Guitar tuner tecnical question

Posted: 4/28/2010 1:56:28 AM

Joined: 4/17/2010

Hi Folks.
I'm new around here (just posted a 'hello' in the newcomer section), so please go easy on me when I ask this...

A quick technical question, if you please. A guitarist friend has offered me use of his Boss TU-2 guitar tuner foot pedal as a means of finding (and hopefully) holding notes on my new Etherwave. But surely I'm going to blow this up if I feed it the line out signal, aren't I?

From the Mood Hot-rodding PDF, I think I'd need to add the tuner output circuit, which I'm guessing will supply a lower 'guitar-line' output.

I'm not very electronically minded, but I'm pretty convinced that the Boss will go pop unless fed a much throttled signal.

Words of advice much appreciated. I will of course be working with the proper 'by ear' method, but this seemed like a useful add-on in the beginning.

Posted: 4/28/2010 8:06:40 AM

From: Kansas City, Mo.

Joined: 8/23/2005

Radio Shack sells an attenuating patch cord that will allow you to connect a line-level output to an instrument-level input.

You can also run your line-level signal through a 47K Ohm resistor to bring it down to a usable level.
Posted: 5/4/2010 4:12:20 AM

Joined: 4/17/2010

Thanks KK

I've since heard back from Boss themselves; they claim such a level will be fine through their new TU-3, so I'm going to risk it - my friend will appreciate a new pedal anyway!

I'm also seriously considering the resistor 'fix' as the KB1 is only just 'off the stop' on it's volume control before it's way too loud. Has anyone else experienced this with that amp?


Posted: 5/4/2010 11:38:33 AM

From: Canada

Joined: 8/1/2008

I have a BOSS TU-12H chromatic tuner. There is no level problem regardless of input. The TU-12H will even operate acoustically with no line input whatsoever (it has a little built-in mike).

Posted: 5/4/2010 12:22:17 PM

From: Hampshire, UK

Joined: 4/24/2009

Getting off topic...

I have a KB2 amp, I was going to get the KB1 but I saw this one secondhand and priced at only a tenner over the KB1. How could I say no? ;)

I'm no expert so feel free to disregard this, but I don't think adding a resistor would be a "fix" in this case since the KB1 is designed to receive a line-level input in the first place, that's it's normal behaviour.

I'm not entirely sure what you mean by "off the stop", but if you mean that it gets very loud very quickly as you turn the dial, then I have experienced a similar effect. I haven't tried to resist the line from the theremin, though I may give it a go as an experiment! :P

My concern with that though is that you may end up with excessive buzzing/hissing from the speaker, since the input signal is weaker than the one it was designed to receive. But as I said, I haven't tried it!

In the mean time I've just been playing around with the volume field dial. In the past I've tended to go with quite a tight volume field, like Thomas Grillo does in his free Theremin lesson videos on YouTube. They're very helpful, thanks Thomas! :)

Since getting the KB2 though I've been practicing with a much loser field, and I quite like it personally. I feel like I can put more expression into my otherwise mediocre playing! ;) You also don't seem lose too much of the advantage when playing stacatto since the amp is louder to begin with.

Just my two pence.

Posted: 5/13/2010 10:19:43 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

Dan said: [i]"My concern with that though is that you may end up with excessive buzzing/hissing from the speaker, since the input signal is weaker than the one it was designed to receive."[/i]

An attenuator on the input will attenuate signal and noise equally, and will only add a tiny bit extra noise (thermal noise from resistor - insignificant) PROVIDED the unit is well constructed and well screened.

The problems with attenuators and noise mainly occur if a good input level is attenuated to below the level specified, and then the amplifier gain is cranked up to compensate for this attenuation.. Doing this certainly does increase noise, as one is increasing the gain and therefore increasing the amplification of both the needlessly reduced signal level, and all noise seen at the amplifier input.

The circuit below is a simple adjustable attenuator - use a good quality preset or log potentiometer, and build the assembly into a tin or plastic box screened with aluminium foil.. If you use a log potentiometer rather than a preset, and construct this well, you have a useful universal audio attenuator (and you will wonder how you ever managed without it).

link to Circuit for attenuator (

The potentiometer value is not critical - 47k to 100k probably best. If you want to use this as a general purpose remote volume control, use a log potentiometer - if it is only to be used as a 'set and forget' attenuator, log or lin will work fine.

Best way to set it up is to set the attenuator potentiometer for minimum signal output (wiper to ground), and crank the amplifiers volume / gain up to maximum.. Then increase the attenuator until the amplifier starts distorting, and back it off a bit..

With the wiper adjusted to the top position (on schematic) there will be almost no attenuation, and at the bottom there will be almost no signal. The quality of the potentiometer is critical - if the wiper does not make good contact with its track all the time, all sorts of nasty things happen - I have had wipers which (particularly in loud environments)cause horrible distortion because they vibrate and intermittently make/break contact with their tracks.. some of the cheap cassette portastudio's and some synths I serviced suffered from this.. Fortunately, pots seem to be a lot more reliable these days.

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