Fenderizer (found this schematic on the net)

[newbiediy]

Found this schematic while browsing. Apparently it was made by a jazz player named Mark Smart (http://www.marksmart.net/gearhack/fenderizer/fenderizer.htm).
He said err.. wrote that it's a Fender Stage 160 preamp in a pedal. No distortion. Just Fender clean sound.
Thought I'd just share it here. Any comments would be appreciated.

Note: I haven't build it yet. So please don't ask me how it sounds.

[J M Fahey]

*Looks* similar to the original one, (didn't check part by part though) and is roughly the same used in most modern SS Fenders, so it should sound the same as any of them.

Interesting for a clean sound.

Should drive any normal SS power asmp.

[Roly]

Corrected link;

http://www.marksmart.net/gearhack/fenderizer/fenderizer.html

errr ... um ... I'm at a bit of a loss to know what to make of the text that goes with this, but if you want to add some EQ and level control to your chain...


Some observations; using a split 9V rail gives very little signal headroom and I would personally be more inclined to use two 9V batteries for +/-9V supplies.

He comments that the true bypass switching isn't silent, and it's not hard to see why - there is no DC tie down resistor at the input, allowing the voltage on C1 to wander where it likes.  A 1Meg from R1 to the ring of J2 should fix that.

Some of the resistor values are right off the wall, from the 0.5% E192 range, 511k, 182k, 27.5k, 6.98k, etc.  Standard E12 10% values should be quite sufficient.

[J M Fahey]

Agree and add: the powering and grounding is WRONG.
He *calls* it "split supply" or "+/-4.5V" powered circuit but it is NOT.

Of course it will POP ... big way !!!
The ground is tied to the -4.5V rail , just look at the input and output jacks, what is the sleeve connected to?

Plus if he uses this pedal together with others, fed from the same wall wart, the others will short the -4.5V as soon as their grounds touch .... which will happen as soon as you connect them to each other with shielded cable .... *or* ground won't actually connect but will be separated by caps, pick one, none good.

This is one of those circuits which may simulate well (because the simulator knows nothing about the case it lives in, or shielding or The Rest Of The World) but on actual construction is a nightmare.

In a nutshell, switching in/out (which he claims he never does ) , besides the audio signal, applies or removes 4.5 V DC mixed with it.

REALLY, this is a conventional dual rail circuit, where input/output "sleeve" contact is actual Ground, (and decoupling/NFB/signal in general should be referred to it), what he calls "ground" is actually the +4.5V rail (which at most can be called an "artificial" ground, which exactly means it's not a real one) and a +9V rail (which he calls +4.5V) .

Let's have something clear: soundwise it must be good, but as Roly suggested  it deserves at least 2 9V batteries to have real +/- rails and spending 50 cents in an actual SPDT switch to switch both rails on/off at the same time.

I think GGG or DIY stompbox shows how to switch 2 batteries with a single jack contact, but it involves adding 1 or 2 extra transistors.
I'm quoting out of memory, of course.

EDIT: to newbiediy: thanks for posting an interesting circuit; if you actually start to build it, just ask here  

[Roly]

I think the reason that case is -ve rather than signal ground is mainly due to the way the battery is switched.  One of the stereo TRS sockets I commonly use is not only isolated from the mounting/case, it is also blessed with two change-over contacts that are isolated from everything else, so if you wanted to switch two batteries for +/-ve supplies one of these would be even easier than the electronic switching solution.

You can still use external power, but an AC plugpack and suitable rectifier would be the way to go IMO, e.g.;



This one was actually for a stomp with rechargable batteries, but I hope you get the essential idea.

I get a bit suspicious when I see high tolerance components specified where they aren't needed because it is often an indication that the designer didn't actually know what they were doing, didn't know where precision matters and where it's spurious accuracy that serves no useful purpose (and may actually make life needlessly more difficult).  When you see this combined with a cockup, such as the power supply here, then that pretty well seals it.

The main implication is that you can drop any assumption that the designer was being really cunning if/where they do something that you don't understand, and assume they were pretty well clueless and that you are free to modify things to be more sensible.

[newbiediy]

I've already suspected the power supply section, since I've thought of a similar scheme, but fahey told me that it's wrong. Using it as an amp's preamp with ±9v would be ok, I guess.

[phatt]

Hey newbiediy, What about running it from single supply? Not that hard to tweak.
Then it can run from any old wall wart from 12 ~ 30 VDC.
If you need help then just ask. :tu:
The circuit reminds me of my old Nobels SST it had two types of cab sims built in.
Also (speaking from experience) You might need a buffer on the output as a similar circuit had me head scratching for ages until I worked it out. :grr
Phil.