Buffing a Rogue Stereo 90

[rollo]

 Hey String welcome aboard. Not familiar with the Rouge so no opinions. The only issue with Chinese tubes is shipping. Some just do not hold up. That is the only reason for me to purchase from Grant. Reliability.
  However Bunkys' recco sounds very inviting . Actually to good to be true, but it is. Great move Bunky and thanks for that info. it makes a lot of sense especially with new tubes BRILLIANT!!!!!


charles

[stringdriventhing]

Thanks for the salutations Charles.

Well the Rogue arrived, and I'm scared spitless. It shipped, NOT double-boxed in the manner I'm inclined to ship very HEAVY, very BREAKABLE, very PRECIOUS stuff, no it was sent in the original Rogue box. Huh? What's the problem? Well, the freakin' mildew that's eating the damn box for one big thing. Might as well have wrapped the beautifully BEEFY 60 POUNDS IN A BUNCH OF DAMP KITCHEN SPONGES. Sorry, yes I was yelling, just not at you. Definition of adding insult to injury? How about losing the original, custom-molded, high density foam surrounds and replacing them WITH FOAM PEANUTS?!?! Jeez, apologies again. All I know for a fact is the box in question is sitting downstairs, in a dark corner, and I can't find the COURAGE to open the blasted thing. Not only am I terrified of what awaits in terms of visible damage, or worse yet INVISIBLE, I'm quite, quite sure that some very large and ferociously UGLY species of spider must have nested in the miss-stored box in question, and that IT, and all it's hatched - in -UPS -transit little ITS are gonna launch themselves from the blighted box in a freakin' fury. - String

[rollo]

  Helmut on String. Weapon in hand, open sesame. The sky will open the will Angels sing. When ya plug in in may it do its thing.


charles

[stringdriventhing]

Been a bit since any update here - well no more. The Rogue has been removed from the funky, mildewed shipping package. No sign of visible damage - relief! Mediocre tube varieties that came with it have been installed, the unit placed on shelf, and cabled to upstream gear & newly refurbished Klipsch speakers. So far, so good. Fire it up, AARGH! - MASSIVE HUUUMMM! Can hear it from 20' feet away as I enter the listening room. Not good.

Spent time with Rogue chieftain Mark Obrien, by phone & email, attempting to trouble-shoot the noise pollution. Everyone in this situation wants the problem to exist in someone else's piece of gear. Failing that, they'd like it to be a very simple ground-loop problem, with an even simpler solution. Failing that, they'd like for you to, please, just go away! Well, can't blame Mark much as the unit was purchased used off Audiogon. I had hoped though, before fading on me entirely, that he could at least venture his expert opinion on what the possible causes MIGHT be for a caustic hum issuing from the speakers, CLEARLY and ANNOYINGLY audible at my listening position 8' away with the amp connected ONLY to AC & the speaker load and sporting a "cheater plug" during testing.

I power all my system components from a BPT BP-1 Ultra and the only other occasion over the years, and systems, that I've owned it was when the transformer went bad on a Unico integrated. So I'm keeping my fingers WAY crossed that the seller will honor his responsibilities in covering any repair expenses and that any evaluation/repair done won't deprive me of the music for too long.

I've got to do some study online today to attempt to identify possible sources of malfunction that can cause these symptoms. So, I know a faulty transformer can be a cause, and that "bad" small signal tubes are another possibility. I hang here to, in part, absorb some of the genius you true-to-life audiophile "hear-os" possess. Any of ya'll with a cure for what ails the Rogue step forward and lay your healing hands on the damn thing, please! - String   

[rollo]

  Sorry to hear that.
  Now the issue at hand. Clean the sucker, tube pins, RCAs and power plug. Check to see that the ground connection is in place not corroded. Check RCA connections to pre. replace IC to check integrity.
  If all fails replace try different tubes if you have them. I think its a tube, if all gear is plugged into one source there should be no ground issues. BTW one channel or both hum ?



charles

(edited to remove name calling)

[tmazz]

It would seem pretty simple to me. You were running the DAC right into the power amp with no hum. Insert a preamp in between the amp and the DAC and it hums. All you inserted into the system was the pre and another set of cables.(I assume that you are using the same cables that went from the DAC to the amp somewhere in the new chain. First thing I would do (because it is the easiest)  is to swap out the additional set of cables with something else (even if it is a cheap cable, all we are looking to see is if the hum goes away when you change it out.) If the hum disappears the problem was that cable, if not it has to be the pre.

Do you have anything else you can plug the Pre into (HT receiver, boom box, anything with an RCA line level input? If the hum is coming from the pre you will here it there as well. If you have a tape deck you could also plug the pre outputs into the record inputs, put the tape deck into record and listen via headphones to see if you hear the hum. (Be sure to turn up the volume on both the pre and the tape deck record level.)

It's really a buzz kill when the new toy doesn't work properly. I hope it is a quick and easy fix.

[stringdriventhing]

Hey Tom - thanks for responding. Actually, the EE DAC is acting as my preamp for the interim until I'm able to glom onto a dedicated pre. The connection is from the Minimax analog outs to the inputs on the Rogue. With absolutely NOTHING from upstream connected to the Rogue, it hums when powered up. So, I can't think of anything else that could be the source of the noise. I know for certain that the BPT BP-1 Ultra isn't the source of hum as it was the BP-1 that made relatively noise-free performance possible and it has performed without fault for over 4-5 years now. So, something IN or ON the Rogue is generating a substantially high, according to Mark O. as well as myself, level of hum. Mark feels strongly that even with my high efficiency Klipsch speakers (101db) that hum should not be audible beyond 1-2' from the speakers. Unfortunately I can clearly hear the hum, even during quiet musical passages, from my 8' vantage point. It'd be sweet if it's something simple like a faulty input tube or two, however I don't have back-ups in the house in the varieties required to test. - String

[tmazz]

Brain Fart! I was thinking that the Rogue was a pre. 

Ok,  if it hums with nothing connected to it what happens if you connect the EE to it and leave the DAC powered down just to the amp is seeing a terminating impedance? If it still hums then I would try bypassing the BPT and plug right into the wall. And also try another power cord if you have one. I know these are all long shots, but much past this it will involve bringing it so someone to put on a bench. I would hate to bring it in only to find it was one of these things. Also, if the hum is only in one channel you should swap the left and right tubes to see if the hum follows the swap, if so you can move the tubes one at a time to finds out which one is the culprit. It the hum is in both channels this unfortunately won't help.

Good luck.

[stringdriventhing]

Thanks again for your suggestions Tom. I've tried three different power cords - stock, BPT, Wireworld - and I've had the DAC connected while powered down: HUM HUM HUM. Haven't attempted the direct-to-wall outlet approach partly due to the problem it would cause with reducing the available outlets, mostly due to my stinkin' surgically repaired back that makes crawling on the floor to get behind the audio cabinetry, to wrangle power cords, sound like a day in hell. But of course I'll do it! Gotta say though, as unappealing as a possible battle with the Audiogon seller over repair costs seems, having my audio feast spoiled by this crappy hum is an unacceptable situation. - String

[tmazz]

Rather than crawl on the floor with your bad back why don't you just take a different power cord a plug it into an extention cord run to an outlet that is easier for you to get to. It's not a permanent thing, it  will just be up long enough to see if this last configuration helps the hum problem.

[richidoo]

Hey...
Why did the tube amp hum?

Because it forgot the words. 


String, you already tried physically disconnecting the input to the amp (right?,) and you are isolating power input with the BPT. So there can't be a ground loop. If you have any source component connected to the amp input even if the source is not powered on there can still be a ground loop through the source if it is plugged in. If source and amp are both plugged into the BPT then there should be minimal loop current. But if source is plugged into the wall while amp is in the BPT that could be a problem since BPT has floating ground potential while the outlet is earthed, making a potential which will hum. But with nothing connected to the amp except its own PC the amp should be quiet as possible unless it is broken. But consider another possibility before you seek revenge or repair.

Your speakers are extremely sensitive. The problem could be as simple as a minor ground loop being amplified by way too much gain for your speakers. You probably only need 20dB total voltage gain for sensitive speakers and a strong DAC like EE. Adding a tube preamp will add even more gain and make any ground loop hum even louder. The Stereo 90 gain spec is not published but you can ask for it. Usual amp gain is 26 dB (20x amplification.) Tube amps are often higher than standard. 20dB is only 10x amplification, which makes full scale digital signal put 20V into your speakers. That's still enough to blow you out of the room with 97dB speakers. Hum and noise are amplified also and become very annoying. This is the other edge of the sword for sensitive speakers. Solid state is the easy answer, but you don't seem like an "easy answer" kind of guy, if so you would have used Rustoleum flat black instead of veneer.... 

If it's not a ground loop on the input signal, remember that hum can also originate as EMI from the power transformer inducing current in nearby conductors with magnetic leakage. That can't be fixed so easily. It should be at a very low level, but a circuit modification or a EMI sensitive tube could exaggerate it. Phono preamps use metal shields over their 12AX7s for this reason.

Check with Rogue to make sure it is OK to run it on balanced power, should be no problem with simple tube amp but it is worth asking. Also ask if you can swap a low gain 12AU7 for the 12ax7. I bet the answer is no.

BTW, it's a good idea to check over the whole amp for obvious problems, inside too, if you're comfortable with that. You just never know what you'll find inside a used tube amp. If there are mods you may not be able to tell without the real schematic, but usually the workmanship is not so pro and it is easy to spot.  Adjust the bias, make sure it is stable and doesn't drift over time which indicates old tubes. Check the output offset voltage too, just to be safe.

If a loud hum is still there with totally ground isolated amp, with only PC and SC connected (no input physically connected), then try some normal midfi speakers typically 88ish sensitivity. If you can still hear the hum seek repair. I personally would send it to Rogue if you need repair. 
Rich

[tmazz]

Hey...
Why did the tube amp hum?

Because it forgot the words. 

 

[stringdriventhing]

Thanks again for all replies and recommendations. Charles, I somehow missed your initial post about the hum bummer, thanks. Rich, wow, a lot to digest and all very enlightening and helpful. I SHOULD have stated at the git-go that it is a two-channel hum, both speakers. I've also now noticed that the amp itself is issuing a noticeable hum, audibly similar to the hum from the speakers, though this may be standard operational noise, dunno.

Mark was made aware that I'm powering my system from a BP-1 Ultra, and I probably just assumed that he would understand that meant a "balanced" power supply. I'll have more contact with him tomorrow and will be more specific in asking about compatibility. I also intend to ask about swapping out the 12AX7's for lower-gain 5751's. It could kill the proverbial two-birds in that if those particular input tubes are part of the problem, either by way of their higher gain and/or if they're failing, it SHOULD make an audible difference in the noise levels.

The only other strategy to throw at the situation, at least until the new week begins and folks are available to be contacted, will be to attempt powering the amp directly from the Furutech wall outlet to see what that might change, if anything. - String

[stringdriventhing]

Some "movement" in getting the Rogue hammered into shape. Nick Gowan of True Sound, and his associate Lee, came by my place on Saturday to evaluate the hum issue with the Rogue. By the time we had revisited all of the basic ground-loop trouble-shooting techniques Nick admitted he was both mystified and intrigued by the hum. He's so experienced with tube gear he is able to pinpoint sources of noise through the harmonic content of the hum. Probably not a good thing that he was scratching his head over the hum issuing from my amp! Anyway, he carted off the amp to his shop and will be bench testing it to determine the problem. Great news that my A'gon seller is being completely supportive in offering to cover the cost of evaluation / repair, always a bummer to have to fight to recover costs of repairing damaged goods. If any of you living in the SF Bay area require expert audio service/repairs, I can feel comfortable in referring you to Nick & Lee at True Sound, in Campbell, CA.   - String

http://www.tsound.com/

[stringdriventhing]

Well, this might be my last post in this thread. I'm driving down to pick up my Rogue Stereo 90 from Nick, who's been working hard to find a solution to the amp's bodacious hum problem. He has arrived at the determination that the noise is transformer-based with inadequately implemented unit grounding being the chief culprit. So nothing's "broken" per se, it's just a very noisy design, evidently due to cost constraints in the design, coupled with my high-efficiency speakers. Nick could, for a lot of coinage, alter the circuitry to include, amongst other things, star grounding and toroidal transformer(s) but he does not recommend the Rogue as being "worthy" of such expense. So, I got caught in the switches on this one and I'll have to see about selling the amp to someone with lower-efficiency speakers. - String