taha_never Posted September 24, 2015 Share Posted September 24, 2015 Hey all. got myself a hand built tube preamp (2xRCA12ax7s). not much high quality components though. at the beginning everything were working fine and it was quiet till suddenly it decided to hiss! there's a very obvious white noise which increases with the volume control including crackles when turning the knob. unfortunately the builder has migrated to another country and i can't get in touch with him. do you have any idea what is the common cause of such problem? dirty board or pot? broken caps or tubes? what can i do to fix it myself? i need your advice and i will appreciate your help. Quote Link to comment Share on other sites More sharing options...
JTUK Posted September 25, 2015 Share Posted September 25, 2015 I'd swap out the valves to see if they had 'gone'... Quote Link to comment Share on other sites More sharing options...
taha_never Posted September 27, 2015 Author Share Posted September 27, 2015 none of the preamp knobs affect this hiss. only the volume knob. is it still a suspicious tube? Quote Link to comment Share on other sites More sharing options...
taha_never Posted September 27, 2015 Author Share Posted September 27, 2015 with all the valves removed it's still there. unchanged. so the tubes are ok? so what else should i try? please shed a light Quote Link to comment Share on other sites More sharing options...
ahpook Posted September 27, 2015 Share Posted September 27, 2015 (edited) Is that the output at the top-left of the picture ? A close-up of the main board and the one at top-left would help I think. Edited September 27, 2015 by ahpook Quote Link to comment Share on other sites More sharing options...
taha_never Posted September 27, 2015 Author Share Posted September 27, 2015 [color=#282828][font=helvetica, arial, sans-serif]hello "ahpook"[/font][/color] [color=#282828][font=helvetica, arial, sans-serif]yep thats the output. what a messy interior i have here! here are some details [/font][/color][attachment=201665:IMG_6432.JPG][attachment=201666:IMG_6434.JPG][attachment=201667:IMG_6436.JPG][attachment=201668:IMG_6438.JPG] Quote Link to comment Share on other sites More sharing options...
ahpook Posted September 27, 2015 Share Posted September 27, 2015 (edited) I'd guess that if you took out the valves then you should get no sound at all.....I'd start by having a good look at output board.... It's difficult to say without knowing what circuit is being used - it all depends how confident you are at trying to fix it, given the high voltages used in a valve amp. Edited September 27, 2015 by ahpook Quote Link to comment Share on other sites More sharing options...
Passinwind Posted September 27, 2015 Share Posted September 27, 2015 (edited) You could try replacing the socketed IC; looks like an NE5534 or 5532 opamp (can't quite read the number), which are common and pretty inexpensive. If that fails then further self-repair is not such a great idea IMHO. A good tech could most likely trace that circuit by sight in 5-10 minutes tops. Edited September 27, 2015 by Passinwind Quote Link to comment Share on other sites More sharing options...
taha_never Posted September 27, 2015 Author Share Posted September 27, 2015 thank you JTUK you helped me figure out that my valves are ok. thank you ahpook for your time, yep i don't dare, but as you and Passinwind suggest i will chase the output part. thank you Passinwind for your advice i'll take my unit straight to a techie. have a good time friends Quote Link to comment Share on other sites More sharing options...
Passinwind Posted September 27, 2015 Share Posted September 27, 2015 [quote name='Yawn_Blah' timestamp='1443375497' post='2874222'] thank you JTUK you helped me figure out that my valves are ok. thank you ahpook for your time, yep i don't dare, but as you and Passinwind suggest i will chase the output part. thank you Passinwind for your advice i'll take my unit straight to a techie. have a good time friends [/quote] Cool, and good luck. With the right tools and a little knowledge that should be pretty easy to fix, most likely. Quote Link to comment Share on other sites More sharing options...
ahpook Posted September 27, 2015 Share Posted September 27, 2015 [quote name='Passinwind' timestamp='1443375911' post='2874230'] Cool, and good luck. With the right tools and a little knowledge that should be pretty easy to fix, most likely. [/quote] Very much so - do let us know how it works out. Quote Link to comment Share on other sites More sharing options...
taha_never Posted September 27, 2015 Author Share Posted September 27, 2015 [quote name='Passinwind' timestamp='1443375911' post='2874230'] Cool, and good luck. With the right tools and a little knowledge that should be pretty easy to fix, most likely. [/quote] yep. in fact i'm pretty strange with circuitries. i swapped some pickups and pots the other day, but when it comes to ICs and such i'm a noob. but yes i'll get a replacement for that IC and give it a try. Thanks a lot again. Quote Link to comment Share on other sites More sharing options...
Passinwind Posted September 27, 2015 Share Posted September 27, 2015 [quote name='Yawn_Blah' timestamp='1443376449' post='2874239'] yep. in fact i'm pretty strange with circuitries. i swapped some pickups and pots the other day, but when it comes to ICs and such i'm a noob. but yes i'll get a replacement for that IC and give it a try. Thanks a lot again. [/quote] Make sure you get the right part number, if it is in fact one of the two I mentioned they are not interchangeable. Quote Link to comment Share on other sites More sharing options...
taha_never Posted September 27, 2015 Author Share Posted September 27, 2015 [quote name='ahpook' timestamp='1443376314' post='2874235'] Very much so - do let us know how it works out. [/quote] sure. thanks mate. Quote Link to comment Share on other sites More sharing options...
taha_never Posted September 27, 2015 Author Share Posted September 27, 2015 [quote name='Passinwind' timestamp='1443376824' post='2874245'] Make sure you get the right part number, if it is in fact one of the two I mentioned they are not interchangeable. [/quote] yep i'll read and write it down from the part. cheers. Quote Link to comment Share on other sites More sharing options...
BanditSid Posted September 28, 2015 Share Posted September 28, 2015 (edited) NE5534 OP Amps are designed for low impedance circuits where they are fairly low noise, in a high impedance circuit however they don't perform nearly as well from a noise point of view. A good low noise replacement is TL071/T072, it's not the best but is cheap and reliable and gives good results - if the existing chip is an NE5534 use a TL071 (single op amps) if it's an NE5532 use a TL072 (dual op amps). Edited September 28, 2015 by BanditSid Quote Link to comment Share on other sites More sharing options...
3below Posted September 28, 2015 Share Posted September 28, 2015 Tantalising image, as Passinwind notes, it is a 553?..... Looking at the stripboard back, I suggest taking a close look (magnifying glass) between pins 7 and 8 (pin 7 has the brown wire, pin 8 above on LHS of image). Is there a clear gap between the pins (no solder bridge / whiskers)? It is not clear in the image but the solder from pin 8 looks 'blobby' towards pin 7, however this could just be a camera angle artifact Quote Link to comment Share on other sites More sharing options...
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