Diezel VH4 Channel 3 + 4 Problem

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cameron711

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H all, I have a diezel vh4 head loaded with the 6550 power tubes. it sounds unbelievable in channels 1+2, minimal background noise at all. But in channels 3 and 4 there's this really weird bassy muffle that is there every time i'm not playing something. normally in my limited experience problems with preamp tubes are either a cut in volume or high pitched microphonic sounds. Anyone have a clue where I can figure out how to fix this?

thanks!
 
If things are sounding pimp on the 1st and 2nd channel, then it's more than likely not your power tubes. So check the V3 preamp specifically, but try all V1 to V4 to make sure.

V.
 
thanks! is it as simple as v1-v7 goes from left to right when looking into the chassis from the back?

also, if i'm replacing a matched quartet of tubes with the exact same brand, do i still need to rebias?
 
Hi,
https://dl.dropbox.com/u/795852/Memo.m4a
is a sound clip of an issue i'm having....at 19s, you'll hear the sound that ails my channels 3 and 4....i tried replacing preamp tubes v2 to v7 one by one without success. i have 6550 power tubes with the 100k mod (which i think is to accomodate how hot the 6550s run). channels 1 + 2 are perfect withoiut any problems.

please help!
 
Mark2C or Peter, I've been trying assist with this one, it's kinda freaky...

Mo
 
You get this noise at 19s with closed guitar
volume pot ? Or is the pot always cranked up ?
 
Hi Peter! I have to say it's pretty cool that the designer of my amp is helping me out!
I apologize but as tube amp vocabulary goes for me, all i really know is how to change preamp and power tubes. I'm not sure what a 19s is?

I can tell you this:


I bought this amp used from a rig-talk and sevenstring.org user from columbia, sc in early august of this year. As far as i know it's been going on since i had it. Unfortunately when I bought the amp, i lived in an apt and never really was able to put it up past volume 1 or 2 per channel with master volume at 1! now i have a storage unit where i can get higher volumes and that's where i've noticed it.

I feel like it's at any presence, treble or deep setting. I have put the gain down to 11am on each channel and still get it. At lower volumes, it's still there but tolerable, but just gets exponentially worse as the volume increases.

I will say the owner before me had his treble at the highest setting and presence at highest setting on both channels. But ever since my presence as been at 10 o clock and treble at 1 o clock.

The only mod i know that was done was he had it "professionally modded" with a 100k resistor or something so it could handle the 6550 valves.

And lastly I live in Birmingham, AL!

Any help or thoughts would be much appreciated!
 
Have you tried a new guitar and speaker cabinet ?

I could not get the clip to work so I did not hear the issue.
 
Dear Cameron,

my question again:

Do You have the volume pot on the guitar closed
or open, when the noise comes up ?

Your issue sounds like a normal feedback.

Thanks,

Peter
 
From what I've gathered with C711 is that this is happening with low volumes on the amp and happens only with 3 and 4. Never asked about a different guitar or cable... I assumed it was pre's as apparently the amp sounds perfect and operates extremely quietly on 1 and 2.

Something about a 'mod' being done to accept 6550's - which sounds suspect to me :confused:

Hope we can sort this out for ya Cameron... And yes, it's a very special place to have the assistance of the actual amp designer so willing to help. Diezel is a very, very special amp and a special group to be part of.

Peace,
V.
 
Ahhh I see! Sorry for my ignorance. So when the guitar volume is at 0, there is no sounds out of amp. I have tried 3 different guitars, alighted same issue with my vh4 but no issues with my Mesa boogie amp. I agree most of te feedback on the recording above is normal, but at 19 seconds is where it sounds wrong and if I have the guitar volume up but my hands silencing all the strings it still makes that sound.

Thx for all your help!
 
What do you have your gain set at and how far are you away from the head during that recording? If you have it above 1:30 on channel 3 especially with high output pickups its going to feedback pretty bad because its ALOT of gain. Sounds like normal feedback really. This is why Pete is asking if you have the guitar volume rolled back or not. If the guitar volume is off it's a mechanical issue inside one of the tubes. If your volume is up you just have the gain too high or you're too close to the amp at high volume. If your volume is up during those you have two/three options really. Lower the gain some, find some less microphonic tubes, or use a noise gate if you really need to have the gain that high. Really try lowering the gain... you'd be surprised how much the amp opens up and becomes more percussive and brutal actually. You can actually hear the low end open up while backing the gain down doing big chords and chugs. It should be more than enough gain to get harmonics out of it too btw with it lower. It will be harder to play obviously cause your going to hear your faults much easier, haha.

Hope that helps somehow :rock: ,

-Nick
 
The clip works now, so I can tell you 1000% there is nothing wrong with the amp.
What your hearing is the ferocious gain potential of the VH4 coming from your
guitar pickups. It is feedback. For most of us, it is a beautiful feature of the VH4.

Move further away from the amp and it will decrease the feedback. If your pickups
are not potted it does not help suppress the noise.
 
thanks for all the input....how right you have been re: ferocious gain; i dialed channel 3 back to 11 o'clock and it sounds unbelievable with the appropriate feedback and none of that boxy boomy bass-y feedback. channel 4 apparently needs to be dialed back even more which makes sense, but now i'm trying to stand like 15 ft away and this helps...only negative is i'm still finding the right settings for me but i'll figure it out!

Questions:

re: volume knob on guitar being potted or not; what does that mean?

also, i'm thinking of switching v1-2 with the ruby 12ax7ac-hg+ and v3-v7 12axac-hg as the tubes are some russians, some mesa boogie, none that appear to be the recommended ones by peter.

re: the 6550 power tubes, i like the sound of them but the 160 watts is insanely loud. if i went with the el34bht instead, how much headroom would i be losing on channel 1?

anybody have thoughts on using a thd hot plate with this amp?

also, i'm thinking about using both fx loops: the serial one for my tc electronic g system and the parallel for a jamman looper...with the parallel being the looper it seems like i can control volume of the looper with the secondary volume control knob? does that sound right?

thanks for all your help and sorry for all the questions: i just want to make the most of this beauty.
 
Um, wow dude... Lots of questions indeed.

Frist off, potted is in reference to the pick up's - some pups are potted (waxed, polymers, whatever) some are not. Potting them makes them less prone to feedback and squeeling but sometimes takes the jingle jangle out of them too. It's not the volume knob, it's the pups.

Don't use volume bleeders or hot plates - BIG no no according to Peter, and secondly, that's what this amp is all about man - tons of ball shakin' power.

Don't screw with your tubes - preamp or power - not yet. Get to know your amp first. 6550's are the tits in these heads and ya, they've got gobs of power, but that's again why we all buy Diezels, they melt faces :D

Just get to know it man, you'll love it - but ya can't be screwing around the playing field till you know what you've got, and it seems thus far, you've got some learning to do - respectfully of course - and you'll love the ride dude...

Hang in there!! :rawk:
V.
 
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