Structo wrote:I'd like to see one like the second stage of a Dumble is
220K grid stopper, 150K plate, 2K2 cathode, 4.7uF bypass, .05uF coupler.
Ok, can you please give me a link to the schematic you are referring to? Do you want to know Gain vs Frequency, an analysis of the clipping behaviour of the single stage, or whatever? I think it should be more useful to understand how to simulate stages, rather than simulate (you know the old story of the fish and the fisher?).
Structo wrote:Not sure if you can model it but the 220K grid stopper is bypassed by a 500pf cap.
Has anybody installed the software?
Any comments on suggestions?
It could be useful to have some people simulating to look at some aspects of gain stages (EG why 220k Rp before a CF reduces THD of the two stages, or share preamp stages' circuits).
Tip of the day:
don't use RC stages on supply, but one supply for each node.
Otherwise you'll need too long times to charge capacitors, so too long simulating times.
I have been using LTspice with the drop-down menu tubes from Steve Bench (link ) on various circuits, most recently an little ECC83 / EF86 / EL84 single ended amp with tremolo.
I have been staggered how closely the predictions match the real circuit, even for over-driven signals. It's a lot quicker and easier to try things in the simulation, then go and try the best options 'for real'.
Lots of help for LTspice with tubes/valves at Interactaudio - including a drop-down output transformer library that I must install...
The hard part is relating what I hear to what the data tells me!
Basically you can see that low order even harmonics sound smooth, while low order odd harmonics make the amp feel harder under the fingers, but are useful. High order harmonics are less accurate and usually sound harsher.
You can check this by the FFT analysis. Do not forget that you also have sin input on the simulation, but your guitar has fundamental plus various harmonics, so the story is a bit more complicated.
The 1M vs. 1meg for resistors being 1 Meg depends on the software. I know Altium likes 1meg but Orcad uses 1M. NI's Multisim uses 1M for meg as well, although I think both this and Orcad recognize both 1M and 1meg.
Moral of the story: Know your simulator and check how it interprets values assigned to parts!
roberto wrote:
Basically you can see that low order even harmonics sound smooth, while low order odd harmonics make the amp feel harder under the fingers, but are useful. High order harmonics are less accurate and usually sound harsher.
but your guitar has fundamental plus various harmonics, so the story is a bit more complicated.
The story is yet more complicated by the fact that harmonic distortion only dominates below clipping. As soon as you clip the signal, IMD becomes the dominant form of distortion, and it's a lot more difficult to characterise than simple THD!
Yes it's absolutely true, but I also can't simulate the way the guitar sounds when picked in a different way. I use to simulate some parts of the amp as a starting point to obtain different voicings, then I do the "fine tuning" by ear.
EG: one of my latest amps has a 220k 1k8 to 100k CF switchable to 220k 820R to 47k CF. This was simulated (with different configurations) and then applied as is.
It's important to understand that you need to build your rosetta stone from the FFT to the sound you can obtain. This way you'll be able to save time and explore more sounds.
I've used wav files as the input for my spice sims. It processes it through my simulation and then writes the resulting wav file out which i can compare to the original input. I don't know how accurate it is but it is fun to fiddle with.
Some simulations about plate snubber dampening. The analysis is from the input to the CF of a 4 stage lead channel, eq not included. This is the effect of two plate snubber cap (across 2nd and 3rd gain stage's Rp) with a resistance in series (see the attachment). Vin goes from 0 Ohm (so no dampening, more high cut) to 10k, 100k and 1M (virtually no cap, less high cut). Look on how the frequency shape changes, expecially around 1kHz-10kHz.
