An inductor to make new e-capacitors seem more vintage?

[roberto]

Hi,

last night I was looking at some new electrolytic capacitors for the power supply of some of my amps and I noticed how old e-caps showed small differencies in impedance between 100 Hz and 10 kHz whilst new ones, due I guess to the egemony of SMPS, have highly improved performances at high frequencies.

So I was thinking how to restore this small difference between low and high frequencies, and first thing that came into my mind are those small cheap inductors seen in battery chargers.

After a short calculation, I saw that in the range of 10-30 uH we can restore that ratio of impedances of the cap. Other point is current. I would consider around 2 Arms to be on the safe side.

While ordering some stuff from mouser, I would add some small cheap inductors (we are talking aroun 20 cents each) to perform some tests.

Has anyone experience in anything similar?

Thanks in advance

Roberto

[Stevem]

So what notes or harmonics are present on a guitar above 10k, the widest frequency range guitar speakers do not even go up that high with any SPL efficiency.

[roberto]

Ciao Stevem,

So what notes or harmonics are present on a guitar between 100 Hz 10 kHz, the frequency range I'm talking about in the post?

[pdf64]

I guess such a characteristic might enable some parts of the circuit to couple via the HT?

[roberto]

Thanks pdf64, a simple resistor of some hundreds of mOhm is indeed another simpler option.

[TUBEDUDE]

Is this for use with cathode bypass e-lytics, or supply reservoirs?

[R.G.]

This is a good idea
It's a sub-set of a concept I keep - the Immortal Amplifier. The idea is to replace parts that have wear-out mechanisms or decay mechanisms with parts that last much longer. In particular, you can replace electrolyitcs with motor-run film capacitors, which have no definite wear-out life. As a side effect, motor run caps have lower ESR and ESL than electros of similar voltage and capacitance. This idea always brought up comments that "well, well, it won't sound the same. God made electrolytics perfect for use in guitar amps, and it will sound too sterile/too hifi/too <whatever>. To which I'd reply that you can come remarkably close to the "dirty" electros by adding small resistances to fake ESR and small inductors to fake the ESL. That gets you pretty darned close. A more nominally perfect part can always be dirtied up to act like a less-perfect part.

The same idea can be applied to solid state rectiifiers to fake tube rectifiers. Weber sells or used to sell a line of tube rectifier replacement which were solid state with "dirtying" resistors.
Good on you. Go for it!

[roberto]

Is this for use with cathode bypass e-lytics, or supply reservoirs?

Hi Tubedude, supply caps. Screens node mainly, with a resistor between plates and PI nodes.
But plates node as well.

[roberto]

This is a good idea
Good on you. Go for it!

Thank you very much R.G.
You perfectly got my point, and I'm very happy that you wrote that post.
I'm buying some small inductors from mouser to perform some tests and will report the results.

[R.G.]

One thing to be aware of in the case of the first power filter after the rectifiers. The peculiar nature of rectifier-capacitor filter set ups causes the current into the first filter caps to come in the form of short, high amplitude spikes. ninductance before the cap (or inside the cap) spreads out these peaks and lowers their amplitude, but adding only small inductance doesn't change the spikes a whole lot. So "dirtying" inductances will have to cope with high currents. This means you will need to think about high current inductors for this job. Otherwise, they may be saturating on peaks; especially since they will be carrying a net DC current.

[roberto]

I was thinking about the screens more than the first node, but in any case this would be my choice:

https://www.mouser.it/ProductDetail/652-RLB0912-330KL/

1.7 A nominal
2 A saturation

it should be enough and it's very cheap.

[Colossal]

Roberto,

This is a great topic and timely. I am considering using film caps for the power supply in the bass amp we've been discussing. Of course the response of very low ESR/ESL film caps might really be desireable to respond quickly to transients with a bass amp, so dirtying them up with series resistance or inductance might not be for the best (?).

Me:
Everyone Else: just build the damned thing!

[brewdude]

Could the inductance be switched out or bypassed?

[roberto]

Sure it is.

[roberto]

I am considering using film caps for the power supply in the bass amp we've been discussing.

Film caps are even better to do so, because you can add resistors and inductors in series and the film capacitor won't age with time, so characteristics will stay as per initial design. e-caps will age on top of the "premature ager" due to the resistor and inductor in series.