Hi, I ordered the board (from Peter Millet), the components for the board and Edcors PM-102.
Managed to build a quick set up to see what I bought and hear what I built... 🙂
I have alot of hum in da speakers...
When I power up it is there and a lower hum mixes in 3 seconds later...
Where should I start to eliminate da hum?
Managed to build a quick set up to see what I bought and hear what I built... 🙂
I have alot of hum in da speakers...
When I power up it is there and a lower hum mixes in 3 seconds later...
Where should I start to eliminate da hum?
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Hello Hifi, I built the Mighty Midget a while ago and it's quite as a mouse. Your pictures aren't very big so it's hard to tell but here is a quote from Pete Millett, "Note in the last photo the wire that connects the case to ground. Turns out that this is important - without it the amp was noisy and tended to oscillate. So do ground the chassis!"
Here is the link: The Mighty Midget and a picture.
P.S. Just wanted to add that the amp sounds fantastic!!
Here is the link: The Mighty Midget and a picture.
P.S. Just wanted to add that the amp sounds fantastic!!
Attachments
Thanks for your reply... but I have no chassis... at the moment... 🙂
It shouldn't hum even without a chassis... I am not living next to a power plant... 🙂
It shouldn't hum even without a chassis... I am not living next to a power plant... 🙂
Your pictures do not help much, too small - Pete Millet's board should be out of the question, they are usually very well though through. I would doublecheck part population and grounding and feedback. Relax, have a beer, say "omm" - you'll find the issue 🙂
Between all the ommmmmmm sessions I had time to check all parts... all ok...
grounding what? The board has fixed all groundings... I guess... AND, I do not have a chassis to ground...
What feedback?
Boy, I am shortly before giving up...
Definitly, this will be my last adventure with tubes...
grounding what? The board has fixed all groundings... I guess... AND, I do not have a chassis to ground...
What feedback?
Boy, I am shortly before giving up...
Definitly, this will be my last adventure with tubes...
One thing I notice in the schematic is the connection from the power receptacle ground to the ground lift diode bridge.
I can not tell from your pictures if you have this connection. Without it you will most likely get hum.
I can not tell from your pictures if you have this connection. Without it you will most likely get hum.
You must have a metal chassis! Preferably put it in a metal box. Tubes are high impedance and will pick lots of ambient crap.
Does grounding the transformers change anything? Guess they are floating on the board...
To go further, you might also try an alternative B+ (HV DC) supply to see if this changes anything...leave the heater connected for the time being, and you dont need 300V for this...but dont give up, toobes are worth it!
To go further, you might also try an alternative B+ (HV DC) supply to see if this changes anything...leave the heater connected for the time being, and you dont need 300V for this...but dont give up, toobes are worth it!
Is there an elegant way to ground the transformers? Over the screws? The transes seam to be covered with some shiny substance... and the screws are isolated with plastic washers...
Definitly not the CT from the power trans... 🙂
On the schematic, the HV B+ is DC...??? With D2,D3,D4,D5...!!!
The heaters are AC...
By the way, I always thought these wires must be twisted...??? Doesnt work on a board... Or am I missing something?
Definitly not the CT from the power trans... 🙂
On the schematic, the HV B+ is DC...??? With D2,D3,D4,D5...!!!
The heaters are AC...
By the way, I always thought these wires must be twisted...??? Doesnt work on a board... Or am I missing something?
No elegant way, short wire to board ground under your mounting screw, simply to try. And yes, you would twist heater wire when you have heater wire, but since this is a pcb, dont sorry about it, this is not the source of your him issue, providing the board has no production failure, like a short.
On PC boards, one can not easily twist the traces, so careful layout is necessary to avoid hum from heater wiring.
Pete is experienced enough to understand this and take the necessary precautions.
Pete is experienced enough to understand this and take the necessary precautions.
Your filter chokes appear to be directly below the output transformers. While I wouldn't think there would be a huge amount of stray pulses following a 100uf cap, it is possible, especially since you said you had hum immediately, that there is pickup from either the chokes or from the power transformer. Bypass the chokes with a jumper to see if it diminishes the hum, especially at start up. You can insert a piece of iron or steel between the power and output transforms to see if the PT is the source.
I grounded the transes... no positiv results...
There is something I noticed when I held a humming speaker to my ear...
Touching the attenuator 6mm rod does make a noise... like a microphon... tubes are very microphonic also... I hear my fingers touching both devises in the speaker...
Maybe the attenuator is picking up or producing the hum... or the tubes?
Yes, Pete does know what he is doing!
So, material seams okay... wireing seams okay...
Would a metal top plate maybe do the job? Would it keep some magnetic fields from the electronic?
My very first set up was all pieces laying on a wooden board...in the middle the board, left and right the OPTs and in the back the power trans. I remember the same humming! I even had a freakout turning the transes party!!! 🙂 Nothing helped...
I will build a metal plate to divide transes from electronic...
I will be back 🙂
Thanks so far!
Making progress 🙂
There is something I noticed when I held a humming speaker to my ear...
Touching the attenuator 6mm rod does make a noise... like a microphon... tubes are very microphonic also... I hear my fingers touching both devises in the speaker...
Maybe the attenuator is picking up or producing the hum... or the tubes?
Yes, Pete does know what he is doing!
So, material seams okay... wireing seams okay...
Would a metal top plate maybe do the job? Would it keep some magnetic fields from the electronic?
My very first set up was all pieces laying on a wooden board...in the middle the board, left and right the OPTs and in the back the power trans. I remember the same humming! I even had a freakout turning the transes party!!! 🙂 Nothing helped...
I will build a metal plate to divide transes from electronic...
I will be back 🙂
Thanks so far!
Making progress 🙂
When you have hum in both channels, it is unlikely the tubes, as both must have an issue at the same time. If it hums when you touch the Alps rod, this is definetly wrong. Verify if the body of the pot is grounded, if not, I would ground it. In a metal box, it would have reference to ground.
Btw: nice chassis plate
Btw: nice chassis plate
Looks nice, but didn't change anything...
Grounded the plate and pot...
Some more pics...
I am not sure about these rectifiers I bought:Infineon IDH03SG60C SiC-Diode 3A 600V Silicon Carbide Schottky for D2,D3,D4,D5... are they the right ones?
And the bridge rectifier D1 : 250V 1,5A Gleichrichter flach B250C1500 A + ~ ~ – 094666
Hope they are right... or should I hope they are wrong? hahaha
I also had to take two 180 Ohm in series for 360 Ohm... 🙂 Those are the standing up ones... 🙂
Grounded the plate and pot...
Some more pics...
I am not sure about these rectifiers I bought:Infineon IDH03SG60C SiC-Diode 3A 600V Silicon Carbide Schottky for D2,D3,D4,D5... are they the right ones?
And the bridge rectifier D1 : 250V 1,5A Gleichrichter flach B250C1500 A + ~ ~ – 094666
Hope they are right... or should I hope they are wrong? hahaha
I also had to take two 180 Ohm in series for 360 Ohm... 🙂 Those are the standing up ones... 🙂
There are several resistors in series, and as far as I notice the once in front of your last picture are two 270k for R24/R25, I would only use one, but that is not the issue...it is hard to tell from here would kind of hum do you hear: when you ground the body of the Alps, is it still touch sensitiv? Can you measure how the hum looks like (oscilloscope at output)? Remove C10/C11: does it still hum?
Just notice...do your R16/R17 match 360k, they should...
Just notice...do your R16/R17 match 360k, they should...