trinityamps.com

Hey folks,

I mentioned this in the meat of another thread, but I suspect it got overlooked.

Last week, I discovered that my lightning had a 12AT7 in V2 instead of a 12AX7....So I switched out the tube with a known good one..and fired up the amp. The amp sounds great clean. Alot more punch and clarity...

However, when I turn up the gain...I get buzzing...a fizzy almost metalic buzz. I was able to issolate where the buzzing starts....by plugging into the low input, put it on mid-gain...and do some light/hard pick attack.

On hard pick attack, (into the low gain input/low-medium gain setting) The buzzing cuts in and out very sharply. Hard pick attack, it (the buzz) comes in...but before the signal fades, it abruptly drops out.

On greater gain settings (or the higher input) the buzz is pretty much there all the time.


Any thoughts guys? Where do you suggest I start looking first?

-Frank

Tubes can go that way. Even new ones. They can get a mechanical/buzz to them. Try damping the tube (with your fingers I guess) to see if that makes a difference. Try another tube in V2 - a known good one. If none of that works, we'll work back from that.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

OK,

We'll it's been a while since I was able to turn my attention to the amp....but I just tried several known good preamp tubes in all sockets...I can say with some reasonable certainty that the buzzing is not caused by a bad tube.

It did change slightly with one of the tube swaps, but I m going to attribute that to possible variances in gain factors of the test tubes I used, since this buzzing wasn't entirely apparent during the period of time where I had an ECC81 in v2...

Any other ideas? I'm tempted to get out the chopsticks and start going to town on the lead dress.....and if I can get a buddy over here later to play the guitar while I do that, I'm going to do so...

But I'd love to amass a good checklist of things to try before I crack open the amp......

Any ideas?

I just went through something similar with my 5e3 build. In fact, I think reading threads here and on 18watt.com helped fix it. I did my 6v6 heaters at 5 instead of 6.3, though they still worked, but after I fixed that the buzz/noise was still there. I noticed my ground scheme had the filter caps' grounds going to the same point as the other grounds, so I moved those to a different PT lug, and that fixed it.

Are you using shielded cable? Are your leads short, and when they have to cross each other do they do so at a 90 degree angle (ie minimize interaction)? Check for cold solder joints? Heater wiring twisted good, and tucked down as close to the chassis as possible? Tried swapping the OT wires just in case phasing is in there? Twisted the OT to the output jack? Probably all stuff you have already checked, but you never know. Hope this helps.
john

It sounds like it could be:

1. Something parasitic
2. Mechanical
3. Crossover distortion

Does it do this with the volume up and master down? If so, it must be #1 in which case I would check lead dress--especially grid wires. Be sure your input wires are shielded and the grid wire running from the volume pot to V2 is shielded. You can also put a 470K resistor on that wire right at the tube socket to help block interference and shave just a tiny bit of the upper treble registers off your signal.

It could also be 3, but that is more likely if it buzzes with master up. Mechanical stuff can be as simple as filter caps vibrating. They can make a rattling sound (obviously), but they can also be microphonic and inject noise into the signal.

Crossover distortion is trickier to solve. I recently had a Lightning with this problem and ended up running V1 without paralleling it. It didn't make too much difference in gain and it solved the problem.

_________________
--s2
www.s2amps.com
www.category5amps.com

Hmm, Steve....interesting. Thanks for the insight. I suspect, right off the bat, that it's three. As I don't believe there's anything mechanical going on.....and it tends to happen when there's significant volume.

Altoouuuughhh....I'll have to try it out tomorrow low volume just to be sure.

I'll get back to you about it....I'm also goign to reflow all the solder joints, just in case there's a cold joint somewhere...

-F

Hey everyone...

Ok, it's been a while since I've had the time to crack open this amp and start giving it some attention...but I finally spent a good 2-3 hours with it this afternoon. I reflowed every flippin solder joint in the amp, swapped tubes, shortened lead dress on pretty much every lead where there was even a 1/2 centimeter of excess....

I've still got the problem...

here's some more info for anyone who feels it in their kind heart to help troubleshoot.

This problem happens at ALL points on the master. I guess that would fall in line with s2's suggestion that it's parasitic.

I've also noticed that it *really* is noticable on the low input...but the higher input it's harder to hear. I still believe I'm hearing it on the high input, but perhaps since theres more signal coming into the amp, that the buzz gets covered up more...eye dunno!

But it's definitely there...when I plug my tele into the amp, on the lower input...it's great until about 5 on the volume (gain) knob...then between 6-8 and the buzz/static comes in and cuts out when the signal dies off....and after about 8, it's pretty much there full time.

I'm half tempted to tear out the input section from v1 to the input jacks and rewire things and see what happens...

If this is a combo, then I'd be checking for mechanical problems. Heads are less suceptable to this. I had a cap that buzzed against the board once. Got worse the louder it was played. The other experience with rattle was bad tube mechanics. It took a signal generator to find it.

Are your input jacks in good condition? Did you resolder them. Sometimes the contacts done make perfect contact.

I have to say, I've never had this problem on a 15 though. What layout did you use?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

This problem doesn't get worse with volume. I can have it pretty darn low, and it still buzzes. It's dependant on the volume than the master...



Yeah, twice...no change.



Don't shoot me.....Yours!!

Check the bias resitors. Maybe one is off and one tube is one theedge and goes over when payed hard.

Got any interior shots?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Here goes

Checked resistor values...everything seems ok...

-F

Frank,

I checked against the layout and from 'what' I can see things look fine. I'll give it some more thought.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Stephen....I thought everything was ok. Being that it's only my second amp, I am totally anal when it comes to double checking layout...and this seems to be inline with things.

Two questions I had...lead dress looks ok...right?

I had concerns about the leads from the pots to the board...since they seem longer than other Ceri@tone chassis's I've seen. I think Nik moved the board mounting holes closer to the PT. If you look at s2's lightning, his board seems to have more clearance on the PT side.

Also, Could it be components. For example, I'm using these really small xircon caps for the cathodes on the preamp. Everyone seems to use the atom/vishay stuff....maybe that's a problem...

-F

Lead dress looks OK to me. The caps should be fine, but it could a faulty cap. Is there any way to isolate around which tube this happens? Since you talk about the volume affecting, I would start looking/poking around V2. This is a post PI master volume design. What are the volatages?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I though the voltages we ok...My voltages were a tad high, even with the non-hammond PT. Regardless, a 5-ohm 10-watt resistor inline with the incoming AC (you can see that in the picture above) knocked my B+ down to normal ranges...I can run another voltage audit, but I think I remember things were ok.

As for isolating where this happens...how do you suggest I start doing that? I've swapped tubes and it doesn't seem to change that much...

Obviously, since this happens at all volume levels on the master, I have to assume it's happening prior to the master...but that's not eliminating that much of the amp, given that the master is pretty much right before the el84s?

-F

You know...I plugged into the amp just now, and it seems actually worse!

So I recorded it...halfway through the recording, I dropped the volume knob down to 5 (it was at 6 or 7)...and you can hear it go from almost always buzzing...to intermitantly buzzing.

Perhaps hearing the sound could tip off to someone what exactly the noise is...and it might help in troubleshooting.

http://www.ic.sunysb.edu/Stu/fbenenat/lightningnoise.mp3

Also, I might add that this was recorded with the master BARELY above 1. You could talk very softly above the volume of the amp.

-F[/url]

Loose connection? Did you try another guitar? Bad guitar cable, try another one?

Bad cap somewhere? For fun, try a lower gain tube in the PI.

Could be a maxed out tube - too much gain - bad parts around the tube or bad bypass cap.

Hang in there..

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

That's definitely not a possibility. Problem exists on multiple guitars and multope cables.



You know, I initially built this amp with with a 12AT7 ( I think it was in the PI) and it wasn't nearly as noticable...but I still heard an underlying fuzz...so I suspect that it just reduced the buzz in the overall mix.



You know, these are the two possibilities I keep coming back to...somewhere in here, there's gotta be a bad component that's forcing a preamp tube to act nasty. The problem is issolating the part. I know that I can determine a bad cap by seeing if there's voltage on both ends (thanks to s2)...but if there's a resistor in parallel...how do I then determine that?

For example, let's take v1. The off the cathode, you've got a 1.5K resistor and a 25uf cap. Without soldering....I'm sure I can determine that the resistor is ok....but if I crank up the amp and measure voltage on either end of the cap/resistor pair...Wont I get voltage on either end of the cap, since a resistor is in parallel with the cap?



Don't you worry....I'm not giving up on this one, if it kills me....or I die before I solve it! ... or both!

Well, I did another voltage check....I've always been on the seemingly high side of things. But regardless, here goes:

Transformer is putting out 295vac per side on the secondary and 6.4vac on the heater line.

Positive leads on filter caps (starting from PT side, going left to input)

361v
235v
322v
360v
268v
333v


V1 (pin/voltage)
*************
1/123v
3/1.36v
6/123v
8/1.36v

V2 (pin/voltage)
*************
1/165v
3/1.38v
6/267v
7/165v
8/171v

V3 (pin/voltage)
*************
1/239v
2/25v
3/68v
6/236v
7/25v
8/68v

V4 & V5 (pin/voltage)
******************
2/9mv
3/7.4v
7/358v
9/234v



Hope this helps....

-Frank

DAMN!!!

Well, as some of you might know...I had to replace the V1 tube socket on this amp. Pin 1 snapped on my when I was sucking off some solder...

I had assumed that a faulty lead connection from the inputs was the cause of the sizzle...and upon replacing the socket, it would correct itself.


I was wrong.

At this point I'm desperate...it sounds like frying eggs...the amp sounds only if I keep it on the low input with the volume under 3...after that, it's just nasty.


Please help guys, I'm desperate here...I've reflowed every freaking connection on this amp....

Thanks for any help!

-Frank