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Chip Amps Amplifiers based on integrated circuits

Joe Rasmussen "Trans-Amp" - 40 Watt Transconductance "Current Amplifier"
Joe Rasmussen "Trans-Amp" - 40 Watt Transconductance "Current Amplifier"
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Old 3rd December 2019, 12:08 AM   #441
Joe Rasmussen is offline Joe Rasmussen  Australia
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Quote:
Originally Posted by Ken Newton View Post
Hi, Joe,

We haven't corresponded in some time, so I just thought I would drop in here to say hello. I hope all is well with you and your family.

I see from your Custom Analogue website that you are still developing unique approaches to obtaining good sound. I check the site from time-to-time to see what new ideas you are currently about. I've always appreciated your rejection of rigidly doctrinaire thinking, which, as you well know, entails enduring slings-and-arrows from the self-righteous, who, with minds closed, reflexively defend orthodoxy.
Hi Ken

Thank you. Great to hear from you, just gotten back from a short holiday break, visiting windy Tasmania.

Take a look at this:

Click the image to open in full size.

Local feedback, about 20dB. This kind of feedback works in real-time unlike NFB. The coupling caps is not shown as I want the focus to be on those resistors and what they do. Note that the input Grids act near 'virtual earth' as the voltage drops from 10V RMS to 1.1V RMS. The input impedance is a high 150K and does it not look a little bit like an I/V converter?

The output tap is 8 Ohm, so the whole thing has a negative gain -24.4dB and hence the challenge is that it needs a driver that can swing massive amounts of voltage. Do the maths and you need to swing more than 900V peak-to-peak. Designed such a front-end that does just that, indeed if the PS voltage is available, can swing up to 1800V peak-to-peak:

Click the image to open in full size.

You have probably seen that PCB on my website.

Note to Moderator, this is not off topic (which was started by me in the first place), as the topic is about the current in amplifiers and speakers, and how they interact. I built the transconductance amplifier as part of my work (some would call it research) in exploring these things. I then shared this simple design because when used right, it sounds surprisingly good.

So Ken, this new (dangerous word these days) amplifier is all about the current. Even that front-end is about current, the input stage converts the source voltage to current, then the 900V Power MosFets are driven via their Sources as the inputs. There is absolutely zero voltage swing on the Gate that is normally used as input, so the non-linear capacitance there has no effect. I was very lucky, through a personal contact I was able to get the circuit computer modelled by one of the world's best, the head of Power Electronics, part of SpaceX. He actually designs the guidance systems in Elon Musk's rockets, indeed Musk's right-hand electronics guy. I can't give you his name here, only via PM and in confidence. Unbelievable linear, ultra-low distortion.

If you haven't seen it yet, go to my Facebook page for more info there, just go back into the past a few years.

Joe Rasmussen | Facebook

The overall circuit is very configurable and highly changeable sound wise. It took me a long time to figure things out. Just looking at the schematic does not tell the whole story and also not shown the Power Supply that was quite challenging to get it right. I am 68 today (I don't celebrate birthdays) and in my life this has been the single largest project and really only finished last month. Started in October 2016 and I was pushed into it by Brian Gurr in Auckland, New Zealand, when I was visiting. Brian was also a friend of the late Allen Wright.

I am working with a group that is looking into how amplifiers react with speakers on the current side, because we now know that so many things are either taken for granted or just put away as too hard and not so important. Maybe also because we have all been a bit lazy in the past, and I include myself.

I will be doing some measurements soon that will show distortion on the current of an amplifier that does not show up on the voltage side. A crude measurement has already been done, but needs to be done more critically and documented right, as well as capturing the distortion on the acoustic side of the speaker. I have about twenty people that the results will be shared with and we will have a private discussion online where the trolls cannot shout it down with noise.

Keep in touch if you have an interest in the above. My email address is publically known joeras@customanalogue.com and I trust you, so I can fill you in on those measurements.

Cheers, Joe
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Old 3rd December 2019, 11:32 AM   #442
Joe Rasmussen is offline Joe Rasmussen  Australia
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Quote:
Originally Posted by esl 63 View Post
JOE Update your picture link on page One.
Done!

The "http://" had to be changed to "https://"
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Old 4th December 2019, 12:25 PM   #443
esl 63 is offline esl 63
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JOE Nope... does not work...
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Old 4th December 2019, 12:44 PM   #444
Joe Rasmussen is offline Joe Rasmussen  Australia
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Quote:
Originally Posted by esl 63 View Post
JOE Nope... does not work...
You may need to use the refresh button or else it will just reload that page out of the cache.

I have repeated it here:

Click the image to open in full size.
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Last edited by Joe Rasmussen; 4th December 2019 at 12:59 PM.
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Old 4th December 2019, 12:46 PM   #445
padamiecki is offline padamiecki  Poland
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for me it does not work too
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Old 4th December 2019, 01:43 PM   #446
lohk is offline lohk  Europe
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images from the first pages do no show up
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Old 4th December 2019, 06:10 PM   #447
planet10 is offline planet10  Canada
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Joe Rasmussen "Trans-Amp" - 40 Watt Transconductance "Current Amplifier"
That i can see the image in post 1 with no extra effort i suggest no picture is a local issue not a global one.

The worldwide change to all https: has caused some grief.

dave
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Old 4th December 2019, 06:29 PM   #448
Mark Tillotson is offline Mark Tillotson
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Local and negative feedback are not opposites, negative feedback can be local or global (and can be shunt or series), and is real-time in all cases. Any kind of a delay element in a negative feedback network is bad news for stability as this reduces phase margin directly.
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Old 4th December 2019, 08:41 PM   #449
lohk is offline lohk  Europe
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pretty ennoying to extract the images from the source code

Click the image to open in full size.
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Last edited by lohk; 4th December 2019 at 08:44 PM.
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Old 4th December 2019, 08:52 PM   #450
Joe Rasmussen is offline Joe Rasmussen  Australia
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Hi Dave, hope you are doing well.

Quote:
Originally Posted by planet10 View Post

The worldwide change to all https: has caused some grief.

dave
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It certainly has caused me grief. It seems that I have a website that responds to both http and https, should I get in touch with my provider and tell them to get rid of http? Maybe that is causing a problem?

Where I am, using https for images is working. But elsewhere, in some places, it is not?

This is the old http:

Joe Rasmussen Pages

This is thhe https:

Joe Rasmussen Pages

Right here in Sydney, both links work. Is that a cause for problems?

Cheers, Joe

Edit: I have, as much as possible, been using https, correcting old and only using https for new images and posts.
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