ODS #183 Build

[martin manning]

which amp uses that extra eyelet there? In the PI tail zone?

ODS's with a common master volume, 124 e.g., use that eyelet as a tie point between the MV wiper and FX send.

[pfarrell]

Thanks Martin, I did happen to deduce that after I asked... took a look at the #124 files...
Iron has been ordered! Be a couple of weeks for delivery...

[ijedouglas]

... made the under board connections and the one ground leg... nothing soldered yet

I try do a crimp of the under board connectors on top of the eyelet....nothing worse than one of them coming out once you have the amp together

[pfarrell]

Some woodwork!

PF-183_04.jpg

[pfarrell]

I went ahead and made the 1x12 for this build since I was making a 1x15 for my VibroVerb... Came out nice. (I will most certainly make a 2x12 at some point—to try with all my amps—and more speaker options for that config.)
Will try to work on the PSU board this week—still waiting on iron delivery. I don't really want to cut the chassis up until I have it all in hand. I did get some rivnuts for securing the amp to the case...!

PF-183_05.jpg

[pfarrell]

Thanks for making this quite straight forward Martin...

Spacing wise, the caps I have do kinda cozily touch the 470K resistors in the array—not tight at all, just perfect... think that matters? I could source different caps...

PF-183_07.jpg

[ijedouglas]

I don't think so. All my boards have a fair distance between them. I checked them with a thermometer and they don't get any hotter than the surrounding components.

[talbany]

think that matters?

2) The caps that were in there were ok, but Howard wanted a different cap composition than the regular Sprague caps. Turned out an Illinois capacitor had the construction he wanted.

3) Then there was the spacing of the caps from each other. He insisted that EMSR or ESR (???) was restricting the tone because they were too close together. A new board spaced them the distance he wanted to see.

https://ampgarage.com/forum/viewtopic.p ... 26#p386326

Tony

[martin manning]

Pfarrell, the drawing specifies 30 mm and 16.5 mm diameter caps. Are yours larger than that? Is the eyelet spacing the same? The 470k’s dissipate at most 0.11 W That’s for the screen, at 450V, and those are on the end. More spacing would be a bit better for cap life. You can offset the 270k’s a little to keep them away from the snap-in caps.

Tony, I believe that linked discussion is about preamp cap spacing and possible crosstalk via the electric field around them.

[talbany]

Tony, I believe that linked discussion is about preamp cap spacing and possible crosstalk via the electric field around them.

Martin? i thought he said IC's Illinois Capacitor's (Power Supply). No?

IC caps.jpg

Tony

[martin manning]

Illinois makes film caps too.

[pfarrell]

Thanks for all the feedback guys... Martin, of course your layout specifies 16.5mm, I happened to have the Panasonics on hand (18mm). I could have changed the board layout slightly...but forgot! I do have some other caps that are ~12mm... but they are for another project—also a tad too tall I think— I just ordered some others for this PSU....(Oh, and edit—the big caps are 30mm—the image makes it look like the 270Ks will be close, but they are the spacing in your layout, Martin.)

[talbany]

Illinois makes film caps too.

Could be? however I don't ever recall, Dumble using IC Film caps? in the preamp of any of his amps/rebuilds/Mods...Have you?

311674_10200537220651783_1464032435_n.jpg

DSC00483.jpg

234ods.jpg

So then if Dumble was serious? the question I have would be which cap (or position) is most susceptible to this phenomenon? pre or power and why?
relevant papers anyone?.(IMO Fascinating topic or Hijack.. )

Tony

[martin manning]

I am not aware of different compositions of electrolytics being significant to sound quality, but film caps with different dielectrics are known to sound different. Like lead wires, the proximity of all components that carry signal voltages is important so I suspect the reference is to film caps in the preamp. I am aware of cases where placing preamp caps too close together (on a pcb) has caused oscillation, so they can have significant interaction.

[talbany]

Back when I was running VVT and we were Cranking out Lindy Fralin Model Amps (Combos) one of the suppliers had a huge sale and were trying to unload a bunch on Radial caps. (I believe they were Xicons) So we bought a few hundred to try and see if we could work them into the design. We modified our P.S boards to accept them and started using them. The result was two fold? A buzzing like sound in the high end when the amp started to breakup as well as a slightly looser or softer low end again when you started to really push the power supply. we thought this might have been something else so we we built 3 all together and all 3 had the same problems. Although the lows were not that big of a deal and we could have maybe lived with it the buzzing in the treble frequency's we couldn't let them go out like that. Ultimately we rebuilt those amps with the JJ multis stage (40+20+20+20) and the problem went away on all 3 amps. This was a costly mistake as we had the new caps the new boards and all the time it took to draw up those boards and rebuild the amps. Needless to say we never went back to those smaller radial's. we never figured out what this was ultimately? could have been how we designed the boards or maybe it was just the plate cap or the caps we got were bad or suffered from ESMR? (which is why I am curious about this) these are all logical possibilities we were already behind on amps after this little experiment so we simply ditched the endeavor and moved on.

My experience with those small computer style radial caps.
BTW. There are other builders out there that won't use them and experienced the same sonic issues in the treble range.

Tony