Noiseless feedback amplifier - UK Vintage Radio Repair and Restoration Discussion Forum

dmowziz · 29th Jan 2023, 4:53 am

Please, anyone heard from professor Jeremy?

Trying to measure the noise of this amplifier...

Another problem is that, expecting about 6dB gain but getting as the first image. (I want to model the inductor and 33 nF decoupling cap close to the potentiometer - not shown in image). Maybe the 'layout' is also a problem?

Also, the core. First time using this kind of coil with 2 holes. I used only 1 hole (1 turn is 1 pass through the hole.) Is this good?

Thanks for any contribution

Julesomega · 29th Jan 2023, 3:12 pm

Your twin-hole core looks like one of the EPCOS types: only the K1 material is suitable for VHF use. The RS page offers a download of a datasheet, which now shows the manufacturer as TDK, and says these are suitable for matching transformers and baluns up to about 250 MHz in antenna feeders or in input circuits of VHF and TV receivers

Your plot shows a big peak around 550MHz - could this be due to capacitive bypass of the transformer rather than inductive coupling?

Radio Wrangler · 29th Jan 2023, 3:47 pm

A single turn on that core goes through one hole and back through the other.

Count the single turn winding this way, and also count the turns of the other windings the same way. Each there and back again counts as one turn.

Several other manufacturers also make that shape of core. Not all materials will work well in that frequency range.

2N3904 is a general purpose audio/low frequency transistor. It's fallen to just unity gain by about 300MHz IF you have it biassed at the optimum collector current. This is likely your biggest limitation.

These amplifiers are called 'noiseless feedback amplifiers' and follow on from patents by David Norton and more complex ones by Q-bit corporation. Chris Trask came along a bit later, popularised them in amateur circles and added a bit more to the subject matter.

I'll edit the title. As it is it sounds like an amplifier for amplifying transformers!

The noisless bit means that the proportioning of feedback to set the gain is done without using resistive potentiometers, but by transformer turns ratios.

David

dmowziz · 29th Jan 2023, 5:46 pm

Thanks Julian...The peak

At first, the amplifier was not working until I added a decoupling cap at Vcc... I tried earlier to model the through hole caps but was not getting a good result. I'll try again today.
Is there a way to model the 3 turns transformer? There's no visible capacitor around it. Just input and output coupling. With a decoupling cap at Vcc
The core is a BN-61-202. Sorry I did not state this.
https://toroids.info/BN-61-202.php

Thanks David, I'll readjust the turns. Thanks

I think the transistor is ok, because it is original and I'm simulating with the s2p from Jeremy.

dmowziz · 30th Jan 2023, 8:32 am

Thanks again David, yet to make the winding change. Doing it today

Please, do you have access to the "Applied Microwave and Wireless Magazine" ?
It is not online

Thanks

Radio Wrangler · 30th Jan 2023, 3:36 pm

No, I used to work for a firm which had a superb library and two librarians. There was an extensive collection of books, learned journals from many organisations and they took almost all the mainstream ones. Everything got archived. It was wonderful. I think it's nearly all in landfill now, or paper recycling.

So there wasn't much incentive for me to build a private collection. I've got a few useful books, but for the past 17 years I've been working off what I have in my head.

David

dmowziz · 31st Jan 2023, 10:09 am

Quote:

Originally Posted by Radio Wrangler

No, I used to work for a firm which had a superb library and two librarians. There was an extensive collection of books, learned journals from many organisations and they took almost all the mainstream ones. Everything got archived. It was wonderful. I think it's nearly all in landfill now, or paper recycling.

So there wasn't much incentive for me to build a private collection. I've got a few useful books, but for the past 17 years I've been working off what I have in my head.

David

I think, keep putting the brain to work so you don't lose what you've built up

Please someone, is there something wrong with this image? The winding direction/phase dot

Thanksss

Radio Wrangler · 31st Jan 2023, 12:31 pm

It's a common base amplifier, and they don't invert.

You likely prefer negative feedback, so the transformer coupling needs to invert

Emitter goes to a dotted end, collector goes to a non-dotted end. Simple!

David

dmowziz · 31st Jan 2023, 6:11 pm

Yeah, thanks... Just realized it's exactly what I was doing on prototype but the dots on 1 and 3.
Sleepy eyes

Thank you

29th Jan 2023, 4:53 am	#1
dmowziz Pentode Join Date: Nov 2021 Location: Toronto, Canada Posts: 131	Noiseless feedback amplifier Please, anyone heard from professor Jeremy? Trying to measure the noise of this amplifier... Another problem is that, expecting about 6dB gain but getting as the first image. (I want to model the inductor and 33 nF decoupling cap close to the potentiometer - not shown in image). Maybe the 'layout' is also a problem? Also, the core. First time using this kind of coil with 2 holes. I used only 1 hole (1 turn is 1 pass through the hole.) Is this good? Thanks for any contribution Attached Thumbnails

29th Jan 2023, 3:12 pm	#2
Julesomega Nonode Join Date: Dec 2012 Location: Stockport, Greater Manchester, UK. Posts: 2,102	Re: Transformer amplifier Your twin-hole core looks like one of the EPCOS types: only the K1 material is suitable for VHF use. The RS page offers a download of a datasheet, which now shows the manufacturer as TDK, and says these are suitable for matching transformers and baluns up to about 250 MHz in antenna feeders or in input circuits of VHF and TV receivers Your plot shows a big peak around 550MHz - could this be due to capacitive bypass of the transformer rather than inductive coupling? __________________ - Julian It's good here

29th Jan 2023, 3:47 pm	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,866	Re: Transformer amplifier A single turn on that core goes through one hole and back through the other. Count the single turn winding this way, and also count the turns of the other windings the same way. Each there and back again counts as one turn. Several other manufacturers also make that shape of core. Not all materials will work well in that frequency range. 2N3904 is a general purpose audio/low frequency transistor. It's fallen to just unity gain by about 300MHz IF you have it biassed at the optimum collector current. This is likely your biggest limitation. These amplifiers are called 'noiseless feedback amplifiers' and follow on from patents by David Norton and more complex ones by Q-bit corporation. Chris Trask came along a bit later, popularised them in amateur circles and added a bit more to the subject matter. I'll edit the title. As it is it sounds like an amplifier for amplifying transformers! The noisless bit means that the proportioning of feedback to set the gain is done without using resistive potentiometers, but by transformer turns ratios. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

29th Jan 2023, 5:46 pm	#4
dmowziz Pentode Join Date: Nov 2021 Location: Toronto, Canada Posts: 131	Re: Noiseless feedback amplifier Thanks Julian...The peak At first, the amplifier was not working until I added a decoupling cap at Vcc... I tried earlier to model the through hole caps but was not getting a good result. I'll try again today. Is there a way to model the 3 turns transformer? There's no visible capacitor around it. Just input and output coupling. With a decoupling cap at Vcc The core is a BN-61-202. Sorry I did not state this. https://toroids.info/BN-61-202.php Thanks David, I'll readjust the turns. Thanks I think the transistor is ok, because it is original and I'm simulating with the s2p from Jeremy.

30th Jan 2023, 8:32 am	#5
dmowziz Pentode Join Date: Nov 2021 Location: Toronto, Canada Posts: 131	Re: Noiseless feedback amplifier Thanks again David, yet to make the winding change. Doing it today Please, do you have access to the "Applied Microwave and Wireless Magazine" ? It is not online Thanks

30th Jan 2023, 3:36 pm	#6
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,866	Re: Noiseless feedback amplifier No, I used to work for a firm which had a superb library and two librarians. There was an extensive collection of books, learned journals from many organisations and they took almost all the mainstream ones. Everything got archived. It was wonderful. I think it's nearly all in landfill now, or paper recycling. So there wasn't much incentive for me to build a private collection. I've got a few useful books, but for the past 17 years I've been working off what I have in my head. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

31st Jan 2023, 12:31 pm	#8
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,866	Re: Noiseless feedback amplifier It's a common base amplifier, and they don't invert. You likely prefer negative feedback, so the transformer coupling needs to invert Emitter goes to a dotted end, collector goes to a non-dotted end. Simple! David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

31st Jan 2023, 6:11 pm	#9
dmowziz Pentode Join Date: Nov 2021 Location: Toronto, Canada Posts: 131	Re: Noiseless feedback amplifier Yeah, thanks... Just realized it's exactly what I was doing on prototype but the dots on 1 and 3. Sleepy eyes Thank you