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Old 9th January 2013, 11:10 AM   #1
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Default Lundahl LL1660 OPT Franks 6SN7 linestage

I want to know if I can use Lundhal LL1660 as opt for Frank's 6SN7 lineastage to match the impedance of 300 ohms of my Sennhs HD600
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Old 9th January 2013, 01:04 PM   #2
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Hi!

If your headphone has 300 Ohms impedance, you want to drive it with a lower Zout. I would consider 100 Ohms as minimum, preferably lower. That cannot be reached with a 6SN7 into a LL1660 4.5:1, even with both halves paralleled

Thomas
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Old 9th January 2013, 01:10 PM   #3
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Thanks for the advice Thomas, could you recommend me some nice tube heaphone for my Sennhs HD600?
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Old 9th January 2013, 01:21 PM   #4
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Hi!

A higher step down ratio transfromer should do it also with 6SN7, for example the Lundahl LL1689 which offers 9:1 and even 18:1 ratios. That would bring the Zout with paralleled 6SN7 down to about 60-70 Ohms including the copper losses of the transformer.

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Old 9th January 2013, 01:40 PM   #5
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Quote:
Originally Posted by Vinylsavor View Post
Hi!

A higher step down ratio transfromer should do it also with 6SN7, for example the Lundahl LL1689 which offers 9:1 and even 18:1 ratios. That would bring the Zout with paralleled 6SN7 down to about 60-70 Ohms including the copper losses of the transformer.

Thomas
Using the same posted schematic?
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Old 9th January 2013, 02:04 PM   #6
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Hi!

The schematic you posted shows a cathode follower. So you need to adapt it for use with such a transformer. Gain would be different compared to the schematic you posted. If you use a similar 2 stage approach with the last stage changed to transformer coupled, you will have about 6dB more gain with a 9:1 step down. The cathode follower is unity gain, a 6SN7 transfomer coupled with 9:1 has again of approx 2 (2 divided by 9 and then with some losses) which equates to about 6dB difference

Thomas

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Old 10th January 2013, 08:00 AM   #7
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Hi Thomas,

As you know I'm a newbie, could you drive a schematic or link me to a schematic?

Thanks

Felipe
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Old 10th January 2013, 09:49 AM   #8
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Hi Felipe,

there are plenty schematics of transformer coupled stages for example in the 26 thread.

In my Octal preamp I use a transformer coupled 6SN7 in the linestage, with ultrapath cap:

VinylSavor: 6SN7

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Old 13th January 2013, 09:53 AM   #9
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Thanks for the link to your blog, can I use the attached schematic modified from your octal preamp? Could I use without the choke 60H/40mA? Could you write or let me know the voltages to be sure the schematic is working properly?
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Old 13th January 2013, 10:45 AM   #10
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Hi!

I thought you wanted to modify the schematic of your opening post and adapt it for transformer out? That would mean keep the first stage and replace the cathode ollower with the transformer stage.

You need to check if gain is ok for you. Using both stages you will have more gain than with the cathode follower. Using just the transfomer stage it will be significantly less.

The dropping resistor is not needed it is only used in my preamp since I need higer voltage for thephono section. The 250V in the original schematic would work

You can implement any suitable power supply. If you need the choke depends on your power supply implementation.

Also keep in mind the 1660 will not be a good choice to drive a 300 Ohm headphone.

At a certain point you need to just build something then check what comes out and adapt.

Best regards

Thomas
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