Looking to re-tune an OSC from a RITM-2

[zgogor]

Hi all,
let me present myself as a brand new human on this forum.
I'm Igor Bolender, from Paris/France.
I'm a french producer and I play vintage synths on stage with my band called Pamela Hute ( pamelahute.com).

I would like to use an old RITM-2 on stage but it is out of tune ( 5, 8 % approx ...) , even with the fine Pitch access, it is not possible to tune it correctly, it is too low ...

I found the scheme on the cool ruskeys webSite but I am not able to find how to retune the main OSC of this synth.

Is there someone who can point me on the right direction and give me some advise ?

here is some scheme and info about the RITM-2 :
http://www.ruskeys.net/eng/base/ritm2.php
scheme pict of the electrical board available but in Russian , I don't read Russian, I just drink vodka

thank you for your help

zGo

[Maschinengeist]

Didn't know those schematics were online... good to know. I don't speak russian either but I will try to help during the weekend. Don't hold your breath, I already got a lot on my plate.

[deeplodok]

Hi, I also had this problem and it was discussed on that ruskeys forum in russian, so I'll try give you an advice.
First of all you need to chek the VT1 chip, is it hot? it makes a temperature stability for vco and if it is not hot it is impossible to tune the synth properly.
You can turn R5 slowly and check does it affects a temperature or tune? if tune goes up while turning R5 and the VT1 is getting hot then it seems that things go right way, but you need to do this slowly and be carefull not to burn the chip (50-60С is a perfect temperature for it) if the temperature of the chip doesn't affects probably it's dead.. ca3046 with bended up pins can replace it (cause it has a mirror pin placement to the K198HT1)

when the chip is already hot try this:
While pushing keys through an octave turn R18 to tune a perfect octave on keyboard - and after that turn R193 to tune the perfect octave for the octave shift switch on panel.
also I strongly reccomend you to replace all electrolitic caps for the newer quality ones.
this helped mine, hope it would work for you too.

[zgogor]

Deeplodok, I will try what you explain !
I just hope to be able to do it
Can you point me where is the VT1 ? I can see written VT1 on the schematic but without any logo design printed instead of the others VT ( I can see clearly VT5 ,6,7,8,9 etc... but the number 1 ???


how can I thank you !!!!!

Igor

[deeplodok]

VT1 can be seen clearly in the left part of this assembling pic http://www.ruskeys.net/pasp/ritm2/c/ritmcxem2.jpg
chip mark is K198HT1("А" or "Б" in the end)
but I may suppose that if you already have a tune wich is not correct at 5, 8 % approx and not floatig with time(this means that the temp. stability is fine), then you just need to do preciese tuning with R18 and R193.

[zgogor]

in 2010 the ritm -2 will be alive again

big thanks !

Igor

[zgogor]

hello everybody !
Some news about the re-tune of the RITM-2.
First, it seems that there is 2 different kind of RITM-2, a black one and a metal one.
Mine is black.
@Deeplodok : there is no CHipset VT-1 on the board of the Black version of the RITM-2, well, on mine... it looks like it is a prototype version !!

To correctly tune the machine, I need to know the tuning protocole they used, like for the MiniMoog who has to be tune from the F .

The RITM-2 schematic on the web is not the same than mine !! this is why he took me so long but I'm on it again ...

If someone can send me a pic of the inside board circuit it will help me A LOT !!! ( igor@pamelahute.com)
I will keep you posted.
ZGO

[vicd]

Hi, I also had this problem and it was discussed on that ruskeys forum in russian, so I'll try give you an advice.
First of all you need to chek the VT1 chip, is it hot? it makes a temperature stability for vco and if it is not hot it is impossible to tune the synth properly.
You can turn R5 slowly and check does it affects a temperature or tune? if tune goes up while turning R5 and the VT1 is getting hot then it seems that things go right way, but you need to do this slowly and be carefull not to burn the chip (50-60С is a perfect temperature for it) if the temperature of the chip doesn't affects probably it's dead.. ca3046 with bended up pins can replace it (cause it has a mirror pin placement to the K198HT1)

when the chip is already hot try this:
While pushing keys through an octave turn R18 to tune a perfect octave on keyboard - and after that turn R193 to tune the perfect octave for the octave shift switch on panel.
also I strongly reccomend you to replace all electrolitic caps for the newer quality ones.
this helped mine, hope it would work for you too.

(Just my 2c, even if your physical layout is different to the one on http://www.ruskeys.net/pasp/ritm2/c/ritmcxem2.jpg )

According to the schematics at http://www.ruskeys.net/pasp/ritm2/c/ritmcxem1.jpg, I'd start from checking the +13V and -13V voltages that should be coming out of the PSU. If any of these are wrong, it's a good reason to recap the PSU (at least the "final" filters C1 and C5, maybe also the entry ones, C2 and C6), and then retune the output voltages using trimpots R11 and R24.

Next I would turn to the obvious trimpot R1, which is clearly labeled as responsible for frequency adjustment. Per the scheme, it looks it provides a reference voltage sitting between -13V and +13V rails - hence the importance of having correct voltages on those. Think of R1 as a voltage divider - it does essentially the same as R103 (which is the front-panel frequency adjustment pot), but R1 has just more effect, as it drives the control line through a lesser buffer resistance.

Then proceed as deeplodok recommended above, and don't forget you also have the R41 for fine-tuning the higher octaves.

Here's your image with some added clues...

Image resized to 24% of its original size [2500 x 1530]