The Secret Society of Lathe Trolls

flozki · Joined: 19 May 2006 Posts: 168 Location: switzerland

here the circuits i used for test on my dsikomat

it is a VIVANCO cd_to_phono convertor i found on the fleamarket.
i just changed one resistor.
now the attenuation is not that high. only 20db on 1 kHz.
ok the 20khz curve is 2dbs off or so.
but thats fine for simple heads like moving iron (prestos)
i used a grampian and it sounds quite good.

here the schematics:

and the simmulation:

this little box is very handy and will be now always ready for quick and dirty cutting test. hehe

f.

motorino · Joined: 24 Aug 2005 Posts: 330 Location: Aragón, ZGZ

Flo you are the best!

Very good contribution for me

In this world getting electronic designs is the most difficult, many thanks!

Simon · Joined: 05 Mar 2008 Posts: 452 Location: London, England

What was the model number of the unit

VIVANCO PA111 ?

_________________
Happy to learn something new.
Wanted: Stylus for Presto head, Mono heads Grampian, Fairchild, Presto, Fairchild 740 lathe, Presto 8n, 8d 8dg or Neumann AM31 or A131, Presto, Rek O Kut or wot ever recording Amps, PM me what you have for sale.

cuttercollector · Joined: 11 Jun 2006 Posts: 431 Location: San Jose, CA

Probably something like this -
http://www.mcmelectronics.com/product/MCM-CUSTOM-AUDIO-50-7240-/50-7240
not a pre-amp - the other way !

Simon · Joined: 05 Mar 2008 Posts: 452 Location: London, England

http://www.epanorama.net/circuits/phono.html

I found this on my travels...

_________________
Happy to learn something new.
Wanted: Stylus for Presto head, Mono heads Grampian, Fairchild, Presto, Fairchild 740 lathe, Presto 8n, 8d 8dg or Neumann AM31 or A131, Presto, Rek O Kut or wot ever recording Amps, PM me what you have for sale.

piaptk · Joined: 25 Jan 2008 Posts: 118

On this thing, would you even need to switch out the resistor? It seems like this thing does exactly what you need it to do already?

Simon · Joined: 05 Mar 2008 Posts: 452 Location: London, England

Make model?

piaptk · Joined: 25 Jan 2008 Posts: 118

Simon · Joined: 05 Mar 2008 Posts: 452 Location: London, England

Sorry I did not see it in the other post
_________________
Happy to learn something new.
Wanted: Stylus for Presto head, Mono heads Grampian, Fairchild, Presto, Fairchild 740 lathe, Presto 8n, 8d 8dg or Neumann AM31 or A131, Presto, Rek O Kut or wot ever recording Amps, PM me what you have for sale.

piaptk · Joined: 25 Jan 2008 Posts: 118

piaptk · Joined: 25 Jan 2008 Posts: 118

I bought one of those Line level to Phono input attenuaters, and in the 3 min I spent on it, I couldn't get it to work at all... Signal goes in, but doesn't come out. But I was several beers deep in the evening and didn't spend a lot of time trying to figure out what the problem was. I do know that is significantly drops the input signal, and since my amp is already running at 7, Id rather find another way around this problem.

Would a 31 band eq be capable of approximating the riaa curve? I haven't looked at one up close so don't know if it has the correct frequencies.

piaptk · Joined: 25 Jan 2008 Posts: 118

Nevermind, I think I found the answer in another thread... So, from what I'm reading elsewhere, it is just as effective, if not more so, to use an eq and experiement to find the appropriate equalization for your particular cutter head than it is to build or buy an riaa attenuator. Am I incorrect in this thinking? Sorry for all the nube questions, but I have limited electronics knowledge coupled with unbridaled enthusiam for learning this craft!

Simon · Joined: 05 Mar 2008 Posts: 452 Location: London, England

piaptk

If you could put a link into your post that would be great

Wink

_________________
Happy to learn something new.
Wanted: Stylus for Presto head, Mono heads Grampian, Fairchild, Presto, Fairchild 740 lathe, Presto 8n, 8d 8dg or Neumann AM31 or A131, Presto, Rek O Kut or wot ever recording Amps, PM me what you have for sale.

piaptk · Joined: 25 Jan 2008 Posts: 118

markrob · Joined: 28 Nov 2007 Posts: 161 Location: Philadelphia Area

Hi,

The device has a large insertion loss so you may need a good deal up makeup gain to get any useful signal out. I think you would have a hard time creating the curve with a 1/3 octave graphic EQ given that you need about 40 db of total boost over the audio range (see Flo's plot earlier in this thread). Most EQ's only give 12-15 db of cut or boost. Better to use the EQ to compensate for any other errors in the signal chain.

Also note if you are using a Presto head, the device you have is wrong. The 500 hz turnover is built into the head providing if you have the correct series resisitor connected. In ths case, you could get away using the EQ, since you don't need as much total boost/cut.

Mark

piaptk · Joined: 25 Jan 2008 Posts: 118

markrob · Joined: 28 Nov 2007 Posts: 161 Location: Philadelphia Area

Hi,

Partly. The high freq's still need a boost and there is a low freq boost below 50hz. That might not matter too much. IIRC, you need about 14 db of boost at 10Khz with the rise begining at 2125Hz. You should be able to come close to that with a 1/3 octave EQ. You have to add a resisitor in series with the head to get the low freq cut correct. The 1-C was out before the RIAA became standard. I think the value they originally used is for a 250Hz turnover, so youy may need to adjust it a bit to get hings correct. The value depends on the head impedance. Do you know what type your head is? If you do any computer based DAW work and can use VST plugins, I have one I created for the Presto. PM me with your email and I'll send it to you to try.

Mark

yann de Kéroullas · Joined: 01 Jun 2009 Posts: 30 Location: barcelona

Just finish a super simple Flozky riaa encoder with a srpp gain stage and ... sounds nice !
I plugged it directly in the feedback / mod mixer of the sal

Easy to build using the SRPP gain stage of the Gyraf pultec clone , just changing the pultec filter by the Flozky super simple RIAA encoder
many thanks !

Yann