DIY Audio Projects Forum

Thanks! Once it's good to go I have to clean up the wiring and throw in a 7805 for some blue-led action. (just can't help my self sometimes )

Thanks for the heads up! My tube / analog skills are kind of weak. I'll probably rummage around for some 10k resistors and
tack them the bottom of the pcb tonight.

Thanks for the *great* tube project! It looks cool, (will hopefully) sound great, and is a great learning exercise on tubes!

I will be using a wall adapter that are used in modem/router. It is a 12V1A dc... I presume it is good enough for the project...

Bypass and decoupling caps, what's that?

Hi santik, that power supply will work, but unless it is regulated it will likely result in unwanted power supply noise (hum).

The bypass / decoupling caps would be a tweak to try improve the sound. Basically they will lower the ESR.
Cheers

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[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]

So to actually connect the trimpot:
Pin 1 to +12V
Pin 2 & 3 to plate (anode) and also the gate of the MOSFET?

Isn't all chips pinouts are the same regardless the brand?
LM317 and the IRF510?

How to add in bypass/decoupling caps? Or it is already in the circui?

Hi,

bypass and decpipling capacitors are little helpers in nearly every amplifier or other circuit.

Power supply decoupling capacitors can be used in the supply rails (12VDC / B+) of the circuit.
They charge when the power supply or the circuit is switched on and then act like a second supply.
Capacitors store energy and this energy can supply the rail (where they are mounted on) for a short time.
That results in a decoupling effect and a better channel separation and crosstalk is decreased.
Once they are charged they also can deliver high current peaks on demand.

the schematics does not provide power supply decoupling capacitors.
They usually mount nearby the amplifier components on the supply rail.
Also they are mostly electrolytic capacitor types as film type capacitors do not have such a high capacitance.
The positive side mounts to B+ (12VDC) and the negative "-" to the circuit GROUND.

Usable values would be 100uF to 470uF / 25VDC (voltage rating) per rail.


Bypass caps (C2) are especially used for bypassing the 12AX7 cathode to the circuit ground.
The circuit provides a cathode resistor (R2) which sets the BIAS for the tube. It allows to adjust the
flow of quiescent current through the tube and also sets the negative voltage on the tube's grid that
must be negative - relative to the anode.

When a audio signal is applied to the grid of the tube (signal input), the audio signal changes the
voltage of the grid to positive and neagtive. Low ammounts of the audio signal are also allowed to
flow through the cathode by the cathode resistor. The audio signal is not a plain signal wave or plain signal.
Once the signal flows, it could change the current that flows through the cathode resistor.
More signal = more current = more voltage dropped at the resistor. The result of this is that the
bias changes it's current at the same time. The cathode bypass capacitor provides an short circuit
for the audio signal. It blocks the DC from the cathode to ground, but shortens the AC from the Audio Signal to ground.
Once the audio signal is shortened to ground, it can not flow through the cathode resistor and the bias is stabilized.

That's what the cathode bypass cap does.

The bypass capacitor is already included in this circuit. The power rail decoupling capacitors are not.
It is simple to add some..


Have fun and a nice weekend!

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.

Sweet explanation Tom!!

_________________
Kind Regards,
Dinesh

Some of my diy audio projects:

• Elliot Sound Products - P3A 100W Amplifier
• TMM 2.5 Way Loudspeaker with Scanspeak 18W8546
• 2-Way MTM Loudspeaker with Scanspeak 21W8554 and D2904-7100

After a couple weeks on this project ,now i am finished my Amp, I am taking the enclosure from western digital network HDD
here is some picture

Finished mine today! Took maybe 5 hours in total, and the stupidest thing I did was wire the tube backwards. It sounds really good when there's music running through it but my power supply (which I bought off mouser) isn't the greatest and produces the classic hum. Going to try a few other power supplies then build one if I can't find any good ones. Plus if I plug it in my laptop, or even to my iPod charging from the laptop, it produces a really digital sounding crackle which I think is from the laptop's massive power supply. The power switch also pops really loudly when I flip it, but it isn't really a problem if I don't have my phones plugged in. Here's some photos:





The heatsinks are mostly just for looks and adding weight. I just kept the MOSFETs in the case because I didn't have any mica pads to isolate them, and the IRF1510s don't have a metal back on them so I threw them up against the heatsinks. I didn't think heat would be that big of a deal anyways because I'm just running 12V 1.5A. Tube is a Russian Electro-harmonix 12AU7 which seems to be working great as well, but doesn't light up too much or get too hot (which is probably due to the low voltage and not a problem).

One thing I really want to do is wire an LED under the tube as a few others have done, but I don't know where to connect it to in the circuit so any advice on this would be awesome.

I've done kits in the past but doing the point to point wiring took a lot of planning, and making sure it was identical to the PCB layout took awhile. Overall it was a great project and I learned a lot.

Hi solo

The enclosure is a good idea, it's beautiful and different.