NAD, Leaking Capacitor Question, Craziness!!

[strings_ibanez]

(Well, I can't seem to figure out why Rig-Talk won't let me log in with my actual account and wants me to solve a reCAPTCHA that doesn't seem to exist, but anyway.. I suppose this alternate account with an underscore in it should work just as well...)



So, a few months ago (August) some members here helped answer a few questions for me (viewtopic.php?f=14&t=190847) and, after 8 years of Einstein ownership, I tracked down what I was looking for and expanded my arsenal with this:

Wow! This is definitely an amazing sounding amp!! ..and even better with the brand new set of power-tubes I just swapped into it.

I'm enjoying everything about the Herbert, however, I'm experiencing an above-average amount of hum in the amplifier's output (similar to ground-loop hum, but it doesn't appear to be that). I haven't had any luck eliminating the hum, but while I was re-tubing & biasing it.. I took it out of its headshell to try the hum-trimmer pot (also unsuccessful), and noticed this:

I'm curious if these two leaking capacitors might be causing the hum that I am experiencing in the Herbert's output?
Also, how hard would it be to replace them? / Would the brand make a difference? / What values are required?



That said / in other related craziness -> I also just grabbed this for good measure:

Also an amazing sounding amp!! Different, but still obviously the same underlying DNA... and between the two of them I literally can't stop smiling
Craziness, I'm ridiculous.. totally don't regret it though.


No issues at all with the sound or operation of the VH4 (I'll probably re-tube it soon either way), but I did notice that at least 2 of the large capacitors located just in front of the power tubes appear to be bulging at the tops.
So.. same questions I suppose: How hard would it be to replace them? / Would the brand make a difference? / What values are required?


Thanks in advance for any answers / advice on the cap questions.. I'm super stoked nonetheless!

 

[Vin Diezel]

Congrats!

The required values are specfied on the capacitors themselves,
The have a polarity. Do not forget that. A tech could easily replace them.
Personally, I am not fond of people buying a cheap soldering iron and then immediately starting to learn how to grill the circuit board of a 4000$ amp iykwim.

Does the hum come out of the speaker cab or only from the amp itself?

The transformer in my vh4 hums even with the standby off, but that does not affect the sound that comes out of the cab.
I guess your hum is due to defective caps and can be heard through the cab.

 

[strings_ibanez]

Thanks for the response.

I'm still on the fence regarding whether or not I'd attempt to replace the caps myself, or find a tech do to it (my soldering work is typically relegated to cables, wiring rack rigs, patch-bays.. that sort of thing. Circuit boards are not something I would typically be working with.)

Regarding the Herbert's hum: Yeah, it is coming out of the speaker cabinet. The amp does have a decent amount of transformer hum I suppose, but I'm only concerned with what comes out of the output.
Both amps could stand to have some caps replaced, but only the Herbert is making any unwanted noise.

 

[Peter Diezel]

There is a chapter in the service manual on our website.
Please read it.

 

[strings_ibanez]

There is a chapter in the service manual on our website.
Please read it.

Thanks for the reply Peter!
So I read the section in the service manual. It definitely appears to be the 22mf/500V caps in the Herbert which are leaking.
I do have a couple of questions:

1) Does it matter what brand of capacitor is used for the replacement?
2) What type of glue should be used to glue the new ones down?


Lastly, what are the values of the big ones located in front of the VH4's power tubes. I can't make out the writing through the front grill and I would like to be able to order the parts before I take the amp out of its headshell.


Thanks again.

 

[Hey_bert_whtcha_doin_bert]

The VH4 ones are most definitely fine as long as you can press on the tops and they aren’t hard(they push in a little)it’s just the tops of them separating and not an issue. The other question is just regular old hot glue from a glue gun and as long as they’re in spec it’s only smoothing the power and isn’t so much a sonically sensitive part other than value.

 

[Peter Diezel]

For both questions is doesn´t matter.

Be sure to replace the 2k2 filter resistor into 4k7 / 5 watt. This will save the new caps.

 

[strings_ibanez]

Thanks for the responses and information

www.thetubestore.com sells F&T caps with the right values so those should be easy enough to get. (I'm in Canada and near enough to them.. so it's the easiest/fastest source).

I might have to do some searching and call around to find a resistor with that value. There aren't too many electronic parts suppliers around anymore and so it could come down to online ordering or driving a city or two over.


Either way, I look forward to cleaning up those couple of caps and the reduced noise that should come along with doing so.

 

[strings_ibanez]

Well, unfortunately I have to resurrect this thread after putting it off for a while...

I finally got around to replacing the three bad 22mf/500V caps inside of my Herbert (as well as the one resistor mentioned in the service manual).

Anyway, the amp still functions as before, but replacing those parts seems to have had no effect on the annoyingly loud hum that is always present in the Herbert's output.


-Disconnecting everything (input, midi, loop, etc.) except for the power and output cable has no effect. (Obviously.)
-The hum is present/audible through the cabinet with the master volume at 0 and upon further investigation doesn't seem to really change much/at all as the level is increased, but it's still frustratingly loud and since the amps primary focus is recording, I'd like to get it to be quiet like my other amps.
-The hum only stops when the amp is in standby.
-The hum trimmer pot inside of the Herbert does absolutely nothing. There is no difference at all at either extreme or at any point between.
-The hum coming through the cabinet sounds exactly the same as the hum coming from the transformer on the power-cable/switch side of the amp... just louder.

Any next steps/ideas would be welcomed and helpful.

Thanks.

 

[Vin Diezel]

Take it to a tech?

 

[strings_ibanez]

Well, that is certainly an option.
I might have to do some research in that regard to see who in my area would be qualified for diagnostic work on it.

That said, is there any chance it's something else obvious / easy?

 

[SpiderWars]

Just to be sure...you have checked all the preamp tubes? Plugged a cable from Send to Return and it makes no difference?

 

[strings_ibanez]

Just to be sure...you have checked all the preamp tubes? Plugged a cable from Send to Return and it makes no difference?

In fairness, I've only really done a "tap-test" (like to listen for extraneous ringing or whatever) on the preamp tubes. Usually when I've encountered bad preamp tubes the noise produced would hiss or "wooosh" and go up and down with the volume or gain controls...
..but I'm absolutely open to the possibility this is just a different type of symptom. I've got 2 spare (new) one's on hand I could try swapping into each V# position as a diagnostic.


I'm not entirely sure I know what you're suggesting with the Send to Return thing? I do use the serial loop (I've never touched the other 2), but part of my testing so far did include disconnecting everything except mains power and speaker cabinet. Should I be attempting to jumper different loops for a reason I'm not aware of?

Thanks.

 

[ChurchHill]

The fact that the hum level doesn't change with changes to either the channel or master volume controls suggests that the problem is between the master volume and the speaker out. While I'm not familiar with the schematic or layout of the Herbert (I do own one, though), I'd guess that this includes the effects loops as well as the phase inverter.

I'd test the various pre-amp tubes first, and I'd try both of your spares in each position, one at a time. That should help in the rare, but possible, case that you have a bad spare. I'd start from the position farthest from the input.

If that doesn't help, try jumping the effects loops by just using a single cable from the send to the return, as SpiderWars suggests. A possibility is that one of the jacks might be slightly dirty and the connection that's normally made when not using the loop may not be connecting as it should. By using a single, known good cable, you're manually making this connection and will be able to tell if this is the problem. Also, you need to check all the loops, not just the one you use, as all of the jacks have been exposed to the same environment. It's more likely, if this is the problem, that it's one of the jacks you don't use. Using them can keep them clean, while not using them can allow humidity or dust to build up.

If that doesn't help, I'd suggest taking it to a tech who can trace the signal through the amp. In any case, I hope this helps to explain what was meant with SpiderWars' suggestion with the loops. My guess? I'm thinking the phase inverter tube is on its way out, but that's just a guess. Best of luck to you!! I love my Herbert and don't want to think about it ailing in any way.

 

[strings_ibanez]

The fact that the hum level doesn't change with changes to either the channel or master volume controls suggests that the problem is between the master volume and the speaker out. While I'm not familiar with the schematic or layout of the Herbert (I do own one, though), I'd guess that this includes the effects loops as well as the phase inverter.

I'd test the various pre-amp tubes first, and I'd try both of your spares in each position, one at a time. That should help in the rare, but possible, case that you have a bad spare. I'd start from the position farthest from the input.

If that doesn't help, try jumping the effects loops by just using a single cable from the send to the return, as SpiderWars suggests. A possibility is that one of the jacks might be slightly dirty and the connection that's normally made when not using the loop may not be connecting as it should. By using a single, known good cable, you're manually making this connection and will be able to tell if this is the problem. Also, you need to check all the loops, not just the one you use, as all of the jacks have been exposed to the same environment. It's more likely, if this is the problem, that it's one of the jacks you don't use. Using them can keep them clean, while not using them can allow humidity or dust to build up.

If that doesn't help, I'd suggest taking it to a tech who can trace the signal through the amp. In any case, I hope this helps to explain what was meant with SpiderWars' suggestion with the loops. My guess? I'm thinking the phase inverter tube is on its way out, but that's just a guess. Best of luck to you!! I love my Herbert and don't want to think about it ailing in any way.

Well, I spent a while doing some further investigation.

A quick check of all the send/return/loops with a working jumper cable indicates that the problem doesn't seem to reside there. So I extracted the Herbert from its head-shell again and have it sitting behind me for testing.


I went through each pre-amp tube and tried swapping it out with these results:

V6 -> No change.
V5 -> No change.
V4 -> No change.
V3 -> No change to the hum, but significantly less noise/whooshing type sounds with master volume past noon. There is, however, also a narrow buzzing noise present that was not before and goes away when swapped back.
V2 -> No change.
V1 -> No change.

At this point I decided I would try leaving one new tube in V3 to reduce that noise and try re-swapping the others with V3 replaced.

V6 -> Hum significantly reduced.. except for maybe a very very low frequency component, but the most audible part seems gone. However, I then discovered I was getting no sound passing through from input to output. Tried swapping it back to original... same thing.. Turns out V1 was apparently now dead? Set that aside and swapped for the second spare.

So with V1 and V3 now replaced using my two spare tubes -> No change to the original hum issue.

Did some digging and found a spare (new) ECC-83 I had on hand for a mic-pre that likes that particular tube.

ECC-83 in V6 -> No change to hum.

Alternatively:
I moved the new 12AX7 from V1 to V6 and put the old 12AX7 I'd removed from V6 into V1 -> Hum appears to behave the way it did above when I first thought it had been reduced, but this time I have sound. Less noise on sweeping the master volume up, but if I remove the input cable the amp produces scratching sounds and other noises I'd typically associate with a bad preamp tube. (And also an unfortunately loud sounding pop when I put it back into standby). So the amp definitely didn't like that combination, but I might be getting somewhere?

Next I tried the ECC-83 in V1 and oddly still experienced some unusual behaviour and sounds from the amp?


As it stands right now I have moved the newer 12AX7 back to V1.
I can't decide if I suspect both the original V6 tube AND the ECC-83 or if I think there is an further underlying issue or what.


My plan for tomorrow is to drive myself over to http://www.thetubestore.com (which is maybe 20~30minutes from where I live) and pick up an entire new set of preamp tubes per the recommendations from Peter/the website (assuming that is possible)... or either way enough to swap out all of them.

Once I've done a full swap of all 6 preamp tubes I'll hopefully know where I'm at with everything and go from there.

 

[ChurchHill]

If it matters, I do think you're getting somewhere. You now know which tubes seem to improve (but not resolve) the issue, and I think you're correct that there may be multiple issues.

Also, just to be sure, you might check the caps and resistors you changed by tapping them with a wooden stick while the amp is powered on and not on stand-by. It is possible that you've got a cold solder joint. I had one, once, that took me several months to finally track down. Having said that, I still think it's highly likely you've got a couple of tubes that are nearing death.

While you're at The Tube Store, think about taking your Herbert with you so you could have a look at the power tubes, too, just in case. Also, they might be able to refer you to a reputable tech if it seems there may be something more than just tubes going on.

In any case, keep us posted, and good luck tomorrow!

 

[CrazyNutz]

Given the fact that you had several of those ruby filter caps leaking makes me suspicious of the electrolyte batch being botched. Therefor the main filter caps (the bigger ones) may be bad too, even if they are not showing the visual signs.

The main filters being bad are most likely to cause hum than any place else, because this is the spot where most of the filtering/smoothing happens right after the rectification.

I would replace the rest of the filter caps ( the big ones )

 

[Peter Diezel]

I don´t assume the main filter caps are bad. The issue might be the
mechanical hum from the transformer. We used a M102 core on the
Herbert MK1 and that transformer is noticeable on bedroom levels.
I don´t know if it helps to re place the main transformer.

 

[strings_ibanez]

If it matters, I do think you're getting somewhere. You now know which tubes seem to improve (but not resolve) the issue, and I think you're correct that there may be multiple issues.

Also, just to be sure, you might check the caps and resistors you changed by tapping them with a wooden stick while the amp is powered on and not on stand-by. It is possible that you've got a cold solder joint. I had one, once, that took me several months to finally track down. Having said that, I still think it's highly likely you've got a couple of tubes that are nearing death.

While you're at The Tube Store, think about taking your Herbert with you so you could have a look at the power tubes, too, just in case. Also, they might be able to refer you to a reputable tech if it seems there may be something more than just tubes going on.

In any case, keep us posted, and good luck tomorrow!

Well, I now have a completely fresh set of preamp tubes in the Herbert:
No change to the annoying hum and that part I mentioned before about a bit of a buzzing is present in the sound (most noticeably with the master above half-way / noon).

So it looks like what I was noticing yesterday may simply have been some strange interplay of whichever preamp tubes were faulty? I'm not sure.. but I've now got 10 new 12AX7B's between the 2 I tried yesterday and the 8 I bought this afternoon... and none of the musical chairs/tubes I've been playing seems to solve things.

Regarding power tubes, the 6 that are in the Herbert right now were just put in new the same day as my initial post of this topic, and unfortunately the hum was already present before that.

I don´t assume the main filter caps are bad. The issue might be the
mechanical hum from the transformer. We used a M102 core on the
Herbert MK1 and that transformer is noticeable on bedroom levels.
I don´t know if it helps to re place the main transformer.

Hi Peter,

The hum does sound similar to what I'm hearing if I put my ear up to the amp, and I can hear the hum coming directly from the transformer(s) when the amp is on standby in my control room.
My main issue is the hum is coming through the speaker cabinet so it is in the audio path.

Is this normal? (Neither my VH4 or Einstein do this.)

If I was only hearing it from the head itself I wouldn't care because I place the cabinet in a different room than the head during tracking, but since it is coming through the speaker output my microphones would hear it on recordings.


I guess at this point I have no other choice but to find a good tech in southern Ontario, Canada where I live and hope they can figure it out. Any suggestions/recommendations?

.

 

[ChurchHill]

Wish I could help you there, no idea of any good techs in Ontario. Hope you find someone who can help get this sorted out. Please let us know how things go, OK?