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Rockstah humming issues...any advice?
Posted: Mon May 18, 2015 11:37 pm
by Sean_McFly
Hey guys, my Rockstah Mod 5 (a 1980 2204 with one or two original Transformers and v1 and v2 preamp tubes I believe) is making some serious hum and also making some odd buzzing overtones when the volume is rolled back on the guitar. What do you guys think it could be? I could send an audio clip to you guys of the sounds I'm talking about. Now I'm hesitant about bringing it to a local tech (even though he's apparently amazing with tube amps) mostly because if he messes the tone up, there's no getting that tone back from the original modder, as we all know (R.I.P. Mark). It's a struggle all Rockstah owners share (as well as Jose Arredondo owners). But hey, a great boat to be in nonetheless. So, could anyone shed some light on this, or even give their two cents regarding if I should bring it to a tech or not?
Re: Rockstah humming issues...any advice?
Posted: Tue May 19, 2015 7:56 am
by stef
Preamp tube(s)
Re: Rockstah humming issues...any advice?
Posted: Tue May 19, 2015 8:38 am
by garbeaj
I would recommend making a note on the tubes and any components that Mark used. Take lots of pictures of the amp removed from the chassis. Make sure to tell the tech to keep the circuit the same...I know what you mean about some guy messing with it. One tech that I used screwed something up when I first got the amp from Mark and I had to have Mark call the guy and walk him through what to do. And this was an experienced tech...I've been lucky so far since then and my amp has operated well.
Good call to check with the guys here that Mark got his knowledge from in the first place. Somebody here will be able to help you, I'm confident of that.
Re: Rockstah humming issues...any advice?
Posted: Mon Jun 01, 2015 10:56 am
by Megaro
This has happened to me before. Before you take it in to a tech, make sure you have put in a fresh set of tubes all around that you know are good and replace all your cables with known, working cables. Hopefully, it is something basic like a bad tube or a weak connection in the signal chain. If not, then it starts to get into the guts of the amp which can get expensive and very frustrating.
Re: Rockstah humming issues...any advice?
Posted: Mon Jun 01, 2015 11:38 am
by Strat78
Yep, techs do get expensive. I got an idea, why don't we start an amp building forum so we can build and learn about amps.
We can call it MetroAmp.
Re: Rockstah humming issues...any advice?
Posted: Mon Jun 01, 2015 12:06 pm
by white noise
Re: Rockstah humming issues...any advice?
Posted: Mon Jun 01, 2015 8:59 pm
by JimiJames
Re: Rockstah humming issues...any advice?
Posted: Tue Jun 02, 2015 9:38 am
by garbeaj
Nice one Phil
Re: Rockstah humming issues...any advice?
Posted: Tue Jun 02, 2015 10:28 am
by rgorke
Strat78 wrote:Yep, techs do get expensive. I got an idea, why don't we start an amp building forum so we can build and learn about amps.
We can call it MetroAmp.
It will NEVER work!!!!!
Re: Rockstah humming issues...any advice?
Posted: Tue Jun 02, 2015 11:21 am
by mightymike
I needed that laugh.
Re: Rockstah humming issues...any advice?
Posted: Wed Jun 03, 2015 1:46 pm
by Megaro
Great, he is in the right place. Now what ? I am interested in this too.
Let's say he has ruled out any tubes or external cable issues. He pulls the chassis, flips it upside down onto proper stands,
drains the caps, has out his voltmeter . . . what next ?
Re: Rockstah humming issues...any advice?
Posted: Wed Jun 03, 2015 2:06 pm
by fhn_lopes
Megaro wrote:Great, he is in the right place. Now what ? I am interested in this too.
Let's say he has ruled out any tubes or external cable issues. He pulls the chassis, flips it upside down onto proper stands,
drains the caps, has out his voltmeter . . . what next ?
I get you.. Even though it's an amp builders forum, not all of us are builders (or experienced ones)... on the other hand I laughed my ass out with Phill's joke... anyways
Hum can be many things, including grounding issues. I'd look for that first, I mean, check the star ground (if the amp has one), the chassis and other harware grouding and so on.... Oh, an I'd try to change the place where you are pluging the amp into the walll... maybe it's not in the amp..
Next I'd check the PS filter caps. Assuming that the amp didn't have any hum issues before, I beleave we can discard bad wiring layout and other building errors ... the power supply has many spots that can create hum.... after that I"d go with the coupling caps between the stages and then the PI coupling. The list goes on and I beleave that most lilkely it's a bad tube or a simple grounding issue.
PS: I'm not an experienced builder. just my 2 cents
Re: Rockstah humming issues...any advice?
Posted: Wed Jun 03, 2015 5:01 pm
by scriptphase
Sean_McFly wrote:Hey guys, my Rockstah Mod 5 (a 1980 2204 with one or two original Transformers and v1 and v2 preamp tubes I believe) is making some serious hum and also making some odd buzzing overtones when the volume is rolled back on the guitar. What do you guys think it could be? I could send an audio clip to you guys of the sounds I'm talking about. Now I'm hesitant about bringing it to a local tech (even though he's apparently amazing with tube amps) mostly because if he messes the tone up, there's no getting that tone back from the original modder, as we all know (R.I.P. Mark). It's a struggle all Rockstah owners share (as well as Jose Arredondo owners). But hey, a great boat to be in nonetheless. So, could anyone shed some light on this, or even give their two cents regarding if I should bring it to a tech or not?
I recommend Carl Esparza out of Whittier, CA. He goes by Fusionbear on several gear forums...maybe this one too? Carl does part-time amp repair and custom builds. He worked for Jose Arrendondo back in the day.
A couple of years ago, I sent Carl my Mod 5 due to a white noise issue. He knew the Mod 5 circuit well and was careful not to change anything that would effect the sound of the mod. The work was very affordable with a quick turnaround. Highly recommended.
Re: Rockstah humming issues...any advice?
Posted: Wed Jun 03, 2015 5:02 pm
by scriptphase
Here's Carl's website with some contact info:
http://biblefreak.org/fusionbear/
Re: Rockstah humming issues...any advice?
Posted: Wed Jun 03, 2015 6:08 pm
by Strat78
Megaro wrote:Great, he is in the right place. Now what ? I am interested in this too.
Let's say he has ruled out any tubes or external cable issues. He pulls the chassis, flips it upside down onto proper stands,
drains the caps, has out his voltmeter . . . what next ?
I haven't used a stand in years.
Could be a ground loop, or even as simple as a bad power bar. It's all pretty easy, but dangerous if you don't do your homework. You can find topics on most any amp problem here by using the search. You can poke around with a chopstick while the amp is on to see if there are any obvious cold solder joints. Push the nfb wire away from other wires (Do all this with your left hand in your pocket as a rule, you don't want to take 375v through your heart). Check to see if the bias has not drifted out of range. Then turn the amp off and drain the caps. Re-flow suspect solder joints. I would take out the old radial silver mica caps (the little black ones) and replace them with Lemco's. These particular radial caps that were widely used back when Mark was modding, seem to go bad with use. Where are the CC resistors in the circuit, they might be causing noise. Posting gut shots always helps too. On another note, the clips of this amp sound a little brittle, anything higher that 100pf for the mix cap seems to emphasis that twangy harshness, but then again the Mod5 can be hard on the ears with out the presence functioning in combo with the cascade.
