How to get preamp overdrive with fx loop?

[Jacew]

Re: How to get preamp overdrive with fx loop?

Well you can design the loop to go after the PI so you can get the over drive from it. slaving is the best if you also want to dime the mv and make the el84's clip too. But I'll give you a few ways to accomplish putting the loop after the distortion generation in that amp.

Would be neat if you can do that, thanks!

How is that accomplished, after the PI? It's two signals with opposite phase after that, if I've understood the technology right. MV has dual gang pot to dial both, where they continue to power stage.

Being hobbyist I am, I thought adding a working loop there would be at least way too complicated, if even possible.

[Joey Voltage]

Re: How to get preamp overdrive with fx loop?

Would be neat if you can do that, thanks!

How is that accomplished, after the PI? It's two signals with opposite phase after that, if I've understood the technology right. MV has dual gang pot to dial both, where they continue to power stage.

Being hobbyist I am, I thought adding a working loop there would be at least way too complicated, if even possible.

No more much complicated than building and making any active loop. There are a few ways you could go about it. since all you are interested in is the clipping behavior of that PI, you don't have to use both outputs, you could just use the signal from one to drive the signal to the buffer, and disconnect the other. If you really want to keep them for whatever reason, (completely unnecessary) you could use a summing amplifier as your send stage instead. your loop recovery stage will then do the job of splitting the signals for the power tubes, and you will use a stereo cable and jack to re-enter the amp.

[Joey Voltage]

Re: How to get preamp overdrive with fx loop?

Sorry for the delay. This is the easiest method as far as construction. You would have to do something like this:



Note you would need to supply the circuit with 300v and you need stereo jacks for the output from the unit to the input into the poweramp of the tiny terror. Every thing inside the red box is the outboard fx loop unit. The one issue with this method is that this outboard loop would need to be connected all the time, as you would have to take one output from the phase inverter preferably the non inverting one.

Edit: r20 in the scheme should be 1meg not 10k. Sorry 10k is the default value in the program I use.

[Joey Voltage]

Re: How to get preamp overdrive with fx loop?

Forgot about the Photobucket garbage. I'll try to put the file into a jpg extension

[Jacew]

Re: How to get preamp overdrive with fx loop?

Wow. Thank you! I'll look closer into that when I have time.

The one issue with this method is that this outboard loop would need to be connected all the time, as you would have to take one output from the phase inverter preferably the non inverting one.

What happens to the other output? is the idea behind this to halve the signal, so the inverted one works as dry and non-inverting as wet signal?

Or is this going to halve the power of the amp as well?

[Joey Voltage]

Re: How to get preamp overdrive with fx loop?

Wow. Thank you! I'll look closer into that when I have time.



What happens to the other output? is the idea behind this to halve the signal, so the inverted one works as dry and non-inverting as wet signal?

Or is this going to halve the power of the amp as well?

No, Neither, it functions just as a typical series loop. Since the job of the splitter is just to provide two signals of equal amplitude but opposite phase to the power tubes, you only need one of the outputs if you are driving fx. Both of the outputs conducts 360 degrees 100% of the time. The other output is just disconnected. If you look at the scheme, the return amplifier of the outboard loop then resplits the affected signal for the powertubes, and connects to the dual ganged volume pot that was originally attached to the pi. you will get the full output as you had before.

Just remember r20 on the scheme is supposed to be 1meg

[Jacew]

Re: How to get preamp overdrive with fx loop?

Ok. Thanks for the clarification. So the fx-loop circuit is doing phase switch, and the PI is simply left there for distortion?

I'll inform how it works when I have time to build this.