Mainline as a guitar headphone amp

[dth31]

I’ve recently taken up guitar and the wife would appreciate it if she didn’t have to listen to me!  Don’t blame her.

In order to preserve happiness at home, I started wondering if anyone has actually *tried* using the Mainline as a guitar amp played into headphones?  It seems that guitars have widely varying voltage output depending upon how hard the strings are strummed/attacked.  I’ve seen values ranging from ~5 mV for quiet strumming to 1V.

Any help would be appreciated.

[Thermioniclife]

I think you will need a preamp to run into the Mainline. the output of an electric guitar is quite low and needs to be amplified to at least 2 volts to run the Mainline. There are hundreds of units that seem complicated. You probably need a simple preamp. There are a lot of schematics available. Perhaps PB, PJ or Doc can help you with a Eros or reduction phono preamp. There  kinda handy that way. Good luck.

[dth31]

I suspected that might be the case, given the low voltage output of the guitar.

[Paul Birkeland]

You can pair a Reduction with a Mainline to do what you want to accomplish.  You'd have to modify the Reduction to take out the RIAA EQ, but that's not that big of a deal.

[dth31]

Thanks for the input, PB.  Two questions:

1. Would you have any concern about the Reduction overloading the Mainline?  I know the Reduction is designed for cartridges with ~2.5 mV output.  Soft strumming on a guitar with  a single coil pickup probably generates output voltage that is not much higher than that, but hard strumming and humbucker pickups seem to be more in the 200 mV output range.

2. Is there a reason you recommended the Reduction (36 dB gain) instead of the Moreplay (9 dB gain)?  (I will say, my favorite preamp tube sound-wise is a 6922/6DJ8/7308).

[Larpy]

Keep in mind that what sounds good through a hifi amp and what sounds good through a guitar amp is very different.  Guitar amps are designed to distort; hifi amps are not.  I'm assuming you're playing an electric guitar rather than an acoustic guitar with a pickup.  If so, I suspect you'd be better served listening to your guitar through a guitar amp with a headphone jack: even an inexpensive one would sound better with a guitar than a BH headphone amp.  Unless, of course, you want the most squeaky clean electric guitar tone you can get.

I'm a BH fan and don't want to take business away from them, but I'd recommend you build a Fender 5F1 "Champ" amp clone and add a headphone jack.

[Paul Birkeland]

1. Would you have any concern about the Reduction overloading the Mainline?  I know the Reduction is designed for cartridges with ~2.5 mV output. 

The Reduction is made for cartridges with 5mV of output.  Your guitar has a level pot on it right?

Soft strumming on a guitar with  a single coil pickup probably generates output voltage that is not much higher than that, but hard strumming and humbucker pickups seem to be more in the 200 mV output range.

200mV will overload the second stage of the Reduction, so you'd either want to turn down the level pot on your guitar or install a level pot in the Reduction itself.

2. Is there a reason you recommended the Reduction (36 dB gain) instead of the Moreplay (9 dB gain)? 

9dB of gain isn't enough and the Reduction is quieter.

[dth31]

Well-reasoned and thoughtful, as usual.  Thanks PB!

[Paul Joppa]

The RIAA equalization in Reduction reduces it's specified gain from 58dB to 38dB. This happens between the two stages. You could put an attenuator in place - even just an L-pad - to set the gain you wanted without overloading the second stage.

[Paul Birkeland]

PJ's method has the added benefit of improved SNR as well since you would be letting more of the signal into the first stage from the guitar.

[dth31]

Larpy made a very good point which I had considered.  For now, I pretty much only play my guitar “clean”.  I’ve found that overdrive, boost and distortion can hide a multitude of technique issues.  I can hear those errors much better when I play clean and it helps me play better.  As my technique improves, however, I will definitely want to play with more distorted tone.

What I hadn’t considered was just buying a 2nd amp with a headphone output.  I was trying to save some money and use what I already have on hand.  I might buy a cheap guitar 12AX7 preamp for $40-50 and use that to drive the Mainline.  There are tube units with variable gain and drive/volume that might give me both clean and distorted tones, too.

If I do so, I’ll post some follow-up.