what about calss D

[kldguitar]

Who know Class D amp? could it used in guitar amp? How about it noise?

[Don Moose]

As I understand it, a Class D amplifier is a switchmode power supply being fed audio as a reference signal. No reason it can't be used for guitar, but you'd want some serious shielding between any tube circuits and the class D section, and strictly segregate the D grounds and tube grounds approaching the grounding star point.

I was wondering the other month about using an SMPS as an output transformer.

[Enzo]

The point of digital amps is to get a lot of power at high efficiency. WHile 100 watts of guitar seems loke a lot - it is very loud after all - it is not a lot of power. That is why it would be more likely to see it on a bass or Pa amp, where hundreds or even a thousand watts is output.

[kldguitar]

The point of digital amps is to get a lot of power at high efficiency. WHile 100 watts of guitar seems loke a lot - it is very loud after all - it is not a lot of power. That is why it would be more likely to see it on a bass or Pa amp, where hundreds or even a thousand watts is output.

Class D is not means digital, it is wrong name

[Enzo]

What do you consider class D?

[Bruce / Mission Amps]

Class D is not means digital, it is wrong name
I don't work on that stuff and know very little about it, but don't those kind of amps need some kind of digital sound processing?
If so, that's why I would call it a digital amp too.

[kldguitar]

What do you consider class D?

Class D like PWM,Pulse width modified. when pulse width changed,the current changed so the power add the speaker is changed.
But it mainly use motor drive,so I don't know how to use it in amp

[Enzo]

PWM meaning pulse width. That means the output voltage is switched on an off for a variable period of time - the pulse width. On and off, not analog - that means digital to me.

[Shea]

They dont need any digital processing. They can use completely analog circuitry to convert the audio signal to pulses of varying width. It's sort of like amplitude modulation, but instead of modulating the amplitude of a carrier frequency, it modulates the width of the pulses at the carrier frequency.

Here's an explanation: http://www.ee.ucr.edu/~rlake/EE135/Class_D_amp_notes_AL.pdf

The only real similarity to digital is that the output devices are either on or off at all times. But that's it. It doesn't have registers, doesn't have A/D or D/A converters, and doesn't necessarily need logic circuity (other than one comparator) or a clock.

Class D has already been used for guitar amplication, in the Crate Power Block -- 150 watts in a package that's smaller than a toaster, weighs less than 5 pounds, and doesn't get hot. And it's also the best sounding solid state guitar amp I've ever heard.

Because a Class D amp has reactive compenents connected to the output, in order to filter out high-end noise from the carrier signal, the Power Block's tone is more dependent on the speaker than a typical solid-state amp. That's both a blessing and a curse. The good part is that you can expect your speaker choice to affect the tone pretty much the same way as it would with a tube amp. The drawback is that they sound a lot better at higher volumes than lower volumes, also like a tube amp.

Shea

[Enzo]

OK, I'll accept the distinction. To me, any amp whose output was devices switching on or off I just called digital. If the whole amp has to be digital circuitry for that name, then I stand corrected.

[TD_Madden]

Take a look at the Crate PowerBlock...Class D and not bad sounding at all.

[kldguitar]

They dont need any digital processing. They can use completely analog circuitry to convert the audio signal to pulses of varying width. It's sort of like amplitude modulation, but instead of modulating the amplitude of a carrier frequency, it modulates the width of the pulses at the carrier frequency.

Here's an explanation: http://www.ee.ucr.edu/~rlake/EE135/Class_D_amp_notes_AL.pdf

The only real similarity to digital is that the output devices are either on or off at all times. But that's it. It doesn't have registers, doesn't have A/D or D/A converters, and doesn't necessarily need logic circuity (other than one comparator) or a clock.

Class D has already been used for guitar amplication, in the Crate Power Block -- 150 watts in a package that's smaller than a toaster, weighs less than 5 pounds, and doesn't get hot. And it's also the best sounding solid state guitar amp I've ever heard.

Because a Class D amp has reactive compenents connected to the output, in order to filter out high-end noise from the carrier signal, the Power Block's tone is more dependent on the speaker than a typical solid-state amp. That's both a blessing and a curse. The good part is that you can expect your speaker choice to affect the tone pretty much the same way as it would with a tube amp. The drawback is that they sound a lot better at higher volumes than lower volumes, also like a tube amp.

Shea

It is good and right explantion about class D. Thanks

[Enzo]

Here is another explanation of class D:

http://www.irf.com/technical-info/appnotes/an-1071.pdf

[Marc]

Ramsay electronics sells a 20W class D kit. It will fit on the back of a speaker magnet (one of the suggested mountings) I built one and used it in a subwoofer.
Pretty nifty, I think it was about $35.
I did remember a few short words when I was soldering the surface mount parts...made my eyes hurt too.
I used a laptop power supply to power it.


Marc

[Steve Conner]

I'm actually working on a Class-D amp just now. I bought a ready-made 400W power module from Coldamp and hooked it up to my own design of JFET preamp. It sounds surprisingly good, even on guitar overdriven with a boost pedal.

I ended up limiting it to 200W because I had trouble with the switching power supply I was using, and had to go back to a regular iron-cored transformer. A transformer big enough for 400W wouldn't fit in the size of case I wanted.

[Joe Bee]

So you jumped at the chance and bought one of their modules - thats great! I just checked their website, they seem to be in Spain so shipping should not be too much trouble, is that correct?
Also, while 100€ is a bit of an investment (especially if you are after HiFi and need four or more modules) I guess it is far cheaper than brewing your own. I am just rather surprised you are not building your own switching supply for it, isn't that exactly the kind of thing you like doing?

Oh, and I'd love to hear more about your JFET preamp, did you find an effective way to fight the huge variance in parameters that other people who use JFETs seem to be fighting with?

[Steve Conner]

Hi Joe,

The Coldamp module seems good so far, but I've had a lot of "issues" with the SPS30 power supply! I think they overfill them with smoke at the factory :(

I could probably make a better one, but it would take up time and effort that I'd rather spend on parts of the project that actually affect tone. And I don't really need the full 400 watts of cone-shredding power. I just stuck a linear power supply in there and got on with something else. Besides, if I want to sell these amps, a linear power supply makes the EMC and safety approval issues slightly less of a nightmare.

Yes, I have a simple technique for getting round JFET parameter spread, but I'm not telling what it is!

[Shea]

Hi Joe,
Yes, I have a simple technique for getting round JFET parameter spread, but I'm not telling what it is!

Does it involve a constant current source?

[kldguitar]

I'm actually working on a Class-D amp just now. I bought a ready-made 400W power module from Coldamp and hooked it up to my own design of JFET preamp. It sounds surprisingly good, even on guitar overdriven with a boost pedal.

I ended up limiting it to 200W because I had trouble with the switching power supply I was using, and had to go back to a regular iron-cored transformer. A transformer big enough for 400W wouldn't fit in the size of case I wanted.

Switching power is not good power supplier ,It has many noise,But it is high efficience power supplier