Re: Chime Amp (Punch Amp v.2)
Posted by Neil mcNasty on Dec 22, 2015; 11:59pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/Chime-Amp-Punch-Amp-v-2-tp8493p26736.html
Regarding the issue about motor-boating (I've experienced this myself):
Are you getting this when using it with a power-supply, or only when running on battery power?
The reason I ask is that; lately it struck me that a single 9v battery probably does not have enough milliamps to run a 1 Watt amp at max (and then some...).
And therefore; when the current draw exceeds what the battery can deliver, it results in a lowering of the voltage supplied to the amp, which in itself makes the amp circuit more prone to oscillation and misbehaviour, since this is something that often happens when the battery is low in small amps like these (my experience)
What I suspect is that: when pushing the input of the JFet buffer front-end, the current draw increase quite a bit, exceeding the capabilities of a standard 9v battery.
As far as I understand the JFet transistors: the voltage at Gate has an effect on the (amount of) current-flow to the Drain, and therefore a strong signal at Gate will increase the current consumption (resulting in sag/lower voltage from the battery), and therefore there is no motor-boating/oscillation when lowering the input signal/voltage.
Remember that the IC is doing the amplification involved here, and that it all-ready consumes a fair share of the milliamp capability of the 9v battery. AND: if this current surge happens in the JFet as a result of high gate voltage, it could drain the battery to hard and then also bringing everything down in voltage.
from what I've experienced, it only happens when pushing the input on battery power.
So I guess that it has to be an issue linked to the signal strength/voltage at the Gate of the JFet
Is this correct logic?
Could we be under-estimating our power supply capability, compared to what we are trying to achieve?
Though I have to admit that I do not have any clue about what I am talking about here...
This is just the way my logic works on this subject, based on my limited knowledge...
Great if someone can correct me if I'm way out there! Love corrections!
(If I'm on to something though...), my conclusion will be that: in order to solve the problem, we have to increase the performance of the battery in use (increase milliamp capability), either by running several 9v batteries in parallel, or by using a "stronger" 9v battery.
It would not surprise me that these amps are capable of high power consumption, because you can get a hell of a lot of volume and rage out them, if you push them really hard.
They are great recording amps and they sound HUGE in the mix!
I've had my brother's kids coming into the room holding their ears, complaining about loud volume from an amp like this. That's pretty cool... And that demands POWER!!!
Rock On!