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PostPosted: 05 Apr 2019, 10:41 
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Joined: 09 Aug 2018, 03:15
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Location: Forsbacka Sweden
Heffa wrote:
ForsbackaKalle wrote:
So I got some output transformers from Greece. Same spec as the Edcors and built toroidal. Will fit headphones up to and around 75ohms.

Could you please tell where you got these?
My Audeze LCD-2 are 70 Ohm, so these would be perfect for me - also toroids are cool :-)

I think you va buy from www.giatras.com but I found mine at ebay.

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PostPosted: 05 Apr 2019, 11:07 
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Hi! Now I have done some progress with this one.. i have done this amp with external transformers. And this is going to be really nice.
Sins I have the transformers aside i went with a pretty narrow case. I have now done some listening sessions and I think the Giatras transformers performs better than my Edcors. More dynamics and bass. I use them with Bowers&Wilkins P7 and they are in the range of the transformers.B&W P7 ca30ohms and Giatras up to 75ohms. So i stick with Edcors for my Sennheiser HD600 with 300ohms. But I will try them anyway later on..
But I have a problem with groundings. when i put the grounds for the transformers and this new box together I get problem with RCDs. In Sweden we have RCDs with 30mA limit. I think this can be put together with x2 caps. Or do you have other suggestuions. Also problem when switching on of is on outgoing transformer side gets a heavy load in the first second. How can I smoothen this step?
Thanks and regards all of you.


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PostPosted: 05 Apr 2019, 12:24 
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Location: Belgium
Update after having swapped the R1s for 680R ones: Plate voltage is now sat at near dead on 150V.

I did notice that my build isn't quite as quiet as I first thought though, at least not with my HD598s (50 Ohm headphones). My 80 Ohm DT770s don't seem to have an audible hum though. I'll look for some metal shielding I can put in between the power transformer and the output side.
Tube wise, I think I have a wonky JJ tube. There's a crackle in the channel with said tube for about 15-20 minutes after turning on the amp. I've ordered a NOS pair of Novosibirsk 6N1Ps to see how those will do instead of the new JJs.

-Nim


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PostPosted: 05 Apr 2019, 15:43 
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Joined: 23 Feb 2017, 02:02
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"Also problem when switching on of is on outgoing transformer side gets a heavy load in the first second. How can I smoothen this step?"

Theres nothing wrong with this as is like pulsing, with pulse like loads (short durations) you can safely go to very high power levels without damage for resistors, transitors transformers etc.

You only get a plorbem with transfomrters when the average load is higher than maximum rating, you can have continious pules of power like start on and as long as maximum power disipation over time dosen't exceed rating it is 100% safe and reliable.
EG max rating 100w.
You can draw 200w pules and have a dutcy cycle of 50% having it on at half the time and off half the time without exceeding transformer ratings

"Update after having swapped the R1s for 680R ones: Plate voltage is now sat at near dead on 150V. "
Voltages are not crictical to be precise, as long as you know the amp schematic is operating within maximum power limits and nothing will overheat.


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PostPosted: 06 Apr 2019, 21:57 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, Educate me...what is an RCD? You can use many different output transformers. Ones for push-pull triodes are great. I used the Edcors as this is a budget diy project. They are quite inexpensive here. Where you are others are quite suitable and easier to get.

Good listening
Bruce

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PostPosted: 07 Apr 2019, 01:25 
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RCD detects the current fllowing in ground line of the mains, it shuts off the power if there is any current fllowing.
This will help reduce the risk of being hurt from electrical shocks.


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PostPosted: 07 Apr 2019, 08:54 
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Hi, Thanks, I thought that might be it. Here it is often referred to as ground fault current and while I don't know of a standard, devices like ground fault interrupters (found in bathrooms and near sources of water) are set for 5 ma. If you are getting as much as you indicate then I suspect that a transformer winding is not well enough insulated. Whenever I measure it here on gear it is typically below 100 micro amps often as low as 20-30 ua.

Good listening
Bruce

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PostPosted: 08 Apr 2019, 10:29 
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This is why my transformer dosent work. A cheap solution is not always the way forward .... Now I know why my RCD does not like it.. I have learned something :confused: :idea:


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PostPosted: 08 Apr 2019, 16:55 
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Location: Australia
ForsbackaKalle wrote:
This is why my transformer dosent work. A cheap solution is not always the way forward .... Now I know why my RCD does not like it.. I have learned something :confused: :idea:

I’d call that an auto transformer. Similar to original car ignition coils.

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PostPosted: 08 Apr 2019, 17:00 
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Hi, I agree. It can not provide any isolation from the mains and IMO is dangerous to use. It is not suitable for the project.

Good listening
Bruce

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