Does this seem like too much filtering?

[iknowjohnny]

I just recently upped the filtering in part of my amp in a BIG way. But it has me curious as to why it worked so well for two reasons. One, i never see this much filtering in other amps, and two, i tried this before tho when the amp was different and it was horrible.

What i did was to add a couple 80uf caps in parallel with the V2 node which is only a single stage since i eliminated the cathode follower in favor of a plate driven tone stack, and the other cap for the PI. So i now have 100uf at the PI and V2. The amp sounds thicker and overall better. So the questions are 1-why other amps don't use this much filtering, and 2-what could account for the reason the amp sounded way too stiff before with a lot of preamp filtering but great now? As to question #2, the differences that i'm thinking could be responsible in the order that i believe they are the likely reason are smaller choke, (now 5H vs older one being 20H) elimination of the CF, and 150MA/475v PT (475v being the resulting B+ voltage) verses a 250MA/425v PT. What would you guess? By the way, V1 where the main 2 gain stages shape the tone is at 60uf up from 20. But adding more than that there doesn't seem to work as well.

By the way, when i tried it before it was on the previous build that was exactly the same aside from the iron and now the change i made eliminating the CF.

[FYL]

Most amps are very poorly filtered because the bean counters want low parts costs and the clueless customers believe that less is more.

[Jana]

+1 what FYL said.

[iknowjohnny]

Still i wonder why even builders like those here who are doing it for thier own use, many of whom seem quite knowledgeable seem to use standard values. I know you don't Jana, but you seem to be more the exception than the rule. In any case, what do ya'll think is the reason this amp is loving more filtering while the last one didn't ? You think it's that the 20H choke i had before just made a lot of filtering too stiff? Thats what i'm thinking because the 5h choke certainly felt looser, and the difference between less and more filtering is generally loose vs tighter. i think it was just too much of a good thing with big filters and a 20uf choke.

[BTF]

Just wondering:

When increasing filtering dramatically, does the possibility of increased inrush current from the extra capacitance ever trouble you? I know increasing the capacitance in Twins used to be a somewhat common mod for steel guitar players looking for headroom and frequency response (most of the time I could tell but scant difference). Although I never saw an amp power transformer or rectifier section damaged by increasing the capacitance, I just wondered.

Regards, BTF.

[FYL]

Still i wonder why even builders like those here who are doing it for thier own use, many of whom seem quite knowledgeable seem to use standard values.

Most people stick to known formulas & recipes.

In any case, what do ya'll think is the reason this amp is loving more filtering while the last one didn't ?

Time constants weren't right, maybe. A filtering node seems simple but has a very profound impact on overall performance.

You describe a supply with a big 20H choke. Did you calculate the TC's for the circuit? With such a big choke C1 should be roughly 1/4 to 1/3 of C2, something very counter-intuitive.

[FYL]

When increasing filtering dramatically, does the possibility of increased inrush current from the extra capacitance ever trouble you?

You've got to calculate/simulate the supply.

Big caps aren't usually a problem with solid-state rectos but valves are another story: inrush current kills them very easily.

[BTF]

Very true. Fortunately, most steel and bass enthusiasts don't tend to go for the valve rectifier-amps. I've been using increased capacitance in my 100W (solid state-rectified) Fender for years with no trouble. Originally I was seeking increased headroom, but in the end the difference for me was miniscule.

Regards, BTF.

[Bob-I]

Soldano uses huge filters, 220|220 and 220|220 for the plate and screen nodes. It makes for a vrey tight fat bottom end.

I built a SLO clone awhile ago and where it has great lows, I just don't like the SLO section, too compressed.

[Jana]

Inrush current:

Remember, each node has a resistor in it and subsequently each of these resistors will mitigate the inrush current to a degree (how's that for a string of ten-dollar words?). What I mean is having large values of caps at each node isn't the same (when speaking of inrush current on the rectifier) as having all that capacitance at the first node where it gets slammed with no limiting.

That's one of the tricks used with tube rectifiers: have the lower capacitance value at the first node, typically 40 uf or so depending on the rectifier, and then have a larger value after the choke and for the PI. The choke and the resistor going to the PI node create a time constant to charge those caps. All the nodes don't charge to full voltage in one bang.

[BTF]

Plus (at least on Fender amps) the standby switch will help with current draw somewhat. Most of the time the first filter stage and the screen filter are usually the only caps which get boosted, so the standby switch provides a bit of relief from downstream draw.