Extending the Phono and earth leads of a Pro-ject P1

[Edward Huggins]

Never has such a simple query expunged such an in-depth diatribe....

[mhennessy]

Ah well - if it's only 1m of extension you need, then just sell him one of these: http://cpc.farnell.com/pro-signal/ps...-sk/dp/AV13847

I've just measured a similar lap-screened cable of identical length at 106pF - you'd be hard pushed to find less. If the customer notices any change in tonal balance or hum pickup, then sell him a phono preamp. Or preferably, cut out the middle man and send him to Richer Sounds or Maplin or similar. Or simply tell him to relocate things, referring him to this thread if needed.

I agree with Paul here. Don't get involved with the innards. If you break something, that's your profit gone out the window. At best...

IIRC, this deck uses a rubber belt to suspend the motor from the deck. These are getting old now, so careful not to disturb that too much.

I honestly don't think that tuning drive cord would work very well for an anti-skate weight. I've got some really thin stuff here from an old Grundig set, and even that is too thick and inflexible. Cotton might be better. The original was thin plastic (nylon or similar). Presumably the weight is still present? If so, you'll get what I mean because of how very light it is.

[McMurdo]

The problem with very cheap leads is poor screening

Indeed. I sometimes service record decks with mag carts. and I use a 3m extension lead (male to female twin phono). A cheap one I bought would pick up the hum from the bench fluorescent light, a better one didn't. Apart from that, no problems.

[mhennessy]

Originally Posted by Edward Huggins

Never has such a simple query expunged such an in-depth diatribe....

Diatribe

[bikerhifinut]

Originally Posted by mhennessy

Diatribe

I think Edward means that the issue has become fogged with well meaning but complex solutions?
I'm with Paul Sherwin and as Paul knows my somewhat audio**** leanings He might be a bit surprised but I've done enough personal "fiddling" to know that its always worth trying the simple solution first. Just get or better still make your own extension lead, use something decent from maplins or your preferred supplier, keep it short, don't worry about the earth lead just extend it with a bit of ordinary thin flexible wire its only there to ground any floating bits of metal so to speak. Gold plating works for sure, until the plug has been removed and reinserted a few times it doesnt take long beleive me. De-oxits a better investment.
have a listen and i reckon "it'll be reet" as they say round here.

A.

[bikerhifinut]

Oh........ and a nice shelf is probably the BEST way to support a non suspended turntable like the Pro-ject. i have used a few from the basic cheapo pressed steel "L" bracket from the diy shop to the current cosmetically nice frame style shelf with fancy spike supports for the shelf and frankly the cheapie job was about as good and it was mounted on a stud plasterboard wall to boot. I didnt even screw the shelf to the brackets, just used "sticky fixer" pads.

A

[paulsherwin]

Let's keep things friendly please. We don't want arguments to break out, especially as a result of misunderstandings.

[bikerhifinut]

Originally Posted by paulsherwin

Let's keep things friendly please. We don't want arguments to break out, especially as a result of misunderstandings.

Sorry Paul if I said anything to offend.

[paulsherwin]

No problem, my post was a general caution rather than a response to anything you've posted.

[mhennessy]

diatribe
noun
a forceful and bitter verbal attack against someone or something.

For what it's worth, I didn't see any forcefulness, bitterness, or attacks - or indeed anything that could be construed as such - anywhere in this thread. It was probably just a bad choice of word, but also could be seen as provocative - hence my asking for clarification first precisely so we could avoid any misunderstanding.

I don't see a problem with setting out the issues of noise and capacitance, so the OP (or countless others in the future) can make an informed choice. In fact, everyone in this thread appears to be singing from the same hymn sheet. And Edward at least didn't realise that you get HF lift from increased capacitance in this scenario, so that was worth chucking in IMHO - it's actually quite interesting when you first come across it. So, no diatribe - just the usual well-intentioned exchange of information. Business as usual, and long may it continue

['LIVEWIRE?']

Thanks everyone, and Mark in particular for your detailed explanations. Despite working with electronics, in particular Audio gear for over 45 years, I'd forgotten some of the theory and maths! Regarding the way the arm is fitted, with hindsight (a wonderful thing, that!) I shouldn't have undone the screws securing the arm to the baseboard, but, in my own defence, I didn't expect an 'upmarket' brand like Pro-ject to use non-captive nuts for this purpose. At the moment I've refitted the arm, as stated, using self-tapping screws, though whether they are a suitable long-term solution might be debatable. As far as the antiskate cord is concerned, I'm certain it wasn't present. The owner's manual tells you how to set it for different tracking weights, but gives no info. other than that, so it may be a case of contacting the Pro-ject distributors to obtain the correct item, hopefully at a reasonable price. To return to the original problem, I may well obtain a decent quality ready made extension lead and plug it in, extend the earth lead with a lentgh of similar gauge wire to the original, then see how it all works.

[Ted Kendall]

And my bit of pedantry - "expunged" is not a synonym for "provoked" - it means "to eliminate or destroy"

[Herald1360]

Originally Posted by mhennessy

For what it's worth, I didn't see any forcefulness, bitterness, or attacks - or indeed anything that could be construed as such - anywhere in this thread. It was probably just a bad choice of word, but also could be seen as provocative - hence my asking for clarification first precisely so we could avoid any misunderstanding.
:

Since the diatribe if there ever was one was expunged anyway, presumably it was disposed of at source.

http://www.dictionary.com/browse/expunge


Malapropism alert

Returning to the original question- the lead needs to be about 50% longer and ideally the same capacitance- if the original is about 100pF per metre, replace it with the required length of URM70 at 67pF per metre. Simples.

[Edward Huggins]

What I was meaning here in my perhaps overly cryptic comment, is that in the first round of Posts offered some excellent, practical and low-cost advice and it could have been left there...... but then it all became convoluted with multiple-choice options, only to come back almost to its starting point. And not just confined to this Thread either.

[Ted Kendall]

I agree there - no field is fuller of half-digested received opinion masquerading as gospel truth than audio in general and hi-fi in particular - no reflection on present company, this has been so ever since I've been interested in the subject...and that is more years than I'm prepared to admit...

[Radio Wrangler]

Magnetic cartridges (all sorts) are by their nature inductive. Higher output ones ('moving magnet) 'achieve this by having coils with lots of turns. The output voltage goes up roughly proportional to the number of turns, but the inductance goes up roughly proportional to the square of the number of turns. Along with the capacitance of the connecting cable and the amplifier input, this inductance forms a resonator.

Cartridge designers have to handle this, by trying to keep the resonance up high with its Q controlled, and by shaping the response of the cartridge to compensate for it.

The preamp I have on the bench at the moment actually has a front-panel knob to switch input capacitors so the loading C can be changed to suit the cartridge, so the resonance can be put where the designer allowed for it to be.

Moving coil cartridges generally don't have the space for many turns in their coils, so their output is low as is well known, but their inductance is particularly low, and the resonance with the capacitance of the load which it sees is much higher. So fussing over load C is mostly a moving magnet cartridge sort of thing.

Doubling the load capacitance will shift the resonance down by half an octave. (one over two-pi-root-LC) and affect the flatness in the treble region.

The ideal solution is to stick with the usual cable length between the cartridge and the first stage of amplification. This can be achieved either by having the turntable close enough to the existing amplifier, or by using a remote phone stage closer to the turntable (what I called 'plan B' earlier).

Many amplifiers have deliberate loading capacitors at their front-ends. If the spec of the cartridge is known, and the cable capacitance is measured, these can be changed to bring the total back to the specified value. In an ideal world, this ought to be routine. Some preamps have plug in boards where these components are intended to be changeable. The B252 I've just got has a bowden-cable from a front panel knob to a switch by the phono inputs. The approach in the hifi magazines is that you arenot allowed to change any components, or have any equalisation controls, but must keep changing entire piecees of equipment until you get the right sound.

Maybe it's OK to extend the cables and leave the loading capacitors untouched, but it is a matter of judgement whether the effect they have is tolerable or even noticeable.

David

['LIVEWIRE?']

Thanks for that analysis, David. The P1's owner tells me he has no option to place the turntable where it needs longer leads to reach his amplifier, and doesn't want to invest in a magnetic cartridge preamp., so extended cables are the only way to go.(BTW, I haven't seen the owner's's set-up, though I know he has a Sony Amplifier) All I can do, as mentioned earlier, is to play a record or two, including my test disc, on the unmodified Turntable, then repeat the performance with extension leads, using the same records and amplier, which will probably be a 1970s Wharfedale or my Sony TA-D505, and compare the two. I may also, out of interest, compare the Pro-ject P1 with it's Ortofon Cartridge, with my TEAC PX300 DD Turntable and Audio-Technica Cartridge.

[mhennessy]

Funnily enough, quite a lot of hi-fi phono preamps do offer switched loading, just like the Revox. Often, they are DIP switches on the back or bottom panels, but they are sometimes brought to the front. Very occasionally, they are under software control, so you can fiddle from the comfort of your listening chair. Quite a contrast - and a welcome one - to the usual hi-fi minimalism.

In lieu of adjustments, 47k||100pF is the nominal "default" for MM pre-amps. Exceptions to this exist - for example, the Marantz PM7200 has a massive 470pF (followed by 220R in series, then 680p to ground).

I was looking at Douglas Self's take on all this earlier, and his graph shows a 5dB peak at 9kHz for 370pF! Obviously, it depends on what values of R and L you assume for the cartridge.

Basically, with MM cartridges, you're between a rock and a hard place, and extending cables is surprisingly complex. As I said earlier, improving screening to tackle the noise pickup problem often results in more capacitance, hence a peaked-up high end. Trying to reduce capacitance might compromise screening. As always with engineering, everything is a compromise.

Earlier, I posted a link to a cheap lap-screened cable with 106pF (88pF/m). Out of curiosity I went looking for a better cable at CPC - http://uk.farnell.com/pro-signal/jr9...-1m/dp/4258927 - but as is usually the case, no specification for capacitance was given - luckily, I have one here, and it measures 150pF/m. Hmm...

However, I do have some "Puresonic" cables here - these would have come from CPC originally, but they don't do them any more. These were about a fiver each, and are well-made and double-screened (braid and foil) - a worthwhile step up from the lap-screened cheapies. The diameter of each is about 6mm. They measure 70pF/m, so are probably the best bet here - a rare combination of good screening and low capacitance - if you can fine them! Example: http://www.cables4all.co.uk/puresoni...metre-97-p.asp

Is it possible to visit him and try a cheap lap-screened cable in-situ? He might be lucky, depending on local conditions. If hum is apparent, at least that demonstrates why he needs to fork out a bit more for a double-screened cable. Do explain that a decent cable might be £20 or more, and that a phono preamp can be had for that sort of money

Good luck

Try a cheap extension, it will be fine and the money left over (for an expensive one) can be used to buy another record or two.

[dseymo1]

For the bias wieght cord, haberdashers sell nylon sewing thread, which is as good as anything, abd may well be identical to what was used originally.