Powering a Distortion Device With Phantom Power

[abbey road d enfer]

No, I'm thinking of running off a DC wall wart.

Since the circuit draws less than 1W, I woud use the 1W version. A 3W converter must operate with a load that draws at least 0.5-0.6W for correct operation.

 

[cpsmusic]

Since the circuit draws less than W, I woud use the 1W version. A 3W concerter must operate with a load that draw at least 0.5-0.6W for correct operation.

Thanks!

 

[cpsmusic]

So take a few minutes and think about what you really need. Do you need input and or output level controls? Is that going to require any additional buffering? You started out with a simple unbalanced circuit, and now have balanced input and output buffers. Most unbalanced gear uses different operating levels that balanced gear. Have you considered what you want your default input and output nominal levels and headroom to be? Where in that nominal input/output range do you want noticeable colouration/distortion to kick in? Do you want to control that strictly with the send levels of the upstream device and the input attenuation/make-up gain on the downstream device? Or do you want a gain control before and after the colour circuit so you can control the distortion level independent of the operating audio levels (kind of like the gain and master volume controls on a guitar amp)?

I've been thinking about this a bit more and I can see that your advice is right - the device would be more usable if it had Gain and Master controls. What would be the best way to add these?

Also, I've been thinking about adding a Dry/Wet control too - would runoffgroove's Splitter-Blend work for this?

Cheers!

 

[ccaudle]

the device would be more usable if it had Gain

Sorry, got distracted by day job stuff for a while and forgot to come back to this.
If it were me, and mind you it isn't, I'm not going to be using this, so you will need to decide how much trouble it is worth for you, but if it were me, I would treat the input like a low gain balanced microphone input, and use an instrumentation amp style device.
Back in the day the TI INA devices were the hot new thing for single chip mic amps, something like an INA103, INA163, or INA217, which basically just needs power supply, and a single resistor to set gain, and if the gain setting is left open circuit it is unity gain.
Besides the TI parts there are also Analog Devices and ThatCorp devices that are very similar.
Here is a page at ThatCorp that compares some of the different devices available:
Single chip mic amp device comparison

The output of all of those is a single ended signal driven by an op-amp style circuit, so you should be able to connect that to your JFET amplifier circuit at the "in" point.

and Master controls

At the output of the JFET colour circuit you have a single ended output. Assuming you don't want to use it directly, you should decide (or maybe measure from an existing board) whether the output is hot enough, and you always want to either use it directly or attenuate it, or if you might want to amplify the output in some cases.

I think in either case the most straight forward thing to do will be send the output of the circuit into a potentiometer, and take the output from the wiper into an op-amp buffer. Depending on whether you only want to attenuate or you also want to be able to amplify, use either a unity gain buffer, or add two resistors and have a fixed gain of a few dB, depending on how much you might want to amplify. Don't forget a resistor to ground at the non-inverting input if you keep the capacitor on the output of the JFET circuit. Actually it is better to keep DC out of a pot, so put the pot after the coupling capacitor, and the pot will also act as the DC bias path for the op-amp.
At that point you just make an impedance balanced output from the op-amp buffer output and you're done.

 

[abbey road d enfer]

I've been thinking about this a bit more and I can see that your advice is right - the device would be more usable if it had Gain and Master controls. What would be the best way to add these?

Since you'll be playing with the level diagram, you'll need some kind of level indicator, whether it is a simple LED or a full meter is amatter of choice.

Also, I've been thinking about adding a Dry/Wet control too - would runoffgroove's Splitter-Blend work for this?

While you're at it, why not add a High Pass filter, a 4-band EQ and a compressor?

 

[cpsmusic]

I recently came across these:

https://www.analog.com/en/products/ltc3265.html#product-overview

Any reason why I couldn't power the device with one of these?

 

[abbey road d enfer]

I recently came across these:

https://www.analog.com/en/products/ltc3265.html#product-overview

Any reason why I couldn't power the device with one of these?

As long as you have a suitable source for the incoming voltage and the current draw does not exceed about 20mA, it could be used.
Note that the app note is in contradiction with the datasheet. The negative voltage absolute value cannot exceed the input voltage, so with 12 V input, you can't get -15V.
In order to get + and -15V, it takes a different connection and the output current is limited to about 10mA, which is not enough for the intended circuit.
From the schematic, I think the current draw is close to 20mA. I guess you could power the circuit with +/- 12V.