UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Reply
 
Thread Tools
Old 10th Apr 2021, 8:15 am   #41
stevehertz
Dekatron
 
stevehertz's Avatar
 
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 5,750
Default Re: Goldenears amplifier

Excellent, great job you should be proud.
__________________
A digital radio is the latest thing, but a vintage wireless is forever..
stevehertz is offline   Reply With Quote
Old 10th Apr 2021, 9:16 am   #42
Cobaltblue
Moderator
 
Cobaltblue's Avatar
 
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 5,327
Default Re: Golden Ear Laboratory Amplifier Build

New posts moved to original re-opened thread.

Original thread was not closed by Mods. Threads auto-close when there is no activity I think its 6 months, last activity in this case a few days short of 3 years

Cheers

Mike T
__________________
Don't care if it was a bargain why's it in my kitchen
Mike T BVWS member.
www.cossor.co.uk
Cobaltblue is offline   Reply With Quote
Old 13th Apr 2021, 2:34 pm   #43
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 6,249
Default Re: Golden Ear Laboratory Amplifier Build

Grand work Joe, it'd be nice to see these finished. Can send you some ferret adrenal glands, stuffed with hand selected coffee beans if you need a bit of get up and go : )

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline   Reply With Quote
Old 24th Apr 2021, 12:46 am   #44
joebog1
Octode
 
joebog1's Avatar
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 1,582
Default Re: Golden Ear Laboratory Amplifier Build

A bit of progress in last few days. I made the power supply umbilicals. All wire is 24/.2mm. So about 1.2mm CSA. I also made the plugs and sockets for the amp and power supply chassis. These Chinese connectors are really quite excellent, YES that's a plug, $10 for a mating pair, around 5 1/2 quid for most of you guys. Err hmm having said that, it's fiddly to solder biggish wire to small contacts, although when done correctly it's a perfect fit so their rating of 5 amps and 500 volts sounds pretty close to the truth.

A few self explanatory pics.

Before any of you jump on my head, the photo "wiring" is to show biggish cable onto smallish contacts. Yes I haven't pushed the heat shrink on to show the fit.

Inside the amp and power supply chassis all the wiring will be laced using WWII lacing cord .

Joe
Attached Thumbnails
Click image for larger version

Name:	umbilicals.jpg
Views:	142
Size:	58.5 KB
ID:	232465   Click image for larger version

Name:	umbilicals1.jpg
Views:	132
Size:	58.7 KB
ID:	232466   Click image for larger version

Name:	wiring1.jpg.jpg
Views:	136
Size:	45.2 KB
ID:	232467   Click image for larger version

Name:	right_channel.jpg
Views:	126
Size:	45.3 KB
ID:	232468   Click image for larger version

Name:	left_channel.jpg
Views:	118
Size:	51.4 KB
ID:	232469  

joebog1 is offline   Reply With Quote
Old 27th Apr 2021, 5:54 am   #45
joebog1
Octode
 
joebog1's Avatar
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 1,582
Default Re: Golden Ear Laboratory Amplifier Build

So started a bit of wiring today. I had forgotten how I HATE heater wiring!!!
NOT to mention the fact that I can't solder anymore, or perhaps it's the wire that keeps melting back from the solder joint, and won't tin properly, even with flux.
Anyway, one single solitary photo showing four resistors that are 47 ohms!!!! NOT as the digital photo shows as 56 ohms, ( play a C boy, NOT an F ).
The heater wiring and a few transformer primary wires terminated but not laced down yet.
Main reason I posted the pic is that its the result of 7, SEVEN hours work!!!

Am I getting old?

Joe
Attached Thumbnails
Click image for larger version

Name:	heaters.jpg
Views:	126
Size:	92.8 KB
ID:	232722  
joebog1 is offline   Reply With Quote
Old 28th Apr 2021, 5:05 am   #46
joebog1
Octode
 
joebog1's Avatar
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 1,582
Default Re: Golden Ear Laboratory Amplifier Build

Fixed the flying trapeze screen resistors. Started lacing up looms.

Joe
Attached Thumbnails
Click image for larger version

Name:	SLOW_but_rough.jpg
Views:	95
Size:	69.6 KB
ID:	232816  
joebog1 is offline   Reply With Quote
Old 28th Apr 2021, 6:14 am   #47
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 6,249
Default Re: Golden Ear Laboratory Amplifier Build

Quote:
Am I getting old?
Getting? No, it's too late you've arrived at dribbling absent minded senility : )

I'm not a huge fan of wiring heaters either Joe but after some cogitation I hit on the idea of wiring the heaters with enamelled wire as used in tfmr's. It's still a pain but there's no insulation that turns to mush. If using normal wire I use a reet hot iron and decent copper wire. After cleaning the base pins with a dremmel nip in quick, nuke the joint and bobs your uncle.

Check out a fellow Aussie how he wires his chassis's - https://www.youtube.com/watch?v=BhHE60yn3Y8

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline   Reply With Quote
Old 19th Oct 2021, 7:03 am   #48
joebog1
Octode
 
joebog1's Avatar
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 1,582
Default Re: Golden Ear Laboratory Amplifier Build

So, as I now have TWO bionic eyes ( best money I have ever spent ), I have restarted a project I dropped a while ago. I suppose I should have started with the power supply
( my normal cart before horse operation ) but as I still need repaint it ( it came out cp ) I continued on.

The pic shows it needs LOTS of lacing, and organisation of wiring, but I am happy so far.


Joe
Attached Thumbnails
Click image for larger version

Name:	output_driver.jpg
Views:	178
Size:	136.2 KB
ID:	243719  
joebog1 is offline   Reply With Quote
Old 19th Oct 2021, 9:50 am   #49
sortedradio
Hexode
 
sortedradio's Avatar
 
Join Date: Jan 2008
Location: Sheffield, South Yorkshire, UK.
Posts: 413
Default Re: Golden Ear Laboratory Amplifier Build

Looking very neat Joe. I must re-learn the art of lacing!
__________________
Martin
BVWS member
GQRP Club
sortedradio is offline   Reply With Quote
Old 21st Oct 2021, 9:43 am   #50
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 6,249
Default Re: Golden Ear Laboratory Amplifier Build

Looks grand mate, very well laid out. There's a few videos on lacing Martin on Utoob I think, but a simple blanket stitch with each end terminated by constrictor knots does the job.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline   Reply With Quote
Old 25th Oct 2021, 11:49 pm   #51
joebog1
Octode
 
joebog1's Avatar
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 1,582
Default Re: Golden Ear Laboratory Amplifier Build

So as a dummy, I am asking for advice. Negative feedback is supplied overall from the output transformer. Would there be, or is there ANY benefit in earthing screened cable at the output terminal, or at the input valve?

So to enlarge!.
I was thinking to run the overall feedback from the output terminals to the input stage as per normal.
I will take into account the amount of capacitance that is contained within the shielded cable when determining the response of the amplifier proper.
This cable has to run from the very back panel, to essentially the front panel, via the switch to setup balance and to zero the phase splitter.
Only ONE end of the screen will be earthed, so the question is:
Do I earth the screen at the output terminals?
OR the input terminals?.

Thanks in advance for ANY discussion on this subject.

Joe
joebog1 is offline   Reply With Quote
Old 26th Oct 2021, 10:19 pm   #52
trobbins
Heptode
 
trobbins's Avatar
 
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 585
Default Re: Golden Ear Laboratory Amplifier Build

IMHO the OPT output ground should connect only to the input stage star ground point where the feedback is being applied.

I assume the OPT speaker windings exit the OPT as flying leads (from the photos) and the first point of termination (perhaps that is the output socket) is where the feedback connections would be made - with perhaps separate wires going to the speaker terminals. So I can't see why you wouldn't use shielded cable for a long run to the input stage, and use the screen for the ground connection back to the input stage.

Perhaps better to locate any series feedback resistance/compensation networks at the OPT end (to keep high level signal away from the input stage and reduce signal current level in the shield).

There would be signal parasitic coupling current from the OPT primary windings to the secondary windings, and that would loop to the input stage star ground and back to the output stage star ground.
trobbins is offline   Reply With Quote
Old 26th Oct 2021, 10:39 pm   #53
joebog1
Octode
 
joebog1's Avatar
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 1,582
Default Re: Golden Ear Laboratory Amplifier Build

Thanks Tim
My "ground" is the 2X1mm solid copper bus that runs pretty much from rear to front.
So far its not connected to chassis at all. Both wires from the OPT are so far, only terminated to the output banana sockets.
{( those cheap 19mm/3/4" gold plated test terminals from WES )
Today I will finish the input heater wiring , did I mention I hate heater wiring ?. It is floated at about + 50 volts so wont be earthed at all, so the cathode follower driver doesnt exceed its heater cathode voltage rating. }

The actual screened cable will run to the ceramic wafer switch, which is a decent distance away from any valves, or sensitive input grids. All power supply wiring will be terminated using as short as possible wire direct to my central buss bar. Output transformer earth will be terminated directly to the "common point" of the two main capacitors on the right of my photograph. Im hoping this will prevent any heavy circulating currents reaching any sensitive areas. Four 807's in pretty much class A WILL have some current!! !!.

I guess I didnt explain my question very well, sorry for that. I guess I will earth the screened cable to the main buss, but I am unsure of whether to tie it down at the power supply end, or the input end of the buss. Actual resistance will be very small. ( I dont own a micro ohm meter) The copper wire is Mount Isa pure copper dropper cable used from power poles to factory installations, and is one strand of wire from 25mm CSA cable.

I suppose at the end of the day it will be determined at final testing.

Thanks again

Joe
joebog1 is offline   Reply With Quote
Old 31st Oct 2021, 6:53 am   #54
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 6,249
Default Re: Golden Ear Laboratory Amplifier Build

I always use screened cable for the NFB and either ground the screen at the IP/bus or have done so at the OPT. The OPT ground does carry a lot of current though,so praps best at the IP. Often with amp builds though it's finding a convenient place to connect things too, sometimes there isn't one and one has to wing it.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline   Reply With Quote
Old 31st Oct 2021, 11:28 am   #55
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 18,600
Default Re: Golden Ear Laboratory Amplifier Build

With negative feedback connections you want to avoid series resistors and screened wire capacitance creating an R-C lowpass characteristic. This acts in the direction of reducing your loop stability by adding some phase lag. With valve amplifiers having output transformers, the build-up of phase lag hasn't got a lot of margin to start with, so you don't want to increase it by any avoidable amount in an easy place.

So run your screened wire from the output of the transformer, and have the series resistor at the end where the feedback is applied near the amplifier's input.

Any R-C roll-off in the feedback path not only lessens phase margin, it creates a rising frequency response for the whole amplifier. As the phase margin diminishes the rise forms a peak before the response falls right off. The less the margin, the sharper and taller the peak, until the thing will oscillate on its own.

So a swept frequency response, looking for any suspicious bump at the top end can show how thin the ice is.

The capacitor you'll see in parallel with the series feedback resistor puts an HF lift in the feedback path. This compensates for some of the phase lag of the whole loop. By increasing the strength of feedback, it causes a roll-off in the overall amplifier's response.

So wrangling feedback loop designs is a tradeoff between how much gain and bandwidth your naked amplifier has, and how much gain and bandwidth you dare let it have with the feedback loop operating. The basic amplifier will roll off eventually, but the trick is to roll it off in such a way as to still have some phase margin in hand when the gain around the loop falls below unity. You can also look at stability effects by using a scope on the output with a square-wave input to look at the ringing.

In theory, the whole business can be taken care of by some maths. Not actually difficult, but involving some rather alien concepts such as imaginary frequency/time. Of course, the maths still needs some input numbers to work from, so you still have to know the characteristics of the different blocks of your amplifier, and thus some measurements.

If you want to push an amplifier pretty much to the limit in terms of bandwidth and distortion, then care is needed. Analysis of some commercially made 'boutique' amplifiers I've come across suggests that not all firms have anyone who can do this to the levels achieved by Leak, Baxendall, Walker, Hafler, and Bailey.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 1st Nov 2021, 2:55 am   #56
trobbins
Heptode
 
trobbins's Avatar
 
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 585
Default Re: Golden Ear Laboratory Amplifier Build

All wiring and layout typically requires assessment for parasitic characteristics in hi-fi amps. As an example, Williamson laid out his chassis to minimise capacitance coupling from parts to chassis, and to maintain balanced levels of any parasitic effect like capacitance to chassis (especially with respect to the signal paths from PI stage to output stage).

Using any type of screened cable would require care to try and use cable with the lowest practical shunt capacitance, and minimise the cable length, and even then to calculate the likely RC corner frequency and compare it to the phase margin frequency. As an example for the Williamson amp for an 8 ohm speaker output and nominal 3k5 series feedback resistor located at the transformer end, the shielded cable shunt capacitance probably needs to be no more than about 50pF to keep the corner above 1Mhz and hence the start of some phase shift to above 100kHz, although even that could reduce phase margin somewhat if the output transformer was good enough and the forward gain wasn't being throttled in the interest of stability.

In this Golden amp the frequency of the stability margins was not mentioned when using the TO-330. And there would be some doubt about HF resonances with this diy OPT unless measurements were made (which would not be easy), so it will be interesting to see what you can measure Joe. And if you can't see the speaker cones whilst testing then I liked the article's advise to look in the top of the output stage valves and check for 'periodic ionization'

Joe did you include speaker impedance taps, or just wind for one speaker impedance?
trobbins is offline   Reply With Quote
Old 1st Nov 2021, 3:48 am   #57
joebog1
Octode
 
joebog1's Avatar
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 1,582
Default Re: Golden Ear Laboratory Amplifier Build

Hi Tim,
Its wound for 8 ohms only. Four sections interleaved with five primaries. Leakage is very small and primary inductance is over 100 Henries. The primaries are sectioned from inner to outer, then back to inner where the screen taps lie, and thence to the centre tap. All plaigiarised from Hafler and Keroes design. My transformer impedance meter is also home made, essentially that found in the red brick, so I havent mentioned "figures".
I used the last of my onion paper in this build.
( Its my last "amp for me". )
Iron is 5% SiGO made in Newcastle before they shut down the plant of John Sankey.
Each traffo is around 7 kilos in weight, so I figure for a maximum of 50 watts its "big enough". My maths for 50 watts is 1 Tesla, although I use 64500 lines/inch.
( Chapter 5 of the red brick )

I have several "lots" of screened cable, from ordinary to audiophool hot pink. I will be measuring the capacity of each and of course will use the lowest capacity I have.

I have paused in the build while I mull all this over, and pick others brains, because I know very well I aint the brightest spark on the wheel.

Thanks to David as well.

Joe
joebog1 is offline   Reply With Quote
Old 1st Nov 2021, 7:31 am   #58
trobbins
Heptode
 
trobbins's Avatar
 
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 585
Default Re: Golden Ear Laboratory Amplifier Build

There is a lot of frequency compensation going on in that amp.

In addition to square wave type testing, and checking a variety of loads for stability, do you have instrumentation to measure gain-phase frequency response for open and closed loop, as a way of confirming response and when tweaking any compensation?
trobbins is offline   Reply With Quote
Old 1st Nov 2021, 11:30 am   #59
joebog1
Octode
 
joebog1's Avatar
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 1,582
Default Re: Golden Ear Laboratory Amplifier Build

Is it "compensation" or "extension" ? By that I mean Marshall went to great lengths to extend stability and response to oscilloscope accuracy for want of a better word.
It is, after all a vertical amp from a CRO, but with BIG current capability at the end.

I have only basic instrumentation now, much of it home made or cobbled together with what I have.

Cheers

Joe
joebog1 is offline   Reply With Quote
Old 1st Nov 2021, 9:52 pm   #60
trobbins
Heptode
 
trobbins's Avatar
 
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 585
Default Re: Golden Ear Laboratory Amplifier Build

I'd say both words are valid. The forward gain of the amp will have frequency response dips and bumps and roll-offs, and with global feedback applied the designer can play with the level of dips/bumps/roll-offs to achieve more stable operation (ie. large gain and phase margins) - imho that is circuitry level compensation for an outcome of 'better' stability, but can also be traded off for extension of frequency response (eg. extension of bandwidth before loop gain starts to fall, or extension of 0dB/180deg cross-over frequencies).

Just basic instrumentation is what most people have had for many decades. I guess we have become luckier over the last decade or so in that 2nd hand expensive instrumentation is now cheap and/or relatively cheap soundcards and PC software allow diyers to easily do stability related testing that was once only achievable with quite expensive instrumentation, or access to such instruments. It's not that a gain/phase plot of an amp's frequency response can't be done from 1Hz to 1Mhz at home, it's just that it takes time and effort, and I am always amazed that Williamson did that as a young 20-year-old back in circa 1945.
trobbins is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 12:18 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.