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12J8 Headphone Amplifier
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Author:  ILoveHiFi [ 11 Jun 2019, 23:25 ]
Post subject:  Re: 12J8 Headphone Amplifier

Thanks
Quote:
This hasn't stopped some people from using them as radio transmitters or series pass tubes in DC supplies.

You got me thinking that I should use a 12au7 as regulator for my next project with hv.
Since just upgrading to high quality valve rectfiers makes some diffrence, I want to try transitor regulator to valves.

I do have some old 8r headphones and the vocals are not as crystiall clear as the latest headphones at same class 8R and 3-4inch speaker size.

Author:  BowToEd [ 11 Jun 2019, 23:34 ]
Post subject:  Re: 12J8 Headphone Amplifier

ILoveHiFi wrote:
You got me thinking that I should use a 12au7 as regulator for my next project with hv.
Since just upgrading to high quality valve rectfiers makes some diffrence, I want to try transitor regulator to valves.


Been there, done that. The 12AU7 is an effective regulator for very small current (say, 10 mA or less). You'll want to use a higher gain tube for the error amplifier. When I ran my experiment, a change in voltage from 160 to 140v on the input resulted in a change of 120 to 112v on the output. The regulation wasn't great.

I also built a regulator using HV transistors. Look into the TIP50 for the series pass element and MPSA42 for the error amp. There are other parts. Mine performed okay but not great, built back in 2010 and long since dismantled. I've been doing a LOT of studying into making switching regulators, so I could develop a high-current HV supply. Any power transformer that's got high voltage AND high current is $$$$$$$$.

ILoveHiFi wrote:
I do have some old 8r headphones and the vocals are not as crystiall clear as the latest headphones at same class 8R and 3-4inch speaker size.


I've never seen 8-ohm headphones. The standard seems to be 32 although I've seen 24. 2000 ohm headphones are very old and use Moving Iron technology, something that was phased out when better speaker technology was developed. Mine were made in the 1920s.

Ed

Author:  ILoveHiFi [ 12 Jun 2019, 00:09 ]
Post subject:  Re: 12J8 Headphone Amplifier

A massive plorbem I had with the transitor regulator is that hv zeners are very noisy, even with 2mA accross the hv ones. (Just one zener and a pass transitor)

The one I find cheapest on rs components is the tsc136, low gain arround 20-30 when 7.5mA measured in custom gain test circuit.
But high voltage dosen't ahave low drop out requirements so esaily fixed the plorbem by using a darington configuration.
Sure dirt cheap ones from china can be used when you test to make sure it can be reliable. But the genuine ones are not that expensive anyways so just gone geniune.

Maybe not so good with convetional valve regulators schematics, but I'm thinking of a innovative solution with very low noise and audiopile design.
I do have rough design in mind currently and is very advanced but actuall testing is required, currently only a dream on paper. (Which I am very excited about)
I'm also thinking of a valve only design for the regulator so it makes things harder. (Zero transitors)

I'm actually using MPSA44 94 for the control transitors and they can come from china very cheap. No plorbems runing them on 330V to get 250v.

If you wanna have some cheap upgrades, instead of the transformer.
You should try changing the input capacitors to some hifi ones, rs components have free shipping even just buy one resistor.
And either fine gold nichicon or geniune metalised polypropene will upgrade you current ones.

I've seen the photo and I don't think the current one is the hifi one.
Once I tried the hifi caps never looked back, so nice to have them in the schematic and you won't feel like the caps are holding you back from hifi sound. Absolutley love them.

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