Hi everyone,
I purchased a used Rogue Cronus Magnum II last fall. The amp is in excellent condition, was available about an hour away from me, and I got it for a couple hundred less than they typically sell for. I am new to tubes and wanted to try something modern with a pair of vintage Altec 604-8Gs I picked up last year. I had a feeling the Rogue might not be the best match for those speakers, but I decided to take a chance on it based on the rave reviews this amp receives online. I also liked the fact that it had a phono stage, balance control, and a remote, which seems rare with tube amps. If it wasn't a good match, I figured I could resell it easily since I was getting it for a fair price.
Well, as soon as I connected it to my speakers I heard a hum that was audible from 20 feet across the room. I had previously tried three different amps with the Altecs including a vintage Yamaha CR-420, a more modern Yamaha RX-797, and a vintage Scott LK-72-B tube amp, and never noticed any hum with those amps. The Scott was on-deck for restoration, and that's another reason why I bought the Rogue. To use while I was working on the Scott.
I noticed speaker hum was mentioned in the Trouble Shooting section of the manual and it said "If hum can be heard from more than a few inches from the loudspeaker, there is probably a ground loop. If this fails to cure the hum, call customer service at Rogue Audio for further advice." I disconnected everything from the amp except the speakers and plugged it into a dedicated 20amp circuit, but the hum was still the same. I also tried using a cheater plug to disconnect the ground prong, but that made no difference either.
I emailed Rogue and they said my Altecs were very efficient and used a large woofer. So they would expect some level of hum, but they also asked me to mute the amp and listen for transformer hum. I did that and could hear the transformer from several feet away. So they said the bridge rectifier may be on it's way out and it would be a good idea to replace it. I did that at a cost of about $70CAD, but it made no difference to either the transformer or speaker hum.
I also tried the amp with a pair of vintage Celestion 332 speakers in my basement system. They are considerably less efficient than the Altecs, around 85-86dB by modern standards I believe, but I could still hear the speaker hum from across the room. I measured the hum with a Decibel Meter on my phone and it said the frequency was around 120Hz
I really want to like this amp, but the hum is unacceptable to me. I have also finished restoring the Scott and it sounds great and is dead quiet in comparison. So I would like to sell the Rogue, but I can't sell it in good conscience without mentioning the hum and transformer buzz.
Rogue ran out of ideas and said I could send it back to them for service, but that would cost at least $150CAD one way and if the transformer needs to be replaced that would be $400USD plus return shipping. I have also read a few forum posts from other people who have experienced similar issues with hum and transformer noise with this amp (wish I'd seen those before buying). So I'm also worried that if I ship it back, they might say it's operating within factory specs and return it to me. Then I'll be right back where I started, but I'll be out 300 bucks for shipping.
I did listen to the amp before I bought it, but I have to admit I didn't listen for things like hum or transformer buzz with no music playing. LESSON LEARNED! I also spoke with the seller and he assured me he never had any problems with hum, but his speakers were much less efficient.
Oh, I also purchased a couple 12AU7 tubes to try in the preamp socket, but none of them made any difference. One was an RCA Cleartop and two others were vintage Baldwin organ tubes that the seller said are factory selected to be ultra-quiet non-microphonic.
So now I have an amp I don't want to listen to and may have trouble selling. Does anyone have any suggestions at all for any other troubleshooting or diagnostics I can do? I purchased an oscilloscope recently, but all I've used it for so far is identifying the outer foil on the capacitors for the Scott.
Sorry for the long post, but I wanted to explain everything I've been through with this amp. This Rogue was one of the most expensive audio purchases I've ever made and it has also been one of the most disappointing. 🙁
Any suggestions would be much appreciated.
Thanks,
Andy
I purchased a used Rogue Cronus Magnum II last fall. The amp is in excellent condition, was available about an hour away from me, and I got it for a couple hundred less than they typically sell for. I am new to tubes and wanted to try something modern with a pair of vintage Altec 604-8Gs I picked up last year. I had a feeling the Rogue might not be the best match for those speakers, but I decided to take a chance on it based on the rave reviews this amp receives online. I also liked the fact that it had a phono stage, balance control, and a remote, which seems rare with tube amps. If it wasn't a good match, I figured I could resell it easily since I was getting it for a fair price.
Well, as soon as I connected it to my speakers I heard a hum that was audible from 20 feet across the room. I had previously tried three different amps with the Altecs including a vintage Yamaha CR-420, a more modern Yamaha RX-797, and a vintage Scott LK-72-B tube amp, and never noticed any hum with those amps. The Scott was on-deck for restoration, and that's another reason why I bought the Rogue. To use while I was working on the Scott.
I noticed speaker hum was mentioned in the Trouble Shooting section of the manual and it said "If hum can be heard from more than a few inches from the loudspeaker, there is probably a ground loop. If this fails to cure the hum, call customer service at Rogue Audio for further advice." I disconnected everything from the amp except the speakers and plugged it into a dedicated 20amp circuit, but the hum was still the same. I also tried using a cheater plug to disconnect the ground prong, but that made no difference either.
I emailed Rogue and they said my Altecs were very efficient and used a large woofer. So they would expect some level of hum, but they also asked me to mute the amp and listen for transformer hum. I did that and could hear the transformer from several feet away. So they said the bridge rectifier may be on it's way out and it would be a good idea to replace it. I did that at a cost of about $70CAD, but it made no difference to either the transformer or speaker hum.
I also tried the amp with a pair of vintage Celestion 332 speakers in my basement system. They are considerably less efficient than the Altecs, around 85-86dB by modern standards I believe, but I could still hear the speaker hum from across the room. I measured the hum with a Decibel Meter on my phone and it said the frequency was around 120Hz
I really want to like this amp, but the hum is unacceptable to me. I have also finished restoring the Scott and it sounds great and is dead quiet in comparison. So I would like to sell the Rogue, but I can't sell it in good conscience without mentioning the hum and transformer buzz.
Rogue ran out of ideas and said I could send it back to them for service, but that would cost at least $150CAD one way and if the transformer needs to be replaced that would be $400USD plus return shipping. I have also read a few forum posts from other people who have experienced similar issues with hum and transformer noise with this amp (wish I'd seen those before buying). So I'm also worried that if I ship it back, they might say it's operating within factory specs and return it to me. Then I'll be right back where I started, but I'll be out 300 bucks for shipping.
I did listen to the amp before I bought it, but I have to admit I didn't listen for things like hum or transformer buzz with no music playing. LESSON LEARNED! I also spoke with the seller and he assured me he never had any problems with hum, but his speakers were much less efficient.
Oh, I also purchased a couple 12AU7 tubes to try in the preamp socket, but none of them made any difference. One was an RCA Cleartop and two others were vintage Baldwin organ tubes that the seller said are factory selected to be ultra-quiet non-microphonic.
So now I have an amp I don't want to listen to and may have trouble selling. Does anyone have any suggestions at all for any other troubleshooting or diagnostics I can do? I purchased an oscilloscope recently, but all I've used it for so far is identifying the outer foil on the capacitors for the Scott.
Sorry for the long post, but I wanted to explain everything I've been through with this amp. This Rogue was one of the most expensive audio purchases I've ever made and it has also been one of the most disappointing. 🙁
Any suggestions would be much appreciated.
Thanks,
Andy
Last edited: