BOSC - HiFi Monoblock Class-D Amp

[orchardaudio]

Some updated BOSC performance plots for 8 ohm load, these will most likely be the same as the final measurements. I really like the way that BOSC sounds right now and don't plan to make any more tweaks to the production version.

SNR (A-Weighted)​

SNR (No Weighting)​

THD Ratio vs Measured Level @ 1kHz

THD+N vs Frequency @ 10W

THD+N vs Frequency @ 1W

64k FFT @ 10W Output

Frequency Response

IMD vs Measured Level

​

 

[DonH56]

Can you run a wideband FFT to show out-of-band spurs? I expect them to be very small, just curious.

 

[orchardaudio]

Can you run a wideband FFT to show out-of-band spurs? I expect them to be very small, just curious.

64k Wideband FFT 1kHz at 10W

 

[DonH56]

Thank you! Very clean!

 

[orchardaudio]

An awesome review for the BOSC amp:

"Class-D amplifiers generally trigger reactions and opinions of a generic, mass-market sound. And I’ll admit, I tend to not be too curious about anything based around that amplification method. But Leonid (Leo) Ayzenshtat’s Class-D amplifiers continually force me to think differently. They prove that it isn’t about the type of thing, but rather about how skillfully a thing is made."

"I wanted to stop my heart so I could hear the music better. I was being sucked in, pushed out, and unable to focus on anything else but the music. There were all the little bird-like chimes, dancing between clicks and pings and bongs of xylophone harmonics with dry reed raspy sounds zooming in and out, floating on top of deep rolling strings and organ-like bass. I didn’t want to miss a moment of it."

Read the full review here:
https://theaudiobeatnik.com/reviewin...sc-monoblocks/

 

[Music1969]

There will be two versions, the 4 ohm version will have 1.41 times less gain, so that power stays at 150W.

Stable at 3 ohms?

I've seen many 4 ohm rated speakers dip down to 3 ohms (in 3rd party measurements like Stereophile).

 

[orchardaudio]

Stable at 3 ohms?

I've seen many 4 ohm rated speakers dip down to 3 ohms (in 3rd party measurements like Stereophile).

Yes.

 

[orchardaudio]

Part 1 of another BOSC writeup: https://theartofsound.net/forum/sho...oor-of-HiFi-Auditioning&p=1114154#post1114154

 

[restorer-john]

Instead of picking a best case (or near to best case) THD at some random power output (7W) and single frequency for your headline figure, how about specifying THD properly and in line with FTC standards?

The standard is: THD less than X% for any power from 250mW to Rated Power over the bandwidth (min) of 20Hz-20Khz.

Example:

The customer then knows the worst case advertised THD over the power output and frequency range instead of a cherry-picked best case number.

 

[orchardaudio]

Instead of picking a best case (or near to best case) THD at some random power output (7W) and single frequency for your headline figure, how about specifying THD properly and in line with FTC standards?

Is this better for you?

It has been updated on the website.

 

[restorer-john]

Is this better for you?

Marginally. The specification at 75W is still only half rated (150W) power.

The FTC mandated Amplifier Rule is crystal clear and has been for nearly 45 years. Any amplifier over 2W output power must state any power output claims in accordance with the Rule conditions to be sold in the US.

And the test period is 5 minutes minimum after preconditioning.

The headline specification advertised is the worst case THD from 250mW to full rated power across the frequency range specified. It cannot be best case or cherry picked numbers.

https://www.ecfr.gov/cgi-bin/retrie...ty=HTML&h=L&r=PART&n=pt16.1.432#se16.1.432_13

 

[orchardaudio]

What that standard is asking, is not a real word scenario.

First of all there is no such thing as running an amplifier at 150W for 5 minutes when playing audio.

It is also extremely unlikely that a person would play anything through any amp that would even peak at 150W, as your ears would not be able to handle that.

A very realistic scenario is audio that peaks in the 10 to 25W range. This is where BOSC will have the best performance.

If all amplifiers are specified based only on that standard it would actually not tell consumers how the amplifier performs at levels that they will be using it.

 

[restorer-john]

What that standard is asking, is not a real word scenario.

First of all there is no such thing as running an amplifier at 150W for 5 minutes when playing audio.

It is also extremely unlikely that a person would play anything through any amp that would even peak at 150W, as your ears would not be able to handle that.

A very realistic scenario is audio that peaks in the 10 to 25W range. This is where BOSC will have the best performance.

If all amplifiers are specified based only on that standard it would actually not tell consumers how the amplifier performs at levels that they will be using it.

It doesn't matter whether you like, or agree with, the established standard. Lobby the FTC to change the rule if you think it is flawed in any way. Otherwise, advertise your products in accordance with the various ratings requirements if you are selling those products into markets where such adherence is mandatory (pretty much all countries AFAIK). It's very straightforward, and hundreds of respected manufacturers have been doing so for 45+ years.

Manufacturers have tried in the past to water down the amplifier rule and apart from some very minor concessions, the FTC has left the standard as it is. There is good reason for that- it keeps manufacturers honest and ensures customers get what they paid for.

It seems you want the perceived legitimacy of using an industry standards based AP analyzer, but aren't prepared to specify the amplifier according to the industry standard required for advertsing power and THD. Can you see the irony?

 

[restorer-john]

And here's an example of how to specify power the correct way. This may help you avoid making mistakes going forward.

Notice the main specifications are bold and in clearly larger print.

The other specifications cover THD at lower levels (which happen to be less than half the headline number) and the burst/short term powers etc.

 

[restorer-john]

And another random one from Yamaha

And a random Pioneer one:

 

[orchardaudio]

@restorer-john

 

[pjug]

This looks good. What is the switching frequency?

 

[orchardaudio]

This looks good. What is the switching frequency?

It is not constant and varies with load between 300 and 900kHz

 

[restorer-john]

Thanks Orchard audio. See, it's not that hard to finally come clean.

The compliant specification would therefore be:

With 8 ohm loads, from 20-20,000Hz, 150 Watts minimum RMS with no more than 0.015% THD from 250mW to rated output.

 

[pjug]

It is not constant and varies with load between 300 and 900kHz

Thanks. Are you able to give an idea of the magnitude of the residual? Is the wideband graph not showing this since the plot only goes to 500KHz?