faint distortion sound with my trace elliot head

[ahpook]

i usually use my trace elliot head for practise at home as the cooling fans on the bigger rig tend to annoy after a while. so now that it's driving my new cab that's on top of my old 4x10 i can hear the sound coming out of it a lot clearer as it's right by my ears...

..and i can hear a very slight distorted sound 'behind' the sound of my bass when i'm playing. it's not loud, but it is there.

this doesn't happen with my other amp(s) and i've tried different bases and cables and it's still there.

it's quite an old head - could it be time to replace the caps ?


any advice before i bung it in for service would be good.

Edited May 15, 2008 by ahpook

[JakeBrownBass]

Hmm thats odd, it could just be the old components dying. If theres somewhere to service it locally, id just take it in and get a tech to look at it!

Jake

[ahpook]

well, i guess it's at least 15 years old, so a bit of tlc is prolly in order !

[thinman]

[quote name='ahpook' post='199567' date='May 15 2008, 01:37 PM']well, i guess it's at least 15 years old, so a bit of tlc is prolly in order ![/quote]

I've read quite a bit that states it's a good idea to replace the electrolytics after 10 years as a matter of course. I've done it one of my heads. Apparently a symptom of power supply smoothing caps not working as well as they used to is a strange harmonic/overtone on dying notes.

[ahpook]

[quote name='thinman' post='199576' date='May 15 2008, 01:48 PM']I've read quite a bit that states it's a good idea to replace the electrolytics after 10 years as a matter of course. I've done it one of my heads. Apparently a symptom of power supply smoothing caps not working as well as they used to is a strange harmonic/overtone on dying notes.[/quote]

hmm...interesting. i may have to open mine up and see if there's anything obvious.

when you say 'the electrolytics' do you mean all of them, or just the psu smoothing caps ?

[thinman]

[quote name='ahpook' post='199590' date='May 15 2008, 02:14 PM']hmm...interesting. i may have to open mine up and see if there's anything obvious.

when you say 'the electrolytics' do you mean all of them, or just the psu smoothing caps ?[/quote]
IIRC the distortion or overtones are caused by the psu smoothing caps not smoothing fully so there's a bit of 50Hz ripple on the power supply which can get imposed on the output signal. I'd try these first. They're also the ones likely to fail most catastrophically.

The other smaller electrolytics may also degrade. I think inter-stage couplers degrading means their capacitance falls so the bass response may be reduced.

[ahpook]

[quote name='thinman' post='199598' date='May 15 2008, 02:23 PM']IIRC the distortion or overtones are caused by the psu smoothing caps not smoothing fully so there's a bit of 50Hz ripple on the power supply which can get imposed on the output signal. I'd try these first. They're also the ones likely to fail most catastrophically.

The other smaller electrolytics may also degrade. I think inter-stage couplers degrading means their capacitance falls so the bass response may be reduced.[/quote]

thanks for the advice ! i'll open it up this arvo and see what the psu caps are.

i love half-days from work !!

[thinman]

[quote name='ahpook' post='199600' date='May 15 2008, 02:27 PM']thanks for the advice ! i'll open it up this arvo and see what the psu caps are.

i love half-days from work !![/quote]
Just remembered.

If you're going to give it a going over it's also worth getting a magnifying glass and going over the solder joints on the board - especially for the larger components like big caps and anything mounted to another surface that can move independently, e.g. pots bolted to a front panel etc.
Look for hairline cracks around the component legs and resolder any that look dodgy. Solder gets more brittle as it ages and anything that can vibrate can get stress fractures. I'd expect things like big caps to be clipped, strapped or glued down.

I had a lot of prolems with a boiler controller due to cracked solder joints - it's quite common but easy to fix and can cause all manner of odd problems.

[yanto]

Also check the screws holding the PCB are tight-some of mine were slack and gave me problems
Iain

[ahpook]

cheers guys...i've looked at the psu caps and got the ratings so i can try some replacements first - it turns out (top marks thinman !) that they're glued to the board, so i'll have to resecure them properly once the work is done. when the board's out i'll have a look at the underside, see how the tracks look.

i may pull the preamp board too...just check it looks ok.

i'm just gonna hoover it out and give it a good old dose of servisol for the time being, and then get the caps tomoz.

do we want pics ? kind of work in progress/see how filthy the carpet is thing ?

Edited May 15, 2008 by ahpook

[Merton]

[quote name='ahpook' post='199641' date='May 15 2008, 02:53 PM']do we want pics ? kind of work in progress/see how filthy the carpet is thing ?[/quote]
Yes, would be good for people who don't know to learn what's what in an amplificatory device

[ahpook]

ok...here's some pics...

first of all the view into the chassis from the back to the front

at the back left is the power supply and power amp circuitboard...the large silver blocks are the heatsinks for the power transistors, and to the right of the heatsinks are the smoothing capacitors that i'm going to replace. finally the round thing on the far right is a toroidal transformer.


next, the view from the back to the front

here you can see the backs of the heatsinks and the preamp board at the front of the unit.


and finally...the dust, crud and spiderwebs that accumulate next to a cooling fan ! and also the name of the design of the power amp...'the bipolar bear' ! lol !

Edited May 15, 2008 by ahpook

[ahpook]

well, maplins have proved to be no use trying to source the replacement caps for the power supply....

i'm actually wondering if it's worthwhile just biting the bullet and getting it serviced professionally...it's possible i may be selling it soon anyway...


oh, and in pulling the board for the power supply just i noticed that there's more etching humour on the bottom of the pcb. right in the middle it says 'make it so number one'

ahhh....the late 90's eh ?

Edited May 18, 2008 by ahpook

[tauzero]

[quote name='ahpook' post='201581' date='May 18 2008, 03:55 PM']well, maplins have proved to be no use trying to source the replacement caps for the power supply....[/quote]
Tried [url="http://rswww.com/"]RS[/url] or [url="http://www.cricklewoodelectronics.com/Cricklewood/home.php"]Cricklewood Electronics[/url]?

[ahpook]

[quote name='tauzero' post='204412' date='May 22 2008, 04:49 PM']Tried [url="http://rswww.com/"]RS[/url] or [url="http://www.cricklewoodelectronics.com/Cricklewood/home.php"]Cricklewood Electronics[/url]?[/quote]

thanks for the tip, but all i can find is snap-in caps, not the usual 'wire' type that you solder in.

i've had a quote of £65 for a service from electronic music services...


hmmm

Edited May 22, 2008 by ahpook

[thinman]

[quote name='ahpook' post='204437' date='May 22 2008, 05:26 PM']thanks for the tip, but all i can find is snap-in caps, not the usual 'wire' type that you solder in.

i've had a quote of £65 for a service from electronic music services...


hmmm[/quote]

If not RS or Cricklewood then try CPC Farnell. I've bought from them - they do a very wide range - not just snap-ins. Probably only cost you £5 or so.

[ahpook]

[quote name='thinman' post='204460' date='May 22 2008, 06:03 PM']If not RS or Cricklewood then try CPC Farnell. I've bought from them - they do a very wide range - not just snap-ins. Probably only cost you £5 or so.[/quote]

farnel's eh ?

my dad used to sell components to farnel's when he worked in industrial automation.


actually, i'm going to pull the psu pcb again tonight and see if i can find a way that a push-fit cap would go in there ok.

Edited May 22, 2008 by ahpook

[tauzero]

[quote name='ahpook' post='204437' date='May 22 2008, 05:26 PM']thanks for the tip, but all i can find is snap-in caps, not the usual 'wire' type that you solder in.[/quote]
There are [url="http://www.cricklewoodelectronics.com/Cricklewood/home.php?cat=159"]radial wire-ended caps at Cricklewood[/url] and there's a fair few at RS as well. What capacitance and voltage are the current ones?