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Permalink Reply by Clark Rowden on October 23, 2015 at 11:08am

Most of the modules do have a volume control on them. Unfortunately, they are usually a "trim pot" soldered on to the board. The little blue thing with a white cap on top in the following module is the volume control:

http://www.mpja.com/LM386-200-Gain-Audio-Amplifier-Module/productin...

If you want an "off board" volume control, you have to carefully de-solder the trim pot and remove it then run wire leads to the potentiometer.

The pot you replace the trimmer with should be the same value as the trimmer (usually printed right on the part). Looking at the the replacement pot from the bottom and the "legs" pointing up, the leg on the far left will get the lead closest to the "IN" pin. The middle leg will go to the middle leg of the trimmer and obviously the far right leg will go to the last leg on the trimmer.

If your soldering iron is too hot and unwieldy, there's a chance you can fry the whole module board. If your serious about getting into this, I suggest that you get a good soldering station that has heat control. I recommend this one:

http://www.sra-solder.com/aoyue-469-60-watt-soldering-station

I've had my Aoyue 936 for several years know and I am very happy with it. Also get some "helping hands" similar to this:

http://www.mpja.com/Helping-Hands-with-35in-Lens-Large-Base/product...

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You can easily add an on off switch by simply putting a SPST (single pole, single throw) toggle switch between the "+" side of the battery and the "+" connection on the module board.

http://www.mpja.com/SPST-On-Off-Mini-Toggle-Switch/productinfo/3188...

Want a LED to light up with the power? That's simple too. After the switch (between the switch and the module) just put the LED running to circuit board's ground with a resistor in front of it. The resistor's value will depend on several factors but thankfully there is a calculator here:

http://led.linear1.org/1led.wiz

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Permalink Reply by Paul Craig on October 23, 2015 at 7:25pm

Mine wasn't a module. Board and parts. Wired and soldered myself with real pots.  C3 on the chart below shows a .1uf cap, some schematics show a 100nf. I used the 100nf, but I don't think there is much difference in the two.

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Permalink Reply by Clark Rowden on October 24, 2015 at 5:06am

I've built a few Rubys my self and your right, there is a real advantage to them as compared to a ready made module. For one thing, they sound better for guitar and using a socket for the IC (LM386) allows you to swap out different chips - especially that LM386N4 you mentioned. For another, Runoff groove lists a number of mods that can shape the tone in various ways (I like the Bassman mod).

On the FAQ's page at Runoffgrove.com they use to have a schematic for a Ruby amp with a Fetzer Valve in place of the input buffer but that is gone now and in it's stead is the following question and answer:

Can I use one of your FET-based distortions to drive my Ruby or Little Gem amp?

When placing any distortion circuit before a 386-based amp, you need to keep the output volume at the same level as the dry guitar signal. Otherwise, you'll overdrive the 386 and lose the character of the distortion.

http://www.runoffgroove.com/faq.html

I've built the Fetzer Valve as a pedal and it sounds great! But when I tried the Fetzer-Ruby that they had posted, I did run into the problem. I came up with a solution for it but only on paper... I never actually built it. That solution is a Fetzer Valve with a single knob tone control added on that - theoretically - can be used as an input buffer on any chip amp.

The idea is that the addition of the gain/tone controls allow you to tame the Fetzer Valve down while still providing the 2nd order harmonics. It probably wouldn't work as a stompbox (because of the tone control signal loss) unless you added another stage in front of it as in the ROG "Professor Tweed:

http://www.runoffgroove.com/professor.html

That tone control is the basic Fender tone used in it's early Tweed amps as documented on this page:

http://chasingtone.com/yourguitaramp/guide-to-single-knob-tone-cont...

Any way, should you want to try it, here is the schematic for it that I scrounged together along with a Fetzer-Ruby schematic that I never built. It should work "as is" with a supply voltage between +9 to +12 volts. If you use a lesser or greater voltage or use a different JFET, you'll probably need to use the calculator on ROG's Fetzer Valve page for the source resistor and cap values.

Attachments:

• Fetzer Valve Preamp for Chip Amps.png, 5 KB
• Fetzer-Ruby Amp.png, 6 KB

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Permalink Reply by Paul Craig on October 24, 2015 at 9:10am

Good to have those schematics, thanks for posting them.

The bassman mod is a good one, I did that on my dual chip Ruby amp and on a First Act 4watt amp I found on the curb and wired a surround sound subwoofer to for bass/acoustic guitar play. The sub sounded better than the little cheap speaker that came with it.

Anyway, I'll have to redraw and post a schematic of my dual chip ruby. Runs on a 9 volt walwart. 2 stages of volume and gain so you can double your gain. It's a gain MONSTER.

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Permalink Reply by Bob Clark on October 24, 2015 at 3:05pm

The only thing I have used to hack and make a amp with is a old small record player. keep all the electronic intact and take the wires of off the needle and solder them to a cord jack. You can use the original on/off switch and volume switch from the unit or wire them to another style if you like.     

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Permalink Reply by Paul Craig on November 5, 2015 at 11:14am

Here's that schematic for the dual chip Ruby-ish amp I made.

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