# Vivitar 283 mod (Variable Power)



## Sark (Jan 16, 2009)

Hi all.

Anyone made their own Vari-Power module for this unit. I just want to know whever to use a logarithmic, or linear track pot.

Cheers

Sark​


----------



## JerryPH (Jan 16, 2009)

Doesn't the Vivitar 283 already have a variable power pot integrated?






This is a 25+ year old flash... you will not find many that own this unit,much less modify them.


----------



## chrisburke (Jan 16, 2009)

i havent done it,  but a simple google search returned this  "With a standard 250k linear taper pot, the pot will go from 0-250k smoothly,"

heres a link to what i was reading:
Modding the Vivitar 283 - Canon Digital Photography Forums


----------



## JerryPH (Jan 16, 2009)

Your google has to be different from mine, I could not find anything... lol.

I was wondering why... I thought it was becuase it maybe did not have variable power, which was not the case, it just likely doesn't have "infinitely variable" adjustment settings.


----------



## Sark (Jan 16, 2009)

Jerry...This is a very popular unit and they're still making them in China today believe. The 285 has Variable manual output, but the 283 has a seperate plug in unit...that is over priced and not too well made (I've owned one). Modifications are also quite common.

I asked because the resistance for stopping down is non-linear, but the mods I've found seem to be linear pots, or they don't mention the tracking. I was really just wondering if anyone with any experience had used a logarithmic pot.

Chris...Thanks for the link. I hadn't found that one.

Cheers

Sark


----------



## chrisburke (Jan 16, 2009)

JerryPH said:


> Your google has to be different from mine, I could not find anything... lol.



i tend to include as much info as possible in my searches.. for this one I searched 

"Vivitar 283 mod Variable Power logarithmic, or linear track pot"

and that link i provided was the very first result


----------



## JerryPH (Jan 16, 2009)

Sark said:


> Jerry...This is a very popular unit and they're still making them in China today believe.



Yup, you are right... around $50 on the net here and there. 



Sark said:


> The 285 has Variable manual output, but the 283 has a seperate plug in unit...that is over priced and not too well made (I've owned one). Modifications are also quite common.


Ah, so my pic of the 283 above with the adjustment knob is incorrect?  That's the one that I found was going for $50.

I own a 285HS and its not "infinitely variable" either.  full, 3/4, 1/2 and 1/8th are the only settings (if I recall correctly).



Sark said:


> I asked because the resistance for stopping down is non-linear, but the mods I've found seem to be linear pots, or they don't mention the tracking. I was really just wondering if anyone with any experience had used a logarithmic pot.



Sorry that I was not able to get you the answer you were looking for.  Chris found it, FTW.


----------



## Sark (Jan 17, 2009)

JerryPH said:


> Sorry that I was not able to get you the answer you were looking for. Chris found it, FTW.


 
Always happy for the input.... There was no link to the unit you found, but the 283 has a removable adjustable thyristor on the front that controls the light output depending on the aperture you wish to choose (_Vivitar's own vari-power module replaces this_). Not sure how the 285's work. I guess the limited manual control of the 285 is why modding the 283 is not uncommon.

Finally, for those interested. A little more delving on Google suggests a logarithmic track is the way to go. Also a 100K switched pot gives full output when off, and variable ...from about 3/4 power... when on...A better option than a 250K pot for those who still want full power. This is the option I'll choose.

Thanks again.

Sark


----------



## RyanLilly (Jan 17, 2009)

I would avoid logarithmic pots, the vast majority of log pots are not actually log, they are to linear sections put together, and the taper will not seem right when you adjust the power.

Adding a resister across the ground and output of a linear pot  will give a more logarithmic response than a so called log pot.

Here is a link. This is for a volume control, but the same circuit should apply for this project.

ESP - A Better Volume Control

Here is a link to the main page, there is some good stuff here if you are into DIY audio, and Audio Theory. 

Elliott Sound Products - The Audio Pages (Main Index)


----------



## Sark (Jan 20, 2009)

RyanLilly said:


> I would avoid logarithmic pots, the vast majority of log pots are not actually log, they are to linear sections put together, and the taper will not seem right when you adjust the power.
> 
> Adding a resister across the ground and output of a linear pot will give a more logarithmic response than a so called log pot.
> 
> ...


 
An interesting article. Whilst it functions as a logarithmic pot for audio, I'm curious how this would relate to the 283. The example curve shows the affect on volume but does not quote resistance values throughout the rotation range. As it is shown as an alternative, I'm guessing it must approximate a standard 100K log pot, which could be worth investigating.

The problem with the 283 is that, full power is about 250K, half power (-1 stop) drops to about 80K, and between -3 to -8 stops down there is a difference of just 18K.
A 100K switched pot enables full power without wasting rotation on that first stop, but without some kind of non linear resistance the lower end would be very crammed.

I had originally considered Charles Krebs approach... Fixed resistors on a rotary switch...This could offer -6 stops in half stop increments on a 12 pole switch, but I'm not sure if I could produce it small enough to fit on the front of the 283. I've got sensor cords for my 283's, but I'd prefer to be able to avoid using these.

I might just try metering the example linked and see how the values are spread. I'll post back here when I've got something up and running. 

Thanks for the input, it's appreciated.

Sark


----------

