** Class D amplifier upgrade for your favourite boomer**

Hi Guys,

Let me ask one question - 'Do you have a 12 volt box that has nice low-medium bass that tends to crap out as you crank it loud?

If the answer is yes, then maybe a main amplifier upgrade is for you. On the weekend I completed just such a project on my Sanyo C35. (The same box I did a speaker upgrade to a while back).

Let me just say the improvement was astounding.

Between the preamp and the main amp is usually the headphone jack. If you intercept the signal at this point (after the headphone jack), you can feed the signal to the new class D amp. The speakers are then wired to the new amp.

As you are intercepting the signal after the pre-amp stage, all controls including your VU meters, volume, balance, bass, treble etc controls operate as per normal.

If you get a class D amp with a volume pot, you can control how much power is being fed to your speakers. Keep the class D amp volume at modest levels and you can keep running your factory speakers.

If you really want max performance, upgrade your speakers, crank the new amp volume pot and you'll have around 20 watts RMS x 2 coming out your M9990 for example!

Keep your power feed for the new amp away from your tuner, but make sure your feed is not powered when the unit is powered down.

Good luck and have fun. Remember, with this mod, you won't need to buy an M90 or C100L to get big power anymore. This would be an especially good mod for Wheely owners!!!

James....


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Hi Jimmy. Wondering how you implemented the integration? I just looked at the schematic for the C-35 and it appears to be a single ended design with common ground. Most all of these amp modules require floating ground. That change in and of itself to the speakers isn't challenging. The problem is that the headphone interface usually cuts into the circuit by switching out the speakers and diverting the audio signal to the headphones which generally share a common ground. Since the new amp modules require a floating ground, this could be problematic, no?

Hi Norm,

This amp has a common earth input (3 wires - red, white, black) - Yamaha chip.
View attachment 37124
Works great.

Hm, very interesting mod...
Give more info about power - how you turn on-off to new amp?

Hi Jimmy. I guess you added to your original post after my post, or I missed part of it your original post when I responded. However my question really pertained to whether or not the headphones feature still worked like it was intended. In other words, plug in a set of headphones & sound to the speakers should be cut. Otherwise, why put headphones around your ears if the speakers are blasting away the exact same tunes to your headphones.

I see now that you are suggesting tying the class d amp inputs to the headphone source. Just keep in mind that this source is actually a high-level source (after amp) that is attenuated across 100 ohm resistors. If the original amps chips have distortion, then this distortion would be passed to the new class d amp which could then parlay and further add its own distortion as well. Luckily in practical use, because actual load to the original amps is low, it hopefully does not pass nearly as much distortion as it normally would when powering speakers. Still from a design perspective, it would be far preferable to source the signal at a point aft of preamp but before the output amp. Unfortunately, experience shows that this tap location can be finicky as a low level source is typically more susceptible to interference, ground loops and impedance mismatching. But I digress.

Going back to the headphones question, if the new amp is tapped to the headphone jack solder pads, does that mean then that plugging in headphones will no longer cut sound to the speakers?

As the signal for the new amp is connected after the headphone jack, the headphone jack should still be operational and will still cut the output to the new amp/speakers when a plug is inserted.

Thanks for tech info regarding the main amp feeding output to the headphone jack - didn't realise the main amp was powering the headphone jack - makes sense if you think about it.

The signal being fed to the class D amp does sound very clean - (i.e no hiss or other static).
The bass hits don't distort at all like they did before the mod.

It's weird adjusting the original sliders and suddenly having all this extra clean power on tap like a turbo charger.

BTW, the original speakers don't stand a chance if you crank the new amp - they'll just flap around helplessly not knowing what to do!

8 ohm speakers all of a sudden are suitable replacements if you don't have 4 ohms units handy as you no longer need extreme sensitivity to make it loud.

Interesting! Might have to experiment with this idea

This will be an innovative way to upgrade our boomboxes for more power.

James the Genius in action!

That's really cool Jimmy! Is this the same amp you use in your diy boxes? And what model is it?

Interesting, and something I had thought about doing with a couple of vintage receivers I have lying around. I bought a chip amp kit (class D) off Ebay recently for about $15 and built in myself - it was super easy to do, with the IC socket being the only tricky bit. I've been trying to find an actual, practical use for it, so I may have one now !


This is what I bought -

https://www.ebay.com/itm/2-X-15-Watt-8-Ohm-Class-D-Audio-Amplifier-DIY-Kit-TPA3122-15W-Stereo-Amp/350586608737?epid=1731646599&hash=item51a0971c61:g:bG4AAOxyk99R1Avv

No affiliation to the seller.

I've been looking into a Class D amplifier for my boombox; I've got some speakers that I could use as an upgrade. See thread: https://boomboxery.com/forum/index.php/topic/27400-newer-speakers-different-ohms-watts-what

My biggest question now is how to power additional components, such as a Class D amplifier, off of the same power as the original audio components? I know this is probably some basic electronics/circuitry, but I am new to this and would rather learn from some good advice than fry my boombox or myself.

Can anyone recommend how to power new components in an old boombox;is there a good thread for me to read or other resources? Thanks!

It’s difficult providing you specific advice re powering new components without the schematics of your particularly box. I’d just run power from the DC output from the batteries / AC transformer via a discretely placed external switch. Use a ground loop isolator for your amp and BT receiver - use only 12 volt based components to simplify things.

You’ll need a class D amp that uses a common earth for the signal inputs so you can use the terminals from the headphone jack for the amp inputs. T class amps won’t work as the left and right channels do NOT share a common earth.

Is there a particular model D-class amp you prefer Jimmy?

My wheely has been left in the dust over the years, but this has always been an option. I tried integration at the pre amp stage and ended up frying an IC when signal testing and didn't get any further than that.

trippy1313 said:

Is there a particular model D-class amp you prefer Jimmy?

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You need to look for an amp with a 3 pin input plug indicating a left channel, right channel and common earth set up:

jimmyjimmy19702010 said:

“...... T class amps won’t work as the left and right channels do NOT share a common earth......”

Click to expand...

Jimmy, I don’t doubt that certain T-amp boards might require non-common ground inputs but I highly doubt that it is a characteristic specific to T-amps vs D amps. In fact, t-amps to my understanding is nothing more than a D class amp with proprietary switching algorithm for the TriPath chips. Amps that will accept true low level inputs (as opposed to attenuated high level inputs probably all share common grounds. Or.... did you read something somewhere that suggests that is the case?

All the T amps I’ve come across require individual left and right channel earths. Running a T amp with a common earth will result in the amp momentarily going into protection mode (Tripath amps).

jimmyjimmy19702010 said:

All the T amps I’ve come across require individual left and right channel earths. Running a T amp with a common earth will result in the amp momentarily going into protection mode (Tripath amps).

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Take a look at the Sure Electronics class-T tripath user's manual below:
https://www.parts-express.com/pedocs/manuals/320-334-parts-express-manual.pdf

It makes absolutely no mention of requirements to use differential (or non-common ground) inputs. In fact, the manual clearly states that input source can be any audio source including MP3 type players. They are virtually assuredly all common ground sources. In fact, I just now tested every audio device I have easy access to... tape decks, tuners, equalizers, component amplifiers, MP3 audio devices, without exeption, every one of them had common ground on their outputs. If you don't believe me, test any and all of your audio components (just use ohmmeter across the RCA jack shelds) and you'll see this to be the case. IF there exists 1 in a hundred that have floating ground line-outs, surely SURE Electronics couldn't limit their product to such a small number of audio sources to amplfiy right? Furthermore, since floating ground outputs can't have their grounds tethered together, this is inherently a huge risk to the audio source product unless a warning label is clearly affixed to those jacks. The reason is that most amplifiers actually have the line-in jacks grounded together! Therefore, I surmise and conclude that virtually all signal sources will output common grounded signals.

Now, that being said, the momentary protection mode issue you speak of could be related to making connections "live." The manual says not to do that, and it's good practice not to do that in any case and which might indeed cause the system to go into protection mode momentarily until it recovers.

Anyhow, if you have a t-amp board handy (I do not) and wish to test it to reaffirm one way or another, that might be useful info, but from what I have read in the SURE manual and from my own testing, I don't believe it is the case to require or expect floating ground inputs.

==========

On an unrelated topic to what was discussed above.

I personally have listened to many class D amps and have never been impressed with them other than power and efficiency. For that reason, if I were to build a custom boombox, I think I would only use digital amp to power it if (1) efficiency was a primary concern, (2) it would only be used for certain music genre (that I don't listen to), or (3) if it is to be used in combo with an AB amp whereby the class D would power the low frequency drivers and the mid/highs are handled by a class AB. Some folks say they can't tell the difference. Some people swears they can hear the difference. I am of the latter -- I can clearly hear a difference and I simply am not satisfied with them. Everyone's ears are different and I'm from a family where some members have slight hearing deficiencies. To their ears, everything sounds normal, in other words, they don't know what they are missing so if you were to add some details that they can't hear anyway, then they won't be able to tell the difference. Consider just the normal population of people and see how many people have 20/20 vision. Some are better than 20/15 and some are 20/200. If you can't tell the difference between the output produced by class D as opposed to a class AB amp, then you should be very happy with a class D upgrade since they can produce good power at a very high efficiency, perfect for portable applications. For me, I know the benefits already mentioned and I've tried to love class D amps but I just can't unless they are powering subwoofers.

For car amps, class D amps have been out for a long time now and with all the benefits mentioned above, you would think they would have pushed out class AB amps already, but they haven't. Why not? After all, they are cheaper to manufacture, run cooler, are much more energy efficient, and require far less heatsinking. Still, class AB amps are plenty. Anyhow, here are the pros and cons of each class and rather than type the whole thing when someone else has already taken the time to type it in, I'm borrowing it from another website (copy/paste, hehe):

• Class A amplifiers are very inefficient and produce lots of heat because there is a large amount of current flowing through the output transistors even with no audio signal.
• Class B amplifiers are more efficient but will have a 'notch' distortion.
• Class AB amplifiers are moderately efficient (depending on bias current) but notch distortion is eliminated by the idle (bias) current.
• Class D amplifiers are very efficient but are generally used for non high fidelity or subwoofer applications.

Don’t bother talking to me about the $5-$15 Chinese class D amps - they all sound bad with a lack of low end plus harsh mids often reported.

Have you tried the original Lepai LP-2020A+ amp for yourself? Spend $20 and try it if you haven’t already. Hook it up to some quality and high efficiency 6-8 ohm book shelf speakers and a 7.2 aH + sized SLA battery and be prepared for a very surprising and enlightening listening experience.

Now if you want even better sound quality, upgrade to the class T equipped Topping amps for that next level listening experience.

The little 20 watts RMS per channel T amps are said to be the sweetest sounding.

Ultimately, it will all come down to your choice of speakers. Inefficient speakers (84dB or less) won’t respond to a low powered amp like this. 91dB + speakers will sound strong.

Norm, I think that link you posted is for a D-class amp. At least that's what I think I read when I opened it up?

blu_fuz said:

My wheely has been left in the dust over the years, but this has always been an option. I tried integration at the pre amp stage and ended up frying an IC when signal testing and didn't get any further than that.

Click to expand...

I'll take it off your hands! Haha.