DIY Audio Projects Forum
http://diyaudioprojects.com/Forum/

6DJ8 (ECC88) Tube Headphone Amp Project
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4161
Page 4 of 67

Author:  gofar99 [ 25 Jun 2013, 18:21 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

What brand were the tubes?

Good listening
Bruce

Author:  laurie54 [ 26 Jun 2013, 08:31 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

JJ from www.jj-electronic.com Made in SLOVAK REPUBLIC. Yellow and blue box. They only light up on top and nothing underneath even though part of the fillament can be clearly seen under the main body coming from the pin links. They work wonderfully after initial turn-on and heat-up but still really bright at first compared to after. Scary bright actually. I am going to just keep using and see what happens over time.

Author:  gofar99 [ 26 Jun 2013, 09:46 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi, I have used those ones too and hadn't noticed the situation, I'll check the next time. Personally I would not worry about it. My general thoughts on tubes are they can do one of three things: work perfectly (even if it isn't what you expected), not work at all, or go soft and lose gain. So if they are doing the job, I accept it as is.

Good listening
Bruce

Author:  laurie54 [ 26 Jun 2013, 10:38 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Thank you Bruce. The music is great when tubes are warm and that is the main thing. The most stunning aspect is absolutely NO noise, hiss, rush, or any indication that it is even plugged in until the music starts. Spooky This build has been the most educational experience in years. Next i will be experimenting with different types of shielding etc (Faraday cages) . After that perhaps Chu Moy's ver of Morgan Jones headphone amp. Using the same tubes (dead quiet) but cap's in the outputs. Not as good as trans in my eyes but not as prone to outside magnetic radiation fields. One more for my family.

Author:  gofar99 [ 26 Jun 2013, 11:23 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi, Glad to hear you like the end results. To make something quiet...resistant to EMI I use Mu metal. It is available in adhesive backed sheets about 8 X12 inches in size from a number of places on the WEB. It generally runs about $25 per sheet. Not cheap, but really super stuff. It is many times better at shielding than anything else you might try. It is easy to cut with scissors, but has razor sharp edges so beware.

Capacitor coupled output stages are fine, but do not allow for the current multiplication available from a transformer coupled stage. Both capacitors and transformers introduce some non-linear artifacts in the sound stream and it is pretty much a toss up as to which is better. A direct coupled stage is best, but then trying to implement that with all tubes is a bit difficult and takes away from the simplicity of the original design. For a DC stage I highly recommend using a SS based design. Low noise op amps are a good choice for this.

Good listening
Bruce

Author:  laurie54 [ 26 Jun 2013, 14:31 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

I found the sheets and will order. Thanks again. In the past year i have built the Millitt Mosfet Maxed using J74/K170's and Soha II both having SS outputs and each sound great. Max using caps at output for blocking DC and the Soha using split pwr eliminating the DC. But can't help but want the tubes all the way threw. Somehow going SS 1/2 way threw seems like not tubes. Technically yes,, but just doesn't feel right. They all have their own distinctive sound and work best with particular phones. I see a lot of talk on here to back that up. An impedance issue as much as design and materials issue. The question,, "is the blue i see, same as the blue you see?" keeps coming into my mind but i think 1/2 the fun is building, 1/2 is exploring and experimenting to gain knowledge, and the enjoyment is in the listening. Really, once one has the bug it just doesn't go away. I prattle but next is using the shielding to get best results placing trans as close as possible. I hear Matt cringing in disgust from here but i too often take worst case and experiment outward from there.

Author:  Suncalc [ 26 Jun 2013, 18:14 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

laurie54 wrote:
I prattle but next is using the shielding to get best results placing trans as close as possible. I hear Matt cringing in disgust...
Not really. ;) I would never discourage good experimentation. It's computer modeling that makes me cringe.

And remember, to serve as a magnetic shield, it should be ferromagnetic. If you can't pick it up with a magnet, it shouldn't be used as a magnetic shield. Any conductor is good for a Faraday cage. The lower the resistivity of the material, the better.

Author:  laurie54 [ 26 Jun 2013, 19:24 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Matt, i was talking about small builds after reading your sight. hee hee
If you will let me be Devils advocate.
"But, metal that can not be picked up with magnet should never be used as shield." Yet aluminum is used as shielding in more cases than any other metal. Also in most cases, not, in a Faraday cage. If tested with magnet on one side of aluminum plate and steel on the other side, the magnet will barely hold to steel. This would suggest aluminum to be a good shield.

P.S. I am ordering the Mu-Metal shielding in 8 x 11 sheets with adhesive backing. Slick

Author:  laurie54 [ 02 Jul 2013, 02:42 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

I have been using this amp every day (70) now, and after being entranced by the shear number of discoveries in really feeling as well as hearing music, 1 observation regarding these JJ ECC88's from an electrical point and that is,
--the changes each tube goes threw at initial power-up seems to be completely dependent on the ambient temp or it's environment. I have just turned it on after 24 hours of rest, and "strait" into soothing Bach. As for the day i feel like a greased pig in a slow cooker oven. With a smile on my face.

Author:  blakebart [ 13 Jul 2013, 10:25 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi Bruce,
Is the PCB for the power supply available to purchase? That would make using the PCB-mount Edcor transformer easier. Otherwise I have a couple questions about variations to the supply design. In terms of generating the high voltage rails you start with 200V RMS from the transformer, and then eventually drop the voltage down to the 135-150 VDC plate supplies. Given the small amount of current required by the amp have you found it a good thing sonically to start with such a high voltage? Anything magic about this approach that you can share?

Thanks and best regards,
Blake

Page 4 of 67 All times are UTC - 6 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/