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6DJ8 (ECC88) Tube Headphone Amp Project
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Author:  ForsbackaKalle [ 14 Sep 2018, 03:07 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

And now some testing. Its alive! :up: 144V on both channels. Heaters also working good with just a little voltage drop below 6V. Just tested music with my telephone in and it works, a little low output perhaps (phone is maybe not a good driver)... will try later direct drive with my Rega DAC. Will come back with my thoughts soon. Absolutely no hum :D

Author:  cbueche [ 14 Sep 2018, 04:24 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

ForsbackaKalle wrote:
And now some testing. Its alive! :up: 144V on both channels. Heaters also working good with just a little voltage drop below 6V. Just tested music with my telephone in and it works, a little low output perhaps (phone is maybe not a good driver)... will try later direct drive with my Rega DAC. Will come back with my thoughts soon. Absolutely no hum :D

Hello Kalle?

same issue with my phone's output. In fact, a smartphone output is no line output. As you say, a DAC or CD will provide much greater voltage. The amp can provide a lot of power on its output, if you provide appropriate input levels. Clipping is far away, you will be deaf before clipping.
Charles

Author:  ForsbackaKalle [ 18 Sep 2018, 02:47 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Yes, this headphone amp rock. Works great with my Rega DAC and absolutly no hum. And the power is also more than needed. Used with Sennheiser HD600 and DIY streamer with Raspberry pi, HiFiBerry Digi + Pro and a decent power supply using Volumio. :headphones: : headphones:

Author:  Nim [ 18 Nov 2018, 10:51 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi folks.

After having discounted tube projects as too hard or complex for ages, I finally decided to actually commit to one, this one, and have ordered the transformers. I wanted something that could add to my FiiO E10K that's been my desktop DAC/amp for a while now, and this looked like both a nice entry into tube projects, as well as a somewhat budget upgrade to my audio gear.
Now as a first in probably a long line of questions: How inadvisable would exposed tubes be when there's a desktop PC sitting a few feet away from the amp. As much as I like the visuals offered by a nice glowing vacuum tube, I have the feeling they'd pick up a fair bit of noise from all the HF signals in a PC?

Greetings

Geoff

Author:  gofar99 [ 01 Dec 2018, 17:09 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

HI, I have been travelling and didn't see this question. The tubes in this design can be exposed. The gain is small and the tubes generally not sensitive to direct EMI or vibration. Just keep them away from AC power transformers as that would tend to couple hum into the circuit which would certainly be audible. A CRT monitor might also cause problems.

Good listening
Bruce

Author:  Suncalc [ 01 Dec 2018, 17:28 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Nim wrote:
How inadvisable would exposed tubes be when there's a desktop PC sitting a few feet away from the amp. As much as I like the visuals offered by a nice glowing vacuum tube, I have the feeling they'd pick up a fair bit of noise from all the HF signals in a PC?
Just for reference, I had my build (the one pictured below) by my computer.
Attachment:
6DJ8_front.jpg
It was sitting on my desk at work for over a year. It was about 18" from my laptop computer dock and within two feet of dual widescreen 26" monitors. There was also florescent lighting directly over my desk.

I never experienced any noise or interference from either my work computer or the lighting.

Author:  laurie54 [ 01 Dec 2018, 18:06 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

I see not only does the 6EM7 have it's own personality,,,,,, it has a "mini me". Beautiful work Matt.

Author:  Nim [ 04 Dec 2018, 18:06 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Thanks for the replies! Managed to get the transformers so far, which came in pretty fast considering I'm in the EU. I hope to be able to tinker away around Christmas

Author:  gofar99 [ 23 Dec 2018, 16:07 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi Everyone, I had an odd thought this morning (so what is new). I have had a number of inquiries about a slightly more powerful headphone amp. It is easy to alter this one to use other tubes like the 6CG7 for more muscle, but thinking that there is no such thing as excess in audio....I amp contemplating a design with push-pull U/L and triode mode 6AQ5s. At modest votlages of about 150 a pair should easily deliver a watt or more very clean. Using the direct input like in the existing headphone amp the output wol dlikely be limited by the input signal, but in U/L there should be sufficient gain to be very loud. Any thoughts?

Good listening
Bruce

Author:  Bradley [ 23 Dec 2018, 17:41 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

You had me at triode mode. Sounds like I'll be buying some tubes.

In my 6CG7 build, I used a 5-connection (two stereo pairs plus shared common) headphone jack to switch between headphones and speakers. My speakers are about 6 Ohms so I used GXPP10-10K output transformers rated as such and paralleled 6 Ohm resistors with each headphone channel (only in circuit when the headphones are), which has the effect of presenting the proper load to the tubes with a wide range of headphone impedances, basically flat from 32-600 Ohms and onward.

Of course, the resistors soak up some current, but the 6CG7s have enough power that it's a non-issue. I imagine the same would be true in the case of the 6AQ5, so should I build one, I will probably go the same route. I like the idea of a stellar headphone amp that doubles as a great amp for bookshelf speakers, for the cost of two resistors and slightly upgraded output transformers. Plus I'm itching to try an alternate case design.

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