snorkie635 Posted September 1, 2012 Share Posted September 1, 2012 Recent purchase of DB 751 has led to great joy - but - it hisses (white noise) if either preamp gain or master volume are set over 10.00 o'clock. This happens without any bass plugged in. Just wondered if anyone else had experienced this kind of thing - I've tried replacing the valves in the preamp with no joy (and the tweeter in my cab is off. Hmm? Quote Link to comment Share on other sites More sharing options...
0175westwood29 Posted September 1, 2012 Share Posted September 1, 2012 never had this with my db750 could it be to do with a bad earth supply to the head? def shouldnt hiss tho mate. andy Quote Link to comment Share on other sites More sharing options...
snorkie635 Posted September 1, 2012 Author Share Posted September 1, 2012 [quote name='0175westwood29' timestamp='1346529160' post='1790342'] never had this with my db750 could it be to do with a bad earth supply to the head? def shouldnt hiss tho mate. andy [/quote]I'll see if that's likely - thanks for the heads up Quote Link to comment Share on other sites More sharing options...
0175westwood29 Posted September 1, 2012 Share Posted September 1, 2012 No probs mate Quote Link to comment Share on other sites More sharing options...
molan Posted September 1, 2012 Share Posted September 1, 2012 Definitely shouldn't be doing that. Did you buy from a UK dealer? They should either offer a repair or refer to their official tech in the UK - he's an absolute gem of a technician! Quote Link to comment Share on other sites More sharing options...
snorkie635 Posted September 2, 2012 Author Share Posted September 2, 2012 [quote name='molan' timestamp='1346539092' post='1790460'] Definitely shouldn't be doing that. Did you buy from a UK dealer? They should either offer a repair or refer to their official tech in the UK - he's an absolute gem of a technician! [/quote] I did buy it from a UK dealer - who's the tech? Quote Link to comment Share on other sites More sharing options...
molan Posted September 2, 2012 Share Posted September 2, 2012 Details here : http://basschat.co.uk/topic/185643-aguilar-repair-specialist/ Quote Link to comment Share on other sites More sharing options...
snorkie635 Posted September 12, 2012 Author Share Posted September 12, 2012 thanks for the information Molan. I'll give them a call if necessary. S635 Quote Link to comment Share on other sites More sharing options...
umph Posted September 12, 2012 Share Posted September 12, 2012 [quote name='snorkie635' timestamp='1346528155' post='1790326'] Recent purchase of DB 751 has led to great joy - but - it hisses (white noise) if either preamp gain or master volume are set over 10.00 o'clock. This happens without any bass plugged in. Just wondered if anyone else had experienced this kind of thing - I've tried replacing the valves in the preamp with no joy (and the tweeter in my cab is off. Hmm? [/quote] theres lots of things it could be, it shouldn't be that bad though! is this level of noise without anything plugged in? Quote Link to comment Share on other sites More sharing options...
snorkie635 Posted September 15, 2012 Author Share Posted September 15, 2012 It is indeed. Quote Link to comment Share on other sites More sharing options...
0175westwood29 Posted September 15, 2012 Share Posted September 15, 2012 i'd def get it to a tech man Quote Link to comment Share on other sites More sharing options...
umph Posted September 15, 2012 Share Posted September 15, 2012 are the valve cans missing? Quote Link to comment Share on other sites More sharing options...
snorkie635 Posted September 21, 2012 Author Share Posted September 21, 2012 Everything's there - it was bought new. Quote Link to comment Share on other sites More sharing options...
0175westwood29 Posted September 22, 2012 Share Posted September 22, 2012 id maybe try and get them to exchange it or sort the problem? andy Quote Link to comment Share on other sites More sharing options...
umph Posted September 22, 2012 Share Posted September 22, 2012 [quote name='snorkie635' timestamp='1348263220' post='1811737'] Everything's there - it was bought new. [/quote] try swapping the preamp valves around, see if one has better noise rejection in the first position Quote Link to comment Share on other sites More sharing options...
snorkie635 Posted September 24, 2012 Author Share Posted September 24, 2012 Thanks for the advice guys - it's being checked out as I write this. Quote Link to comment Share on other sites More sharing options...
aircoutix Posted March 30, 2014 Share Posted March 30, 2014 Hi Snorkie635 (MTD 635 player?), I recently got a used DB-751 and it has the same problem (+ the fan noise problem). I guess that it is not a major problem. I replaced the tubes and the AOPs without any effect. I asked Aguilar, mentionning that I was in a position to perform the correction by myself, and would prefer avoiding sending the complete 20 Kgs head for the replacement of a simple less than 1 g resistor. But they only answered that I had to contact my local seller. Living in Europe, I know that asking my local seller would require several months for a repair (friends currently experience several months for an acquisition) and much cost since it is not under warranty anymore. Probably for a stupid less than 1€ component replacement. Can you let me know how you solved yours? Quote Link to comment Share on other sites More sharing options...
BandmasterPete Posted June 23, 2014 Share Posted June 23, 2014 Are you using your DB-amp with a earth ground at the wall? Are you using fluorescent lamps in the room? Are your bass shielded? Many hiss problem is connected to grounding, lightning and so on. Quote Link to comment Share on other sites More sharing options...
aircoutix Posted October 1, 2014 Share Posted October 1, 2014 I searched for a very long time before determining the cause of this hiss (with crackles from time to time). I had to draw the schematics in order to be in a position to follow the signal all along the circuit, Aguilar boss refusing to provide me with the schematics even only the preamp part (I had determiend that the problem was located in the preamp part). It took me hours. Since I got no help from Aguilar, I have no reason to keep for Aguilar only what I discovered. The first thing that I discovered was a dead resistor as R449. My conclusion is that it died because it is simply under-dimensionned in power (having to support 0,8 watts while looking like a resistor dimensionned for 0,5 watts). I thus guess that I am not the only one with this problem. It is not easy to be sure that a head has this problem without opening it since the preamp works rather well with a dead R449 resistor. But the third tube simply does not work properly and this surely degrades the sound. I replaced this resistor by a simply more powerful one (1 watt). But the hiss was not coming from this problem since still being there. I determined the several circuit output stages and, using an oscilloscope, located the output with the biggest problem occurence. I then tried to temporarily amplify or surppress it with the help of a cold spray. But the problem was moving from a stage to another one from time to time. I finally determined that the weldings of the preamp components were involved, despite looking nice. I made back the weldings of one third/one half (left part) of the preamp and it came back to life without hiss. Making back this weldings requires to remove the existing welding and it is a pain since being tin-free. I hope this will help some of you. Quote Link to comment Share on other sites More sharing options...
aircoutix Posted October 1, 2014 Share Posted October 1, 2014 If you have the opportunity, try to insert a Demeter VTDB-201S preamp in the effect loop of the DB-751 and mix the dry signal (from the DB-751 preamp) with the wet signal coming from the Demeter (but first passing in the DB-751 preamp). This keeps the meat of the DB-751 while adding the clarity of the Demeter. This head which is tremendous becomes even more. Quote Link to comment Share on other sites More sharing options...
mybass Posted October 2, 2014 Share Posted October 2, 2014 [quote name='snorkie635' timestamp='1346528155' post='1790326'] Recent purchase of DB 751 has led to great joy - but - it hisses (white noise) if either preamp gain or master volume are set over 10.00 o'clock. This happens without any bass plugged in. Just wondered if anyone else had experienced this kind of thing - I've tried replacing the valves in the preamp with no joy (and the tweeter in my cab is off. Hmm? [/quote] I had an Aguilar many years ago and my sound man complained that it made a hiss out of the DI and changed the output valve. At the time this cured the problem. 'AIRCUOTIX' seems to be well into this problem ........ I figure his comment 'making back' means re-soldering the joints? Good luck, hiss drives everyone mad! Quote Link to comment Share on other sites More sharing options...
GrammeFriday Posted October 4, 2014 Share Posted October 4, 2014 Sorry to hear about your problems but I'm grateful to you for curing my GAS for one of these amps! Quote Link to comment Share on other sites More sharing options...
aircoutix Posted October 5, 2014 Share Posted October 5, 2014 Maybe you shoud not cure your GAS, GrammeFriday. This amp is awesome. I certainly got one of a faulty sample, very likely one of the first manufacturing series. The problem may have been corrected now. The "rather recent" use by industry of lead-free soldering raised new problems, to be discovered once equipments are getting old. This is a common situation applying to any new design. Additional efforts and associated delays before manufacturing launches are made only for equipments involved in safety of life systems, which is not the case with guitar amps. I re-soldered the joints (my apologies for my English language which is not my mother tongue) of the input part of the preamp replacing the lead-free by traditional lead-including soldering, which solved the hiss problem. I should do the same for the remaining part of the preamp but removing lead-free soldering on all soldering joints is such a pain. And noise/hiss problems are much more sensitive on the input stages. The dead resistor on the third tube stage is a second topic. It looks like being the only mistake on this preamp. This should not prevent you to keep in mind all the awesome rest of this amp design. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.