Slowing down a Magnavibe

[danielzink]

Hey All,

Can anyone give a hint as to slowing down a Magnavibe ?

It works great. Using an NSL opto and an ultrabright clear blue LED.

I did the resistor subs on the speed pot (2k2 dropped to 1k5 and 27k dropped to 10k).

Unfortunately - even at the slowest speed - it's still too fast.

I'm operating off this schemo:



Any help would be appreciated.

Thanks !

Dan

[jtn191]

According to Nicofx:

Omit the 27k across the speed pot and double the speed pot to 50k. Let me know how it goes!

[midwayfair]

REMOVE, don't REDUCE the 27k. You made the pot smaller -- less resistance = faster.

But there's a limit also set by R9 -- increase that as well. I'd try 15k there and 4.7k for r7.

If that's still too fast, it's time to look into increasing C5-C7 to 2.2uF.

If you want to get fancy, you can also use a dual gang 50k pot for the maximum possible speed range. Use a 4.7k for R7, remove R8, and replace R9 with a 4.7K + the other side of the dual gang.

[danielzink]

REMOVE, don't REDUCE the 27k. You made the pot smaller -- less resistance = faster.

But there's a limit also set by R9 -- increase that as well. I'd try 15k there and 4.7k for r7.

If that's still too fast, it's time to look into increasing C5-C7 to 2.2uF.

If you want to get fancy, you can also use a dual gang 50k pot for the maximum possible speed range. Use a 4.7k for R7, remove R8, and replace R9 with a 4.7K + the other side of the dual gang.

Yikes.

Okay.

Won't be going the dual pot route as this is in a 1590a and I don't want to go to all that hassle etc.

If I omit the 27k - should I leave the 1k5 in place or put it back to 2k2 ?

And - am I jumpering the connection that was the 27k ? (it looks to me like I would still need the connection ?)

I'll try the other mods and report back.

Thanks !

Dan

[danielzink]

bumping for clarification

[jtn191]

If I omit the 27k - should I leave the 1k5 in place or put it back to 2k2 ?

And - am I jumpering the connection that was the 27k ? (it looks to me like I would still need the connection ?)

I know that you wouldn't need to jumper the connection that was 27k. All that it is doing on the schematic is limiting the value of the speed pot to below 25k.

[lego4040]

Found this Magnavibe today by chance while looking for a project to build. I also seen that there almost was a pcb by Raulduke but that got nixed(understandable) Is the only way to do this on vero? I guess point to point is another option

[culturejam]

Found this Magnavibe today by chance while looking for a project to build. I also seen that there almost was a pcb by Raulduke but that got nixed(understandable)

What happened? Did somebody get all lawsuity?

[midwayfair]

Found this Magnavibe today by chance while looking for a project to build. I also seen that there almost was a pcb by Raulduke but that got nixed(understandable)

What happened? Did somebody get all lawsuity?

No, they politely asked him not to sell PCBs of the classic Escobedo DIY circuit they made minor alterations to. 

[lego4040]

Up and running, only needs a real enclosure and Bpots instead of A