I finished my amp a year ago, classic 18watt tremolo circuit, and now I'm noodling with it. Tweaking if you will. Sounds awesome. No hiss. Lots of grit. I found some old 12ax7s and el84s I'm experimenting with along with resistor and cap value changes.
Question: Should V2 the PI be balanced or unbalanced? High gain or low gain? What would be the ideal choice for this tube. I know how important V1 is to the color of the normal channel (Mullard) and V3 for the trem channel (one that doesn't motor boat), but how about that PI? I know "if it sounds good use it" approach. But I was wondering if you had your choice, what would it be and why? Don't limit yourself to branding, but hot or cold, balanced unbalanced.
Thanks...
Rob
You know I've been searching this forum for a week for info on this and now and I just found this thread which explains it all. Maybe my post will help others find what I was looking for. Here it is..
http://www.18watt.com/modules.php?name= ... ic&t=21323
Phase invertor PI v2 Classic 18 watt trem circuit choice
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dboy
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chabby
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Theres just no short answer for this question - but to simplfy basically the PI is sometimes out of balance 180 degrees so as to balance output in the way necessary for the amp to function with a certain amount of distortion (or lack of). The output can't clean up the distorted signal from the unbalanced PI, so if you want distortion you have an unbalanced PI, if you want a clean signal you strive for balance is my understanding, but I'm still learning too.
More complex an overview is in a push-pull amp, the transition from an unbalanced to a balanced signal path is facilitated by the phase inverter. It takes an unbalanced signal referenced to ground and creates two balanced signal paths of opposite phase. By moving the phase inverter all the way forward to the guitar input jack, you transform the unbalanced guitar signal into a balanced amplifier signal and create an opportunity to preserve balance through the remainder of the signal chain.
Then because of how you set up the PI, is a cascade of events the forms distortion, harmonics and basically the sound of the amp. Whether you want it balanced or unbalanced depends on both your personal preference (within tolerances) and what type of circuit you're working with. But generally speaking the 18 watters have out of balance PI's, which are later balanced by the output section.
So in terms of your question about high gain or low gain, balanced or unbalanced it would seem dependent on how distorted a signal you want. This is what people are considering when they think of the function of the term PPMV post PI master volume versus normal. Its also why a master volume post PI doesn't really work that well in the 18 watter. Its harder to alter the distortion and gain levels post PI compared to PI MV.
And if none of what I'm saying is correct, I'm really open to being educated, but that's my best shot. I guess I like both higher gain and lower which is why I love the TMB better than the original type 18's with it's master volume and tone shaping alternatives.
More complex an overview is in a push-pull amp, the transition from an unbalanced to a balanced signal path is facilitated by the phase inverter. It takes an unbalanced signal referenced to ground and creates two balanced signal paths of opposite phase. By moving the phase inverter all the way forward to the guitar input jack, you transform the unbalanced guitar signal into a balanced amplifier signal and create an opportunity to preserve balance through the remainder of the signal chain.
Then because of how you set up the PI, is a cascade of events the forms distortion, harmonics and basically the sound of the amp. Whether you want it balanced or unbalanced depends on both your personal preference (within tolerances) and what type of circuit you're working with. But generally speaking the 18 watters have out of balance PI's, which are later balanced by the output section.
So in terms of your question about high gain or low gain, balanced or unbalanced it would seem dependent on how distorted a signal you want. This is what people are considering when they think of the function of the term PPMV post PI master volume versus normal. Its also why a master volume post PI doesn't really work that well in the 18 watter. Its harder to alter the distortion and gain levels post PI compared to PI MV.
And if none of what I'm saying is correct, I'm really open to being educated, but that's my best shot. I guess I like both higher gain and lower which is why I love the TMB better than the original type 18's with it's master volume and tone shaping alternatives.
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