Filter Cap for Traynor Darkhorse please.(old thread renamed)

[daydreamer]

(this tread has been renamed to keep everything together, go to last page for actual latest question!!)


Hi Everyone,
I'm getting into amp building / general audio electronics and decided my first project is to fix excessive hum coming from my Traynor Darhorse 15 watt. I figure if I can do that, then I can move onto bigger projects!

Now the background is this. Canadian 110 volt amp unmodified running from a 1200watt toroidal 240volt step down transformer. I figure the first problem I have is that 50hz isn't being changed to 60hz; i would have thought if that was going to make a sound it would be a phasing tone, not a straight buzz.

Ideally I would love to pull the amp apart and make it run off 240v/50hz but that sounds like an extreme project to me, the other idea I had was to design a notch filter and simply put it between the amp and speaker and let it buzz all it likes before that point, sort of like how microsoft fixes their programs!! (Sorry, that was uncalled for )

I was going to go down the whole power conditioning route, but I don't generally have alot of AC buzz in the rest of my gear, atleast not anything like this.

the more I think about it, the more pulling it all apart seems appealing, but I have no idea how much that will involve..

Any opinions on whether that is a do-able first project? Or am I dreaming above my weight

[daydreamer]

Just to follow up, (and to prove I'm not asking to be spoon feed here!) would it help if I were to upgrade, change out, the power filter? I found it referred to in the Trainwreck pages as smoothing out the power and a loud hum could mean a problem with the power filter (in this case maybe just the wrong one for 50hz power). Are these tuned for dealing with 60 hz AC? Anyway, back to the Trainwreck pages, fantastic stuff

[Gibsonman63]

Vacuum tubes (valves) generally don't care about frequency. The amplifier's power supply section converts your wall voltage to high voltage DC. The older Marshalls just have another set of taps on the power transformer and a rotary switch to select supply voltage.

From what I see, this is a relatively new amplifier, so I wouldn't think worn parts would be the issue, although a lot is written about substandard electrolytic capacitors in mass produced amplifiers.

Ultimately, everything gets grounded to the amplifier chassis, which should be connected to the ground connection on your power cord. I don't know your specific arrangement, but this conductor needs to find a way to ground.

Still humming? Divide and conquer. Unplug your instrument cable and test. If he hum reduces dramatically, then it is external to the amp. Lots of things can generate hum before the amp.

If you have spare preamp tubes, try swapping them around. Some tubes just hum more than others.

[Phil_S]

Still humming? Divide and conquer. Unplug your instrument cable and test. If he hum reduces dramatically, then it is external to the amp. Lots of things can generate hum before the amp.

If the amp is relatively new, I'd first look for an external problem.

Is there a shield plate on the bottom of the chassis? If no, you can make one by applying regular or heavy duty kitchen foil to whatever covers the bottom of the chassis.

Does hum change when you move to a different room? A different building? Outdoors? Here, you're looking for environmental issues like florescent lights, cell phones, computers, anything that can generate RF. Are you near overhead power lines? If the building ground is faulty, you may not experience a change. Take it somewhere else. I think it is unlikely you will be so unlucky as to find two random buildings with faulty earthing on the electric supply.

Is the cord the culprit. Some of them hum on one amp and are quite on another. Change cords, change guitars. Change speakers.

You may find nothing. That's not all bad. Most of this kind of thing is benign and easy to do. Once you are convinced it is not environmental RF, you can look inside.

I once had an awful hum that no amount of tinkering would change. An old timer told me to put a piece of sheet metal over the open side of the chassis, and sure enough, all was quiet. I didn't expect that to be the solution.

[daydreamer]

cheers thanks for the help. just finished jamming with it on half power (it switches to 7.5 watts) and had a great time, heaps less hum, which i knew 7.5w would give me, but it is cool when necessity makes one appreciate what one has!.

I think, despite being brand new and aussie built, the external step down transformer may be letting me down, I may have to look into what can be done there if anything. still I'm glad to be learning something about the way these things work, I'm getting right into the dream of building my own.

When you say cheap electrolytic capacitors, I'm assuming that it is all of them and if thats the case then it's a major re-wire. But if it would improve tone as well then i'm in!

thanks

[Andy Le Blanc]

Does the step down tranny have an electrostatic shield? is it correctly connected?
Where I'm at you can see everything from edison dc, two wire knob and tube,
right thru the worst ac miss mash you can think of, check the house ac with a socket tester if you can.

[selloutrr]

if your amp is untouched vintage.

Make sure the power into the amp is the correct voltage!!!

Convert it to a 3 prong (GROUNDED) power cord.
Replace the electrolytic capacitors (ALL of them)
Clean all the tube sockets
Tighten all bolts to the chassis
Spray the potentiometers with fader lube (NOT CLEANER!)

After you have done those things and do them first!

If you still have noise.
Test the TUBES- old burned down preamp, power tube.
Try moving wires it's kind of a rats nets in some of those traynors.

you may need to replace resistors and possibly a tone cap or two. I'm in the process of overhawling a YGL-Mk3a.
It's almost a complete rebuild due to shotty tech work in it's past.

Oh it's a new traynor.... Send it back. They cut corners on the PCB's

[daydreamer]

awesome help, I think I have found the place to be!
After isolating each thing back to the wall, Power leads, surge protector, transformer, amp power lead, guitar leads etc, it is definitely the step down transformer which is making the noise first. To be fair to the maker I guess it could be a mains power problem that is being amplified by the fact it is halving the voltage. I don't know enough to point fingers yet, but I'm actually happy to be having this problem as it has got me thinking and researching about electronics, something I should have done ages ago..

These electrolytic capacitors, I'm guessing they would work to smooth the current coming from the step down transformer?, there is plenty of space in the transformer casing to mount some, but I guess going down that path is essentially building a makeshift power conditioner!

I did a bit of a search on the amp as well and it is getting a rep of having hum even on it's native 60hz power supply, so whatever I do I will keep that in mind.

It has also got me thinking of having notch filters in the between the amp and the speaker, the question I'm researching with that idea is how to maintain the correct ohm load. A filter at this point in the audio chain would be great for live gigs where the quality of the power/ environment can't be controlled easily without lugging a kick-ass power conditioner around and insisting that all the lighting in the building is rewired and shielded and fridges shut down etc before each gig! . Simply let everything buzz and hum and tune it out of the signal once it has had it's fun!. I found products like that for the hi-fi market but not guitar amps which has got me thinking there is a niche there for such a 'band-aid' product....As has been pointed out, there is often more than one source of hum and a lot of it is environmental. It would affect tone by definition, but so does a wah-wah, fuzz pedal etc and we like those sounds...

[daydreamer]

Sending it back means New York from australia, I'm happy to work through the issue even if it means all I'm learning is how not to build an amp by studying it's workings!

I like the stripped down look as well, though 'stripped down' things do tend to get me in trouble

[Dr-Joned]

[quote]It has also got me thinking of having notch filters in the between the amp and the speaker[/quote]

That would be TOO much of a fix. Start with the source of the problem, which appears to be the power source. Is your step-down grounded, is it encased in a cabinet, is the ground(earth) wire continous, can you meter the grounding from the amp to wall outlet? These are some of the basic steps for starting.
Does the amp have a choke? It could be that the filter circuit is not tuned as it should be.

These are just some more ideas to get you started.

[selloutrr]

You are correct the filter caps should still smooth the voltage regardless of the step down transformer. I'm assuming your step down transformer is 2:1 so 220V = 110v that power should be fine. It's no different then running the amp with a variac set to 110v+/-. that is perfectly fine.

I bet it's a simple fix.

Swap the turns for know good ones. Start with the preamps and replace one at a time. if you replace the power tubes make sure to bias for the replacements.

Check to make sure all the bolts and screws are tight to the chassis.

Turn the amp on let it warm up. make a fist and litely tap the top and see if the noise changes. does it get louder, softer, does it go away? don't beat it just give a lil bonk. Work your way around the chassis and if anything changes make a note of the location so when it's out of the cabinet you can go back to that location.

next. Get a chop stick, one hand in your pocket, pock thru the amp and see if anything makes the noise more or less. This could be a poor solder point.

[daydreamer]

I definitely should have some spare tubes regardless, so that is a great idea and pulling it apart to check everything, even better! Like going on an adventure..
Andy Le blanc's electrostatic shield point has got me thinking though; when I opened up the step down transformer to check how it is grounded (it goes back to the mains ground properly), I noticed that the design has the toroidal in the middle of the box which actually means it is pressed up against the wiring for the power plugs at one end, it would have been better offset to the back. I'm thinking of insulating all the wiring (electric tape) and then using aluminum foil to 'ground' the field around the coil. It wouldn't take much to do and it would take any proximity capacitance happening out of the equation. (proximity capacitance?.. like I know what I'm talking about!!!)

i will open everything up and check all the connections, bolts etc on the amp regardless. Nothing like the 'deep end' for learning quick.

[selloutrr]

how hot does the step down tranformer get? you might just melt the tape. I really wouldn't do anything to the step down transformer. easy way to test if it's the step down that is causing the problem. try the amp on another step down. If the problem is the same it's not the step down.

Though with that said... What Freq. is the Toroidal Wound for? 50hz or 60hz?
The transformer is Toroidal it should already be free of hum. Otherwise it's BAD.

http://en.wikipedia.org/wiki/Transformer

*WARNING!!!* If you are not familiar with how amplifiers work you should take the amp to a tech. If you touch the wrong wire it can = DEATH! Even unplugged amps can KILL YOU!

[daydreamer]

that's what I thought, toroidal was meant to be quiet. Ripped off again then.
you are right, I'm not keen on messing with the transformer for both safety and frustration reasons..

thanks for all the great advice everyone, really appreciate the effort. I'm going to start the hunt for an amp to build, I really don't want to keep spending money on soulless gear, and then other gear to try and make that gear work. for the money for a new step down, I may as well buy the parts etc for an amp i will really love (if only because I built it). Then at least if THAT hums, it's MY hum, dammit!

cheers

[Gibsonman63]

Building your own amp will certainly teach you a lot about tube amps and in the long run is much easier than constantly modifying a newer production amplifier. Electronic mentality these days is to swap boards, not troubleshoot circuits, so none of the newer amps are easy (for me) to work on.

For about what you paid for your production amplifier, you can build your own, with impressive results.

Your playing style generally dictates what kind of amp to build, but most recommend that you start with something simple as a first build.

Search the site on how to discharge filter capacitors and then check with a DVM to make sure they are drained if you are going to tinker inside your amp. The guys are serious about the amps containing lethal voltages even when unplugged. More than likely, you have bleeder resistors that will take care of that, but that would be akin to saying "More than likely, that gun isn't loaded." You want proof positive.