SMPS in guitar amps

[K O'Connor]

Hi Guys

Switch-Mode Power Supplies (SMPS) are used in almost every piece of consumer electronics today (2018) and a few guitar and bass amps use them, too. There are some special considerations when incorporating SMPS into audio products and we will explore some of these and their solutions in this area.

Have fun

[guitarzan]

Hi Guys

Switch-Mode Power Supplies (SMPS) are used in almost every piece of consumer electronics today (2018) and a few guitar and bass amps use them, too. There are some special considerations when incorporating SMPS into audio products and we will explore some of these and their solutions in this area.

Have fun

In reality, Class D amps are sort of a ripple filtered SMPS.... lot of those being used these days...good ones...bad ones... Regarding SMPS, many say that the PS isn't in the audio signal chain.... but I disagree.... it is inherent in the chain.  Use a poorly designed PS (or a noisy SMPS) and you have a lousy amp.

[K O'Connor]

Hi Guys

Yes, class-D amps are highly compromised as far as their application to drive speakers goes. They are "functional" enough for subwoofers but no where near what true high-fidelity requires.

As far as SMPS goes, the output is too high an impedance and too variable an impedance to make a proper "other half of the signal path" for linear audio loads. This is relatively easy to fix by adding an active hum filter on the output. Obviously, we do not need this filter hum per se; rather, we use it to provide a low-impedance over the bandwidth of the audio circuit. As always, we follow Galactic Ground methods to assure that the quiet audio ground is not corrupted by the noisy SMPS output.

[guitarzan]

Hi Guys

Yes, class-D amps are highly compromised as far as their application to drive speakers goes. They are "functional" enough for subwoofers but no where near what true high-fidelity requires.

As far as SMPS goes, the output is too high an impedance and too variable an impedance to make a proper "other half of the signal path" for linear audio loads. This is relatively easy to fix by adding an active hum filter on the output. Obviously, we do not need this filter hum per se; rather, we use it to provide a low-impedance over the bandwidth of the audio circuit. As always, we follow Galactic Ground methods to assure that the quiet audio ground is not corrupted by the noisy SMPS output.

Kevin, I would almost never take issue with you.  I hold your knowledge in high, high esteem.... but I would disagree to some extent on Class D amps... there are a very few that do a very good job with full range audio.  But, in reality, there are some really cheap, poorly designed Class D's out there that certainly fit your description.  The company I work for, Extron Electronics, make class D's that really rival good class AB's.  We hold several patents on these "methods".  If you are interested you can see the patent info here: https://www.extron.com/product/patent.aspx.  Extron is a major company in the AV business.  Our class D's really fit well in that world, as many times they are put up in drop ceilings, or tight in a rack where heat and "Plenum space" issues are a problem.  Would I use one in my home stereo... probably not.  I like class A's. But this digresses from the SMPS discussion.  My apologies.

[K O'Connor]

Hi Guys

Nothing to apologise for!

Class-D amps and SMPS share the same appeal of small size and light weight, but also share the same disadvantages compared to pure linear inasmuch as linear deals with load surges and variable loads much better. The output filter for a class-D amp is optimised for one load value where a linear amp can deal with a varying load with much less variation of THD. Similarly, SMPS can handle fixed loads where linear will allow surges at startup, say for tube heaters.

[guitarzan]

Hi Guys

Nothing to apologise for!

Class-D amps and SMPS share the same appeal of small size and light weight, but also share the same disadvantages compared to pure linear inasmuch as linear deals with load surges and variable loads much better. The output filter for a class-D amp is optimised for one load value where a linear amp can deal with a varying load with much less variation of THD. Similarly, SMPS can handle fixed loads where linear will allow surges at startup, say for tube heaters.

I agree completely.

[omarlopez]

good post!