Are there any low-power class D amplifiers that are not crap for guitar amplification

mnesarco

Member
2013-04-05 9:17 pm
Hi Guys,
I have tested PAM8403, PAM8610, OEP20W cheap modules (class D) with a basic op amp stage preamp. All they sound like crap or too low. The same preamp sounds just very good with TDA2030A but TDAs are very inefficient in terms of power dissipation. I like Class D because they are cheap, small, and require very small heat dissipater, but why they sound like crap? Are there any practical module for this use? ideally with a power supply between 9v and 19v.

Notice: I am specifically interested in using this thing as guitar Amplifier. I am not interested in hifi.
 

mnesarco

Member
2013-04-05 9:17 pm
Hi Guys,

What I want is a crystal clear sound, no distortion at all. I want a Jazz like guitar Amplifier but it should be small, portable practice amp.

To be more specific:

1. Cristal clear guitar sound
2. For electric, not acoustic guitar.
3. Be small, with maximum a 6" speaker
4. Guitar bandwidth (60hz - 6khz) aprox

I have used a basic preamp with op amps, and a power amp with tda2003 with good results. But when I replace the power amp with a cheap class d module (this: PAM8610 2 x 10W Class-D Audio Amplifier Board) it sounds too low or too distorted or it starts motorboating, I have same problems with PAM8403 based modules but I have no problems with TDA2003 or TDA2030.

I like the sound of TDA2030 and TDA2003 but the they are deprecated and require big heatsinks and occupy more space....

As power supply I am using a 19V 3.5AMP Laptop PSU with DC-DC converter to 12V.

I have been searching in google for class D practice amps for guitar, but I have found no schematics. All the DIY practice amps on the web are based on old discontinued ICs.
 
One should think if it sounds ok with TDA chip amps u can make class-d sound ok too. But u must be certain not to clip the class-d amp. Have a limiting cicruit or simple resistor divider in front of amp and make sure the signal never gets over a certain amplitude into the amp. All overdrive and distortion should be done prior to class-d power amp.
 

Gnobuddy

Member
2016-03-01 4:10 pm
As power supply I am using a 19V 3.5AMP Laptop PSU with DC-DC converter to 12V.
semperfi said:
u must be certain not to clip the class-d amp
I think we may have found the problem.

With a 12 V power supply, you only get around 1.5 watts RMS of clean audio into an 8 ohm speaker, or 3 watts into a 4 ohm one.

If you happen to be using a chip which actually is two amps in bridge mode (many of them are), then you can roughly quadruple those numbers. Maybe 5 watts into an 8 ohm speaker, 10 watts into a 4 ohm one.

I know those Ebay sellers are probably advertising these things as 400 watt modules or something equally insane, but the power numbers I listed above are what you will actually get.

Putting it mildly, this is not a lot of power for clean acoustic guitar amplification. You will almost certainly frequently clip the amp. And when you do clip them, most class D amps sound utterly nasty.

I think your problem is that you need a lot more wattage. Since cheap wattage is the biggest advantage of class D modules, this shouldn't be much of an obstacle.

At a minimum, try a module that is actually two amps in bridge mode, and run it direct from your 19.5 V laptop brick, and you can get around 17 watts into 8 ohms, or 35 watts into 4 ohms. 17 watts is still rather marginal unless you prefer rather low loudness levels, but 35 watts should be adequate for a small portable amp of the sort you're describing.

-Gnobuddy
 

ravels

Member
2016-10-29 7:01 pm
Also note that the sensitivity of the speaker is an important factor. Many 12" guitar speakers have in excess of 100dB sensitivity (at 1W), whereas an average 5.25" speaker may have 87dB sensitivity. That would be less than half the volume with the same input.

You can get a mono TPA3116 amplifier board and run it directly from the 19V supply you have, or a 24V supply to achieve significantly more power without clipping. Consider using a 8" guitar speaker with 4-ohm impedance. Or couple of 5.25" speakers in parallel.

Also, as pointed earlier, make sure the Class-D amp never goes into clipping. All the signal processing has to be done by the preamp stage, but make sure the input to the Class-D stage is limited to prevent clipping. The quintessential jazz tone is result of non-linear interaction between the pickup and the pre-amp and smooth clipping by tubes, so you may have to use a tube preamplifier or a DSP effects box to get that tone.
 

john65b

Member
Paid Member
2005-01-09 2:32 am
Chicago
I bought a blown Crate Powerblock guitar amp head and replaced the original Class D amp with a ICEpower 200ASP module. Works great, and compared to another properly working stock Crate Powerblock, sounded better (to me - builders bias?)

Anyway the original Powerblock is upwards of 100 wpc, and the one I made with the 200ASC is around 200 wpc (4ohm?), but still sounds great! And with 200 wpc reserve, probably will not run into clipping issues from the amp...
 
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Yeah, Its possible. I've made one.

I've used a Sanwu TPA 3118 PBTL board though. The TPA 3116 is probably fine too depending on the configuration.

I've made a cabinet with an nice sensitive 8" celestion loudspeaker and it is additionally battery powered with a 16,8V lithium battery.

The cabinet/amplifier was intended to be ultraportable and was including battery about 5-6 LB If the battery died you could switch to wallpower if that is available but the battery is good for >2,5 hrs on full power and much more if you don't need full.

The original intended user got out of sight and as I'm not playing guitar myself I have lent it to a guitar player which plays frequently in a local cafe where they have sunday jazz clubs sessions. After a month I met him and he asked to try it a little longer: he wants to use it in the studio for recording so I am pleased with the results.

Although you can plug your guitar right into the combo (and the guitar player tried this with succes) i have combined it with a distortion pedal. This pedal can also function as a "line driver" when you turn the distortion knobb to zero but you can use the level of the footpedal to function as a preamp. Might be advantagous with longer cables.

If you want I can see if i can post some pictures

Or you can look here for some pictures. It is a Dutch forum so you probably cant read the text but the pictures might help:
http://www.zelfbouwaudio.nl/forum/viewtopic.php?f=3&t=24458
 
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