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6DJ8 (ECC88) Tube Headphone Amp Project
http://www.diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4161
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Author:  gofar99 [ 12 May 2020, 14:00 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi, Make sure the capacitor is installed in the proper orientation. They will short out and get really hot if backwards. When that is fixed, if there is still a lot of hum, post some good photos of the insides and we can see if the problem is obvious.

Good listening
Bruce

Author:  zeppedled [ 19 May 2020, 12:34 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

gofar99 wrote:
Hi, Make sure the capacitor is installed in the proper orientation. They will short out and get really hot if backwards. When that is fixed, if there is still a lot of hum, post some good photos of the insides and we can see if the problem is obvious.

Good listening
Bruce



I was able to resolve my issues for the most part. Need to figure out the slight hum (and how I managed to bypass the Alps Pot from actually doing anything....), nothing crazy, just always there. Either way, when pushing sound through the amp, it sounds fantastic, a lot of clarity. I can post pics if needed, my build repurposed an old 1950's amp so I made due with the space I was given (not build for good looks!)

Author:  ILoveHiFi [ 19 May 2020, 17:42 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Did you build the schematic as the orginial one.
The voltage supply and the heater schematic effects the hum, if you did something wrong then it will humm.

Then you want to loook at the grounding and if the transformer which radiates EMI out of the coils will have the amp picking up the fields, try to place transformers as far away from sginal path or rotate it 90 degrees the transformer.

Author:  gofar99 [ 19 May 2020, 20:40 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi, Check the ground connections at the volume control. If they are not good or are missing and the control doesn't work then it would introduce hum.

Good listening
Bruce

Author:  laurie54 [ 19 May 2020, 21:30 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

One picture is still worth a thousand words and can reach so many. Besides WE don't care what it looks like
frankly WE just want to see pics and share. After 30 days of isolation a bit of eye candy would be welcome.
Cheers and be safe

Author:  mike64 [ 29 May 2020, 22:07 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

We have this amp basically completed, and I wanted to test the power supply voltages before final soldering. We have AC power that usually runs 123-125v, and the PT measures 220v at the high voltage secondary, not unexpected I guess. I did expect the B+ to be higher when unloaded, and it measures 290 at the top of the 1st filter cap. The problem I'm wondering about is that it is essentially at the same voltage on both ends of the rail, i.e. it is 290v at the top of the 1st filter cap, and the same at the final cap, as if there is no drop at all via the series resistors. I would rather not solder to the OPT and potentially destroy the 1uf cap if I have a problem, which it seems I might. Any ideas?

Author:  mike64 [ 31 May 2020, 23:17 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

We’re completing a build, so far it sounds great. No hum or noise at all, just music from the first power-on. Decided to dial back the plate voltages and bias current a bit, running at around 129-130 and between 9-12mA (JAN Sylvania tubes aren’t as matched as I would like, but they’ll do for now). Used a 60 ohm Mills on the LM317, and PS resistors are 1k-1k-1.3k (& 1.3k for other channel). Also added a 330k 2w bleeder across the 3rd 100uF cap for safety. I was surprised to see the inrush voltage up around 300, so the 250v 1uF film cap on the OPT center tap will need to be changed out to a 400v version with my next parts order, just to be safe.

Author:  mike64 [ 01 Jun 2020, 16:16 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Here's a photo, still need to punch vent holes in the cover (looks uneven in the pic as its just set in place not screwed down). The box was an old computer network adapter, with a dividing wall for about 1/4 of the space, perfect to segment off the PS. We gutted it, drilled holes in the front panel for the power switch, headphone jack and volume, and also tapped into the original front panel indicator pcb to use the existing led for a power light. Still have room in the box, plan is to add a little class D amp board to turn it into a full integrated amp.

Author:  eslheadphone [ 14 Jun 2020, 22:02 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

I have tried several headphone amplifiers and this one is the best yet. Works great on Fostex TRP50 , Sennheiser HD650, Beyerdynamic 771. The impedance selector is on front next to the volume control. I went through several brands of 6DJ8's and settled with the Amperx.
Thanks Bruce for a great design.

Author:  gofar99 [ 15 Jun 2020, 20:33 ]
Post subject:  Re: 6DJ8 (ECC88) Tube Headphone Amp Project

Hi, I'm glad you like it. It was nearly not a project as I just cooked it up one day to use as a temporary thing. Being so simple I thought just maybe someone else might want one so I posted it. You can imagine my surprise when lots of folks liked it. Simple, clean sound and easy to build.....IMO some of the best traits of a diy project. Good looking build.

Good listening
Bruce

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