[AnA1995]

As I am going to house this amp into a chassis, I decided to build a power supply for it. For 24v, guess I need a 18v-0-18v toriodal transformer. This is the first time building a power supply; so I decided to build a simple un-regulated PSU ( just bridge diode and capacitor). I am not sure if 120VA transformer is enough for this amp. Anyone kindly advise. Thanks.

 

[DKJones96]

I used an ammeter on this thing when it was running and while I don't remember the exact numbers it wasn't over half an amp with the heater running at 300ma. Playing it safe by doubling the power requirement and you've still only got 24VA.

I've got a cheap 24V x 1A (AD-270) switcher supply and it works great except for the fact that I question it actually being a switcher supply. I know it is regulated but it runs hot all the time which switching supplies don't normally do.

 

[ludoo]

I also use a cheap 24V 1A regulated switching supply I bought on ebay for like 12 euros, and it works quite well. If I were you , I would save the time needed to build the PS, get one from ebay, and build the amp in a smaller case. You also won't need to worry about safety, grounding, etc.

 

[Stevesebastianb]

Here is my completed amp, there is blog link: VR2XMQ - Steve's Blog AF through SHF: The Homebrew 6DJ8 Single Tube Headphone Project.

Some photos:

 

[Zigis]

Finally I build p2p prototype of mixing this amp's input stage and 24V Aikido output stage. 2 x LM317 in output, no sk310 at all.
Amp sound surprising nice, some small tweaks needed.

DKJones96, you are right, there is large DC offset on grid, I build amp without input caps and get terrible noise wen turning pot (new Blue Velvet), with pot on max there is 240-300mV on input.
I never had this problem before, just checked 6n1p MJ headamp with 300V powering and SS, both have 0V DC on input at any pot position.

Why this amp work so strange? Too low voltage?
Is it possible to change input stage to avoid DC offset without input caps?

Zigis.

 

[Zigis]

Strange things happening.
I just installed input caps, now on grid is 450-500 mV, on cathode 23-35 mV, trimpot almost can't regulate output voltage - 19-22V (before it regulated from 11 to 22 V).
One channel with trimpot on max and 21.5V on output not work at all, second channel work only with trimpot on max (19V on output)
I connect 1K resistor in series with trimpot, get volt or two less on out with pot on max, but not enough.

There is something wrong, I don't think larger voltage on grid than on cathode is normal situation.

 

[Zigis]

Anyone with good working amp, can you please measure and post here your voltages on cathode, grid and anode?

Thanks, Zigis.

 

[DKJones96]

Anyone? I have mine cased where it is nearly impossible to get measurements easily.

Are you measuring from ground to the tube? Got a schematic for the circuit you built?

What value of resistor did you use between the grids and ground?

 

[AnA1995]

Hi Zigis, below are the readings. Hope it is helpful.

a=17.61V
g=524mV
k=106.4mV

And the above readings are with 6DJ8 tube.

Quote:

Originally Posted by Zigis /img/forum/go_quote.gif Anyone with good working amp, can you please measure and post here your voltages on cathode, grid and anode? Thanks, Zigis.

 

[DKJones96]

Measured the amp. Including regulator losses it runs 22va with a 6922 tube. I would add another 3-5 to that if you are using the 6DJ8.

Also, if you use a 6922 tube your R104/204 and R105/205 values should be 15 and 18 ohms. Not the original 15 and 13.

 

[AnA1995]

As I am using my mobile phone as the source for this amp; and I always heard those usual "receiving/ transmitting" noise from the mobile phone. The noise is so loud and causes the headphone diaphragm to vibrate badly to the extend that I need to take out the headphone out of my ears immediately when it happen. This problem not only will cause damage to the headphone, also cause damage to my ears in a long run.

Wondering anyone has the same problem with their amps? Not sure if the noise is from my phone or the phones nearby. I will use maybe a MP3 or CD player as source and see if the noise goes away. Does those tube "shield" helps?

 

[AnA1995]

Anyway, if come to worse, just switch the mobile phone to flight mode.

 

[DKJones96]

What carrier do you have? GSM(any phone with a sim card) commonly causes interference with audio equipment. CDMA(phones without sim cards) usually provides no interference at all.

 

[AnA1995]

It is GSM with sim card..... no choice I guess, only switch to flight mode when listening.

Quote:

Originally Posted by DKJones96 /img/forum/go_quote.gif What carrier do you have? GSM(any phone with a sim card) commonly causes interference with audio equipment. CDMA(phones without sim cards) usually provides no interference at all.

 

[Nemo de Monet]

If anyone should happen to still be interested in this design, I've tested and found that the IRF510/IRF610 work fine in lieu of the 2SK310s, and the 2N3819 can apparently sub for the 2SK117. I don't hear any difference in character versus the more exotic Japanese parts, and they're cheaper and more readily available. Also, I've become of the opinion that 1000uf for C103 may be inadequate; while 10,000uf is probably overkill

, upping that part to 1500uf or 1800uf IMO improves the performance, particularly the bass end of things, which this amp excels at.