Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - Major Bloodnok

Pages: [1]
1
It is worth noting that, in the UK, construction site mains-powered electrical tools are required to operate at 110V. On a small site, e.g. if carrying out work on an existing residential property, the supply will often be drawn from a 240V system. For this purpose, there are small, robust, portable transformers to effect the necessary step down. These will commonly be available for hire from tool hire depots, enabling them to be tried out as a solution before committing to a purchase.

Travellers' voltage adaptors are fairly uncommon now that portable appliances typically have multi-voltage switch-mode power supplies; and they will anyway be of relatively low power capacity. A small portable site tools transformer, however, will typically handle 3kVA - way more than enough for electrically-powered audio equipment (unless you are rigging for a heavy-metal festival). They can be had for about £50, and you would also need a (matching) bright yellow 16A plug to connect to it.

A transformer of a more practical size and capacity can be had more cheaply from the likes of Farnell or Radiospares (electrical/electronic components suppliers), but it will be necessary to obtain and build it into a separate enclosure, if it cannot be accommodated in the space left by removing the original US step-down transformer. However, such a replacement, as recommended here by OZDOC, is generally the neatest and safest solution, if the equipment tranny does not already offer a 240V winding. If replacing the tranny, do not skimp on quality for the sake of a few quid; and get a competent person to do (or check) any mains wiring work, unless you are justifiably confident in your own capability.
 
Now the boring safety stuff. The reason for requiring 110V on construction sites is that the consequences of receiving a shock at 110V, while painful, are generally less serious than for the same thing happening at 240V. 240V is considered safe for a domestic environment where conditions are less challenging than on a construction site, provided that equipment is properly constructed and maintained, and used responsibly. It is the current that does the damage, but 240V applied e.g. between the left and right hands can easily drive enough current to kill. I mention this to underline the message about getting the mains wiring right. Note also that the design of mains connectors used in some countries - and the old US-style 2-pin plugs perfectly exemplify this point - leaves much to be desired, especially if working at 240V. Authentic vintage mains cords are fine on purely decorative equipment, but not hooked up to the supply. You will probably also need to provide a secure earth connection, unless using a sealed (double-insulated) transformer isolating the DC out. You might need to arrange that there are not multiple paths to earth (which can cause hum loops), but there should be at least one such (insulated) route.
 
Finally, do not let anybody tell you that UK mains voltage is 230V. It is not. 230V (within broad stated tolerances) is now the 'declared voltage' for UK mains supply, for reasons of standardisation of European domestic appliances. In the UK the actual supply is still delivered at 240V, as it has been for a long time, and there are no plans to change that. This will be irrelevant for more modern equipment with an electronically-regulated power supply unit, but older equipment which relies on the transformer turns ratio for its internal DC voltages, and which offers a choice of primary winding connections (sometimes with a mains voltage selector switch), should be set up for 240V operation in the UK.

2
A comment by AndyP, in a separate thread ('Embrace my 79 Stage timbre, or start ripping things apart?') about bringing his Mark II up to scratch, prompts me to think again about soundproofing my Mark I Stage. Tinkling from the innards is not a problem when the amp is fairly cranked up; but when family life obliges me to practise with (closed circumaural) headphones, my activity is still not 100% silent.

AndyP reports some success in this regard with some spare Dynamat, applied to the inside of the harp cover. This is marketed as an automotive sound-attenuating product. My guess would be that such a material applied to my Mark I would work primarily by reducing resonance within the enclosed space, rather than damping vibrations in the cover itself. Possibly the Mark II cover behaves differently, but the Mark I harp cover is a fairly loose fit, especially at the ends. There is also an unnecessarily deep cut-out at the front to accommodate the output jack and controls, such that there is actually a tiny gap between the edge of the cover and the top of the namerail here.

I thought, therefore, that I might first try out ways of effecting a better closure around the harp cover, with a view to reducing direct acoustic leakage, if I can do so without making it unduly troublesome to remove and replace the cover for the purpose of occasional essential tweaks. Judicious use of adhesive-backed foam draughtproofing strip might be a good place to begin. I will report in due course.

In the meantime, has anybody here experimented with soundproofing the Rhodes?

I suppose also that, if I make a really efficient seal and thereby reduce ventilation, I must consider condensation. What will happen if, after I replace the harp cover on a warm, muggy day, room temperature drops on a winter’s night? Perhaps it would be a good idea to place one or two silica gel dessicant sachets in some accessible location within the piano?

3
AndyP, I was interested to note your report of adventures with Dynamat. I would also like to tame the acoustic leakage, or 'Schroeder effect'. This has prompted me to post an invitation to comment on Rhodes soundproofing.
Since that would be a bit off-topic in a discussion of 79 Stage or MarkII timbre. I will post that as a new thread, and try to include a link if I can work out how.

4
The Wurlitzer Electric Piano / Re: Shaking Power Transformer?
« on: October 10, 2020, 01:01:28 PM »
As for voltage, I think that you will find the actual domestic supply in Germany is closer to 220V. Some while back, it was decided that countries across the EU should pretend to harmonise supply voltages; so they hit upon the idea of using a declared voltage of 230V. The catch is that in the formerly 220V countries the adopted tolerance was 230V -10% +6%, whereas here in the UK (formerly a nominal 240V) the new standard is 230V -6% +10%. But the supply voltages did not actually change (hence the jiggery-pokery with tolerances), for the simple reason that such a change would entail an enormous cost in re-equipping the distribution infrastructure (new transformers at all the local substations), not to mention problems with some (mainly industrial) machines which are designed to run within narrower voltage tolerances.
That is not to say that your supply will be spot on 220V - it will vary according to the state of your local distribution grid, and with the time of day (due to fluctuations in total load). I find anything between about 238V and 247V here in south-west England.
This is not a problem for most new domestic electric appliances - those made for the EU market must be able to work over the range 230V ±10%. If I buy a Euro-standard electric kettle in my local Lidl, it will come to the boil faster here than it would in Germany (incidentally affording us a marginal saving in heat loss, thus saving the planet or some such nonsense). Most modern electronic gear working with an internal low voltage from a regulated step-down unit will automatically adapt to a much broader mains supply voltage range. Older kit, which just relies on a fixed transformer winding turns ratio for its internal voltages, is often equipped with mains voltage selectors, jumpers, or requires some soldering to adjust to the local supply voltage. If your tranny is marked 220V, then you are probably OK. But if you are worried, I would first suggest putting a voltmeter on your wall socket at the times when you typically play the Wurli, in order to see what your actual supply voltage is.
Where supply voltage can be a problem is exemplified by the Twin Reverb amp I use with my Fender Rhodes. This twin is a reissue (i.e. modern), and labelled 230V for the European (including UK) market. Now I know that the power transformer has multiple taps on the primary windings to cater for 220V, 240V etc., which suggests that this order of internal voltage accuracy is regarded as important; but the only schematic I can get for it is some years out of date, so I cannot check/adjust the primary connections to suit my 240V supply. In theory, if I am putting 240V across the 230V taps, the B+ and all the related plate voltages are going to be 4.3% too high. Happily, my grid voltages will also be correspondingly more negative, affording some correction, so the set-up is probably near enough to avoid red-plating the output valves (tubes); but goodness knows how Fender set the bias at the factory. Do they anyway use for this a bench supply which gives exactly 230V anyway, or is it 230V ±lots, close enough for those weird folk across the Atlantic?
The moral of this story - take nothing for granted.

5
My copy of this gorgeous book has recently arrived, and I would respectfully add my two-penn'orth to what appears to be a well-earned favourable response here.
There has clearly been a lot of diligent research and honest toil in the making of this book. It's well written, beautifully illustrated, well printed and bound. Worth every penny.
I am looking forward to many happy hours' browsing. Thank you, Messrs. Lenhoff and Robertson, for a veritable tour de force.

6
Until fairly recently (earlier this year), it was possible to find downloadable service information for Fender amps on the official Fender site. This seems to have been withdrawn, ostensibly because of Fender concerns as to liability if home techs should come to grief after taking a screwdriver to their equipment.

I had already downloaded from Fender the service manual for my '65 Twin Reverb Reissue, and copies are anyway still to be found on several other sites, either of the whole manual or of its included schematic. However, the '65 TRRI is a current production model, and the innards of mine, dating from c2017, differ in several significant respects from the FMIC drawing 037627rev.E (notably the power supply wiring, and an ancillary pcb which has replaced the neon optocoupler in the tremolo (so-called 'vibrato') control circuit). Despite Revision E dating from October '96, it is the only schematic version I have so far encountered in the wild.

Continuous product development is fine - it's still an authentic Fender with the basic design essentially as per original 763 circuit - but it is frustrating to find information on the official Fender site with no update in 24 years. Presumably, this problem is not confined to the TRRI model.

It seems also to be impossible now to contact Fender direct on this matter (consistent with their withdrawal of the downloadable manuals).

Does anybody please know of any source(s) for more up-to-date schematics of current production Fender amps?

I am hoping that this amp will outlive me; and I do not imagine it will be any easier to track down a schematic for it a quarter-century hence. Better, therefore, that I should find one now and squirrel it away for posterity.

7
Folks here seem to be agreed that the early MkI Stage output circuit was pretty hopeless - enough top cut to near-silence the upper two octaves, and output across the spectrum heavily attenuated by the resistive component of the shunt. One might then ask, how did that design come about?

It is not unusual - in various Internet fora - to find criticism of FMIC products attributing design or production shortcomings to Leo Fender's personal avarice. I incline to a more generous view: cost control is necessary if one is to sell product to a mass market at an affordable price (thanks to which there are enough MkIs still in circulation that we can find and lovingly restore one for less than the cost of a very basic second-hand car). It is, of course, plausible to suggest that some counter-productive economies were made at the behest of CBS cost accountants.

In the present instance, however, the deficiencies of the pre-1973 Stage V/T circuit cannot be ascribed to parsimony, since its unquestionably improved successor uses an identical component count and is scarcely more difficult to wire up. To look for an explanation as to how the earlier design came about involves largely pointless speculation. Suffice to say that I removed it from my 1972 MkI Stage 73 (as a complete assembly, now stored away for posterity) within weeks of getting it home, and after reading this most informative thread - thanks to everybody who posted here.

What I replaced it with was the 1973+ circuit but with scaled component values - 250kΩ/10nF tone and 50kΩ volume (incidentally, the values as tested by poster Sean, above, in the variant referred to as 'pnoboy's circuit'). This seems to work well, feeding amp inputs of around 1MΩ. I normally have the output volume near maximum, and the bass cut (just labelled 'tone' on the knob on a 1972 Stage) at around about mid-point, with most of the tone pot range being "useful", depending upon whim. Of course, there's volume and a bass/mid/high tone stack on both of the amps I use, but it is still convenient to have the piano controls so close to hand.

Once one is fortunate enough to acquire one of these instruments, it becomes apparent just how much scope there is - within the bounds of the so-called 'classic' Rhodes sound - for varying its character, just by the judicious tweaking of tone controls. And somewhat like well-crafted beers, we might each have our own preference, but even that is not necessarily the same from one day to the next.

Pages: [1]