i have a hartke gt-60 that hums on both the clean and dirty channels. it is predominately on the clean channel. awhile ago i remounted the reverb tank away from the power supply as it must of been made on a monday.the tank was mounted dirrectly over the transformer.the hum is alot less than before,but still not where it should be.any ideas? i have an oscilloscope,but am new to using it. i tested the capacitors and all i get is a dc pattern that is the same on both the negative and positve terminals.i put brand new 2200uf caps in and they read the same.i thought i should get different patterns on opposite sides of the electrolytics.any ideas on learning to use my scope.how can i find the hum with the scope?....any help appreciated. i think this amp had design issues.i notice they have a red and black power wires running across the entire board hooking up on the opposite end. bad engineering...thanks.....ed
getting a noise with the oscilloscope.the sine waves are not smooth @ c105 and c106.can i use a bigger value cap to help filter out more hum at these 2 positions.at present they are 2200uf @50v.can i use a 3300uf@50v in their place. if i do will it help filter out more hum?the wave pattern is a dc sine wave,but it is rough looking????....thanks....
The "funny sinewave" you see on filter caps is actually a "sawtooth" wave, and shows the power supply ripple.
Anyway it should not be heard on the speaker until clipping, where you hear it as a "ghost note", an out of tune low hum mixed with what you are playing.
Does the hum you refer to change with any control?
That will give you an idea on where it comes from; *then* you check with your scope.
The power supply has a lot of capacitance on it so I wouldn't suspect that, especially if you replaced the caps already. Does it make the sound when plugged into other outlets in other hoiuses or buildings? If not, it could be your noisey power at your house. If not, it could be a ground loop hum if it sounds like a 60 cycle hum. Try re-routing those power wires along the chasis edge and twist the cables. Do the same for other wires re-routing as appropriate. Try adding some sheilding to the cabinet or between the trannies and other components. If that still doesn't fix it you may be getting some high or low frequency oscillation (possibly outside of human hearing range) that can affect your sound.
the amp makes noise in any outlet.the noise goes away when the volume and gain knobs are turned to zero. when the volume and gain knobs get turned up the hum gets louder. the clean channel is the loudest. the dirty channel has hum,but is less predominant,but it is still herd.you could probably almost live with the dirty channel hum,the clean channel is pretty predominant.i herd a sound clip with 50 and 60 cycle hum and it probably is 60 cycle hum.i have 2 scopes.i just need to learn more about using them for tracing.i have a function generator also and a signal tracer.what do you think about checking for hum at the volume and gain potentiometers.all the diodes are good...ed!
You seem to have a ground loop or poor grounding at the clean channel, but it probably is a design flaw.
I *can* be corrected, but it's very difficult to do so without having the actual amplifier on my bench.
Fact is, nothing is "broken" .
It isn't as clear cut in "the diode is shorted, put a new one there" but correcting the original (poor) layout.
the schematic shows a star washer and wire going from the input jack to ground,but there is no such thing here.should i try running a wire from it and drilling a hole in the chassis to make a ground....ed
Hi Ed I think yo've post this Amp before (re Reverb troubles)
?
Anyway no matter ...
Unless I'm mistaken this is a Valve Amp with SS reverb (most Are these days)
Either way if you use Valve Amps Most of then do hum.
Side note:
Had a Laney LC30 on my bench a while back and I was flabbergasted at the amoun t of hum that the *Buyers of today* are prepiared to purchase!!!!!
Valve amps do tend to HUM!!!!!!!
It is the nature of the beast,,, (study high imp circuitry instead of trying to understand Os silly scopeZs) unless you go to a hell of an expense to curcumvent these HUM issues in design.
Most *insert Wanker brandnames* (include some of the most revered bOtweaker stuff also)
DO NOT try very hard to to impliment good design practice when adding another half dozen gain stages without any thought to heater hum.
The end result is HUMMMMMMMMMMMMMMMMMMMMMMMMM.
I have not seen the schematic,,,, but my guess is that it's got AC heaters with TMUGS syndrome.
*To many Useless Gain Stages*
Phil.
I *think* it's an SS one, maybe with a tube for distortion.
Problem is, it's really not a *Hartke* but a subcontracted amplifier made by the bidder who offered best terms to the owner of the Hartke *brand*.
It used to be Samson, don't know today.
They used to be made in Korea, maybe now they use a Chinese supplier.
Fact is, nowadays brand does not mean very much.
Peavey and Marshall are still in the hands of their original owners; Fender was bought by one of their former US Sales Managers, but most other brands which were famous but failed were sold to oriental manufacturers who try to maximize return on what they paid.
Some examples: Vox (Korg); Acoustic (???), Dean Markley (Duck Jean Taiwan), Celestion (Taiwan), Ampeg and Crate (Loud Technologies Vietnam), Hartke (Korea), etc.
the amp seems to have the gain control knob make the hum grow louder...any ideas...thanks...ed
Louder when on "10" or on "0"?
hi jm the amp is louder 0n 10 then on 0. with the gain down the hum is gone,,,,ed
OK, that tells us that *that* pot is properly grounded (that's what I was trying to check).
We do not have a schematic, so you will have to trace it backwards.
Try to draw a rough schematic (needn't have *all* the values) of that preamp.
As in: Input jack -> Op Amp -> "Marshall" tone control -> Volume pot -> Fet channel switch -> etc.
What happens if you unplug your guitar? Any change?
i have the schematic. how do i get it to this post?...thanks...ed
Click on *Additional Options*> Browse to the file > Click.
note the fine print;
"Allowed file types: txt, jpg, gif, png, zip, pdf
Maximum attachment size allowed: 2048 KB"
Phil.
hartke gt60.zip amp schematic.
Thanks for posting.
On this schematic I do not see any special reason for the clean channel to hum more than the dirty one, specially since they share the input stage, the most critical one, so the only reason that remains (I do believe what you say) is probably a layout problem, which unfortunately none of us can correct, it's the PCB layout.
A probable cause is that both channels, no matter what they do, *must* converge into U3, a 4053 3 x SPDT switcher, travelling from end to end in that board following not the shortest, best path but the one allowed by the labyrinth of parts and tracks.
The clean channel path obviously goes through some noisy area where it picks up hum.
Grounding signal along itspath may show us where that happens, but you can't rearrange PCB tracks.
Sorry.
And thanks again for posting.
PS: the basic structure reminds of Valvestates.
hi jm
just found somethings i overlooked.c-46 has a 5k resistor in it.r-54 has a green film cap in it and r40 reads 0.00 in all ranges of my multimeter. i checked it in both dirrections.guess i'll have to take it out of circuit and see what it reads.do you think i should change c-46 and r-54 to the proper components and values as listed on the print?maybe i'll get rid of the hum out of this beast yet. i'm not sure if these mods were done at the factory or by an individual.the amp works fine in all regards the way it is except for the humm.any ideas anyone!!!!......ed!
I repeat it, I don't think it's a *parts* problem but a *layout* problem.
Just to check what is the "injection point"follow the clean channel backwards, killing stage by stage (so both hum and signal disappear) until in one of them signal dissappears but hum does keep the same, that's the culprit stage.
*Then* you will have to look around it to find what (bad) happens.
Changing parts at random will solve nothing at all.
i changed c-46 from a resistor to a 223j capacitor,c-54 from a 223cap to a 18k resistor,and r-40 from what looked like a blue resistor with a black band in the middle.it read 0.00 both ways on the ohm meter to a 3.9k resistor as shown on the print.i still have hum and also a hi pitched squeal.if i scope the ic chips in the preamp i get a sine wave on the first ic then the next ic looks simular with a little deformation with the middle parts missing on both sides.i noticed with the scope that if i probe the negative speaker lead i get a square wave pattern with the function generator set for a sine wave.when i probe the positve speaker lead i get a dc type pattern that jumps off the screen till i reposistion it.it looks irregular shaped tatterd.i smelled a small burnt smell after running it for awhile.might be r-40 as my guess since there was no resistance there earlier. i think i'm going to put the circuit back to what it originally was as it might of been a factory mod. i noticed the hum goes away when i turn down the guitar or unplug the guitar from the input.if i touch the treble pot on the amp or the metal guitar tone control it squeals.i will read your last post and try to figure out what you mean and after putting the circuit back to where it was try to locate the hum area....