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PostPosted: 16 Feb 2020, 20:18 
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Joined: 08 Oct 2013, 21:32
Posts: 10
Location: Florida
Which schematic for a stereo tube amp design would you say is the simplest one you've ever seen?

I'm looking for something I can DIY and has the following features (if possible);

** two valves only, one for left and one for right (no more than two tubes in the entire amp)
** point to point wiring is possible and easy (i.e. no circuit boards...green circuit boards intimidate me and deter me)
** can be build it in a wood case that I will customize and cut the wood myself
** 1 to 3 watts is fine because it's for headset
** incredibly simple for me to make the output impedance to be 23 ohm (or very close to 23)
** the least number of parts (i.e. number of capacitors, resistors, diodes, transformers, etc)
** easy to add a volume knob
** I'm not very good at reading a schematic but if it's exceedingly simple, I might be able to figure it out via self teaching

Kind thanks,


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PostPosted: 17 Feb 2020, 10:22 
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Joined: 06 Apr 2009, 10:08
Posts: 1628
Location: US Pacific Northwest
Build this one: DIY 6DJ8 (ECC88) Tube Headphone Amplifier

Here is the project thread for questions: 6DJ8 (ECC88) Tube Headphone Amp Project

Run your headphones off the center tap of the output transformer. It will work perfectly. Here is a link to the version I built: The 6DJ8 Headphone Amp

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PostPosted: 18 Feb 2020, 21:46 
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Joined: 08 Oct 2013, 21:32
Posts: 10
Location: Florida
Matt, I have decided to take your advice and I will now order parts to build that headphone amp (6DJ8/ECC88).
One question, if I change only one thing (the output transformers) will the watt output decrease?
I found those exact EDCOR output transformers and EDCOR offers various options with regards to the ohms of the two taps.
The original schematic that you posted above calls for 10K/150 (8.2 ratio) but I would like to use 15K/600 (5.1 ratio) because the turn ratio would exactly match my Senheiser headphones which are 23 ohms.
What would you guesstimate the loss of watts might be (if I use the 15K/600 instead of the 10K/150)?
thanks so much


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PostPosted: 19 Feb 2020, 12:26 
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Joined: 06 Apr 2009, 10:08
Posts: 1628
Location: US Pacific Northwest
eddiegnz1 wrote:
The original schematic that you posted above calls for 10K/150 (8.2 ratio) but I would like to use 15K/600 (5.1 ratio) because the turn ratio would exactly match my Senheiser headphones which are 23 ohms.
Personally I'd use the originally specified 10kΩ/150Ω transformer. This is for two reasons:

1. There is a misnomer about the value of the center tap impedance. It is at half the number of windings so actually 1/4 (i.e. 1/2 squared) the full load impedance. As such, with the 150Ω transformer the two impedance options are 150Ω and 37.5Ω. The lower of the two is close enough to your headphones as to make no difference in amplifier performance.

2. This amp topology is a direct coupled differential pair with CCS DC drive and magnetically coupled AC loads. This topology is inherently insensitive to load impedance variation. Since Bruce has tuned this circuit for performance with the specified transformer and the 6DJ8 tubes, it is unlikely that the other transformer will yield better performance with your headphones.

I've had a lot of time to play with this circuit and Bruce did an excellent job. I'd build it as specified in the project.

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It's all about the Glass!
http://www.CascadeTubes.com
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