home brew possibly bound for the trash can

[mlp-mx6]

Then I'll ask again if it's possible that a solder blob (or a component lead, or a wire) has fallen low enough below the board to (at least partially) short out. Is this eyelet in G-10 construction? If you're flexing the board perhaps it is losing contact w/ the chassis and restoring your full signal.

[iknowjohnny]

I just had a chance to play with it a bit more and it was the master volume pot, so i replaced that. But after doing that the tone got much fuller and sweet except that treble nastiness was still there to a degree. Not near as much after i replaced the pot, but more than enough to consider the tone defective. thats how i believe it was at first, and the pot issue came later after i replaced it in looking for the original issue. So it seems there were two problems. I had removed the 470pf in the voltage divider at the 3rd stage grid and that helped a lot, but it was still tinny and horrid. So what i think happened was that when i finally nailed the tone and wanted to clean up the amp and leave it like that, it was exactly as the schematic i posted except for that one 470pf cap. Then when i cleaned it up and put it back together i added that cap because when i edited the schematic to reflect the amp's final configuration, i made some mistakes at the 3rd stage grid. And one of those was putting a 470pf on that voltage divider ! So while looking for the issue i replaced the master pot and that cause this second issue which caused the amp to sound horribly trebly *intermittantly*....remember i said it would get worse at times? So that made the situation way worse. Once i fixed that i thought about how things transpired in the last few days and it hit me the 470pf i put in the schematic probably wasn't there. So with that gone and the pot replaced i think it sounds right again. But i won't know till i get home later because i can't really check it where i am. But i think that was it. Whats odd is that i can remove any other brightening cap and the nastiness is still there. It's just that one at the 3rd stage gid voltage divider that was causing it all. It's amazing, but that one cap makes all the difference between killer fat full tone and a nasty top end thats unusable. Not just too bright, but just plain horribly nasty.

Anyways i think this problem is solved, but i won't know for sure till i get home tonite.

[mlp-mx6]

Good luck!

[iknowjohnny]

Thanks, i need all i can get!
If it sounds like it did before i'm going to build a new board with all new components and wire and get all new sockets. This one has been thru too much and i need it to be dependable. This was mainly my fault, but the slop factor has just made it too fragile to depend on.

by the way, anyone know of a brand/model of pots that are better quality than those alpha but not a lot more? preferably with longer threads too, as i use a plexi front over a printer paper face, and the thickness makes some pots unusable.

[Structo]

The only thing I was going to suggest was using a component that you mistakenly installed with the wrong value.
In other words mis-reading the color code on a resistor. We have all done that.

The other thing the several people mentioned is that .001uF cap on the first volume pot.

I was messing around one time and thought I had grabbed a 100pf cap but it turned out to be a .001uF, the tone that resulted sounds a lot like you describe. Sounding like bacon frying in a pan!

Anyway, double check values and clean up the lead dress.

[iknowjohnny]

You know, i always felt that way about a .001uf on the gain pot too, and in fact up till now i had a 300pf in series with a 470k resistor on the pot instead. Quite a bit less in a couple ways. Yet when i found this magic bullet that had the amp sounding awesome, for the first time i felt like a bigger cap and no resistor would be ok. so i tried it and was amazed to see it not only wasn't too much but was just right. i guess it just depends on the circuit. anyways, now it seems a bit much so i'm back to the 300pf and resistor. But the amp definately sounds good again. Still not as good as it was tho and i have no idea why. Before the tone controls and presence were all very usefull over most of thier range and now i'm back to how it was before that "miracle tweek". So it's good, but not like it was. so it's back to the drawing board, a real drag considering for a day i felt i found what i'd been looking for all this time. Oh well.......

[iknowjohnny]

I finally figured it out. You won't believe it. It hit me that i recall using a 470pf mica at the 3rd stage divider and i recall trying a different one earlier in the tone stack in place of the 500pf that was there. not because theres any notable difference between them, but thats what i had at one point. Anyways, it was much much smoother and softer sounding that the 500pf, i guess just because it's a different brand. it's surplus from a store that carries a lot of old NOS stuff and pulls. Anyways, the difference was nite and day. Once i recalled that it was one of those i had in that 3rd stage grid position, i took out the 500 that was there and put that bean shaped 470 in and there it is ! No harsh fuzzy highs at all. that was why it changed after my the clean up. It was simple as a part that sounds very very different. I measured them and they are both close to 500pf. So brands CAN make a huge difference. The right one is the smooth one. The other is the kind i'm sure you all use and get from all the common online suppliers.

[IMG:800:483]http://i24.photobucket.com/albums/c39/dazco/cap.jpg[/img]

[mlp-mx6]

Congratulations!

[Structo]

Cool!
I have heard bad things about those dog bone silver micas.

That's too bad we can't rely on manufacturers to make nice components anymore.
This whole counterfeit cap story and other bad parts really leaves a bad taste in my mouth.

When you are repairing or building an amp, new parts are not supposed to be bad!

Sure, there is always that rare part that is defective but the guys that repair or build amps for a living can really be hurt by this kind of crap.

It's kind of funny in one respect how when I was a young kid in the early 60's, that things made in Japan were considered junk for the most part.
Nowadays you know you have a quality item if it is made there.
Even Korea is putting out some nice product these days.
So now we have to go through all of that again as China gets their act together with their growing pains.
I wonder how long that's going to take?

[iknowjohnny]

The whole picture is apparent now. This is also why the .001uf worked ! I just put one of those bean shaped 470's on the first filter before the gain pot and now the .001uf works great on the gain pot. Those caps almost seem to remove high end ! It's truly bizzare. If I had to describe them in this context i waould say they don't add any highs but they somehow DO add that kind of sweet spongier feel that a 470uf/470k filer does in a JCM 800. Anyways, now i realize exactly what happened, and now it sounds exactly as it did before this whole fiasco started. Crazy !

[M Fowler]

The PEC and Bourns are long thread 3/8 inch that I use for faceplate amps. I get the Bourns from ApexJr.

[iknowjohnny]

i don't see any pots there. can you point me to the exact page?

[M Fowler]

http://www.apexjr.com/Bourns.htm

Its right on the home page too.

[iknowjohnny]

Thanks. Are those bourns any better than alphas? I also see they have CTS with switches for even less in 250k and 1M. I wonder whether those are audio. I would think so. Anyways, let me know what you think about the borns compared to alpha. The threads look long but the pots look about like the alphas as far as quality. Good thing about apex tho....i live 3 miles from them !

[M Fowler]

Sorry its so subjective that we could argue this one for a long time.

I like them and use them all the time. They are stiffer feeling then the Alpha pots which I like better. I like the feel, the construction, the fact that their 3/8 dia shaft hole size, 3/8 long thread shaft and 1/4 shaft for knob.

There cheap enough that you can try them out. I get them at larger quantities because they are what I mainly use. I do like PEC but at $9.95 per pop I use them sparingly. If a customer wants them there going in no problem.