Ruby Mod, snubbers - 18 watt

[Lindz]

Another 2 noob questions from me.

My 18 watt build sounds pretty good, is a little hissy but also has a bit of an odd buzz or overtone that trails the notes or chords when I play and it is really cranked up.

see clips attached, one mine and one from another guy with the same sort of issue from another forum. His single note muted clips probably demonstrate it more than my chords but if you listen to the chords you can hear a swirly buzz overtone as the chords ring.

I've read a lot about "buzzy" 18 watts the past few days and came upon the Ruby mod articles and threads and thought my issue may be along those lines - crossover distortion.

Expert ears may know what is going on, and any input would be appreciated. Both amps are dimed on TMB channel.

http://snowboardmaterials.com/tmb_fizzz.mp3
http://www.unimind.us/fizz1.mp3


If this sounds like crossover distortion, would one of you guru types help me with a total layman walk through of how to do this Ruby mod?? - I've seen schematics but even that is a bit over my head. I'd need a parts list and either layout or super elementary instructions to make it work with my current skill level. If not any other suggestions would be cool too

There is also a Guitar Player mag article about what the author calls snubbers that also seems to address a similar issue - see attached (I hope that mentioning it is GP magazine it is kosher to post article). I've researched what I can about snubbers but the term seems to apply to a variety of different applications - I am more interested in someone schooling me on the type listed in the article. Does this type of snubber address a similar issue to the Ruby mod?? Inquiring minds would like to know and really appreciate any expert commentary

[Phil_S]

Get the Zeners. Likely the proper fix (Ruby Mod).

[Tone Lover]

So which magazine is this from I have never seen that type of set up before, I would read the article.
Thanks Bill

[Lindz]

That article is from Guitar Player magazine

[yowza]

This is from the newest issue of GP (August) on news stand now with Rob Ickes on the cover. The article was written by Dave Zimmerman of Maven Peal amps.

[Structo]

Isn't that like a conjunctive filter on the output?

[dreric]

I don't know about the tech...........but it looks rather Torresesque!

[Tone Lover]

Thanks guys I like to read everything, In case I run into that type of problem. although i dont know how much of a Dan torres fan I am have you ever seen the inside of hos amps. Maybe it was just the one put up on the net but Im a relative newbie and my lead dress looks like a rolls royce compared to his volkswagon.
Bill

[ampgeek]

Hey Lindz,
I am putting together an 18W layout and parts list and will include an option for the the Ruby zener mod in my build. No drawings as of yet but looking at a bunch of things and am getting familiar with the topology.

Shoot me a picture of your amp's guts (or a drawing of the layout that you followed) and a schematic and I will have a go at getting you set up for trying it in yours.

Of course...you must promise to share your results with me along the way!!

Cheers,
Dave O.

[Gaz]

FWIW, I'm fairly certain that Paul Ruby has said that the buzz he was experiencing was finally traced to the less that adequate output transformer. Has anyone else read that?

There's a chance I'm getting it confused with James Marchant who came up with the "giant" bypass cap mod on the output stage (1000uf or so) to keep the bias steadier in order alleviate crossover distortion in 18W style amps. He also concluded that mod was only necessary in a particular amp where the OT was quite undersized.

[ampgeek]

Interesting!

He does discuss swapping the OTs in this article and concludes the buzz isn't totally related to the OTs. Maybe the jury is still out?

http://www.paulamps.com/18watterbuzz.ht ... Distortion

Anyway...it doesn't appear to be much of a physical mod if following the typical 18W topology. Just strapping in the diode network parallel to the existing EL84 470K grid reference resistors.

Pretty easy to try and see it appears.

Dave O.

[Deric]

FWIW I think it's worth a try. I've built several 18 Watters (with both very good AND very questionable output transformers) and the Ruby mod made most of them sound better. Never paid attention to which OT was in the ones that had the biggest improvement.... I do recall on most of them that the change is very minor - just reduced the "fizz" on the decay of notes when cranked. Like Ampgeedk said - it's very easy (and cheap) to try.

[ampgeek]

It sure seems that way Deric!

Sounds like one would measure the voltage at the top of the cathode resistor, go here and buy a hand full of various zeners with VZ both above and below the measured voltage (+/- ~2V). Below in case one finds a little bit of fizz is desirable. And...have at it!

http://ca.mouser.com/catalog/catalogUSD/643/483.pdf


I guess if one were clever, a mechanical connection between the diodes could be devised. Probably want to keep it as close as possible to the circuit board plane as the power tube grids are at the other end. Stray signal interference.

Does this look right? I chose the 18 W layout closest at hand as a model.

Cheers,
Dave O.

[Deric]

Yes - at least that's what I did. Here's a pic of an amp using the same layout (with an added PPIMV or "Drive" control - just ignore the extra wires)....

[IMG:160:120]http://i40.photobucket.com/albums/e243/stumper1/Samplifier/th_LiteIIbIII006.jpg[/img]

[ampgeek]

Nice and tidy!
Where did you end up on the zener value relative to you bias voltage?
TIA,
Dave O.