The Secret Society of Lathe Trolls

Estrada · Joined: 21 Sep 2007 Posts: 8

Hi all,

I have a lathe which I purchased at the end of last year. I need some advice on selecting an appropriate amplifier to drive this lathe. I'm not really sure where to start so any advice with regard to what sort of amp, how powerful etc would be greatly appreciated.

Thanks,

isis · Joined: 11 May 2007 Posts: 6

Just wondering , I'm new too but learning.

Estrada · Joined: 21 Sep 2007 Posts: 8

The lathe originates from Paramount picture studios in hollywood, circa late 1930's. I think it was custom made for the studio so is possibly one of a kind.

Karl Welty · Joined: 12 Nov 2007 Posts: 22

What is the impedance of the cutter head ? I'd start there.

motorino · Joined: 24 Aug 2005 Posts: 207

i believe you have the same cutterhead like me (looks a RCA), y use a "normal" grafic ecualizer 1/3 octave its ok for test..
You need made the riaa curve with the ecualizer, in the next link you have the amount of dbs for the difererent bands of the riaa curve
http://www.hagtech.com/pdf/riaa.pdf

of course, with a 1/3 octave ecualizer you dont made the real riaa curve, but your cutterhead dont reproduce from 20 hz to 22000 hz....you need to cut before with a hpf and lpf frecuencies down 40 hz and up around 10000 hz, my yamaha Q20311B have a adjustable hpf and y use a cut around 35 hz, i put a photo, i use for a grampian type D cutterhead, the first channel its for made the riaa curve, the second channel its for ecualizing the feedback signal

for the amplifier...you need a very low distortion at hi frecuencies, look for a kit like MOS125, and put a 200 miliamperes slowblow fuse in the cutterhead, very important!! of course you can use a comercial or domestic amplifier, be careful

http://www.audiohum.com/docs/wn/cat_mos125.pdf

and a lot of test!!

luck!

motorino · Joined: 24 Aug 2005 Posts: 207

200 miliamperes slowblow fuse its ok for test, i believe after test you can use a little big more but i dont ...

JayDC · Posted: Sun Dec 16, 2007 2:57 pm Post subject:

motorino,
So you use no riaa on the feedback?.
does the phase inversion happen after the amp or before it?.

motorino · Joined: 24 Aug 2005 Posts: 207

i go to made one block diagram..

motorino · Joined: 24 Aug 2005 Posts: 207

http://lathetrolls.phpbbweb.com/viewtopic.php?t=590

Estrada · Joined: 21 Sep 2007 Posts: 8

Hi all,

Thanks for the replies to this. Haven't checked this for a while as this project has been temporarily on hold. I still have a lot to learn about many things. A good place to start might be learning more about my cutting head. Can anyone inform me how to check what the impedance of the head is?

Thanks for the advice on the amp and equualiser motorino. Is this amp available as a kitset?

Also, I have seen a kitset for an inverse RIAA filter, are these any good or is it better to have the control the the equaliser will give you?

Again, thanks for the replies. I am sure I will have many more questions the further I get into this.

bancho · Posted: Sun Jul 06, 2008 5:13 pm Post subject:

Hi everyone!
Recently I got grampian type D head. Before that I had (still have, don't use) presto's 1D running with 90B amp. I hooked up grampian head and 90B amp. There is some sound but very quiet. I think I've driven the amp to it's end capabilities... I think I need some other amp... more powerful.
I got the RA7 schematics and it doesn't look too complicate to make it at home. The valves are obtainable. The only problem I have are the transformers. Is there any possibility to get the exact info on the transformers so they can be made by order?

What are the other amp possibilities? I'd like to have some amp with feedback and powerful enough to drive this head (I think it should be 100W).
Any suggestions beside motorino's kit?

many thanx!

bancho · Posted: Thu Jul 10, 2008 8:31 am Post subject:

Anyone?

Amp doc?

Especially I'd like to know the thing about the transformers...

Please help!

Amp Doc · Joined: 21 Jun 2007 Posts: 109 Location: UK

Sowter audio transformers can make you the transformers the signal input trans is a off the shelf part . They can make the output transformer but its a E core sounds good though think it was about £200 and they can make the psu trans..... Some simple tools and off you go. Sowter is very helpfull just send him the schematics and he can do the rest.....
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