100 volt line transformer ???

[Gus]

Hi!

can i use 100 volt line transformer with my Fairchild 541A cutterhead?

or only 70.7 volt line transformer?

i found one on ebay
http://www.ebay.co.uk/itm/RS-100-Volt-100v-line-speaker-matching-transformer-30w-/281147884784?pt=UK_ConElec_SpeakersPASystems_RL&hash=item4175b844f0

i live in europe and it's hard to find 70,7 volt line transformer.

please help me !

Thanks in Advance!

[EmAtChapterV]

That one should be fine - it has enough taps that you'll be able to find a ratio that works.

IIRC the 100/70/30/whatever volt PA system is volts-versus-watts at clipping. In this case, 30W @ 100V = 0.3A into 333Ω - if this is the impedance of the head, the amplifier will "see" it as whichever low-impedance tap you connect the amp to on the bottom row. (8Ω to be safe; 4Ω is do-able on more modern amps.)

[Gus]

Hey, EmAtChapterV thank you for your quick response

as you can see in the attachment image the dc resistance of cutterhead is 131,3 ohm

[L.K.R.A]

Hi there,

With an impedance like that it is likely your head is a 500 ohm...

What amplifier are you using - I may be able to help you out...

I have 2x 10 watt mono amplifiers with a 500 ohm taps available - all you would need is a USA to EUROPE power transformer

See post

https://www.lathetrolls.com/viewtopic.php?f=4&t=4133#p25175

10 watts don't sound like much, but it's enough to drive my presto 1c 500 ohm or my universal 15 ohm (With 70v/500hm line transformer)

[Gus]

Hi L.K.R.A!

I have a 4/8 ohm brigable amp and i'm planning to use it with a 100v line transformer
but i'm not sure how many watts it must be the transformer.
As EmAtChapterV said 30W @ 100V = 0.3A into 333Ω - if this is the impedance of the head.
The dc resistance of my cutterhead is 131,3 ohm
That means the transformer it should be 100v @ 75 watts to work properly ?
Please correct me if i'm wrong.

[L.K.R.A]

Em has given a calculation for the 100 v line... I'm assuming that your amp has 70 v and 100 v outputs along with the 4 / 8 ohm output... the reading on your head is dc not ac.. AC reading is usually much higher... Given the reading it it a good chance that your head is 500 ohm... the transformers are usually set up on a 100v or 70v line to step down for 4, 8 & 16 ohm speakers..

I have several 70v line transformers. Biggest is rated at 40 watts but all are wound and have taps for 10 watts 500 ohm in & 0, 4, 8 or 16 ohm out..

[EmAtChapterV]

Kind of an aside, but would you mind posting a detailed closeup of the bottom of the cutterhead with the stylus, armature and damping block? I'm trying to re-do the damping on my 541A and the configuration doesn't look quite the same as yours. Also I don't think I've seen one with an advance ball setup before.

[Gus]

Hope these pictures will help you to find the solution
sorry but my camera is not high definition
this head is a part of Fairchild 539 lathe i've found it @ ebay us shop for 200 $
without the turntable.
right now i'm building the lathe from zero
i will upload some images of the progress of the work soon.

Here's the manual for the 539 lathe:

http://www.corporaterecords.biz/Fairchild539.pdf

and one for the 541 cutting head:

http://www.corporaterecords.biz/Fairchild541.pdf

[markrob]

Em has given a calculation for the 100 v line... I'm assuming that your amp has 70 v and 100 v outputs along with the 4 / 8 ohm output... the reading on your head is dc not ac.. AC reading is usually much higher... Given the reading it it a good chance that your head is 500 ohm... the transformers are usually set up on a 100v or 70v line to step down for 4, 8 & 16 ohm speakers..

I have several 70v line transformers. Biggest is rated at 40 watts but all are wound and have taps for 10 watts 500 ohm in & 0, 4, 8 or 16 ohm out..

Hi,

That's true, but in this case you'll run transformer in reverse. Use the 8 ohm tap as the primary connected to the amp output. Connect the 100V, 15 watt tap to the head which will be a pretty close match to a 500 ohm head. You can calculate the secondary impedance from R = (V squared) / power. In this case: 10000 /15 watts = 667 ohms).

Mark

[Gus]

please ignore the 78 rpm stylus is only for my tests

[Gus]

Em has given a calculation for the 100 v line... I'm assuming that your amp has 70 v and 100 v outputs along with the 4 / 8 ohm output... the reading on your head is dc not ac.. AC reading is usually much higher... Given the reading it it a good chance that your head is 500 ohm... the transformers are usually set up on a 100v or 70v line to step down for 4, 8 & 16 ohm speakers..

I have several 70v line transformers. Biggest is rated at 40 watts but all are wound and have taps for 10 watts 500 ohm in & 0, 4, 8 or 16 ohm out..

here is an Altec 70.7 volt /75watt transformer who work in reverse

http://www.ebay.co.uk/itm/Altec-EV-15075-Audio-75-Watt-70-Volt-8-ohm-Transformer-/350262673093?pt=US_Other_Pro_Audio&hash=item518d483ec5

Hi,

That's true, but in this case you'll run transformer in reverse. Use the 8 ohm tap as the primary connected to the amp output. Connect the 100V, 15 watt tap to the head which will be a pretty close match to a 500 ohm head. You can calculate the secondary impedance from R = (V squared) / power. In this case: 10000 /15 watts = 667 ohms).

Mark

Thank you very much Mark !
your answer helps me to find the right transformer for the cutter head.

[L.K.R.A]

Didnt know that you could reverse the transformer... Interesting... even more opportunities for cutters to get up and going...

[Gus]

Finally i bought an 100V/1-25-2-5-5-10-20W line trasformer
R = (V squared) / power. In this case: 10000 /20 watts = 500 ohms
here is:
http://www.ebay.co.uk/itm/Adastra-100V-line-transformer-1-25-2-5-5-10-20W-/290963159558?pt=LH_DefaultDomain_3&hash=item43bec17a06

i hope this transformer to work properly with the cutter head.

[L.K.R.A]

Not sure cauz ive never reversed a transformer... Give it a try... If it is not what you are looking for send me a message and i can help you out with a NOS Peerless transformer...

[flozki]

hello l.k.r.a
totally offtopic but with all my respect to your interesting content.
please please. please! remove your signature graphic, make it much smaller or even better replace with ascii text.
it take so much space and makes the whole thread very annoying to read.... i often read lathetrolls on a handy and not on a 24inch screen. and i guess we have all seen your logo now...
thanks... not necessary to discuss that in this thread. so the moderator can remove this message..but it had to be said....

[L.K.R.A]

Very dissapointed that i couldn't be messaged and asked instead of being told like this... My signature is me and seeing as though it is regarded as "annoying" i'll remove myself from the situation entirely... So from this moment on i will be having nothing more to do with this forum and this is the last time that anybody will have to endure viewing my annoying signature ever again...

[Radardoug]

Have to agree with Flozki!
But if you feel you have to leave the forum, then do, but its your loss LKRA. You won't find all this knowledge easily anywhere else.

[powerstrip]

Come on lkra, don't you think that's a little over reaction?

You don't have to pack up and leave just cause someone said your sign was too big.

[EmAtChapterV]

Could I also possibly impose upon you for pics of the inside of your head, with the front panel removed? I'm interested in how wide the pole/armature gap is and how the coil is secured in a stock 541A.

I just found out what was holding the coil "in place" in mine was friction between the body, the coil bobbin and the moveable pole pieces. No screws, no glue - I undid the pole pieces and it popped right out. No wonder it was making plenty of noise up to 18+ kHz but wouldn't cut anything above 8. Also the poles had been so close to the armature that the centering torque springs were no match for the magnet - the armature was either full left or full right unless I had the damping cranked down so far that it started to crush the lower half of the armature and it took 4 watts to cut 1 kHz at 7 cm. Sheesh. I now have some glue setting between the bobbin and the body; I'll see if it holds things more securely tomorrow.

Also something I'd really love to do if I had the resources for it - imagine putting a 6x6 or 10x10 mm piezo pickup on either side of the armature, between it and the damping cylinders - piezo cutter feedback! I wonder how well it would work? Didn't one of Fairchild's vertical/lateral stereo heads use something like this?

[markrob]

Hi,

I tried something like you are suggesting by coupling a stereo ceramic pickup to my DIY head. The results were promising. I did run into quite a bit of crosstalk from the drive coil(s). Even though you get plenty of output voltage from the piezo element, the fact that it is so high in impedance made it susceptible to stray pickup.

The Fairchild system used an eddy current RF carrier based position feedback element. The nice thing about this method is that the carrier is well above the baseband audio (Mhz range) such that it is not affected the drive coil.

Mark