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

dotneck335

Member
2012-12-11 10:10 pm
I guess even if the micro cube schematics were available, they might not be very helpful since it's circuitry relies on an proprietary signal processor. I've had opened it up and couldn't find much discrete preamp parts on it that could be rebuilt.
Yes, it is true that the MicroCube's sound is mostly buried in the proprietary processing. I just want to modify mine with a Class-D amp (TDA7292), a LiOn battery, and a better speaker (Eminence 620H) to get more usable power. I'm thinking I can figure out the wiring from the other Cube schematics that bucks provided; but I'd still like to see the MicroCube's schematic.
 
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Printer2

Member
2010-04-02 6:34 pm
Look at the top of the transistor - you should see a small rectangle on the seam joining the two parts - flat side and "d" side.

That little rectangle should be right smack in middle - centered on seam. Fakes are offset to one side on the 2SK170 and 2SK117.

Also, the Drain-Source resistance should be around 50 ohms for the 2SK170, unfortunately I cannot remember what it was on the 2SK117...

This may or may not be factual (I found all this out here on DIYAudio), but have no reason to not believe....made huge difference in my guitar preamp and a pacific phono stage that sounded ok/crappy for longest time due to "fake" 2SK170.


Seems they are fakes. Maybe change the bias? I'll have to try it some day.
 

dotneck335

Member
2012-12-11 10:10 pm
The KEY to using ANY Class-D power amplifier is to NEVER NEVER EVER let it go into clipping! Class-D clipping is the most horrendous sound; much worse than any Class A or AB clipping. Put some sort of limiter in front of Class-D---even a pair of anti-parallel signal diodes would be an improvement---to avoid this.
 

john65b

Member
Paid Member
2005-01-09 2:32 am
Chicago
Or just take the Roger Sanders (Innersound, Magtech, Sanders Sound Systems) approach and just use a suitable High-Power Class D amp so that you could never reach clipping before your ears give out.

After all, isn't the cost / size difference between low and high power Class D negligible? Is "Low Power Class D" just straw dog?
 
I made PCBs of my favorite amp - a Roland JC120 (just preamp side). The ultimate undisputed "Clean" guitar amp. Does everything from Jazz to Metal.

I coupled one PCB to an ICEPower 200ASC amp module and it sounds excellent. Also made another coupled to a Gainclone (LM3886). Only one channel, so doesn't do that gorgeous chorus, but can add another channel with a Boss Chorus pedal and achieve that sound....

So good that am now selling my real JC-120.
Hey John,

I was thinking doing the same thing actually. I don't have experience with solid state stuff, so I'd appreciate some details on your build. I noticed many JC players just use the clean side (CH1) because of the noticeable differences between the two channels and they don't like CH2. It might be superficial but I was thinking maybe 2 clean channels pre and a 2 channels power amp could be fun for wet/dry or stereo purposes. If you have documentation I'd appreciate the intel :)

Many thanks!
 

MarioB757

Member
2020-04-06 4:35 pm
Ha, I found it on my laptop...

Also attaching what I built...I removed the third 2SK117 - the one right after tonestack - plenty of gain.

@john65b: THANKS for the free PCB offer! But no, I was just nosing around trying to find a schematic for my Roland Micro Cube. Which has NOT been successful! I do see that the Roland JC-120 and 40 others are listed but NOT the Micro Cube--for some unknown reason. Glad that you are enjoying your homemade Tele. My Gibson ES-335 is an oldie but goodie, made in April of 1961, and has the super-thin neck made only that year of manufacture; I absolutely love it!! It's the best electric guitar I have ever played, and that includes a '59 burst.
Ha, I found it on my laptop...

Also attaching what I built...I removed the third 2SK117 - the one right after tonestack - plenty of gain.
I made PCBs of my favorite amp - a Roland JC120 (just preamp side). The ultimate undisputed "Clean" guitar amp. Does everything from Jazz to Metal.

I coupled one PCB to an ICEPower 200ASC amp module and it sounds excellent. Also made another coupled to a Gainclone (LM3886). Only one channel, so doesn't do that gorgeous chorus, but can add another channel with a Boss Chorus pedal and achieve that sound....

So good that am now selling my real JC-120.

Ha, I found it on my laptop...

Also attaching what I built...I removed the third 2SK117 - the one right after tonestack - plenty of gain.
Hi john65b. When you say to remove the third 2sk117, is it just the transistor or all components between r13 and c10 ? Thanks.
 
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.
In Class D the sinus signal is transformed into a square wave signal (because in a such case transistors are working in short-circuit or are blocked. In both cases, the power is almost null p=VxI, first case V=0 and in second case I=0) --> at the end of signal path, just before the speaker, a low pass filter is added to have the amplified sinus signal. So in the signal path of class D the signal is very transformed and can be considered as "digital" (a square wave is only "0" and "1"). The low pass filter can't be ideal so you never had a very clean signal in the speaker. Class D has been designed for low cost amplifiers in headphone, cars, battery powered applications... not for Hi-fi and not for instrument amplifiers. Class A-B has an efficiency of 78% max and class D is about 90%. Not a very big difference in an instrument amplifier except if you want a small amp powered by a battery but sound is not good. You have to choose ;)

Best sound is achieved with a tube in class A (I have a mesa boogie Express 25 where you can switch between class A-B and A and class A has a very warm sound. I love it).
 

Printer2

Member
2010-04-02 6:34 pm
In Class D the sinus signal is transformed into a square wave signal (because in a such case transistors are working in short-circuit or are blocked. In both cases, the power is almost null p=VxI, first case V=0 and in second case I=0) --> at the end of signal path, just before the speaker, a low pass filter is added to have the amplified sinus signal. So in the signal path of class D the signal is very transformed and can be considered as "digital" (a square wave is only "0" and "1"). The low pass filter can't be ideal so you never had a very clean signal in the speaker. Class D has been designed for low cost amplifiers in headphone, cars, battery powered applications... not for Hi-fi and not for instrument amplifiers. Class A-B has an efficiency of 78% max and class D is about 90%. Not a very big difference in an instrument amplifier except if you want a small amp powered by a battery but sound is not good. You have to choose ;)

Best sound is achieved with a tube in class A (I have a mesa boogie Express 25 where you can switch between class A-B and A and class A has a very warm sound. I love it).
Yes, all the home theatre systems are making people's ears bleed from all the dirty signals. Maybe the extra bandwidth to 20 kHz masks the artifacts the filters leave in? Maybe convert these poor souls so that they can once again hear the song of angel's.

https://www.diyaudio.com/community/forums/class-d.49/
 
To have the original, yous shall keep only the fundamental fo. It is physically impossible except if you have an ideal filter. Of course, with a good filter (at least order 2) you can reduced all these extra frequencies (2f, 3f, ...) to an acceptable level for ears ... this is the reason why the THD of class D amplifiers can be very low BUT you will never had a pure signal as other classes. This is ONLY your choice. For me only advantage of class D is for battery powered application OR for a very power amplifer in a small form factor (cars, in case where you need to move with the amplifier, ...). For DIY AND for instrument amplifier, a class AB is very a good choice and class A is the top !
 

Printer2

Member
2010-04-02 6:34 pm
To have the original, yous shall keep only the fundamental fo. It is physically impossible except if you have an ideal filter. Of course, with a good filter (at least order 2) you can reduced all these extra frequencies (2f, 3f, ...) to an acceptable level for ears ... this is the reason why the THD of class D amplifiers can be very low BUT you will never had a pure signal as other classes. This is ONLY your choice. For me only advantage of class D is for battery powered application OR for a very power amplifer in a small form factor (cars, in case where you need to move with the amplifier, ...). For DIY AND for instrument amplifier, a class AB is very a good choice and class A is the top !
Just skeptical as more demanding applications do not have people running for the door. If the amp is not allowed to clip I doubt many would know the difference. Quilter Labs is one company that uses SS parts in the preamp and Class D amp out back and people seem to like them.