mcnach Posted October 5, 2012 Share Posted October 5, 2012 warning: a bit of a rant coming. So I have this Hartke A100, a 100W combo with a 15" speaker... Nothing special, but pretty nice sounding. Nice deep sound at low volumes, and it can get pretty loud so it's suitable for rehearsals. Now, mine developed a buzzing sound. It's not really noticeable at moderate/loud volume, but it is noticeable when playing quietly at home. It sounds like I had an overdrive pedal with the blend knob set almost fully clean, but letting a bit of distortion through. So I did the following: 1) I disconnected the internal speaker, and plugged the combo's amp into an external cabinet (actual two different ones). It still buzzed. 2) I connected a separate bass head to the internal speaker. I did not buzz. From that I concluded that the buzz was not mechanical, that the speaker and cab is just fine, and that the problem lies within the amplifier. I took the combo to someone that I had heard good things about, not far from where I live, about 20 miles away. I explained the situation, and he kept the amp. Two days later: "the transformer was loose", and something else, and he thinks maybe what I was hearing was some static because of components being loose. I express surprise, pay him £35, and take away the amp. Of course, I plugged it in and nothing had changed. Ok, I blame myself for not having shown the man the buzz I was talking about. My results from swapping amp and cabs above did not seem compatible with his verdict, which shows maybe he did not pay much attention to what I said. I get back in touch, and I take it back to him. This time I make sure he hears the buzz. He jokes "oh, we play rock and roll here, loud! I guess I missed that buzz but I hear it now, yes!". Fine. I also demonstrate the effects of swapping amp/cab, and he agrees that it has to be in the amp itself. Several weeks later he tells me that he "rebuilt the power supply" as he could see something there on his oscilloscope and that it was ok, but that he tried the speaker on its own attached to his signal generator and it buzzed. He concluded it was the speaker and proceeded to give me quotes for new speakers. I said no, the speaker was fine. We agreed I would come round and collect the amp then. I collected it today. He was adamant it was just the speaker, it needs a new speaker. I did not appreciate his condescending tone. I reminded him that he heard, with me, how a separate amp connected to the speaker did not buzz. I reminded him that the amp alone connected to a separate cab produced the buzz... so clearly it was not my speaker. He did not comment. I can accept it if he cannot find the solution, and I would pay for his time anyway. But he ignored everything I said and even what I showed him, in person. He just went on about what his oscilloscope shows... when it's something you can hear (which makes me question whether he knows how to use the oscilloscope) and having a dismissive condescending demeanor. I got home and tried the amp. Exactly as it was when I first approached him, well over a month ago. What a waste of time. There's nothing wrong with admitting defeat. It happens. But I have no respect for someone who does not listen to the customer's indications, and shows no logical thinking. He'd have charged me for replacing the speaker... and I'd be here a week from now, with the very same situation I have now, nothing fixed, and less money in my pocket. Seriously, don't take your amps to this man. Quote Link to comment Share on other sites More sharing options...
Big_Stu Posted October 5, 2012 Share Posted October 5, 2012 I've known Dennis for over 10 years and his roster of clients can't be argued with; but he is still human. I've only known him once over the years to miss something on an amp of mine but would still regard him as a brilliant amp tech. With my valve amp he missed an incredibly hard to see clipped wire which had been done by a previous tech (Slade's Charlie) to kill the normal channel on the amp - why you'd do that I have no idea but that's what it was. This too was only spotted by using an instrument through the amp rather that meters so I take your point. He was more than happy to rectify it gratis. I've referred many people to him as a first port of call - and to be honest you're the first I've heard of to be disappointed. That's not to say I'm not believing you in any way; I'm just saying in my work too I try to achieve perfection, sometimes - but not often - I miss the mark. Quote Link to comment Share on other sites More sharing options...
JTUK Posted October 5, 2012 Share Posted October 5, 2012 I have a guy I use and I think he really knows his onions, but my amp was knocked about a few weeks ago and I think the noise from it under power, with fan on, is louder that it was. I have used the amp in anger and all was ok-ish, but I want to get it checked. The problem is how do you rectify a fault that may not even be a fault..and I am imagining the problem...?? In the case of the OP though..I would feel the same... and would not think well of the guy who worked like that. Quote Link to comment Share on other sites More sharing options...
LukeFRC Posted October 5, 2012 Share Posted October 5, 2012 Jose..... as a scientist your kind of methodical logical approach isn't followed by everyone.... can you not open it up yourself to have a look? it can't be that technical inside Quote Link to comment Share on other sites More sharing options...
Beer of the Bass Posted October 5, 2012 Share Posted October 5, 2012 Hmm, it does sound like he dropped the ball in this case. Have you tried the send and return jacks to confirm whether the distortion is coming from the power amp? Your description (distortion/noise blended with the signal at constant level, more audible during quieter playing) sounds a classic description of crossover distortion in the power amp. If I had a transistor amp making this noise, I'd start by checking the power transistors and their bias voltages. Quote Link to comment Share on other sites More sharing options...
mcnach Posted October 5, 2012 Author Share Posted October 5, 2012 [quote name='Big_Stu' timestamp='1349459374' post='1826681'] I've known Dennis for over 10 years and his roster of clients can't be argued with; but he is still human. I've only known him once over the years to miss something on an amp of mine but would still regard him as a brilliant amp tech. With my valve amp he missed an incredibly hard to see clipped wire which had been done by a previous tech (Slade's Charlie) to kill the normal channel on the amp - why you'd do that I have no idea but that's what it was. This too was only spotted by using an instrument through the amp rather that meters so I take your point. He was more than happy to rectify it gratis. I've referred many people to him as a first port of call - and to be honest you're the first I've heard of to be disappointed. That's not to say I'm not believing you in any way; I'm just saying in my work too I try to achieve perfection, sometimes - but not often - I miss the mark. [/quote] I had heard very good things about him too, that's why I decided to approach him. He seemed nice enough the first two times I saw him, and the second one, when I did all the swapping amp/speaker etc with him I really warmed up to him. I have no doubt he knows a thing or seventeen about amplifiers, that much is un-arguable. I accept that he, like anyone else, can make the wrong call at times. I can accept that he cannot find the fault in my amp as well. This particular amp is not exactly high end and I gather it's heavy on circuit boards and chips... I can understand it if he told me that it's just not practical to trouble shoot it... in fact it was an answer I was assuming would be coming quite quickly. But the way he went about my amp with me was quite disappointing. I don't know what's wrong, obviously But I know it's not the speaker. That is pretty clear, and first I told him about it, later I showed him and he agreed with everything I had established until then. But then, after a few weeks (he was away at one point, then I was away) it's like all that was forgotten and he convinced himself that the speaker was to blame... When I point that out to him (and I am normally a polite person, but I am especially polite with people who have the ability to help me so I was in no way showing disrespect or anything) he dismissed it all, and I felt he was being rather condescending. It was not a pleasant experience. I can accept I'm the unlucky one. I am not upset about his not fixing the amp. But I felt he was being dismissive, and that's what I did not like. Despite it all, I asked him how much I owed him for his time, and he did not want any money, to his credit. Only the initial £35 I gave him the first time. I was working on the assumption that he'd try, and I'd pay for his time regardless of the outcome. Anyway. That was my experience. Quote Link to comment Share on other sites More sharing options...
mcnach Posted October 5, 2012 Author Share Posted October 5, 2012 [quote name='LukeFRC' timestamp='1349460065' post='1826692'] Jose..... as a scientist your kind of methodical logical approach isn't followed by everyone.... can you not open it up yourself to have a look? it can't be that technical inside [/quote] ok, there is science and there is science my approach was just that: logical. Just attempting to isolate the source of the problem. The source is the amplifier itself. I went through it all with him the second time I met him, and he agreed with everything But that's as far as I go... then it's time for somebody who knows his electronics and is familiar with amplifiers to dissect it further. Not me. I opened it, of course. I open up anything even if I have no clue what I'm looking at! [1] BUt there is nothing like an obvious loose connection, or any signs of damage... I can't trouble shoot an amplifier. I may try to dissect whether the issue is the preamp or the power amp section... if they are modular... But really, this is not my field of expertise. [1] my dad had a mortar shell (empty) when I was little, from his military days. I was about 8 when I took it apart. I was not sure whether it was live or not, but I had seen movies where they deactivated bombs from the German bombers by unscrewing the tip etc etc and I figured it would be interesting to see whether these were anything like them. I was pretty nervous Quote Link to comment Share on other sites More sharing options...
Big_Stu Posted October 5, 2012 Share Posted October 5, 2012 (edited) Yeah, I sympathise. I don't know of any other techs in the Edinburgh area that you could go to with confidence. A buzz is often an an earthing problem; I've assumed that you had it away from all of the usual suspects, florescent lights, fridges, CRTs etc. I'm not familiar with the amp; does it have a headphone socket? If so, does that have the buzz? [quote name='mcnach' timestamp='1349464580' post='1826792'] [1] my dad had a mortar shell (empty) when I was little, from his military days. I was about 8 when I took it apart. I was not sure whether it was live or not, but I had seen movies where they deactivated bombs from the German bombers by unscrewing the tip etc etc and I figured it would be interesting to see whether these were anything like them. I was pretty nervous [/quote] When I was a kid the local bike shop had a shell as a door stop in the summertime; after quite a few years it did turn out to be live! Edited October 5, 2012 by Big_Stu Quote Link to comment Share on other sites More sharing options...
mcnach Posted October 5, 2012 Author Share Posted October 5, 2012 [quote name='Beer of the Bass' timestamp='1349460979' post='1826710'] Hmm, it does sound like he dropped the ball in this case. Have you tried the send and return jacks to confirm whether the distortion is coming from the power amp? Your description (distortion/noise blended with the signal at constant level, more audible during quieter playing) sounds a classic description of crossover distortion in the power amp. If I had a transistor amp making this noise, I'd start by checking the power transistors and their bias voltages. [/quote] Not yet. This was something that only occurred to me today on my way back from retrieving the amp. I will definitely try to bypass the preamp that way and see whether the buzz is still there. However, I would not know what to do beyond that. If I still get buzz, I would conclude it's the power amp. But no idea what to do next. If the buzz goes, I'd conclude it's the preamp... in which case I'd still not know what to do but I could bypass it permanently using another preamp in a box. I was on my way to become an engineer, specialising in electronics, inspired by Tom Scholz and my neighbour -who built a whole hifi system for himself- but then I discovered genetics... so I know nothing. And I am not from Barcelona. Quote Link to comment Share on other sites More sharing options...
mcnach Posted October 5, 2012 Author Share Posted October 5, 2012 [quote name='Big_Stu' timestamp='1349464780' post='1826798'] Yeah, I sympathise. I don't know of any other techs in the Edinburgh area that you could go to with confidence. A buzz is often an an earthing problem; I've assumed that you had it away from all of the usual suspects, florescent lights, fridges, CRTs etc. I'm not familiar with the amp; does it have a headphone socket? If so, does that have the buzz? When I was a kid the local bike shop had a shell as a door stop in the summertime; after quite a few years it did turn out to be live! [/quote] seriously???? Live???? well, I laugh now, but I bet there were a few brown underpants when they found out!!! The amp was tested in three different locations, as I wanted to make sure it was not just some oddity of the wiring. The buzz is there. It's not your typical earthing buzz... it's... like an overdrive pedal with the blend knob nearly all the way towards the dry sound. It does have a headphone socket. I tried it at home, and I could not be certain. My headphones are not very good and bass frequencies make them be a bit noisy... so that was inconclusive. Dennis had the same idea and we tried it with a pair of headphones he had. We could not hear the buzz through the headphones, but again we could not be certain that it was truly buzz free, it was not the best sound possible. I should feed the headphone output into my RH450 and into the combo's internal speaker, and see whether it's truly buzz free. Quote Link to comment Share on other sites More sharing options...
Beer of the Bass Posted October 5, 2012 Share Posted October 5, 2012 An old bandmate of mine had a load of gear repaired by Jimmy Gillan (he works from home near the cathedral), and he seems to welcome transistor as well as valve stuff. I've not dealt with him myself, so I can't offer an actual endorsement, but my bandmate was quite happy. I don't think he has an internet presence, but I'm sure I can dig out his number if you want to give him a shot. Quote Link to comment Share on other sites More sharing options...
stu_g Posted October 5, 2012 Share Posted October 5, 2012 i used to have an old session amp many years ago that used to cut out took it to guitar village in farnham and the bloke who did repairs remedy was to solder the internal fuse into its holder?the fuse never blew in first place! it was a mosfet fault of some kind, anyways amp never was repaired but i learnt my lesson and after invested my money into a trce elliot ah300smx which i still have today Quote Link to comment Share on other sites More sharing options...
mcnach Posted October 5, 2012 Author Share Posted October 5, 2012 [quote name='Beer of the Bass' timestamp='1349465547' post='1826813'] An old bandmate of mine had a load of gear repaired by Jimmy Gillan (he works from home near the cathedral), and he seems to welcome transistor as well as valve stuff. I've not dealt with him myself, so I can't offer an actual endorsement, but my bandmate was quite happy. I don't think he has an internet presence, but I'm sure I can dig out his number if you want to give him a shot. [/quote] That would be good, sure. If you can find out and send me a PM I'd appreciate it. Thanks! Quote Link to comment Share on other sites More sharing options...
mcnach Posted October 5, 2012 Author Share Posted October 5, 2012 [quote name='stu_g' timestamp='1349467658' post='1826854'] i used to have an old session amp many years ago that used to cut out took it to guitar village in farnham and the bloke who did repairs remedy was to solder the internal fuse into its holder?the fuse never blew in first place! it was a mosfet fault of some kind, anyways amp never was repaired but i learnt my lesson and after invested my money into a trce elliot ah300smx which i still have today [/quote] Session? later Award-Session? I know the owner/designer, Stewart Ward. You could have taken the amp to him... he's in Basingstoke! I liked his amps. I don't own any of them, but all my cables were made by him Quote Link to comment Share on other sites More sharing options...
stu_g Posted October 5, 2012 Share Posted October 5, 2012 yeah i live in basingstoke too i think i may have phoned him but spares arent available Quote Link to comment Share on other sites More sharing options...
stu_g Posted October 5, 2012 Share Posted October 5, 2012 i have session compressor too wish he could fix that bad boy Quote Link to comment Share on other sites More sharing options...
Beer of the Bass Posted October 6, 2012 Share Posted October 6, 2012 [quote name='mcnach' timestamp='1349473573' post='1826979'] That would be good, sure. If you can find out and send me a PM I'd appreciate it. Thanks! [/quote] Will do. I've messaged my old bandmate, as I can't find Jimmy's business card. Quote Link to comment Share on other sites More sharing options...
mcnach Posted October 6, 2012 Author Share Posted October 6, 2012 [quote name='Beer of the Bass' timestamp='1349516764' post='1827209'] Will do. I've messaged my old bandmate, as I can't find Jimmy's business card. [/quote] thank you Quote Link to comment Share on other sites More sharing options...
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