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Leak Stereo 20 versus current valve amplifiers?

Junaman said:
Anyone up for making a temporary passive for me and if so, how much would you be looking for?
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I would suggest looking at the DIY section for pfmers willing to help.

One thing I do feel strongly about is NOT using leads any longer than strictly necessary to and from the passive. The shorter the better. There are those who will disagree. They usually have systems that are not good enough to reveal the effects. Sometimes they do not have the aural acuity to hear the improvements.

Before doing anything else, I suggest you invest in a flexible tape measure. Measure the distance between your units on their table/desk/supports and decide where the passive will sit. Add a few inches for good measure. Now...you have your ideal cable length runs to and from the passive.

So ...inisist that any passive come with or fit in these measurements. I favour 'hard wiring'- i.e. no connectors into the passive- such as phono sockets. The fewer connectors the better. The improvement in sound following these points is audible. I could tell you a story about a well known speaker manufacturer who invited me to his place. In fact, I will. I arrived armed with a pair of wire cutters. With his permission, of course, I cut METRES off his speaker leads. He was so impressed with the improvement, generally, that he insisted on hearing my own system which, after hearing it, declared it was better than his. I will not tell you the cost of his cheapest speakers compared or the cost of my home built ones.
 
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Reasonably long leads are perfectly fine. The leads on the way TO the passive can be any length you like in fact with most sources. The leads from the passive are more important and the higher the value of the pot the shorter the lead needs to be but up to 2m should be OK with the worst possible situation likely to be encountered of a 50K pot.
8m or so coming from a 10K pot should be fine but as I said if it reacts like the Alps 10K pot I have here then you have bigger problems anyway.
 
Mandryka has kindly agreed to sell me his. I have various 0.5m and 1m interconnects lying about. So will try them all and see which sounds best.
 
Junaman said:
Mandryka has kindly agreed to sell me his. I have various 0.5m and 1m interconnects lying about. So will try them all and see which sounds best.
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It should work out well...I hope so.

If you want further improvement(s) try cutting down your various interconnects further -as much as convenient and your flexible tape measure allows.

For further improvements, you could try RS Belden 78 ohm data cable- BICC electronics cables H8065. From RS. This was reviewed by Martin Colloms years ago as being almost as good as the best audiophile cable he had tested. Its inexpensive. If it is no longer sold, RS technical will advise on the current equivalent.

I use this throughout my system. I bought a reel of it. There should still be plenty for my great, great grandchildren to use.
 
ampedup

Thanks for your interesting questions.

I am not certain that I understand them...however that is no criticism of your questions- only (perhaps) - a criticism of my (lack of) understanding.

1) Your first question is that how do I terminate that? I hard -wire the cable direct to the point within the passive case that they go. That means that I solder it to the relevant connexion point within the passive case. The other end is terminated with a high quality gold- plated phono plug. In the case of my midrange- I have installed rhodium phono input sockets in my Radford STA25/iii chassis in place of the original phono sockets.

These replacements are, I believe, state of the art (SOTA). The cable that plugs into these is terminated with the highest quality gold- plated phono plugs, soldered with silver solder.

2) Your second question is about how I deal with the shielding on the cable. This was done many, many years ago, and so I am relying on my memory- which may be incorrect.

As far as I remember, I followed the usual advice and cut the shileding at the end shortly BEFORE the phono plug. This may be wrong- I may have done this at the other end. However, I can assure you that there is absolutely no audible hum coming from my Radford mid-range amp (my system is tri- amped, and the Radford is used only to drive the midrange speaker).

There was some hum for years until I sent the amp to pfm's Toprepairman with the request that he eliminate all hum from whatever cause.

He eliminated the residual transformer hum completely.

He also eliminated all midrange hum so completely that, even with my ear 6 inches from the midrange driver, there is absolutely no audible hum whatsoever. And this with the (notoriously hum- prone) moving coil stepup transformer on phono input at normal volume.

So congratulations to Toprepairman! He accomplished what no previous repairman since the 1970s came anywhere near doing! Even Arthur Radford didn't do it.

I suffered many repairmen since I purchased the amp in the early 1970s - good, bad- indifferent- and some dreadful- until I put the amp into his hands.

Thats about the best I can do with answers to your questions at present.
 
Picking up a Stereo 20 this afternoon but have to choose between either a bronze or charcoal version. Leaning towards the bronze…
 
Nagraboy said:
Picking up a Stereo 20 this afternoon but have to choose between either a bronze or charcoal version. Leaning towards the bronze…
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I’d go on physical condition and the quality of any restoration work every time. There may be slight differences as the bronze ones can have the earlier output and mains transformers, or some combination (e.g. mine has the early mains, later output). All grey ones are to my knowledge final spec. Regardless I’d still go on condition and avoid anything that has been botched/modified from original spec. Aesthetically I far prefer the bronze myself!
 
@Tony L

Thanks Tony, both are restored by the same person and look very good. They have the Dynaco mod to protect the capacitors (?) and have mains switched fitted neatly. Waiting for the seller to arrive now.
 
Went for the charcoal finish. This one is from 1965 and I’ve got mostly JJ valves in it to start with. The charcoal finish looks so much better in person than any photos show.

Unfortunately, I got big mains hum when using it with my Croft 25 (which I half expected) so I’ve put in the Quad 99 CDP-2 directly from it’s variable outputs and there’s zero hum now, totally silent. After having problems with the Croft today and one of my Quad 33s a while back (which Rob at Amplabs declared perfect!) I think there’s something wrong with my mains wiring. Going to get someone in to check it out. I do wonder if a passive would avoid such hum problems? Would be good to borrow one maybe. I’d still need to plug a phono stage in though…

Anyway, just about to press play for the first time on my new Leak! I’ve got the Leak set with its 16 Ohm taps for the Falcons, should be good.

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Welcome to the club.
20210515-121458.jpg

I also prefer the charcoal.:)
Interesting to hear your using yours successfully with the variable output on your 99 CDP-2.
Once I've moved into my new flat & the hum problem on my own ST20 has been sorted I am planning on arranging my system so I can easily swap between the ST20 & Quad 303.
The plan is to have the fixed output of the CDP-2 into the 33 preamp driving the 303 & the variable output directly into the ST20.
TS
 
Nagraboy said:
Unfortunately, I got big mains hum when using it with my Croft 25 (which I half expected) so I’ve put in the Quad 99 CDP-2 directly from it’s variable outputs and there’s zero hum now, totally silent. After having problems with the Croft today and one of my Quad 33s a while back (which Rob at Amplabs declared perfect!) I think there’s something wrong with my mains wiring. Going to get someone in to check it out. I do wonder if a passive would avoid such hum problems? Would be good to borrow one maybe. I’d still need to plug a phono stage in though…
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I'm guessing the vintage amplifier has a non-grounded AC connection?

You seem to be using long interconnects. Are the shields grounded at both ends, or are they floating? If it's the latter, and the shield is connected at the amp end, and the amp is not grounded, could that be a possible hum source? Perhaps try reversing the interconnects and see if the hum persists?
 
Yank said:
I'm guessing the vintage amplifier has a non-grounded AC connection?
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The vintage Leaks, Quads etc are grounded, the input/output signal, chassis, and mains earth all have continuity, and I suspect it is this some kit upstream doesn’t like.

Things become clearer in a full Quad or Leak system. In the case of the former the 33 has mains earth, the 303 only gets earthed via the 4 pin DIN screen (the switched mains outlet on the 33 is two-prong). Leak power the preamp from the power-amp almost Naim style via an octal lead. The issue we have is we are all using this kit out of original context and I guess some modern kit doesn’t like it. I’d never use a valve amp that wasn’t properly grounded via its own mains plug due to the voltages in play.

FWIW in my upstairs system (CD player, passive pre, Leak) everything is fine as-is. In my downstairs system the DPA DAC gets a really bad earth loop for some reason, so I lifted the mains earth on that one component. I still get electrical continuity from its case to mains ground (via the interconnects to the preamp). I’ve heard from others that Deltec kit can be weird when it comes to grounding, but as long as it gets there its fine!
 
@Yank

I have all sorts of problems in this house with earth loops/hum. One 33 has no problems, but the other 33 does have problems. The Croft pre doesn’t hum when used with a Croft power amp, but does if paired with the 303 (which has been modded to earth via the mains lead). If I move the kit upstairs to my movies system the hum is even worse. I’ve tried running the hifi system all from the wall socket, tried different interconnects, tried eliminating each source as a cause etc etc and it makes no difference.

Seems to be a question of just buying preamps and crossing my fingers, hoping there’ll be no hum!
 
Nagraboy said:
@Yank

I have all sorts of problems in this house with earth loops/hum. One 33 has no problems, but the other 33 does have problems. The Croft pre doesn’t hum when used with a Croft power amp, but does if paired with the 303 (which has been modded to earth via the mains lead). If I move the kit upstairs to my movies system the hum is even worse. I’ve tried running the hifi system all from the wall socket, tried different interconnects, tried eliminating each source as a cause etc etc and it makes no difference.

Seems to be a question of just buying preamps and crossing my fingers hoping there’ll be no hum!
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Yank has good ideas.

One of yours..."Just buying preamps and hoping for 'no hum'..." Not a good idea.

Why not have a go at a serious modification to (one of) your 33's?
Radically.

Quad preaps were never good.

My own Quad 44 (bought new) had to be modified drastically before it began to sing. Now it is an excellent unit. No hum whatsoever. And this with its own, dedicated, powerful home- made seperate power supply.
 
@eguth

The problem isn’t with the 33 as the previous owner and Amplabs had silent operation with it. I really like the 33 actually. Very nice sound with a 303 and LS3/5a speakers - suits me anyway. My 34 is also very good. I think some people just have it in for old Quads and think they need meddling with.
 
Nagraboy said:
@Yank

I have all sorts of problems in this house with earth loops/hum. One 33 has no problems, but the other 33 does have problems. The Croft pre doesn’t hum when used with a Croft power amp, but does if paired with the 303 (which has been modded to earth via the mains lead). If I move the kit upstairs to my movies system the hum is even worse. I’ve tried running the hifi system all from the wall socket, tried different interconnects, tried eliminating each source as a cause etc etc and it makes no difference.

Seems to be a question of just buying preamps and crossing my fingers, hoping there’ll be no hum!
Click to expand...

If you have a preamp that is grounded, and an amplifier that is grounded, then connect their chassis together with a shielded cable, you will have a ground loop (and hum). The solution is to lift one of the components, or connect them with what is known in the pro-sound world as a "telescoping shield".
 
Yank said:
If you have a preamp that is grounded, and an amplifier that is grounded, then connect their chassis together with a shielded cable, you will have a ground loop (and hum). The solution is to lift one of the components, or connect them with what is known in the pro-sound world as a "telescoping shield".
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ok but my Quad 34 and Amplabs modded 303 (earthed through its mains lead) are both grounded through their mains cables and I get no hum with the same interconnect I’m using with the Croft/Leak. So what’s going on there? If it was the same for whichever pre I used then I’d understand but it seems to vary between preamps. Not to mention that one 33 has no hum but the other does. As I say, I don’t get it.

A friend who’s using a Croft 25R with his Leak was given a mains lead without an earth to use with his Leak and he has practically no hum.

I’ve read about people getting very good results using a Croft pre with the Leak 20 but they never mention having to lift components or use specific interconnects. It’s all very confusing.

How would I go about ‘lifting one of the components’. Don’t want to get electrocuted tonight :)
 
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