Poundland 45

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Cressy Snr
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#136 Re: Poundland 45

Post by Cressy Snr »

Well I do hope everyone likes it when they hear it. Unlike the other flailing about attempts at an amplifier I have done in the past, this one has been extremely carefully developed.
A lot of work has been done to voice it to fit my particular preferences. I’ve been far too guilty in the past of building, then evaluating the resulting sound, according to fook knows what, so it’s a bit of a step forward.
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steve s
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#137 Re: Poundland 45

Post by steve s »

Paul Barker wrote: Thu Nov 18, 2021 7:57 am the character of the driver is a big influence, Anth; naughty step!
Your right there Paul, in Steve's amp all the voltage regulation was on the driver.. so if removing that has improved the sound it highlights how critical the driver stage is to get right.

All I've ever heard is a slight dullness combined with clarity with regulated supplys.. but its easy to talk yourself into that being 'right'.. but who knows ?
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Nick
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#138 Re: Poundland 45

Post by Nick »

I have never seen Steve do what I find is needed for regulated supplies, add a small resistor (say 5-10 ohm) feeding a high quality film cap (say 1uf) on the output to isolated the HF from the regulation.

Just saying.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Cressy Snr
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#139 Re: Poundland 45

Post by Cressy Snr »

Nick wrote: Thu Nov 18, 2021 2:24 pm I have never seen Steve do what I find is needed for regulated supplies, add a small resistor (say 5-10 ohm) feeding a high quality film cap (say 1uf) on the output to isolated the HF from the regulation.

Just saying.
I now remember you mentioning ‘breaking’ the regulation at HF with the resistor and cap, years ago. I’d forgotten about that. My memory is not what it was. Should have tried that, but not much I can do about it now.
Moving the goalposts a teensy bit: I was getting concerned too, about the amount of heat being generated under the chassis, in the confined space, by the two heatsinks and the pair of glow tubes.

However, having said all that, I do still prefer the sound of this amp sans the regulators. It is small size of the chassis that is the restrictive feature, and at the end of the day has forced simplicity to the forefront of the thinking. It could be viewed as a textbook case of form over function, but soundwise it works quite nicely.
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Nick
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#140 Re: Poundland 45

Post by Nick »

I now remember you mentioning ‘breaking’ the regulation at HF with the resistor and cap, years ago. I’d forgotten about that. My memory is not what it was. Should have tried that, but not much I can do about it now.
Yep, I was waiting for you to try what you had done, then say it wasn't perfect, then I was going to make some suggestions. Hey ho.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Cressy Snr
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#141 Re: Poundland 45

Post by Cressy Snr »

Remembering how lovely the amp sounded with an old British 4V rectifier (Mazda UU4) I managed to shoehorn in a 4V transformer and re-fit a B5 socket.
I wasn't disappointed. As I've said before, the UU4 is a lovely thing, looks great when lit up and seems to be a really good sonic and musical match with 45s.

The voltages out are identical to the 5U4G, probably because the 5U4G was lolloping along, feeding just a pair of 45s and an ECC81, no real need for a rectifier of that power in an amp like this; the UU4 is far better suited to the job, as would have been the EZ81, but that is nowhere near as handsome.

Now if anyone has a Mullard FW4/500 gathering dust or a Marconi U18/20, and can bring either or both to Owston, I would be interested in trying one in the amp, just to satisfy my curiosity.
PSUU4.png
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izzy wizzy
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#142 Re: Poundland 45

Post by izzy wizzy »

Nice choice. I use the DW4 for my phono and amps front end and think they're lovely. There's something about these DHT rectifiers.
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#143 Re: Poundland 45

Post by steve s »

I took a mazda 4 pin rectifier out of my mofo amp, it didn't seem quite the same as when it was fitted
I have some new 18/20s I can bring..
May have fw/500 too ?
I've also got the cables you left at mine in the summer
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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#144 Re: Poundland 45

Post by Cressy Snr »

steve s wrote: Thu Nov 25, 2021 10:00 am I took a mazda 4 pin rectifier out of my mofo amp, it didn't seem quite the same as when it was fitted
I have some new 18/20s I can bring..
May have fw/500 too ?
I've also got the cables you left at mine in the summer
Thanks Steve, you’re a gent.
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Ray P
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#145 Re: Poundland 45

Post by Ray P »

Apart fro the lovely sounds the Poundland 45 made through Ant's speakers the other thing that struck me was how small it is 'in the flesh' - I'm even more impressed than before that you've build it (and reworked it) in such a small space Steve.
Sorry, I couldn't resist!
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Paul Barker
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#146 Re: Poundland 45

Post by Paul Barker »

Nick wrote: Thu Nov 18, 2021 2:24 pm I have never seen Steve do what I find is needed for regulated supplies, add a small resistor (say 5-10 ohm) feeding a high quality film cap (say 1uf) on the output to isolated the HF from the regulation.

Just saying.
The chip manufacturers used to show this on their suggested schematics. Possibly not these days.

I watched something from Nelson Pass on youtube when i was bored, and he said something like filtering out the smps,s he uses. Shame he didnt give values. I suppose you need a high bandwidth scope, find the frequencies conscerned and go to the charts in RDH4 to notch filter it out.

I suppose I should try to find the frequency affecting VR tubes to address that with a bang on zobel, only problem is Im not bothered. Just copying what someone else once did is as likely to be as accurate as a WW2 Pom Pom gun for shooting down a F14. So I didn't use anything so far, but maybe I’ll look for the frequency of conscern some day.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
Cressy Snr
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#147 Re: Poundland 45

Post by Cressy Snr »

Cheers Ray.
The small size is a blessing and a curse. On the one hand it is undoubtedly a pretty little thing, high in aesthetic value, on the other it is a complete pain in the arse if it needs reworking; the question of regulators being a case in point. Granted, I completely forgot to deal with the HF by the use of the small value cap and resistor after the pair of glow tubes, and Nick reminded me of that omission, but the heat being generated in such a confined space was not good. There was a pair of glow tubes and a pair of heatsinks and nowhere for the heat to go. In the end they were removed. The amp now runs cool and sounds very good as we heard at Owston (hopefully.)

In the future, there is definitely a case for regulating the HT feeding the driver stage, this time with the resistor and cap at the end of the driver feed. It’s something I will revisit eventually. As for DC on the driver valve heaters, I’ll leave that bit out, I can’t see the need for it in a power amp.
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Cressy Snr
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#148 Post Owston Fiddling

Post by Cressy Snr »

After every Owston, I seem to notice something that other amps/speakers have that I would like my own to possess.
Listening to one or two of the systems, seemed to me to expose a lack of treble clarity on my own amp. I know it could have been the speakers, but the good thing about living long term with a pair of speakers is that you get to know their foibles/characteristics.

The two Fane triple cone widebanders are similar enough to be indistinguishable from one another in the mids and top end. Obviously the 15 inch driver has deeper bass than the 12, but apart from that, you can't get a fag paper between them in terms of performance elsewhere in the audible range. No, it was definitely the amp that was responsible and I was fairly sure I knew where the problem was and it turned out I was right with my suspicions. It's funny how you don't notice that your system is doing something wrong, until you hear a system that is doing that particular thing right.

So, we know that this amp of mine is made up from donated power valves and a rather expensive Black Gate WKz power supply capacitor. It wouldn't exist in its present form without the generosity of three people, to whom I'm extremely grateful. We also know the garbage in garbage out principle, or should I say we should, but me being me, I never think in these terms; it's all big picture stuff and I don't tend to sweat the small stuff to the proper degree needed in order that great projects can be made as opposed to also rans.

Anyhow, in my CLCRC supply, the Black Gate Cap is the one after the choke. Due to my slack attitude, the first cap after the rectifier was a cheap arse electrolytic that just happened to be the right voltage and at hand when I initially built the thing. I realised after Owston that the power supply in my amp was arranged in such a way that putting a Black Gate cap, after a cheap piece of crap electrolytic is like putting an SME V on a Crossley turntable and expecting heavenly sound quality. The military spec oil-filled choke before the Black Gate was also being fed crap if we're going to be pernickety about things.

To cut a long story short, I've fitted a 30uF MKP motor run capacitor where the shitty electrolytic used to be:
45underside.jpeg
45underside.jpeg (170.29 KiB) Viewed 2792 times
The capacitor case is earthed via a metal bracket I made up to hold the cap in place. The end stud pokes through a hole in the bracket and is secured by a fixing nut, which is difficult to see on the photo, but everything is bolted in tightly.

In terms of the sound quality, let's just say, I can now hear what all the fuss is about concerning black Gate PSU caps.
Bloody Hell! :love5:
Last edited by Cressy Snr on Wed Dec 22, 2021 4:58 pm, edited 1 time in total.
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pre65
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#149 Re: Poundland 45

Post by pre65 »

Last time I earthed a capacitor mounting stud I did not realise it (the stud) was connected to one of the terminals. :oops:

I assume that is not the case with your one.
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#150 Re: Poundland 45

Post by Cressy Snr »

pre65 wrote: Wed Dec 22, 2021 4:55 pm Last time I earthed a capacitor mounting stud I did not realise it (the stud) was connected to one of the terminals. :oops:

I assume that is not the case with your one.
Dunno Phil. Why would that be a problem?
Last edited by Cressy Snr on Wed Dec 22, 2021 5:12 pm, edited 2 times in total.
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