Feel free - Sensei Goodwin, 4th Dan Ju Jitsu, registered instructor and grading examiner 🙄
Like you say, it's a discussion, not an argument 😀
So how many different amps have you seen where the bias is fixed? - it's pretty unusual, and everyone I've seen over the decades had required obtaining the exact correct spares from the manufacturer.
Worst were those that used special diodes for the bias, long obsolete now - best bet is to redesign adding a Vbe multiplier (with pot).
Both socks first 😀
I must say I've never even heard of any other possible method until this very moment - I'll have to remember that.
Over the top always! 😀
I'm just glad this amp works now. If I had to stuff Swiss cheese into one of the controls to fix it, then that would have been fine for me. I played music through it and it's fine for what it is.
I did do some modifications. Since I never listened to it before the mods, I don't know if they made much difference. I reduced the Miller capacitors from 220pF to 100pF, I increased the input coupling capacitors from 4.7uF polarized to 22uF non-polarized (50V), and increased the DC feedback capacitors from 4.7uF polarized to 47uF non-polarized (also 50V). This should increase bass response and improve slew rate somewhat.
This amp has a DSP chip in it, as well as other preamp stuff which makes for all of the possible sound effects. I think the power amp should just be a power amp and not add anything more to the mix. It is far more powerful than the speakers can really handle anyway. I think I had the gain on "3" and it was really loud. I should have reduced the gain in the power amp also. I also cranked it up full volume with nothing playing and there was hardly any hiss.
Based on the Rusted Root CD I played through it, the amp is now producing all the bass that the little 8" speaker can produce. You never know what kind of stuff people are going to plug into this thing, so I wanted it to perform reasonably well with what ever.
I did do some modifications. Since I never listened to it before the mods, I don't know if they made much difference. I reduced the Miller capacitors from 220pF to 100pF, I increased the input coupling capacitors from 4.7uF polarized to 22uF non-polarized (50V), and increased the DC feedback capacitors from 4.7uF polarized to 47uF non-polarized (also 50V). This should increase bass response and improve slew rate somewhat.
This amp has a DSP chip in it, as well as other preamp stuff which makes for all of the possible sound effects. I think the power amp should just be a power amp and not add anything more to the mix. It is far more powerful than the speakers can really handle anyway. I think I had the gain on "3" and it was really loud. I should have reduced the gain in the power amp also. I also cranked it up full volume with nothing playing and there was hardly any hiss.
Based on the Rusted Root CD I played through it, the amp is now producing all the bass that the little 8" speaker can produce. You never know what kind of stuff people are going to plug into this thing, so I wanted it to perform reasonably well with what ever.
I wouldn't have thought it made any difference? - although I'm surprised how high the miller capacitor was, I've always used 22pF-47pF in the amps I've designed.
Presumably the existing electrolytic's were designed to give a suitable frequency response, and extended it beyond the audio range wouldn't really give any improvement.
Before my changes, -3dB was about 80Hz, which is not low enough. After my change, it goes down to 10Hz.
As sreten said, it was low enough before - and you don't need 10Hz on anything 😀
I presume you coming up with these figures from your sim?, so it might not be correct anyway - simulators aren't real life.
Man, this is a PA amp also, with all kinds of inputs. You don't have any idea what's going to be plugged into this thing. Someone might want to mic a drum, or something that has lower frequencies than a guitar.
Why can't you all just shut up and listen for a change? Low E on a normal guitar is 82Hz. Do you think for a minute that having the FR be -3dB at 80Hz is a good idea? Are you mad? This is from calculations, duh!!! Do you have any clue what the slaps and other percussive sounds on a hollow wooden guitar might be?
Man, I am sick of this stupid nit picking! Get lost! Stop assuming I'm an idiot!
The way I remember it, F = 1 / (2pi * RC).
Now that you've shifted the -3dB point from 34Hz down to 3.4Hz, the amp should indeed be able to reproduce bass drum and suchlike very well. Shame about the little 8" speaker though.
Now that you've shifted the -3dB point from 34Hz down to 3.4Hz, the amp should indeed be able to reproduce bass drum and suchlike very well. Shame about the little 8" speaker though.
Oh dear, another little tantrum like you had in the Doug Self preamp thread. Maybe you should stop assuming everyone else is an idiot.
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