MJ Mini Tube Board

[neutralzz 0]

huangyong, thanks for the tip. You mean a 220:220 + 6.3V or 220:220 + 19V transformer isn't readily available? Is the 220:18 + 18:220 you mentioned earlier thread feasible? Shipping a heavy item like a transformer is going to cost

 

I was just looking and reading about Earmax/Earmax Pro vs the Morgan-Jones and there appear to be something missing in the M-J version. How did the Earmax people get everything into such a small enclosure? The original power adaptor is a 19VAC one, which powers the 3 filaments in series. But how the Earmax/Earmax Pro derive get the 220VDC with the apparent lack of another transformer is the interesting bit.

 

Anyone has one of these babies and don't mind posting photos of its internals?

 

Regards

CK

i got one here,

 

if you point to point solder on a smaller compact board, confirm can fit into the earmaxpro size

 

earmax power supply external, so the size kept to very small

 

huangyong -> checked well audio for transformer yet? martin should have also/ very ex though there..

[ckng 0]

i got one here,

 

if you point to point solder on a smaller compact board, confirm can fit into the earmaxpro size

 

earmax power supply external, so the size kept to very small

The external power supply supplies 19VAC right? How does the EarMax Pro derive the 200+ VDC without a 2nd transformer then? That's the bit I am trying to understand If you don't mind can you post the pics?

 

Regards

CK

[neutralzz 0]

haha its not too difficult! considering our socket is 200+v already, just need to rectify it to get DC

 

 

tubes used to be horizontal but i modified to be vertical, sounds better

[neutralzz 0]

oh ya forgive the messiness at the jack area.. used to be very neat.. hehe i added 2 resistors to decrease "hum", tame the highs a little

[ckng 0]

Thanks neutralzz. I thought you were saying you have the original Earmax Pro, which I am very interested to know how the inside looks like.

 

Reading through some reviews and other information below,

 

http://www.headwize.com/ubb/showpage.php?f...1890&fpage=ptid

http://www.audioxpress.com/reviews/media/902hansen2017.pdf

 

this is what I gathered:

 

1. Power supply has a 3-pin connector to the Earmax Pro. This is probably 19-0-19 since we need 19VAC for the filaments.

 

2. It uses voltage doubler circuit to raise the voltage from the power supply. Since it's a 19-0-19, the max we can get out of it is (19x2) x 1.414 x 2 = 107.46VDC which is still lower than the 220VDC spec'ed for the MJ mini.

 

Has anyone tried it this way vs 2 transformers or a custom transformer?

 

Regards

CK

[huangyong 0]

ckng.. why don't you try first

i will support you, spiritually..

 

here a link, i think the keyword to use is voltage multiplier, m i right?

high Voltage

 

Cockcroft-walton

 

quite fun though.. if not for tube then can make something to give "nice" electric sensation

[huangyong 0]

check out this as well

 

250vDC PSU

 

 

[huangyong 0]

no one trying?

[ckng 0]

Haven't got around to. Been busy.

 

Regards

CK

[edison 0]

a US diyer have finished it.url:http://www6.head-fi.org/forums/showthread.php?t=87661

 

FAQ:

 

- Is this amp based on the ordinary EarMax or the EarMax Pro?

Yes,it is besed on EarMax Pro.

 

hey, digi,

 

The MJ is not the actual EarMax circuit, but a reverse engineered version, not even an EarMax Pro as well. Anyways, I believe they share same essentials and one can build a very nice MJ headamp with great passion.

 

cheers

Edison

[yotiao 0]

 

hey, digi,

 

The MJ is not the actual EarMax circuit, but a reverse engineered version, not even an EarMax Pro as well. Anyways, I believe they share same essentials and one can build a very nice MJ headamp with great passion.

 

cheers

Edison

 

 

Hi Edison, welcome to the forum! Off-topic here, have you tried E288CC tubes in place of the 6DJ8/6922 output tubes in Earmax pro? Can they be used together with the 12AT7?

 

Thanks.

[edison 0]

 

Hi Edison, welcome to the forum! Off-topic here, have you tried E288CC tubes in place of the 6DJ8/6922 output tubes in Earmax pro? Can they be used together with the 12AT7?

 

Thanks.

hi, yotiao!

 

I havn't used E288CC in replacing the 6DJ8/6922 output tube on EarMax Pro. It is not a premium version of 6922 but just a different design by siemens for specific usage. I am not going to try 6N1P too without inquiring the designer. E288CC is much safer than 6N1P, though. The E288CC should work on the EarMax Pro but I doubt the 6N1P will. All E288CC should be siemens made no matter what they are branded, that was what I told.

 

I'd recommend you don't try any of them. Not only because it may damage the amp in the short term or in long term, but also because it won't give you any superior than the 6DJ8/6922 or 12at7 (input). An amp is only good to use the tubes which its circuit is designed for.

 

cheers

Edison

Edited June 18, 2006 by edison