Some years ego I've build an amp with basic PP EL84 circuit similar to Fender Pro Junior etc. But for some reason I've put the Negative Feeddback to the 2th gain stage (2th half of the 12AX7) as oppose to the more common going to the splitter.
I can't remember why I did that but I must have had a good reason since I've spend weeks just tweaking the amp design. (Sorry, no schematic).
Is there really any difference, pros or cons?
I can't remember why I did that but I must have had a good reason since I've spend weeks just tweaking the amp design. (Sorry, no schematic).
Is there really any difference, pros or cons?
Without the schematic, I can not see what the relative phase is of each stage, versus where the negative feedback is applied. It must be applied according to the proper phase, or it becomes positive feedback (and becomes an oscillator).
Many guitar amp experts will already know the particular topology of the Fender amp.
In general, the more stages are included in the feedback loop, the more likely there will be a phase shift of either the low frequencies, or the high frequencies, which can make the amp unstable, even though the negative feedback is applied in the correct phase at mid-frequencies.
Many guitar amp experts will already know the particular topology of the Fender amp.
In general, the more stages are included in the feedback loop, the more likely there will be a phase shift of either the low frequencies, or the high frequencies, which can make the amp unstable, even though the negative feedback is applied in the correct phase at mid-frequencies.
One technique used to get the right feedback polarity is to take the feedback not from the hot output transformer output but the cold output. This will fix the polarity, but you'll still have the phase shift at the frequency extremes to deal with.
Should be in Instruments and Amps.
In a guitar amp you can put feedback to wherever you like, to get whatever sound you like.
In a guitar amp you can put feedback to wherever you like, to get whatever sound you like.
In that case I must have liked the way it sounded there. Reason I was asking because recently I've decided to lower the NF to get little tighter sound and noticed where I connected the NF.
The amp is about 15 years old now but change in music style required tighter punchier sound which is what lowering NF did. I had it at 500k for a long sustain and open loudness, now it's at 140k at the loss of about 20% output but since it's only for recording now, the lower output don't matter any more.
You didn't lower the negative feedback you increased it which will increase bandwidth, lower distortion, and lower output impedance. The latter will give you increased damping which helps tighten things up.
Careful, increasing feedback could cause instability issues.
Careful, increasing feedback could cause instability issues.
Yeah I meant lower the value. But anyway, after some recordings I've put it back to what I had it in the first place. I forgot that more NF will also make it sound more dry and I didn't like that. Kind of sounded like my Fender pro Juinor which is more of an aggressive rock amp tone. I've build the amp to sound close to Fender Blues Deville, more NF takes away the "wet" tone out of it. I didn't think it'll make such big difference. Sounded good on it's own but recording brings a lot of things out we normally don't hear.
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