After VDDmod can't go lower than VDD 1.8V

[Nicowico]

Before I did a VDDmod my VDD was 1.61V. After I did the VDDmod with an adjustable pot a played a little bit with the settings. I tried 1.85V and max. 1.90V and now I can't set my VDD lower than 1.80V.

[muzz]

Do you still have the resistor on that chip?

[Nicowico]

Yep

[muzz]

Well you still have the mod on it, even if you are using a variable resistor, the lowest I can go with a 1K trimmer is 1.74 vdd.
The only way to get it back to stock is to take off the resistor.

[Nicowico]

Strange, you can go up, but can't go down. I learn every day. Thanks

[muzz]

NP

[qwerty57]

use a 10k VR then and you'll be able to go back to about 1.66v..

[muzz]

Iwould NOT suggest using a 10K for any reason myself........ too difficult to adjust PROPERLY <1K ( which is where the voltage increase takes place ) .
But to each his own there..... I understand what you are saying though J.

[Holst]

Absolutely,

if you try using a 10k even a high turn cermet you much more likely to accidentally dial in 2.5v and blow your board.

[nfrenay]

If you want to be able to enable/disable the mod, add a switch in series with the potentiometer. It should work.

Just to emphatise this: don't use a 10K VR! The "usable" part will be extremely sensitive and you'll probably smoke your board.

I think if I had a 8RDA+ and decided to mod it, I would use the following components in series:
* Resistor (470 ohms or a little less)
* Potentiometer 1K or something near this value (Potentiometer = VR)
* Switch (so that you can enable/disable the mod)


The resistor would limit the max voltage for the mod, the potentiometer would be the adjustment (of course) and the switch to enable/disable the mod.

What do you think ?

Shouldn't be much difficult from what you are doing.

[muzz]

If you are going to add a switch in series, I would suggest shutting down the system B4 switching it....... otherwise you will have a sharp current surge taking place, which could EASILY damage the board faster than higher vdd.

[nfrenay]

I'm not very sure if there would be such a current, but there is a possibility.

[muzz]

It doesn't have to be ALOT of current, those IC's are not "power" types , but more of a "signal" type(control- low level).
They are not designed with heavy power switching in mind.
You may get away with it, but definitely not recommended for the above reason.

They will not take the beating a power fet will.

[muzz]

This is the same reason we suggest using 15 ( or any multiturn VR) turn VR's...... make the transition slow and steady, with no spikes.
Rich Ba5tard showed what happens when you go too fast....... that IC burnt up on him.

[Nicowico]

Originally posted by nfrenay


I think if I had a 8RDA+ and decided to mod it, I would use the following components in series:
* Resistor (470 ohms or a little less)
* Potentiometer 1K or something near this value (Potentiometer = VR)
* Switch (so that you can enable/disable the mod)

I'm not that technical, but I know what you mean. I have seen a scheme about it somewhere. Thanks

[nfrenay]

I guess it can happen, so you guys be advised .

If you do it, only change the switch while powered off... Or you can only use the resistor and the potentiometer, so the transition is slow, instead of a peak (switch).

[muzz]

nfrenay I wasn't attacking you or your thoughts on the matter, if you see it that way , then I apologize for that.

I actually think a switch is a good idea if you want to ( for whatever reason ) shut it off........ I just wanted folks to be aware of what CAN ( not guaranteed) easily happen if they switch it on/off while powered.
That is all.

[nfrenay]

Not at all muzz!

Sorry if it looked that way, but English isn't my native language, so sometimes I can write things wrongly .

[qwerty57]

well i use 10k VRs and i find it works quiet well.

[muzz]

I never said it wouldn't work J , I just said it is not ideal because of the area you have to play with at the end of the scale....... You probably measured it B4 hand ( which alot of folks will forget to do).
Not worth the risk IMO when something that is much more suitable cost $2.50... when you weigh that against the board and Vcard cost ( see Rich Ba5tard - and he isn't the only one I'm sure) I personally think the spread out VR to be the better choice.
I say these things because there was a time I used to be a noob when it came to things like VR's ( not saying anyone here is btw), so I feel it is worth throwing out some info gleaned from experience, and if it saves 1 persons gear, then I feel it was worth it.
I could use a 10K, I just don't see the point is all.
Like I said earlier in this thread....... To each his own.

It's all good Mon:beer: