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 51 of 57

Author:  laurie54 [ 08 Mar 2018, 20:04 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

One more thing,,,, and this is, i found, very controversial depending on who you are talking to but, on occasion, i have put a 12v fan in the back and hook it up to the 6v heater lines. The fan will turn slow and <not make any noise>, but, just enough to get air movement other than convection threw the cabinet if heat becomes a worry. Many don't like doing this as it is a step away from the art of a good design but it helps get heat out faster. Great pics guys, congrats and again yes thank you Bruce for this design.

Author:  cbueche [ 09 Mar 2018, 00:34 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

laurie54 wrote:
One more thing,,,, and this is, i found, very controversial depending on who you are talking to but, on occasion, i have put a 12v fan in the back and hook it up to the 6v heater lines. The fan will turn slow and <not make any noise>, but, just enough to get air movement other than convection threw the cabinet if heat becomes a worry. Many don't like doing this as it is a step away from the art of a good design but it helps get heat out faster. Great pics guys, congrats and again yes thank you Bruce for this design.

On the practical side, this is a smart approach. Have to dig my IT spare part stock. If I do this circuit again, I might rise the tube board so they appear through the top. I didn't do it to protect the tubes but at the end they add to the internal heat, and they aren't visible.

The top will then not be flush, but users aren't supposed to stack up papers on top anyway. Well, now I have to find a customer liking the sound of my beast to afford building the 2nd iteration :-)

Author:  WillyKirsch [ 10 Mar 2018, 21:59 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hello All, I'd kept working the ideas in my head and I came with a new approach, note please that I turned the PT, please give your toughs about this orientation, please bear in mind that the top part of the PT and full PSU box, will be steel sheet also.

I added a metallic division to pass through the line in cables to avoid interference.

If the HeadAmp works well, I plan to add a JDS Labs ODAC to play music from my PC, someone has experience with this DAC?

https://www.jdslabs.com/products/39/odac-objectivedac/

Thank You!!!

Author:  gofar99 [ 11 Mar 2018, 20:55 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi. As long as there are vent holes or slots in the top and bottom no fan is needed. The same goes for any of my other projects that have the tubes inside. Even the phono preamp with 5 tubes inside does not need one. Mine runs for many hours at a time and does not get hot enough to cause any problems. IMO fans are never quiet enough and can produce EMI that can find its way into the audio. My suggestion is to not cause yourself problems by fixing something that isn't broken.

The arrangement in the drawing ought to be OK since you plan on using steel as shielding.

Good listening
Bruce

Author:  WillyKirsch [ 12 Mar 2018, 20:24 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Thank you Bruce!! actually I kept drawing and now I will rise up the PSU box, and halve the wooden height.

I agree, no coolers please!!

Best regards!!

Author:  cbueche [ 18 Mar 2018, 10:49 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hello again,

I still had some hiss when touching the volume pot so I had to cable the front-panel and clear alu plate to box ground, I found out the anodisation isolates the front and side panels electrically. The pot case grounding (left-running green-yellow cable) fixed it.

I still have some 50Hz hum. I read the grounding guide and modified my cabling, still not completely silent.

I know the transformers do radiate hum, but the distance between power trans and OPT is already 10+cm, they are oriented 90°, and there is shielding in between. So I now suspect my audio ground cabling. I would be happy if you would look at the connections between the PSU and amp sections, from left to right below:

  • dark blue : psu ground to ground-bus
  • red : twice B+
  • orange : +6V
Attachment:
top_view_small.jpg

I see 2 potential issues:

  • shared ground (dark blue) for B+ and filament 6V. As the ground for B+ and 6V is the same (back of the PCB), I'm not sure it would bring something to run a separate cable for the "HV ground".
  • induction from power tranny to B+ red cables. I tried pushing/moving the B+ cables away without any effect.

The only thing I can imagine is the lack of shielding around the trannies, but when looking at Bruce's original implementation, he didn't have an issue with this either.

hints welcome !
Charles

Author:  WillyKirsch [ 18 Mar 2018, 12:38 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hello Charles, I see a bit messy cabling, note that Bruce wired all the cables twisted and running in straight runs, and crossing at 90 degrees angles to avoid emitting/picking noise...

Maybe that help!!

Author:  WillyKirsch [ 18 Mar 2018, 12:58 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi All!! I think that I have a semi-final design, please comment anything you see weird..

I plan to make a PTP cabling underneath the chassis and all boxes and the chassis finally will be magnetic (AISI 304 I think) polished stainless steel.

I not decided yet the material of the rear plate where the RAC jacks will sit, maybe aluminum.

The bottom plate will be a perforated aluminum sheet to allow full ventilation, and RFI shielding.

The rear big box, it's all the PSU and at the right front of it is a nice PC Graphics card GPU heat-sink for the 7806 regulator

the two foremost boxes are the OPTs

If I finally decides to make the rear plate with aluminum I'l make an small panel out of phenolic resin laminate to mount the RCA jacks

If anybody wants the 3D SW files to make your own just ask me for them!!

Thank You!

Author:  cbueche [ 18 Mar 2018, 14:00 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

WillyKirsch wrote:
Hello Charles, I see a bit messy cabling, note that Bruce wired all the cables twisted and running in straight runs, and crossing at 90 degrees angles to avoid emitting/picking noise...

Maybe that help!!

Hello Willy,

I agree, I'm not that happy with my cabling... it is so difficult to have all correct, and this is the 3rd implementation... will think about it. But I think this Edcor power tranny needs to be in a closed shield. It radiates a lot, from what I can see when I move around a sheet of steel.

Well, the hum can only be heard with a very low-end / low-impedance in-ear headphone. Anything valuable and/or high-impedance is much less sensible to it and make it almost inaudible.

Oh, and I like your implementation ! By the way today I tested Telefunken E88CC into my amp, and man, does it sound good !!! I even started to listen to jazz, usually not my thing, but I just stayed hooked to my headphones.

Author:  WillyKirsch [ 18 Mar 2018, 14:56 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

You are right Charles, the next option is to isolate the OPTs, but as you stated, the Bruce implementation has no shielding and it works!!

Thanks for reviewing my design!!

After reading the 50 pages of discussion about this project my goal was to get all the good ideas and condense them in my design...

I hope it works...

I'd had the telefunken tubes as a first option at TubeDepot, but they are pretty expensive and this is my first audio DIY and tube experience, so I went for the sylvania option they was pretty cheapper, if it works, and my construction its good enough (no hum, hiss or anything), I will swap to telefunken.

I listen to a wide range of music types, but most of them are Jazz or variations of it!!

Try the HeadAmp with FourPlay the first CD they released, I love the sound!!

Or Norah Jones's Not Too Late Also I love it!!

Page 51 of 57 All times are UTC - 6 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/