Street amp build log

[Ben79]

So after some help from some of the guys here, I've started putting together a street guitar rig.

The pictures should explain it all except that I'm planning a few effects to go in that box to use up some of those 'pot holes'.

A 14.5v RC Car battery is the power and that goes straight to the Tiny Giant.  There's a 9v regulator for the effects on that bit of tag board.

The enclosure was a 1970s Park Mini Mixer which I bought for £15 years ago and probably should have kept as it was and sold to a collector but I think its new life will be much more interesting.

The effect roster is so far:

Green Ringer

NPN Rangemaster w/input cap switch for full frequency boost

Tim Escobedo Tripple Fuzz (built one for someone last week and I loved it)

Axis Face w/bias pot mod

Systech Harmonic Energiser w/Mark Hammer gain and clipping diodes mod and expression pedal control

I think that should cover a pretty wide palette of nasty fuzz tones which is what I tend toward if I'm not playing clean.

To control the effect order I'm gonna make a patch bay in the back of the unit.  That way any circuit will be accessible if I just want to use the effects or add external pedals into the chain.

Footswitches will have to be placed as best I can to avoid stomping on the pots.







I ordered the wrong kind of banana sockets so I'm aware that as it stands, the battery will explode if connected!

Any words of advice gladly received before I venture any further with it.

[Ben79]

Effects boards are complete save transistor and diode selection...

Top left is Axis Face
Top right is Rangeblaster (that old electro had the lowest ESR reading of all my 47uf caps)
Bottom left is Tripple Fuzz
Bottom right is Green Ringer with weird jumpers

On its own the Harmonic Energizer





Keeps me motivated to post up here so I will continue even though it's probably not interesting to anyone.

[bluebunny]

You just keep on posting, Ben.  We're interested.  And we're suckers for pictures.   

[stallik]

And we'd like to hear the result too if possible 

[duck_arse]

we like looking at pics best when we don't have to ask for them.

[Ben79]

   Thanks guys!

Here's today's efforts.

Not a huge leap but the patchbay on the backside is in and I've put in a few cables to see how it goes.  Works dandy.

I worked out the pot and switch layout for the fascia.  Input and output for the TG amp still need to go in.  I've got a nice jewel light cover for the power indicator and I'm gonna put LEDs by the footswitches otherwise I think I'll get confused about which are engaged.

The Green Ringer footswitch will go right on top since it has no other control and I need the space.

I should mention that this is largely built from salvaged/secondhand parts.  That's why a lot of those caps are really old and big.  Only new stuff is the silicon and the hole boards.  The bracket for the amp came from a Farfisa organ.  The heatsink was ripped out of a PC on the street and hacksawed to fit.  The jack sockets mostly came from old audio equipment I found at the dump.

[duck_arse]

whack-a-micro-mole game?

[Ben79]

Regulator and paint job beginnings....tasteful isn't really my thing and I recently found a load of paint on the street so this is getting a big dose of colour.

[Ben79]

Enclosure painting....









Boards are all tested and the Axis Fuzz is the only one presenting an issue - dead silent with weird voltages but the resistances all check out good.  There's a hole in the control plate that shouldn't be there that needs patching up somehow and I need to figure out where the in and out sockets for the amp will be located as well as power switches for the amp and effects. 

Given this thing will house a lipo battery that can catch fire if shorted - there ought to be some kind of protection against that.  A diode?  A fuse?  It's a new thing for me, any ideas for this appreciated

[Ben79]

Some drilling, fixing, affixing and considering....

[Ben79]

After a bit of a hiatus I've returned to this project.

The Tiny Giant is wired in and works nicely.

I wired in the first effect, a Green Ringer today and it worked (the circuit had already been tested) but with considerable noise.  I soldered in a 100uf across the 9v rails (after the DC step down circuit) and a 100ohm in series with the Green Ringer's +9V.  The lower frequency noise was gone but still some high pitch noise/whistle, not VERY loud but pretty nasty, sounds like a boiling kettle.

I wondered if it might be something to do with cross talk/interference from the amp since the circuits are close together, so I tried it while the amp was receiving no power (it has its own power switch).  This made no difference so I'm now thinking perhaps the cheap dc-dc step down circuit isn't up to the job for audio.

It's one of these...

http://www.ebay.co.uk/itm/MP1584-3A-DC-DC-Buck-Adjustable-Converter-Step-Down-Power-Supply-like-LM2596-/131784216464?hash=item1eaef38f90:g:13kAAOSwNSxU1lcu

Any ideas folks?

Thanks for any help.

[anotherjim]

Your extra cap goes AFTER the extra resistor in the 9v + feed. The GR doesn't, I think, have any power supply filtering since it was intended originally only with battery power. If ALL your pedal circuits have their own RC filter on the power supplies, then you should be good. Generally, 100R and 47-100uF should be plenty for any of your FX boards, but if they already have an RC power filter, you don't need to add more for that board.....except.....
....with the switching converter there, I would add a 100nF ceramic cap on the 9v of each FX circuit since this will clean up any high frequency noise from the PSU better than the electrolytic alone can. While your at it, the chip amp should have one too if it don't already.

Don't forget to "star" connect the power grounds to the various boards. A tag strip bolted to the chassis with a wire soldered across all the tags makes a good star distribution, though it don't look like a star. A brass stud bolted in the chassis with solder tags - lots of them - slipped over the stud with spacing nuts, totem pole style, makes a proper star ground.

[Ben79]

Thanks Jim, much appreciated.

I forgot to mention I added a 0.1uf across the rails as well as the 100uF but not, as you say, after the 100ohm resistor so I will rectify that and see what happens.  I'm hoping this little converter can do the job since it's all wired and bolted in nicely now.

I've always interpreted star ground as meaning 'connect all the grounds together but with only one chassis connection'.  The ground connection from each circuit will be made like in a normal pedal when the input socket receives a jack.  I've run a wire along the 'sleeve' terminals of all input and output jacks and that goes to the ground rail on the tag board which has one wire to the chassis.

Is it ok for the battery to share a ground with the circuit post 9v regulation?

[anotherjim]

For the battery, I'd give priority to having short/thick connections between it and the amp and regulator. It's quite ok if the battery neg finds chassis ground from it's connection at the amp.

[PRR]

> thinking perhaps the cheap dc-dc

To step a very small current from 14V to 9V? When there is a much larger current (power amp) in the box??

I'd try a few-K resistor followed by 100uFd. That may drop you to 9V, or near-enuff as no-difference.

If you know the "9V" is critical, a analog regulator will do this.

Either non-switcher technique "wastes heat". But 5V drop at say 10mA is 0.050W of waste heat. Meanwhile there is 10W-30W of power going to the power amp. I don't think you will notice if this is 30.05 Watts.

FWIW, too late now... if true battery efficiency is vital, you can buy Class D power amps for 14V which will give much better all-day efficiency than an AB power amp. AB can be 78$ efficient at FULL Sine, but drops to much lower efficiency at lower output levels where speech/music is usually played. The difference is not critical in a car, where the TG got its chip from, but battery-mavens are moving to D for the better battery life. That will make far more difference than fancy-trick with your small stages.

[phaeton]

Class D power amps

Just an aside, Class D is amazing technology, IMHO.


Back on point, Ben79 says "tasteful isn't really my thing" but I think your paint scheme is ghetto-fab! 

Sometimes I myself try to make things look real nice and professional, and the rest of the time I just make them goofy.  I'm almost never unhappy with the latter.

[Ben79]

Thanks Phaeton, I dig the way it's turned out.

I moved the 100uF and .1uF to after the 100ohm and discovered by voltage converter was only putting out 1.2 volts.  Thought maybe I had knocked something so I readjusted it and no...seems to be goosed.  I remembered I had a couple of 7809 regulators so I'm gonna try one of those instead and hopefully the noisy power issues will be ameliorated.

[Ben79]

I'm wondering what value caps to use...2 x 100uf electros and a .1uf ceramic?

[Ben79]

The datasheet is here...

http://www.mouser.com/ds/2/294/NJM7800-196861.pdf

...but it doesn't seem to say.

[anotherjim]

They will do fine.

If there's the smallest chance you can connect the battery wrong way around, then a main series diode, maybe 3A rated, should go between the battery + connection and everything else. Then you don't need another diode just to protect the regulator.