HELP! Stereo Amp Playing in Mono?!?

[Beefheart]

Hello Everyone,

I got a second hand Graaf GM50bII recently. After purchasing a complete set of new valves, I was listening last night and thought I would try the PS Audio tracks that come with the book The Stereo. There’s a couple of tracks that have Paul saying “This is the left channel” & “This is the right channel”, you get the idea.

When I listened to them, his voice came out of both speakers. I made a mental note to check again today.
I also got the audio from a left/right speaker test from YouTube and confirmed that it played 100% on the left and 100% on the right using my PC speakers.

Again, it played through both speakers.
I began a systematic check through my system all the time getting output through both speakers.

Finally, I put my old amp back in and got stereo again.

Plugging the Graaf back in, I tried the second balanced (XLR) input and got the same result, mono.

Has anyone got the slightest idea why the hell this is happening please? I’ve checked the manual and I can see nothing referring to a bridged mode or mono.

Please help!

Beefy

 

[tackleberry]

Has a channel blown and some sneaky bugger bridged it over from the working channel to the blown side of binding posts inside?

 

[dave]

Have you tried an unbalanced signal into one of the unbalanced inputs?

 

[Beefheart]

Hello Gents,

Thanks for posting. I'll be testing the RCA inputs tomorrow, I had to wait for a lead to arrive before I could do so.

@tackleberry I hope you're wrong, but you never know.
I was kind of hoping that there was an overlooked switch on the PCB to to toggle between stereo and bridged mode, but if there is, I can't see it.

I hope it can be fixed, I've just blown about £700 buying valves for it

Best regards,

Beefy.

 

[tackleberry]

I bought an Audiolab 8000p years ago and someone had done that hoping someone wouldn’t notice. I wouldn’t mind, but it only cost me £40 to fix it. I got the p and q (original British) for £200 in the end because it was faulty.

All the best👍

 

[Beefheart]

Well, I wasn’t expecting this!

So, I’ve told the guys at 2ndHandHifi that I’ll make a couple of videos to show what the problem is.

The first that I’ve recorded shows a test track being played using my old amp. So, a baseline video if you will.

After turning on the Graaf, I figured I’d give it five or ten minutes to warm up a bit before I record my video.

Three minutes in, the right speaker makes a pop and then a sound like a mic rubbing against fabric that lasts for about six seconds before fading away. Kind of reminded me of getting water stuck in your ear canal and then it drains away.

Damn, I thought I’d better check to see if anything’s wrong. So I play the test track and it’s playing correctly! I have stereo again! Eh?

If I’m not playing music, there’s definitely more hum from the right speaker, I can hear it from my listening position.

I’m happy it’s working.

But, I’m now a bit suspicious of the amp.

As the previous owner had been running 6922s in place of 6H30s, could this have caused damage to the amp or would the valves have just died quicker?

Has anyone come across this type of thing before?

Is this just part and parcel of owning a valve amp?

I’m also interested in knowing what you’d do in my position.

Best regards and thanks for any help,

Beefheart

 

[egg1dog]

Hi I've been reading your posts with interest! I have the mark 1 Graaf gm50 and it is the quietest valve amp I have ever had, no noise, hum or hiss from the amp or the tweeters when it is on. Pleased that it is now working in stereo but I would ask 2ndhandhifi (as you have only just received it) to send the amp to John Caswell who is the uk Graaf engineer for a full check up/service. He has helped me a couple of times with other Graaf amplifiers in the past. 2ndhandhifi normally sell their 2nd hand items with 3 months warranty I think so this would be my advice if you want to keep it.

 

[m7rso]

This aint normal for a valve amp. Try the old valves back in and see what happens. Either way, i always give 20 mins after turn in before i start listening. Where you buy this amp?

 

[John (big)]

Hello Everyone,

I got a second hand Graaf GM50bII recently. After purchasing a complete set of new valves, I was listening last night and thought I would try the PS Audio tracks that come with the book The Stereo. There’s a couple of tracks that have Paul saying “This is the left channel” & “This is the right channel”, you get the idea.

When I listened to them, his voice came out of both speakers. I made a mental note to check again today.
I also got the audio from a left/right speaker test from YouTube and confirmed that it played 100% on the left and 100% on the right using my PC speakers.

Again, it played through both speakers.
I began a systematic check through my system all the time getting output through both speakers.

Finally, I put my old amp back in and got stereo again.

Plugging the Graaf back in, I tried the second balanced (XLR) input and got the same result, mono.

Has anyone got the slightest idea why the hell this is happening please? I’ve checked the manual and I can see nothing referring to a bridged mode or mono.

Please help!

Beefy

Are both speakers in phase.? check both ends ie speaker & amp... ie no central image if one is out of phase.

If it was mono you would still get a central image.

 

[Beefheart]

@egg1dog Thank you so much for the information! John Caswell, is this the chap that's based in Finchhampstead? If so I'm only an hour or two's drive away from him.

@m7rso 2nd Hand Hifi / HiFiSound LTD. Based in Stockton-On-Tees.

@John (big) Even when it was stuck playing mono, it didn't seem out of phase. It actually took me a while to realise there was a problem. I was playing Depeche Mode's Waiting for the Night. There's a big swing from left to right speaker in the track and it sounded rather underwhelming. I then played a test track from PS Audio's The Stereo and realised that the amp wasn't playing as it should.

I think I'll give 2nd Hand HiFi a bell tomorrow and see if they're ok with me approching Mr. Caswell.

My thoughts are that I want to keep the amp, but it needs to behave itself first!
I think I should refain from using it or keeping it plugged in for the time being though.

Best regards to you all,

Beefheart.

 

[egg1dog]

Yes that's him. 2ndhandhifi should have his details but if they don't please pm me I have his email address. He should be able to sort this for you. Best of luck it is a cracking amplifier currently making my Esoteric pre and Krell power amp redundant!

 

[John (big)]

@egg1dog Thank you so much for the information! John Caswell, is this the chap that's based in Finchhampstead? If so I'm only an hour or two's drive away from him.

@m7rso 2nd Hand Hifi / HiFiSound LTD. Based in Stockton-On-Tees.

@John (big) Even when it was stuck playing mono, it didn't seem out of phase. It actually took me a while to realise there was a problem. I was playing Depeche Mode's Waiting for the Night. There's a big swing from left to right speaker in the track and it sounded rather underwhelming. I then played a test track from PS Audio's The Stereo and realised that the amp wasn't playing as it should.

I think I'll give 2nd Hand HiFi a bell tomorrow and see if they're ok with me approching Mr. Caswell.

My thoughts are that I want to keep the amp, but it needs to behave itself first!
I think I should refain from using it or keeping it plugged in for the time being though.

Best regards to you all,

Beefheart.

Beefheart please humor me do you have access to a test record with an out of phase track, if you have & play said track obviously if it improves odds are something is out of phase.

 

[rabski]

The 'mono then stereo' may not be related to anything else. You mentioned earlier about using balanced connections then trying single-ended. Assuming this is the case, the mono may well be due to the balanced not being wired correctly somewhere along the line.

I'm struggling to think of any fault that could be mono then stereo, though it's possible in terms of a wire or joint touching. I can't see that as down to a valve fault, as it's a balanced design so I very much doubt any of the valves would be handling both channels, though it's nevertheless still possible. Without the right schematic or the amp it's impossible to guess.

The 'pop and rustle' again could have multiple causes, but the firm favourotes would be a dry joint and a dirty valve pin. The latter is very, very possible and by no means unusual. Pull each of them and give the pins a quick go carefully with a small wire brush and see what happens.

Either way, the 'get it looked at' is spot on as it's under warranty.

 

[Beefheart]

Hello All,

Right, that’s it, I’m not experimenting anymore.

I decided to check out @John (big) 's request that I test in and out of phase. I did and out of phase lacks the fullness of in phase, while sounding wider if that makes sense. However, while doing this, I’d stopped the music and was about to try listening to something else when there was a tiny pop from the right channel, followed by a hiss that reminded me a bit of distant waves crashing on the coast.

I let this go on for about 40 seconds, recording the sound for a few seconds. Then it started to get louder and louder. I stuck the amp in standby mode ASAP as I didn’t want to risk a loud pop.

I’m not going to plug it in until it’s been looked at by somebody who knows what they are doing.
Link to an MP3 of the noise it was making. I'd stopped recording before it started getting louder.

Right Channel

Thanks for all your help everyone. Time for this amp to see a doctor or to go back.

Best regards,

Beefheart.

 

[m7rso]

Wotever. rabski said!

 

[It Cost How Much!?!]

Send it back.

I had a dodgy phono stage from them, they refused to accept it would drop one channel and then when they eventually accepted it back (via eBay), they banned me from buying from them. I had a mate test it and one channel had battery corrosion on the underside of a board.

The Graaf GM50b Mk2 is a wonderful amp, mine worked no issues, if you plan to keep it, get the dealer to sort it for free and no postage charges.

 

[Beefheart]

Hello Everyone,

Just thought I'd update you if you’re interested; I got my amp back last week and spent a very pleasurable weekend listing to music with it. The crackling & popping was down to a dodgy cap, but the mono/stereo issue is still a mystery. But, it behaved on the bench for a week, and it worked with no issues what so ever over the weekend.

Very happy with the service provided by 2nd Hand HiFi and very happy with the Graaf! Certainly noticing more detail in the music and I see that people mean about the midrange on valve amps!

A couple of weeks ago I also purchased a pair of GIK 2A diffuser/absorber panels for sidewall reflections. Made quite a lot of difference to the cohesiveness of the stereo image. Very good bang for your buck. In fact, if you can accommodate a pair, and haven’t already done so, go for it!

Kind regards,

Beefy