Using ROG preamp with higher voltage

[potul]

Hi

I'm in the process of building a small chipamp using a kit I got some time ago in ebay, and I would like to add some spice to it by adding some sort of preamp. I was thinkning on a ROG Eighteen, or a similar one. As simple as possible.

I want to run my amp at 12 or 18v, so my question is, will the ROG Eighteen handle the voltage? Will I have to modify something in the circuit or will it work as is?

Mat

[anotherjim]

I don't know, but it wouldn't be hard to run the preamp from a 78L09 regulator, so long at the amp supply isn't less than 12v.
I'd do it like that. It would make it easier for the pre-amp to clip without the power-amp clipping.

[J0K3RX]

Should be fine as long as your caps are rated for about 25v or more... There is really only the 100uF filter cap that I see on the schematic that needs to be considered but, I personally don't even buy anything lower than at least 25v electrolytics period. Running at 18v might give you a little more head room..

[potul]

Great, I will try with 12v then and see how it performs.

Thanks for the info.

Mat

[potul]

One doubt.... if I change the supply voltage, will I have to re-bias the FETs?

Mat

[antonis]

No, as long as you use single power supply...

Their Gates are biased at GND and their Drains are trimmed via Drain variable resistors...

If they already are trimmed properly you shouldn't have to re-bias them..
(but you can easily check for new voltages i.e. 6V instead of 4.5V & 9.3V instead of 7V..)

[sajy_ho]

In theory if you want to use any of ROG fet circuits with different supply voltages, you should adjust drain voltages in proportion to the original design to get similar results.
For example in Eighteen, you should adjust Q1 and Q3 drains to (4.5/9) or half of your supply voltage, so in your case it will equal to 6V. Similarly Q3 should be adjusted to around 9V at drain.
In practice it won't make a huge difference, because jfets are so incosistent and everyone of them will bias differently at the same voltage...
The only thing you should expect from using jfets with higher supply is slightly higher gain.

[Gus]

You need to think about the gate to drain voltage.

[potul]

thanks all, this clarified a lot of things

Now I only need to find the time to build it.

Mat