Ralf Mardorf wrote: Hi Ralf, Thanks for your replies and suggestions, hehe I've received a few mic shocks to the lips over the years when I used to run a vintage amp without a ground (it only had a ground lift toggle switch)... It didn't take me long to upgrade the wiring to a fully grounded cord.. :)..

On Wed, 3 Jun 2015, David Christensen wrote: I don't know about ground switch, but some of them had a "hum" switch or something similar... flipped the ac lines. Sometimes the "neutral" was connected to chassis... which with no keying on the ac plug meant the chassis might just as easy be hot. Nobody has done that for a long time now. The idea was old and outdated 50 years ago. (probably before) -- Len Ovens www.ovenwerks.net

Len Ovens wrote: Len Yes that's what it was, however the toggle switch itself said 'Ground' on the back the amp chassis.. Both the bass player and I had vintage Traynor amps, he had a YBA-1 and I had a YGM4 Studio Mate, If you google the model numbers you can find the schematics, however a quick look didn't show me a schematic prior to 1973 but to my knowledge these amp models date back to the late 1960's. It appears that the 1973 schematics show a chassis grounded plug.. In any case both of these amplifiers had ungrounded 2-prong molded plugs and if the toggle was switched wrong with the wiring at whatever venue we were playing at we would get shocks off of the microphones...lol I heavily modified and sold mine to a nephew many years ago but Traynor actually re-issued both of these amp models in recent years (with proper electrical supplies). Had I known it was a classic... well hindsight is always 20/20... To this day I still keep a respectable distance from microphones when I sing... Glen

On Thu, 4 Jun 2015 10:12:25 -0500, Chris Caudle wrote: The 5 position switch provides usage of 2 single coils at the same time. You could keep one single coil close (e.g. neck and bridge pick ups) and the other far away from the strings (e.g. the middle pick up). You still would get single coil neck and bridge sound, but with a humbucker effect. Most often when I heard too much hum caused by single coils it was simply caused by wrong usage of the gear. Often people connect guitars to line inputs and then use amp and speaker simulation and grotesque much overdrive or they stand face up to a transformer instead with the back to the transformer. Another problem might be to high-resistance caused by the way ground is connected to the strings of Strat like guitars. _____________ string | |^^^^^^^^^^^^|spring of the whammy bar |___ cable The spring is hooked into both sides and the strings moves on the bridge saddles, so there are 3 error sources that easily could make the connection to ground high-resistance. Both ends of the springs and the contact surfaces of the strings should be checked.

LAU: I had a realization -- while the low-pass filter idea may apply to amplifier power supply transformer and related, the Ground switch and capacitor require a different model and analysis: they implement a voltage divider to true earth ground via the parasitic capacitances of the amplifier: H o------+------------+ | | o | \ | S o - o-----+ | / | | o | | | | | N o---+--+ | | | | | = C2 = C = C1 | | | A o---+----------+----+ | = C3 | G o-------------------+ Where: H is the electrical supply Hot (120 VAC) N is the electrical supply Neutral (~0 V) A is the amplifier chassis (and connected equipment and people) G is the earth (0 V) S is the "Ground" switch C is the grounding capacitor (0.047 F, 56.4 kOhm at 60 Hz) C1 is the parasitic capacitance between H and A C2 is the parasitic capacitance between N and A C3 is the parasitic capacitance between A and G I don't have data for the values of C1, C2, and C3, but will assume: 1. The impedance of C is much smaller than the impedance of C1, C2, and C3 (at 60 Hz). 2. C1 and C2 are approximately equal. 3. The series combination of C1 and C3, and of C2 and C3, is 1 MOhm (or greater). To simplify calculations, let: 1. VN = VG = 0 V 2. ZC1 = ZC2 = ZC3 = 500 kOhm There are three cases for calculating the voltage on the amplifier chassis, VA: 1. SW connected to H -- C and C1 are in parallel: H o---+-----+ | | = C = C1 | | A o---+-----+ | | = C2 = C3 | | G o---+-----+ VA = VH * ( ZC2 || ZC3) / (ZC || ZC1 + ZC2 || ZC3) = 120 VAC * (500 k || 500 k) / (56.4 k || 500 k + 500 k || 500 k) = 120 VAC * (250 k) / (50.7 k + 250 k) = 120 VAC * (250 k / 300.7 k) = 99.8 VAC 2. SW in the center OFF position -- C is gone: H o---------+ | = C1 | A o---+-----+ | | = C2 = C3 | | G o---+-----+ VA = H * ( ZC2 || ZC3) / (ZC1 + ZC2 || ZC3) = 120 VAC * (500 k || 500 k) / (500 k + 500 k || 500 k) = 120 VAC * (250 k) / (500 k + 250 k) = 120 VAC * (250 k / 750 k) = 40 VAC 3. SW connected to N -- C is in parallel with C2 and C3: H o--------------+ | = C1 | A o---+----+-----+ | | | = C = C2 = C3 | | | G o---+----+-----+ VA = H * ( ZC || ZC2 || ZC3) / (ZC1 + ZC || ZC2 || ZC3) = 120 VAC * (56.4k || 500 k || 500 k) / (500 k + 56.4 k || 500 k || 500 k) = 120 VAC * (46.0 k) / (500 k + 46.0 k) = 120 VAC * (46.0 k) / (546.0 k) = 10.1 VAC David

On Sat, 06 Jun 2015 06:15:04 +0200, Robert Edge wrote: I didn't know that, but indeed, in a book [1] I see an old Fender: ac switch ~ o──┬─o/ o──────────────)│( │ )│( o ground switch )│ \o────┐ )│( o ┴ C 50n )│( │ ┬ 600V )│( │ ┴ )│( │ ground )│ │ )│( ~ o──┴────────[fuse]─────)│( The audio IOs are connected to ground, so guitar strings would be hot too, if the capacitor has got a short. [1] "Röhren-Verstärker reparieren, restaurieren, modifizieren", Rainer zur Lind, ISBN 3-89576-028-5

Chris Caudle wrote: Chris, Wow, that paper is exactly the kind of thing I was looking for.. Thanks very much for the link and your insight.. Glen

On Wed, June 3, 2015 2:47 am, Ralf Mardorf wrote: Yes, and I guess I should say that the paper I linked is useful, but has to be taken in context. If you are building a million dollar commercial studio that had to be highest quality of everything (pretending for a moment that someone would still do such a thing) your considerations would be different than for a personal project studio attached to your house. And while it may be nice to have the absolute lowest amount of power noise coupling into your vintage Fender pickups, it would be a lot cheaper to change to humbuckers. That wouldn't be so bad, would it? ;) The other good way to reduce power line coupling to single coil pickups is to move farther away from the power lines. You just need to convince your spouse and banker that you really "need" an additional 50% floor space in your studio so you can have less hum in your Stratocaster. :) -- Chris Caudle

Ralf Mardorf wrote: I wanted to make an objective decision with all the facts from both sides so I appreciated that paper had some sound logic (pardon the pun) from one side of the issue, I'm not taking it as the final word at all don't worry. I'm fortunate enough to be able to do this project but only if I do the majority of the construction myself so there ain't no Richie Rich spendin' going on here at all... :) I think in the end I'm leaning toward going with Romex (which does comply with code here). The fact that this space is larger with a higher ceiling to route the wiring through than what I had before will enable greater distances from the single coil instruments generally.. As I said in my original post the single coil noise was only a minor annoyance but I thought it prudent to at least ask for some input before starting from scratch. My gut feeling was that it was not worth shielding it but I appreciate what everyone has shared and that they have taken time to reply. Glen