Mad Professor Ruby Red Booster

Barcode · Post by **Barcode** » 27 May 2011, 00:24

Okay, my layout will likely use J201's so I'll note the difference in the project file

coldcraft · Post by **coldcraft** » 27 May 2011, 01:31

not that I expected it to, but I breadboarded this with 2N5457s and it does make sound, but it doesn't sound good at all. not all JFETs will bias with those resistors so keep that in mind. I wonder if MP does JFET selection or if there's something special about the 2n5952

Barcode · Post by **Barcode** » 27 May 2011, 05:52

I assume we are shooting for a bias point of 4.5ish?

WhiteKeyHole · Post by **WhiteKeyHole** » 27 May 2011, 06:00

Shoot for what sounds good but I would guess that the unit has around 6.5V at the drains.

WhiteKeyHole · Post by **WhiteKeyHole** » 31 May 2011, 03:42

Hm, figured they would have biased up similarly to the SBEQ.

To avoid confusion, the drain and source voltages should be swapped.

Barcode · Post by **Barcode** » 31 May 2011, 21:58

Ah, so it does seem to be biased at half rail. Okay, I may include trimmers in my layout jsut to be safe, or I'll do two versions.

WhiteKeyHole · Post by **WhiteKeyHole** » 01 Jun 2011, 15:34

I'd check around the Treble control first and foremost. Also, resistor values can be tricky due to lighting.

Barcode · Post by **Barcode** » 01 Jun 2011, 17:58

It could also be a biasing issue. If the schem is accurate in that 2n5952 fets were used, and the stock unit is showing source voltages around half of supply, then your source voltages are pretty high. You could need some resistor tweaking.

WhiteKeyHole · Post by **WhiteKeyHole** » 02 Jun 2011, 02:07

As Barcode said, try adjusting the bias (through the source resistors) for roughly Vcc/2. That could definitely account for the 25%.

I'd check R4 and R14, though, as those were the resistors I was most unclear about.

x-tn · Post by **x-tn** » 03 Jun 2011, 13:58

For C14 and C5, what would be the reason using electrolytics instead of film? Any useful effect?

Barcode · Post by **Barcode** » 03 Jun 2011, 15:52

I don't see any functional reason for it, the polarity is not functional in the design so you could just as easily use a film there. .47uF is a pretty damn big cap though in most non-polarized configurations. Most likely the reasoning is not to have two caps take up half the board

WhiteKeyHole · Post by **WhiteKeyHole** » 03 Jun 2011, 19:29

I'm not sure about some of those values. At the right of the board, the resistor you've notated as 47k (in the black box), clearly has the markings for 1M. Also on the right, the "470k" is marked as 470R. Could you double check those, please? Thank you.

WhiteKeyHole · Post by **WhiteKeyHole** » 04 Jun 2011, 00:06

Updated: Corrected resistor values. No circuit/structural changes.

IvIark · Post by **IvIark** » 22 Feb 2012, 00:27

Here's a vero layout for it: