Quote from: Kaz Kylheku on July 05, 2013, 03:04:50 PM

Quote from: belleraphon88 on July 05, 2013, 05:09:04 AM
So here is what i did.
Did the tests with the send into my pc speakers, used 3 different tubes. It didnt change anything.
Next i took the tube out and did the same test, still sounded the same.
So cant be the power amp then or tube

Yes; the tube stage is after the preamp and effect send, so it makes no difference.

This is lucky for you because you don't have to mess around in the power amp where you have higher voltages (especially given the tube).

The thing to do now is to make yourself some kind of adapter so that you can use those same PC speakers as an audio probe. A simple setup would be to have a cable which has an alligator clip for ground, and a multimeter probe for signal.  Clip the ground somewhere to a ground point in the amp, and then use the probe to pick up the audio from various sections of the preamp based on following the schematic.  You can find out the first stage where it is happening. It would really help you if you reproduce the issue with some signal source other than your guitar, like using your PC's audio line out to play some continuous tones into the amp's input.

You said earlier that the issue occurs whether or not you use the gain channel; that you can hear it on a distorted tone that is produced by a pedal going into the clean channel. Assuming this is really the case, the problem is really narrowed down.  There is very little circuitry between the input and the effect send that is common to both channels. What is common to both channels is the IC1A op-amp input stage, and and the channel switching and muting FETs Q4, Q5 and Q6. (Well, Q4 and Q5 are specific to their respective channels, but the circuits could interact in some way since channel switching is supposed to be mutually exclusive).  I can't find the logic that drives the channel switching in that schematic, by the way.

If the voltage at the base of Q6 oscillates for some reason, then you will get volume fluctuations or periodic cutouts.  It's not obvious why that would be the case, since the Q6 gate is driven by a voltage divider that is straight off the power supply. Still, if you had an oscilloscope you could easily put a probe on the bases of these transistors to see what the voltage is doing.  If there is such a thing happening, it is probably a little too fast to register on a multimeter, but a scope trace will react instantly.

There is the possibility that it's an issue with the preamp power supply: that basically the entire preamp cuts out due to a periodic voltage brown-out. Your tech would almost certainly have picked up on such a glaring thing!

I made that audio probe!
just took a while, had to drive pretty far just to buy that capacitor for the probe.
I will do the testing tomorrow.

Ive noticed 2day that if i scoop the mids the tone is pretty nuch normal when i play riffs and palmute,  as soon as i turn the mids up i do get  blocking distortion.
Just thought id bring this up.

Quote from: Kaz Kylheku on July 05, 2013, 03:04:50 PM

Quote from: belleraphon88 on July 05, 2013, 05:09:04 AM
So here is what i did.
Did the tests with the send into my pc speakers, used 3 different tubes. It didnt change anything.
Next i took the tube out and did the same test, still sounded the same.
So cant be the power amp then or tube

Yes; the tube stage is after the preamp and effect send, so it makes no difference.

This is lucky for you because you don't have to mess around in the power amp where you have higher voltages (especially given the tube).

The thing to do now is to make yourself some kind of adapter so that you can use those same PC speakers as an audio probe. A simple setup would be to have a cable which has an alligator clip for ground, and a multimeter probe for signal.  Clip the ground somewhere to a ground point in the amp, and then use the probe to pick up the audio from various sections of the preamp based on following the schematic.  You can find out the first stage where it is happening. It would really help you if you reproduce the issue with some signal source other than your guitar, like using your PC's audio line out to play some continuous tones into the amp's input.

You said earlier that the issue occurs whether or not you use the gain channel; that you can hear it on a distorted tone that is produced by a pedal going into the clean channel. Assuming this is really the case, the problem is really narrowed down.  There is very little circuitry between the input and the effect send that is common to both channels. What is common to both channels is the IC1A op-amp input stage, and and the channel switching and muting FETs Q4, Q5 and Q6. (Well, Q4 and Q5 are specific to their respective channels, but the circuits could interact in some way since channel switching is supposed to be mutually exclusive).  I can't find the logic that drives the channel switching in that schematic, by the way.

If the voltage at the base of Q6 oscillates for some reason, then you will get volume fluctuations or periodic cutouts.  It's not obvious why that would be the case, since the Q6 gate is driven by a voltage divider that is straight off the power supply. Still, if you had an oscilloscope you could easily put a probe on the bases of these transistors to see what the voltage is doing.  If there is such a thing happening, it is probably a little too fast to register on a multimeter, but a scope trace will react instantly.

There is the possibility that it's an issue with the preamp power supply: that basically the entire preamp cuts out due to a periodic voltage brown-out. Your tech would almost certainly have picked up on such a glaring thing!

I will make me that audio probe during this week, just gota buy some parts.
Will update asap
thanks for all the help so far
Andrei

Quote from: Roly on July 05, 2013, 07:56:13 AM
We seem to have eliminated the power amp and the valve.

It does it in both channels, the drive channel, and the normal channel when driven hard externally.

Well there are only two bits that are common to both, the first stage IC , and the last three IC4b, 5a, and 11b.  I rather doubt that its the first stage because it would do it all the time, but the last stages only gets driven hard when internal drive is selected, or when the normal channel is externally driven hard by a stomp.

So I'm on RG_RH G3 Preamp.pdf, ref: C7, IC4b preceded by FET switch Q6.

Now my intuition says, an enlightened guess is, that we are not chasing a faulty component.  I think everything is working as it should, but it's the conditions that it is being exposed to that is causing the blocking problem.  I'm struck by the switching FET Q6 and the diode in its Gate circuit.

The function of this FET switch seems to be to mute the preamp unless something is actually plugged into the input.

We also have a number of connections at this point, a three conductor cable that apparently connects the Fx Send and Return sub assembly, and the contacts in the Return socket itself, all in the signal path.

A known good lead patched between Fx Send and Return would at least eliminate the return socket contacts.

Ive used a patch cable between send and return, didnt notice any difference if that is what u asked

Quote from: stormbringer on July 05, 2013, 05:50:33 AM
That means it should be the preamp that's the issue.

What i would do first is check for electrolytic capacitors with any kind of bulge. (although they can still be bad without it showing). Do the preamp caps look ok?

They all seem fine, no buldges

Quote from: Kaz Kylheku on July 04, 2013, 11:11:49 PM
So, it goes away after a tube swap and then comes back? That doesn't mean that it's the newness of the tube that fixes it, but simply that the tube socket was exercised.  Try confirming your theory by pulling the tube and popping it back in a few times. (Power off, of course; I don't mean live).

Maybe the tube socket needs cleaning. (I use a toothpick with a very small amount of toothpaste to polish inside tube sockets; then another toothpick and lots of 99% pure isopropyl alcohol to clean up after the toothpaste.)

Maybe the tube socket or something else nearby has a cracked solder joint.  Inspect all solder joints and repair if necessary.

Clean all jacks and potentiometers.  Pots can make weird volume changes.

Check all hookup wires, like to the speakers.

You can test whether this problem is related to vibration by taking the speaker out of the amplifier (while keeping it connected) so that you can play test notes without rattling the enclosure.

You said:

Quote
It does have a effects loop. I dont have a external cab to test it with, is there any way i can test it.

You really have to do this test! Plug the effect send into a pair of computer speakers. Get an adapter plug for this: quarter inch plug, with 1/8" socket.

Knowing whether the problem is before the power amp or not is an important piece of information: divide (the signal chain) and conquer.

So here is what i did.
Did the tests with the send into my pc speakers, used 3 different tubes. It didnt change anything.
Next i took the tube out and did the same test, still sounded the same.
So cant be the power amp then or tube

Quote from: stormbringer on July 04, 2013, 03:06:24 PM
I'm really no expert here. Experienced player, kinda new builder. so better wait for the "big guys" here to come with more qualified analysis. (mr Fahey, Roly, hint hint).

But just a thought.. are you sure that the speaker itself is ok? any chance to test the send out to Another amp? and Another preamp or hell even the DS-1 into the return? or disconnect the speaker, and connect to an external cab (Watch the impedance). As somewhat of an amateur, that's what i would try just to find which of those 3 is causing the issue, and move on from there.

Edit: By the way, wasnt that the amp that was modded by some Tech to get cooler? If that is the case, it would really help knowing exactly what was done. Maybe the mod has something to do with your problem? Did it behave like this Before the mod?

Hii
The guy that did the mod told me he went over all the components and they are all 100%, the amp had a stupid buzzing as well that alot of people with these G3 models complained about, he somehow got rid of that as well. The speakers were tested as well, they sound fine. If you can hear the amp in person ull be able to hear the problem much better, my cam doesnt pick up all the weird noises i get when playing the high strings.
Ive been thinking of just taking it back to that tech, he designed mosfet amps for a few years, hes good but he takes forever, he had my amp for 4 months.
The amp did behave like this before the mod, it was even worst back then, the only way i ever got the amp to sound like it should was when i replaced the tube in the amp.

Quote from: J M Fahey on July 04, 2013, 07:51:08 AM

QuoteThis is the first amp i have that does this when the gain channels level gets turned up.

Agree.
That amp has **incredible** gain, way above anything you used before.

To put it in perspective:

a classic Overdrive pedal (Tube Screamer) has gain 100X (500K/4K7) before hitting the diodes.

a classic Distortion pedal (MXR Dist+) has gain 200X (1M/4K7).
Your DS1 is also around 200X gain.

a classic Randall amps (RG100) had 2 20X Fet gain stages cascaded in the Red channel, for a gain of 20x20=400

This was Dimebag's amp, you won't call his sound "puny" or similar.

Your amplifier, in the "Gain 1" channel has (cascaded) the following stages:
IC1A (3X) + IC1B (367X) for a whopping 1100X gain before hitting clipping diodes D5/D6 .
And that's the "mild" channel . :loco

In the "hot" Gain 2 channel, gain stages are again IC1A (3X) + IC2A (41X) + IC2B (142X).  Do the Math.

Ok, to save some time, here it is: 3*41*142=17466 X  xP :duh
With that amount of gain, squealing is guaranteed, with any guitar on this Planet, specially if you are within the same room.

As I said before, such a monstrous amount of gain is somewhat controllable on a big , Rock Festival stage, because you are:
a) typically 10/15/20 yards away from the speakers.
Or more: you'll probably use a wireless transmitter .
b) you are in open air, or if "inside", the roof will probably be 25 yards above and the Stadium walls will be 30 to 80 yards away, same thing.

to which I should add :
c) usually the amps shown onstage are off or just props, and the actual amp miked is **backstage** .

For one real example from a Forum member here, look at this:

http://youtu.be/3QEjiJ56Zac

You'll see our friend onebaldbloke there (I guess you'll recognize him from his nickname), playing in a big stadium, with excellent sustain.
Oh, the wall of Marshalls?  Look nice, huh?

He was *actually* using a little Squire SS amp, plus a Rat or Big Muff pedal:

QuoteI've always had a fondness for SS stuff. The biggest selling album I ever recorded (multi Platinum here in Oz) was done with a $50 SS Squire with an 8" speaker, though everyone seems to think I used valve big stacks - ah well.

QuoteThat live stuff is the same little Squire out the back in a road case with a Sennheiser 421 mic on it.
Fun setup!

QuoteAll those Marshalls on stage and what we're hearing is a miked up Fender Squier 15 hidden in back of a road case! I love it. Sounds good;

The full thread:
http://www.ssguitar.com/index.php?topic=2560.0

PS: in a nutshell: at those gain levels, *any* guitar will squeal, unless you get far away from the speakers.

EDIT: I forgot to mention (although it should be real evident): they are Australians !!!!

I did another vid, with less gain, you should hear it better now, especially at 00:14. no pedals, just the amp
http://www.youtube.com/watch?v=Hd14djOlLu4

Quote from: Enzo on July 04, 2013, 03:11:52 AM
Here is a simple experiment.  Stand away from the amp, and have it set up to play, and presumably the noise will result.   Now turn 90 degrees and face to the side.  ANy change?   Now another 90 degrees, and face away from the amp (well the speakers really).  Any change, and finally another 90 degrees so you are facing the other side.  ANy change?    If the direction you aim the guitar changes the sound in any way, it is feedback.   Feedback in a high gain amp can happen even at low volumes you can talk over.

That only changes the feedback to some degree. But the amp still makes those extra notes. What i found was that chords on the Low strings sound fine, only the high strings are making that ping crackling noise. I tested it with 2 different guitars just to make sure its not my guitar.

Quote from: stormbringer on July 04, 2013, 02:55:53 AM
What are your settings on the sd-1? Normally to boost, you go with lowest possible gain, and max volume. if you run drive full on the pedal and then distort again through the preamp, squealing is more or less inevitable.

If you bypass the sd-1, does it still sound that way?

Hi
My settings on the sd-1 are, drive: 2 and level on 8. sometimes ill max the the level to 10.
If i dont use this method, it sounds the same, just with lots of noise and feedback.

Quote from: J M Fahey on July 03, 2013, 05:16:12 PM

QuoteMy problem is definitively not feedback and too much gain.

Both go hand in hand.

What would you call the permanent howling between plucked notes?

Please reread my comments while listening to the video, time and again.

Plus, others are noticing the same as I do, maybe using different words but the general meaning is the same.

Phatt said it could be blocking distortion. what ive read about blocking distortion sounds more like what im experiencing. Ill record a better vid in the morning, i usually use a boss ns-2 and a boss sd-1, i put the amp gain on 5 and boost it with the boss sd-1.
The howling betwenn notes, do you mean that repeated notes?
what that is do not know. This is the first amp i have that does this when the gain channels level gets turned up.

Quote from: J M Fahey on July 03, 2013, 04:22:39 PM
You have no *tube*, nor even *amp* problem.
You are using way too much gain and your *guitar* is feeding back in an uncontrolled way.

1) you pluck your guitar 13 times.
Count them because it's more precise than referring so such and such second, the video is short, but enough.

2) video can be divided in:
silence/7 plucks/silence/4 plucks/silence/2 plucks/silence

"silence" is a joke, your guitar is howling all the time, in an uncontrolled way, normally at a relatively low frequency, more precisely what the open strings are tuned to.

When you push a string against the fretboard, it will howl at a different, higher frequency.

That higher frequency produced  an unplucked but howling/oscillating string will beat with the frequency of the actual plucked one, and since the amp is *heavily* distorting, it will produce 2 beat frequencies, one the sum (it will sound as a dissonant octave) and one at the difference, which will be a low frequency which to boot will modulate volume, like a crazy tremolo.

That's what you hear as "chirps" or "bursts" because thanks to the unstability the howling string starts and stops at random.

You can hear it *clearly* on plucks nº:

end of 2 , beginning of 3, low frequency modulation, sounds similar to a tremolo/vibrato/phaser/chorus

8/9/10 : higher frequency modulation, sounds like "chirping"

That it's a guitar feedback problem and not an amp one (and even less a *tube* problem, as confirmed by:

Quote
Its only the dirty channel that gets effected, the clean channel is fine, but if i use a OD infront of the clean channel it does the same thing.

Solutions?

a) use somewhat less gain

b) play further away from the amp
It will drive you crazy in the bedroom or garage, won't bother you onstage at an open air festival.

c) keep playing a long time and apparently "it willl disappear on its own" , which really means that it won't "disappear" but when you become an experienced guy instintively you'll avoid it, one way or the other.

d) don't waste time or money on substi-tubes (specially in *this* amp), use the prescribed 12AT7.
That's not a "gain stage" which offers some flexibility but a current buffered speaker driver.

ill make another vid with the gain on 1, it does the same thing.
Ive been playing guitar for a few years. My problem is definitively not feedback and too much gain.

Quote from: Roly on July 03, 2013, 03:37:42 PM

Quote from: phattthat is more like blocking distortion,, nothing to do with microphonics.

Totally agree, that's not "microphonics" in any sense I understand the term.  In fact it sounds almost like a beat note because it changes it's period depending on what note is being played.

When i play chords, especially when palm muting, it like farts out.

Quote from: phatt on July 03, 2013, 10:05:31 AM
Yeah that is more like blocking distortion,, nothing to do with microphonics.

The Amp works it's just got some issues so in time clever people here might nail down the offending part. Unlikely to be 3 bad Valves in a row so maybe a dying Capacitor or something in the design is prone to problems.
Phil.

I did some reading up on blocking distortion, it does sound like the problem im experiencing

Quote from: Kaz Kylheku on July 03, 2013, 11:04:34 AM
Unfortunately, the PDF doesn't give the schematics for the entire amp, just back end sections.

It sounds like the signal is experiencing short volume dips or cutouts, which repeat at a low frequency rate of several times per second.

This suggests itself to be a motorboating oscillation in some circuit that affects the bias of a stage.

There is no outright reason to suspect that it is in the power amplifier. Even if it happens in every channel (which I suspect is not the case from a comment given), there are other common circuits that the signal goes through besides the power amp.

Does the amp have a pre-amp out jack (or effects loop send) and can you hear the artifact in that output? If so, that tends to eliminate the power amp.

Does the artifact occur only in one channel? That tends to blame that channel.

I don't think you're hitting the tube hard just because you turn up the gain on the gain channel a little bit. What can hit the tubes hard is volume. The tube is just the differential summing stage for the amplifier's feedback, generating the error signal that is amplified.   FET TR7 provides the voltage gain after that and drives the output stage.  The gain of the amplifier is fixed, so the tube stage has to have reasonable clean headroom to pass through signal when the amplifier is played at the maximum volume.  I.e. it is overall volume that will drive the tube, not gain on the gain channel.

Ive attached the pre amp and power supply pdfs

It does have a effects loop. I dont have a external cab to test it with, is there any way i can test it.

Its only the dirty channel that gets effected, the clean channel is fine, but if i use a OD infront of the clean channel it does the same thing.

Yip, the gain can be on max, its the level control on the gain channel that causes it to go all crazy.

Quote from: J M Fahey on July 03, 2013, 07:12:33 AM
Agree, you are not describing what happens.

Don't "diagnose" (as in "it's the 12AT7" .... ""it happens because the tube gets pushed" .... etc.) , just tell us:
"I raise volume past 1 and then _________________________ "
Fill in the blanks.

An MP3 or a You Tube showing it *on yours* will help a lot.

EDIT: we posted at the same time.

Sorry but your description is confusing, post some MP3 or Video.

You may have a problem, but I wouldn't describe it as Microphonics.

Hi, sorry if its confusing
here is a video clip i recorded
http://www.youtube.com/watch?v=Onolh61F_Ao&feature=youtu.be