MOSFET power amplifier with error correction

[kchap]

I built this amp and it works quite well and seems pretty bomb proof. https://sound-au.com/project101.htm One problem these days is that you can not reliably get the Hitachi MOSFET's anymore. The vast majority found online are fakes. Luckily you can get a very similar new Exicon ECX10N20 and ECX10P20 directly available from Profusion PLC in the UK and they will be drop in replacements in many cases (not sure about the OP's design as it seems to be optimized for the Hitachi parts).

Keep at it. I admit that I buy class D but if it's DIY I like MOSFET A/B designs.

 

[pma]

Interesting topology. Ever production variation-minded, I wonder how this performs with expected variations in device gain, especially over temp variations and manufacturing tolerances. And is there any predicted need to trim component values in final testing? Or, do the cookbook values and economical tolerances provide good performance? (These trims can cost boucou, or not.)

Thanks for the post. Crossover distortion can seem like an eternal enemy.

This was never expected to be in series production, however, there is no need to change the component values if the recommended genuine Hitachi parts are used. Here, the R17 multi-turn 10k trimpot serves to fine setting of the idle current, as shown in post #1. BTW, the parts used are V-MOSFETs, not the lateral MOSFETs. If you change the MOSFETs to IRF or so, then the EC must be re-calculated. Please also note that nowadays IRF V-MOS are not the same parts as they were 30 years ago and direct replacement in audio amplifiers is often impossible.

Please also note I will not re-calculate the EC parts for another MOSFETs, I am not supposed to support any commercial activities.

Thermal stability is fine if a good heatsink as shown is used. The thermal coefficient is somewhat negative, with increasing temperature the idle current gets slightly lower, but the EC keeps to distortion parameters as shown.

There is another advantage - no audible hump from speakers during turn on and turn off. So the output relay, the most problematic component of any amplifier, may be avoided for DIY use.

 

[Piere]

Nice build! This is the real DIY spirit!

But one thing: The mosfets used here, albeit Hitachi made, are not the lateral Hitachi fets that made mosfet amplifiers famous in the past for their performance sound wise! These are the regular vertical switching mosfets from later on. You can build pretty nice amplifiers with them but their overall transfer behaviour is totally different concerning the critical cross-over region.

As already mentioned, the original lateral mosfets are still (or again?) made by Exicon, available through Profusion in GB. I would say give them a try too. Would be fun to compare

 

[Addicted to music]

If you’re into Lateral Hitachi Mosfets, AEM6000 (Australia Electronic Monthly) that’s now Silicon Chip was designed by a bloke who I believe was a university mathematician name David Tilbrook. I built some of those ETI DIY designs, they had a very edgy unrefined SQ, the AEM 6000 was in a league of its own. The beauty about Hitachi Lateral Mosfets was that they were literally indestructible, just don’t exceed VGS. It drove 1.8ohm ribbons for almost 25yrs until I decided to updated! The negative temp coefficient is what made these indestructable, you can short the output out and they will still run. However, it’s this very nature that lets it down In SQ. Today it’s BJT all the way, just ensure you have a design that has multiple pairs to drive difficult loads. I won’t go back to lateral mosfets.

 

[restorer-john]

If you’re into Lateral Hitachi Mosfets, AEM6000 (Australia Electronic Monthly) that’s now Silicon Chip was designed by a bloke who I believe was a university mathematician name David Tilbrook.

AEM was a spinoff from ETI and had absolutely nothing to do with Silicon Chip. SC was set upby Leo Simpson, the editor of EA. He retired, sold whatever rights etc to some publishers who really have zero idea. Like most good things, it has been wrecked.

I wish I knew what happened to David Tilbrook. Somebody must know.

 

[pma]

I have made some improvements of this amplifier. Installed a softstart board (delayed start) to reduce inrush current of the big 250VA transformer, that sometimes had tripped my home circuit breaker when the amp was switched on. And I made some new measurements, with my improved measuring system.

 

[boXem]

That's definitely a very nice little amp.

 

[pma]

Thank you!

 

[DonH56]

Agreed, sweet little amp. Do you know the output impedance?

 

[pma]

Do you know the output impedance?

Yes, it was measured some time ago.

Less than 50 milliohm at 20kHz. About 24 milliohm at 1kHz.

 

[DonH56]

Yes, it was measured some time ago.

View attachment 477379

Less than 50 milliohm at 20kHz. About 24 milliohm at 1kHz.

Thanks Pavel, that's pretty impressive, both how flat over frequency and how low it remains through the audio band.

 

[bmc0]

Less than 50 milliohm at 20kHz. About 24 milliohm at 1kHz.

Shame, the Purifi 1E9040BA has an output impedance of less than 10µΩ below 300Hz. Any more than 30µΩ makes the bass too imprecise for my taste.

(just in case it wasn't abundantly obvious from the absurdity: the above is a joke)

 

[pma]

Shame, the Purifi 1E9040BA has an output impedance of less than 10µΩ below 300Hz. Any more than 30µΩ makes the bass too imprecise for my taste.

(just in case it wasn't abundantly obvious from the absurdity: the above is a joke)

The statement above, if it would have been meant seriously, would make no sense, because it is possible to get such low value only just directly at the PCB FB/output point. I measure the output impedance at amplifier output terminals, including internal wiring. So, it is impossible to get 30 microohms, then. And, consider necessary speaker cable between the amp and the speaker box . Some companies use various marketing tricks to emphasize advantages of their products.

 

[bmc0]

it is possible to get such low value only just directly at the PCB FB/output point

Hypothetically, one could make an amp with a slightly negative output impedance to cancel the wiring impedance . Anyway, just poking fun at the "damping factor" junkies.

 

[DonH56]

Hypothetically, one could make an amp with a slightly negative output impedance to cancel the wiring impedance . Anyway, just poking fun at the "damping factor" junkies.

I consider output impedance important, at least to a point, like many other specifications. But I suppose if people are going to accuse me of being a damping factor junkie there are worse addictions.

 

[bmc0]

I consider output impedance important, at least to a point, like many other specifications.

I wasn't referring to you (or anyone else in this thread; apologies if this was unclear), but rather the group of "pseudo-objectivists" who seem to believe that better numbers always equate to better sound without regard to audibility thresholds or whether said measures are in fact perceptually meaningful without additional info/context.

 

[Addicted to music]

AEM was a spinoff from ETI and had absolutely nothing to do with Silicon Chip. SC was set upby Leo Simpson, the editor of EA. He retired, sold whatever rights etc to some publishers who really have zero idea. Like most good things, it has been wrecked.

I wish I knew what happened to David Tilbrook. Somebody must know.

AEM was actually bought out by either ETI or EA. Can’t remember who! The publishing rights are now owned by SC

Some time after Electronics Australia closed its doors, Silicon Chip Publications Pty Ltd purchased the titles Electronics Australia, Electronics Today (International), Radio, TV & Hobbies, Radio & Hobbies and Wireless Weekly, along with the copyright to original (non-submitted) material published in those magazines.<a href="https://en.m.wikipedia.org/w/index.php?title=Silicon_Chip&amp;wprov=rarw1#cite_note-SCinterview-3"><span>[</span>3<span>]</span></a> The copyright of some submitted projects and articles for those old magazines technically still remains with the original authors. This is why Silicon Chip have not released Electronics Australia back-issues on CD, as they did with the older Radio TV & Hobbies.<a href="https://en.m.wikipedia.org/w/index.php?title=Silicon_Chip&amp;wprov=rarw1#cite_note-SCinterview-3"><span>[</span>3<span>]</span></a> However they can provide an electronic copy of any Electronics Australia article for a price, which invalidates the previous reasoning. Except that copies are not provided in cases of articles where there is a question over the ownership of copyright.