you can buy 10 of these stereo bridge amps for floating speakers for $13c with no heat sink required. Only 5V

DAOKI 10-Pack Digital DC 5V Amplifier Board Class D 2 * 3W USB Power Mini PAM8403 Audio Module​

 

[ltpitt]

In that case (pun intended) you can buy 10 of these stereo bridge amps for floating speakers for $13c with no heat sink required. Only 5V

DAOKI 10-Pack Digital DC 5V Amplifier Board Class D 2 * 3W USB Power Mini PAM8403 Audio Module​

Thanks for helping!

I looked quite a bit in this small Chinese amps and it is quite hard to find one that also had headphones.

My requirement is to drive the two small speakers but also use the headphones when needed.

 

[Audioguru]

Chinese module makers never tell the whole story.
With a 5V supply the PAM8403 stereo amplifier produces 3 Whats per channel into 4 ohms with horrible 10% of clipping distortion. The power is only 1.2 Watts per channel with low distortion into 8 ohms.

I have never played tiny tweeters by themselves. I like to shake my bones with very low audio frequencies.

 

[D.A.(Tony)Stewart]

Gikfun 2 inch 4Ohm 3W Full Range Audio Speaker Stereo Woofer Loudspeaker for Arduino (Pack of 2pcs) EK1725 with these speakers you can get 6W with 90% efficiency from 5V which is loud and would rattle things inside not to mention distort the CRT image if close with max THD and so reasonable lower THD at 1W. then hide a sub powered amp under AG's chair ​

 

[ltpitt]

After reading a lot of comments and contributions I guess that on this forum you discuss true hifi or...
Nothing

Ok, I tried.

 

[Audioguru]

Sure we talk about hifi. A half-decent hifi system does not cost much more or be much larger than a cheap awful-sounding audio system.

The Amazon EK1725 2" speakers have absolutely no audio specs. Just size and weight like the shoes they sell.