trinityamps.com

that BBQ thing kills me, ha ha

So what are the values that you have that fixed it 100%?

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Les

http://www.soundclick.com/unimind

Don't worry about messing things in your amp just yet. I have order a various supply of parts and different values to play with and will try when they get here ~ two weeks. But of course after i finalized my my order , Dammit forgot the 220k's




Where were you in the PI plate mods at the time the values of R13, R14 and R15 and what was the value of the cap that you had across the plate resistors.

I'm not to sure if its gonna matter if you mix both channels on both sides of the PI looks like r12 is the combined feedback res and presence pot and c7 is the presence cap. (could be wrong on that part)



I'm putting in the mods one at a time too see where they stand and continuing on if there's no issue on the tone gain side of thing. Fizzy fizzy is a whole different matter then the tone gain side of things I believe .


Now if Apple just had SIRI on my macbook I could dictate this instead of typing

I have the 1n4007 diodes and zeners installed as per the attached image though the zeners in my amp are 3v/5w - I also have 220k not 470k resistors as pictured

Here is an exerpt from my thread at Ampgarage that should give people an idea of where I was going with this

Katopan - my question about the Ruby mod is more related to my general lack of understanding of the finer nuances of tube circuits in general - not so much the crossover distortion concept in Paul's article but more that I was going so far below what he proposed for zener values and was not really sure what I was doing by taking it to that extreme

your last few posts in this thread are helping it all gel for me

Gary, essentially I started experimenting with smaller zeners that were tighter in value to those Paul Ruby proposed to kill crossover distortion because I was unable to scale my vvr down without crossover distortion appearing

He suggested 1 - 2 volts higher than grid cutoff voltage, and most threads I have seen where people have implemented Ruby clamps used the cathode bias voltage at idle to set this value - On my amp I had 15v zeners in the ruby clamp that worked ok at 100% power but the distortion reared its ugly head pretty quickly when I scaled down the amp

When I started trying the lower value zeners I noticed on my amp a correlation between the bias voltage and zener value in the Ruby clamp where if the zeners were 10v, I could dial down my vvr to where the bias voltage at idle was -11v and not hear the crossover distortion that is otherwise prevalent in my amps without the Ruby clamp - a 1 volt difference (ignoring the negative).

9volt zeners, I could scale the amp down to -10 volt bias at idle with no crossover distortion - this correlation continued as I went lower in zener values

If I scaled the amp below the correlated zener value, I started to get crossover distortion progressively worse as I went lower

I tried a few lower values until I tried 3volt zeners the other day at which time I could dial my vvr down as far as it goes on my fixed bias amp

I tried 5v zeners on another cathode biased amp that was buzzy without a Ruby clamp and it also seems to work pretty well all the way down

I have not tried the 5v zeners on the fixed bias amp nor did I have every value zener under the sun to try - I just had a few random voltage zeners going down from 16v (which is 2 volts higher than my idle bias voltage of -14v with the amp at 100% b+ voltage on the vvr - again ignoring the negative) and found that a low value zener seems to solve the scaling issue

this is that entire thread:

http://ampgarage.com/forum/viewtopic.ph ... tt&start=0

Not sure I understand the question. I had the same values that are in the Plexi Brown schematic. Cap is 100pf.
It's a little different than that. C7 is the coupling cap for the normal channel.

_________________
Les

http://www.soundclick.com/unimind

Is this a true "fixed bias" as in a negative voltage bias supply? Are you scaling the bias supply as well with the Hall VVR for fixed bias?

Right now with the 6CM6s in my amp I have -29 volts from my bias supply into the junction of the grid bias resistors (100K in my case). I have 12 volt zeners so 12 vs the -29 would be comparable to your 3V zeners to your -12 volt bias. What do you think? I will give it a try.

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Les

http://www.soundclick.com/unimind

Tried it. Did not make one bit of difference. Now I do not know if it matters. I used jumpers to hook it up before soldering but you would think I would notice something.

_________________
Les

http://www.soundclick.com/unimind

the vvr b+ input for the Hall vvr is right off the standby switch and this particular Hall VVR scales the bias along with b+

I'm not sure how low you would go with the bias voltage you have though I can't see why it would be any different on a relative basis with the different tubes.

But for your amp you probably do not need to go as low as I did it is not scaled - I was able to kill the swirlies with zeners that correlated to a positive voltage about 1 or 2 volts below the idle bias voltage as opposed the commonly used suggestion of approx 2 volts above the bias voltage at idle. Using the suggested values in my amp I still had some swirlies though less than with no Ruby clamp at all.

When scaling the amp down it seemed like I needed the zeners to be 1 volt lower than the scaled bias voltage (ignoring the negative sign) to not hear the buzz - several different values exhibited this correlation. I scaled the voltage down and tried 4 or 5 progressively lower zener ratings to see where the buzz occurred or not and each time as I went lower the amp still sounded and operated OK but with no buzz as long as the bias voltage was roughly 1 volt greater (ignoring the negative sign) than the zener voltage value

It was scaling the b+ way down with the vvr that required the really low value zeners.

The part I thought people would find interesting is the correlation I found between the bias voltage and zener rating needed to keep the swirlies in check. Should apply whether the amp is scaled or not

I must have been typing when you posted

did you have the zeners oriented correctly?

If you did it still might be worth a try to use a really low value in case the ratio idea does not hold the same between tube types.

In any event its too bad if this is not a universal fix - sure worked night and day on 2 of my builds

Yeah I followed your diagram as to the orientation with the zener cathodes on the grids and the diode cathodes to the bias supply. I will have to wait to buy some lower voltage zener next week.

I did however find the Heyboer fat stack. It is at http://allenamps.com/parts.php


No 4 ohm tap but I can re-wire my cab to 16 ohm. Now I just need to find an extra $60 somewhere.

_________________
Les

http://www.soundclick.com/unimind

quoted wrong resistors i though u changed r 15 to 820R and r18 and 19 to 220k

What I was getting at was when you first got the fizzs in excess you started playing with the PI to get rid of them. I was just wondering where you tried to off balance the plates. With the standard 470R pi and two 470k PA or the 820R and the two 220k PA. But you did answered the original question.

Interestingly I find that I have r42 no voltage divider on either of my amps - the gain pot has 470k bybassed with 330pf direct to v2a with no voltage divider to ground

I used Unimind's original schem from last year when this thread first started and I missed the 2nd 470k at the cascade switch dumping to ground.

Perhaps that's why my swirlies were so pronounced with all the extra gain. In any event my amps sound great as is but I'll have to try adding it to see if I like it or not

Les, listening to your original "buzz" clips you generally demoed the phenomenon using palm mutes that had a swirly overtone trailing the chord - my "buzz" clips showed ringing chords with the swirly overtones riding on the original notes and the swirl would get worse as the chord decayed. My amp definitely exhibited the same palm mute phenomenon as yours so I assumed we were talking about the same buzz, but perhaps not exactly

Now my amps have NO swirly overtones on ringing notes or chords whatsoever, even dialing down the VVR's - but, they do have a VERY SLIGHT bit of very short lived palm mute buzz, at least more so than other amps I have with el34's or 6l6's. It is only vaguely noticeable on palm mutes or staccato playing and probably only noticeable to me because I spent a zillion hours trying to kill the swirlies on my amps and my ears are so tuned to listening for it. It actually just sounds to me more like a looser bottom end as opposed to a buzz problem now that I chalked up to el84 quirks and does not concern me in the least.

Perhaps that is what you are hearing on your amps vs the crazy swirly buzz I had on mine. I think maybe we were hearing varying degrees of the same thing but perhaps I declared it cured with the my Ruby mod variation when my amps no longer had any weird swirly overtones, where maybe you are still hearing a little bit of palm mute buzz that you are trying to kill?? I don't hear much buzz in any of your new clips..

My amps definitely do not have even a fraction of the amount of palm mute buzz as in your older buzz clips anymore - they did previously

Just thinking out loud

I want to add something here regarding the PI tail resistor and the PI plate resistors mentioned earlier ...

With a Plexi 10k PI tail you need the 82k/100k plate resistors to maintain the balance in the PI plate voltages and output

With an 18 watt 47k PI tail the voltages and output are pretty well balanced with two 100k plate resistors

Ok thanks. I get that. But where should it be plate voltage area + - 10 v or closer ?

And bear in mind that in a guitar amp we generally prefer the PI to be slightly unbalanced, to help prevent all those nice even-order harmonics getting cancelled out. If it was a hifi amp, it would be a different matter.


If you're talking about the PI anodes - with both having 100k resistors, they will be fairly close in voltage to each other, typically a few volts DC. Having said that, the DC voltage at the PI anodes isn't too critical.

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Great tones come in small glass jars!

Ok Since I have a working amp again I will post a clip of a brown mod. Although I have not got the unimind's gift of playing VH riffs here go's

I tried the up close and personal sm 57 but could not get to sound like I hear it, in an open room but I know the mic eq thing was a major part of what was originally done in the studio.

So I opted to an apex 420 (clone of neuman) as close as I could get to the cab without it clipping ( about six feet)

settings where as follows with boost on


VRM was as far down as I could get it without it getting too funky

Cab was a 2x12 closed with late 70's black backs 55hz cones

This is what I did in GB only master effects where the echo and reverb master


and the clip

http://soundclick.com/share.cfm?id=11961921

Now if I could just get the pictures to show where I want them too

Sounds really good. I like the way those blackbacks sound. How are you liking the mods? What guitar/pickups are you using? How does it sound with the settings dimed? (except the master. with the vrm down you want to keep the master down as well)

If you have a 10 band EQ in GB try these settings for VH1 tones.

Tweak to taste. My pickup has a lot of midrange so I cut the 500Hz a little more. Tweak the upper frquencies to taste.

_________________
Les

http://www.soundclick.com/unimind

I Like the mods but I have mostly just done the preamp side of things (a little different than your's) and one change in the power amp an no PI changes yet.

The guitar is a 91 LP STD original pickups, some upgrades in the bridge tail piece and caps.

Cranking every thing is a little different and in the case of the master I still need it up as its an integral part of the way it sounds. Turning the vrm down changes the tone and you need to ajust for that. I did not install ppimv or a fixed bias and have no plans too. The one change I did make from yours as well is I went with a 1meg gain pot.

I got closer to your eq settings when i was playing around with a close mic'd 57 (trying to make it sound like what I hear coming out of the cab). But using a Condenser 6 feet away got me there a whole a lot closer ,quicker. I ll play with the your eq settings next time I mic it with a 57 up close .

I'll check next time and measure the B+ I'm using.

Yeah. I need to get a condenser. The 57 up close gives it a lot of bite but not exactly what it sounds like in the room. Having the condenser gives it more depth. Most studios will blend the two for the best sound with bite and depth. Your amp sounds great, especially with the blackbacks. I would like to hear more clips with a touch more gain.

_________________
Les

http://www.soundclick.com/unimind

Congratulation unimind you AMP is fantastic! Please post sample with ain'talking bout love and Panama. Is possibile one Button for activate Panama or ain'talking bout love tone studio?(see isolated Guitar video on YouTube)

Thanks