Tube Amps / Music Electronics
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|12/16/1997 10:45 AM|
||Ibanez Tube King|
I was thinking about buying a tube king for my rig. One of the things that bothers me about the whole set up is the low voltages that are used for the pedal. Knowing what I know about tubes I would have to think that with the low voltage being run thru the tube the sound would not be really that much affected. The voltages should be much higher in a 12ax7 and this leads me to believe that the tube is in there just for cosmetics and is appealing because of everyones attitude towards tubes. I haven't tried one yet and was thinking about one of the tube screamers instead. Maybe someone in here can enlighten me with their thoughts on the tube and the voltages. Has anyone had a chance to compare the ts9 to the tube king?
|12/16/1997 12:07 PM|
When I got my Tube King, there was conflicting information as to which Ibanez power supply was required. The instructions said either a 12v or 9v supply, which seemed rather loose to me. It turned out to be a 9-volt/200ma regulated supply. I was curious about the voltage used to operate the tube. Did they just use 9 volts, or was there some kind of DC to DC converter to raise it higher?
So I opened up the box and measured the plate voltage to be only 6 volts. I just assumed they were running this tube way down into the nonlinear region of its transfer function. Nonlinear amplifiers produce abundant distortion. Running higher electrode voltages will put the tube in a more linear range, and the higher you go the more linear (accurate) a 12AX7 becomes. Also, at higher voltages it takes a much greater signal level to cause the stage to distort. So you now need more stages in series to get the thing to distort from an initial signal level around 0.1 volts (guitar pickup levels). Multiple stages in series, each mildly clipping, create that desired singing sustain.
I didn't trace the circuit, nor do I have a schematic, so I don't know anything about how the pedal is actually set up. But it does sound pretty good, closer to a Blues Driver than a Tube Screamer, yet different.
There was a thorough test on many OD pedals, including this one, about a year ago in "Recording" magazine. I gave my copy away and could kick myself, because it was an unusually descriptive & objective review of many popular effects pedals.
|12/17/1997 8:30 AM|
>...Multiple stages in series, each mildly >clipping, create that desired singing sustain.
Amen. The singing, compressed, sustains-forever didstortion is the result of multiple stages of soft limiting, each of which contributes a bit of compression without drastic clipping. In general, this requires some padding down the output level between clipping stages - counterintuitive where you're looking for a very compressed sustain.
What is going on here is that the most desireable clipping/limiting seems to be when the limiting is on the output of a stage, not the input. Inputs driven out of range seem to be a harsher, more abrupt stop. Presuming that you've picked a clipping device that HAS a soft clipping mode, the output clipping will be more musical than the input. This seems to be true for triodes, mosfets, and the input stage of the fuzz face. If you keep the overdrive down to the range where the output side of the device limits but the input does not, it seems to sound better.
|12/17/1997 1:57 PM|
This mild limiting or compression of the output waveform is assymetrical, creating a lot of second order harmonics or "musical" distortion. I hadn't actually thought about the input vs. output clipping, but you're right. If the input (grid signal swings high and is clipped, it creates a flat top, which is equivalent to an odd order harmonic series, and not very musical, which then gets amplified as signal.
I knew about the padding down between stages so as to not overload the next stage, but didn't carry my explanation that far. To get a rich, high quality, creamy sustain you need more than two stages with tapped gain. So for economy sake, the Tube King people probably took advantage of the easier to achieve but darker not as well defined OD sound by running the 12AX7 at the beginning, low voltage portion, of its curve.
|12/17/1997 4:27 AM|
>...leads me to believe that
>the tube is in there just for cosmetics and
>is appealing because of everyones attitude
I think you're getting it...
That's my opinion, of course.
The same thing goes for a lot of amps on the market today. Take a look in fx some of the Marshall VALVEstate, they contain only one 12AX7. IMO, they just doesn't sound like a real tube amp.
|12/19/1997 10:37 AM|
In fact, the patent for the Tube Driver discusses this subject. Supposedly the circuit of the TD is more musical at low voltages and works better. Don't know the patent no. off hand but there is a GiF of one of the schematic at my web site.
|12/19/1997 12:05 PM|
Is the Tube Driver schematic at your site for the 4 knob Chandler pedal?
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