Inductor in the SSS (I know, not this again!)

[bcmatt]

I know this has been debated and there seems to be a real lack of conclusive evidence on whether it is doing anything.
I built my SSS without one since it seemed to be a pain to even find one of appropriate value... but we can get back to that.

The reason I am intrigued again after all this time, (It's been about 5 years since my Traynor to SSS conversion build) is due to this particular video about adding inductance to guitar tone caps to get the sustain and liveliness of Bumblebee caps:
https://youtu.be/c6wLLbM_Rls

I do want to try that out in one of my guitars, but it made me wonder about trying out an inductor in my SSS where it was "supposed" to be.

Over the last few days diving back into this site and trying to figure out what inductor would work, I'm guessing we want something in the range of 300-500mH and about 40ohms max DCResistance in order to match the Triad SP-118:
https://ampgarage.com/forum/download/fi ... &mode=view

This is a lot harder to find than I thought. The SP-118 is some huge problem for anyone to sell a single one of for some reason. I can find 2 for like $60 USD shipped to me ($15 each plus $30 shipping), but that is still a bit ridiculous for something so small that may do nothing.... Other places want you to buy at least $100 worth...
It would actually be cheapest (about $35 CAD with shipping) to buy this choke that is pretty similar specs from what I can tell:
https://www.mouser.ca/ProductDetail/553-C-36X/

Anyone have any thoughts? What do you think about the whole bumblebee replacement thing as well?
I guess I should include his other video where he compares a bumble-bee cap to other caps before showing his inductor replacement version:
https://youtu.be/xhqFGzZafa0

[Richard1001]

I used a 'stack of dimes' radial inductor, 330mH. I don't know the shipping costs, but it is cheap and doesn't weigh much.

https://www.tessatronic.nl/index.php?op ... ry_id=2501

[niusia]

My wild guess is that inductor was supposed to be a part of RLC resonant circuit, creating peak in series resistance (thus dip in frequency response) at maybe 400-500Hz range aka 'mid scooped tone'. Knowing values of resistors and capacitors, it is pretty straightforward to figure out required inductance. On simulation I can see effect at around 8 to 12H but it is not easy to find such inductor. I hope to test my hypothesis with one coil of microphone transformer (other coils open) as a inductor.

What is even more interesting that such inductor, creates additional peak in frequency response at around 2kHz, which can give that nice bite to a single coil sound.

I hope to start my build in a few weeks so I will definitely post my results. Chance is it will sound like crap

Jakub

[pompeiisneaks]

Jakub could you share what you're doing with those simulations? From what I've heard here is that several members have agreed that simulations show it has absolutely 0 impact on the circuit where it's placed.

I'd like to know more about how you came to that. Also I think several of the same people still tried a NOS exact one in that spot and couldn't tell the difference with it in or out.

It's a highly debated point, though

~Phil

[niusia]

This is what I got in Spice. You can see there is definite dip in 400Hz with inductor, but its inductance needs to be in the range of Henries not mH. This mid scooped tone can be achieved without inductor by adding series resistance before the filter circuit (like trim pot in #004 or 1Meg resistor in #005) but this series resistance can mess up the frequency response in lower setttings. With inductor the response in all posistions is nice and predictable just like Martin Manning's ploted in his version, the only difference being dip/scoop at 400-600Hz and a small peak at 2-5kHz.

The problem here is that there is not easy to find 10-20H inductor wich will suitable for signal levels we are expecting in this circuit. You could take primary side of guitar output transformer (leaving secondary open), but if you drive it with just a few volts it won't do anything. Filter chokes won't do either because they need some saturation from DC to get to the nominal levels of inductance. On the other hand small signal inductors are usually below 1H. This is why I believe our best bet can be a mic pre input (or output) transformer. If you take its high impedance coil and leave low impedance coil open you should be close enough. But this is just an idea. I never tried it, so can't guarantee your amp won't blow up

If anyone has a source of suitable inductor with 10-20H values please let me know.

Jakub

[pompeiisneaks]

This is what I got in Spice. You can see there is definite dip in 400Hz with inductor, but its inductance needs to be in the range of Henries not mH. This mid scooped tone can be achieved without inductor by adding series resistance before the filter circuit (like trim pot in #004 or 1Meg resistor in #005) but this series resistance can mess up the frequency response in lower setttings. With inductor the response in all posistions is nice and predictable just like Martin Manning's ploted in his version, the only difference being dip/scoop at 400-600Hz and a small peak at 2-5kHz.

The problem here is that there is not easy to find 10-20H inductor wich will suitable for signal levels we are expecting in this circuit. You could take primary side of guitar output transformer (leaving secondary open), but if you drive it with just a few volts it won't do anything. Filter chokes won't do either because they need some saturation from DC to get to the nominal levels of inductance. On the other hand small signal inductors are usually below 1H. This is why I believe our best bet can be a mic pre input (or output) transformer. If you take its high impedance coil and leave low impedance coil open you should be close enough. But this is just an idea. I never tried it, so can't guarantee your amp won't blow up

If anyone has a source of suitable inductor with 10-20H values please let me know.

Jakub

Oh so the inductor I've seen in the layout showed .5H not 10-20H I've never built one so I'm not a great on the details. I was just curious. That's seemingly very obvious.

~Phil

[Roe]

Perhaps I should order one of these chokes (15H for 9 bucks): https://eu.mouser.com/ProductDetail/Ham ... O3x5BvJg==

[niusia]

Roe, I am no expert in electromagnetics, but I am almost sure that you need DC current through filter choke (some core saturation) in order to bring it to nominal inductance. Inductance depends on permeability of the core, and for iron this can change alot with amount of magnetic flux through the core. Without significant flux density there is no inductance, too much flux density (saturation) and inductance drops. So afaik there is always some optimal level of core saturation that guarantees nominal inductance level. Might be worth trying, worst case you will use the choke in next amp project.

If I may add one thing. Other effect of inductor is phase shift around the resonant frequency. Normally it would not matter but this circuit as used in #002 is inside feedback loop. With sufficient phase shift negative feedback becomes positive and maybe this instability can cause what others described as 'clean feedback' or singing. I don't see this effect on simulations but sim is not real circuit. Yet another speculation...


Jakub

[erwin_ve]

With sufficient phase shift negative feedback becomes positive and maybe this instability can cause what others described as 'clean feedback' or singing. I don't see this effect on simulations but sim is not real circuit. Yet another speculation...


Jakub

That is certainly interesting, am I correct to say this not audible with a 500mH inductor because of the inaudible resonant frequency?

Erwin

[ericlc]

Yes, that is the case.
Everything between 0 and 3dB is debatable.
I found a site where you can test it.
https://www.audiocheck.net/blindtests_level.php?lvl=3

Best,
Eric

[niusia]

Erwin, yes you are right. When you look at the frequency plot o Martin Manning's filters, you can see gentle mid scoop at around 400-500Hz area. When inductor is 0.3-0.5H its resonant peak is around 2k-4kHz (depending on capacitors used) and its peak is basically swamped by the high filter action. Increasing iductance value moves resonant peak down frequency range (according to f = 1/(2*pi sqrt(L*C)) and when peak approaches 500-600 Hz range it becomes more pronounced on the frequency plot. Funny thing happens when you try values like 40-50 Henries - resonant peak is exactly at the natural scoop frequency of the filters and the whole frequency response has very sharp dip and sharp phase shift. I hope it makes sense.

My "phase shift theory" is rather a nod to the original circuit and small value iductor. In other words, if you can not see any change in a frequency plot with original inductor, there is still a chance there is audible effect, because of the phase shift and feedback interacting with rest of the circuit. Looking at the sims, circuit seems stable (there is not a a lot of signal used for feedback to start with) but maybe (or definitely) I am missing something.

Anyway I hope to start my build soon and I will definitely do some experimenting with different inductors - my take on it is "Don't give up on inductor - it must be there for a reason"

Jakub

[erwin_ve]

Thanks for sharing Jakub, that certainly is a new view to me regarding the SSS inductor.

[markusw]

See
https://ampgarage.com/forum/viewtopic.p ... or#p206073
and
https://ampgarage.com/forum/viewtopic.p ... 95#p208695

[martin manning]

See
https://ampgarage.com/forum/viewtopic.p ... or#p206073
and
https://ampgarage.com/forum/viewtopic.p ... 95#p208695

Thanks, Marcus, I was looking for Gary's breadboarding experiment and came up empty.

[niusia]

@ Erwin
I would like to add one last thing. Maybe it is other way around. There is a chance that inductor was included there to kill oscillation or to control it, not to induce it.

@Marcus
I completely agree with results posted before. As far as frequency response, 300mH inductor or even 1H inductor is as good as a piece of copper. But there is noticeable phase shift, even with .3H, so one can argue that cited experiment tells only half the story - signals are in fact complex numbers.

As much as I would like to know how and why the inductor found its place there, I strongly believe ones ears are the only judge.

Jakub