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Sunn SL260 Help Needed With Pot Orientation

Started by Tassieviking, October 10, 2021, 11:55:10 AM

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I am drawing up the Sunn SL260 into KiCad so I can make the preamp PCB for myself.
I have hit a roadblock as I cant work out the orientation of the Pots in the tone section
can someone please check and advice me how they should be mounted, ie, pin 1 on pots.
That's the Bass, Mid, Mid frequency, Treble pots.
I have also made some mods to the original circuit, power supply and foot switch circuit for reverb, do they look ok ?
Thank you for any help.
There are no stupid questions.
There are only stupid mistakes.


Pin 3 of your pot symbol appears to be the clockwise terminal, therefore, the Mid, Treble and Bass controls are backwards.


Thank you LoudThud for that information.
I don't suppose you would know the Dual Pot orientation in the variable frequency circuit for the Mid control, If I can't find out I could just leave the viper (leg2) disconnected, and then short it to the correct leg after i build it. The viper (leg2) has to be shorted to leg 1 or 3 of the pot.
Even better if someone could identify what kind of circuit it is so I can do some research on it, it has to be some kind of active notch filter I presume.
Again, thanks LoudThud for your help.
There are no stupid questions.
There are only stupid mistakes.


Hi Michael,
for info on the Sweep mid section just search for Parametic circuits.
Yours is a mid sweep circuit with a set low Q.
(Q is the width of the boost or cut)
For Q control you need an extra pot.
It looks like it sweeps form ~200hZ up to about 1,200hZ.

Info here; http://www.geofex.com/article_folders/eqs/paramet.htm

I just did a quick simulation of the tone section you posted and it's about a +/- 5~7db boost/cut at whatever freq is set.

Can I ask if you have used this Amp?
If not be aware there are a lot of pitfalls when one just goes straight into a build without at first Bread board testing to see if it actually does what it claims.

OK I'm no teck geek but I've spent 30 plus years building many amps/circuits and I can tell you the short cuts are the most painful learning curves. :'(

I bread board everything now which takes longer but you learn so much more and end up with a far better design. 8|

I have a bottom draw full of pcbs that seemed like a great idea at the time but ultimately ended up as land fill. but better to keep as spare parts. :tu:

If I find a circuit that looks promising then i break out the breadboard and test if it actually works ""Looong"" before I heat up the solder. ;)

Having just simmed the tone of the sun I'd be reluctant to go ahead as I question if it works as well as other circuits which may well prove far better. My best tone circuit design does a 30dB cut at 400hZ, while many parametric circuits can only achieve 15dB max.

Of course if this Sun circuit is *Exactly* what you want then disregard my ramblings. :dbtu:

Oh yeah I doubt the reverb is going to be stunning as it looks like the drive section will be too weak to give a strong reverb. I maybe wrong but I've built many reverb circuits and a lot of them are crap. :trouble :grr

If you want to get a better handle on Spring rev circuits it's hard to beat this page,
info here; https://sound-au.com/articles/reverb.htm
I use the Transformer circuit down the page,, I came up with this idea and Rod kindly perfected the Drive circuit.
Unlike a lot of rev circuits found on the net Rods basic Rev/mixer circuit worked as claimed.
hope it helps,, Phil.
ps judging by your handle I take you are in Tassie Au?


Thanks for all that info Phatt.
I definitely live in Tassie, where the Devils roam free. ( I have had them under the bedroom, makes you jump when they scream at night. )
I was born in Sweden but moved to Australia when I was 12, I still remember climbing on Viking rune-stones as a kid, they were all around the area where I lived.
I went back to Sweden in 1976 when I was 16 for a holiday, but it was still too bloody cold, stayed down under since then.

I am interested in solid state guitar amps off all kinds, I am going to order PCB's for Marshall Mosfet 3310 and Sunn Beta very soon and I just wanted another type of preamp for the order.
I order my PCB's from JLCPCB and find it better if I have a lot of different boards in one order, postage is the killer, but does not increase too much for more boards.

I like to stick circuits into KiCad and making circuit boards up for myself, I find it relaxing, I will have to learn the simulation bit soon in KiCad or some other software.
I don't have much experience in audio circuits, but been a sparky since 1980, mainly industrial maintenance repairing DC and AC drives and any other electronic boards that needed it to keep machinery running. My only tube experience was with high voltage spark testers checking insulation in cable manufacturing.

I have never seen a Sunn SL160 or SL260 in my life, but I might just have the preamp made by Xmas. (Just for fun)
I do love Rod's circuits and have looked at nearly all of them, I have read up on the reverb circuits on his page, but I will stick to what was original on the Sunn SL260 circuit.

Again, thank you for your help, I' gonna start reading up on what you mentioned now.
There are no stupid questions.
There are only stupid mistakes.