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Old 8th April 2007, 01:52 AM   #1
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Default ECL82 Headphone amp

Hi Boys,

I'm seeing to make a ECL82 Headphone amplifier, using the pentode of ECL82 in a Cathode Fallower mode to buffer the courrent, and the triode making the amplification of the signal.

Can anybody know a good schematic in these condiction?

I'm thiking to use the Pentode to make a buffer of corrent to drive mine SENNHEISER HD580 who has a impedance of 300ohm.

Is this a good idea? The pentode of ECL82 is very similar of the EL84... Is this will be good?

Can anybodody comment it?

Best Regards,
Felipe Navarro
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Old 8th April 2007, 07:05 AM   #2
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Default Re: ECL82 Headphone amp

Hi Philipe

Quote:
I'm seeing to make a ECL82 Headphone amplifier, using the pentode of ECL82 in a Cathode Fallower mode to buffer the courrent, and the triode making the amplification of the signal.

Can anybody know a good schematic in these condiction?

I'm thiking to use the Pentode to make a buffer of corrent to drive mine SENNHEISER HD580 who has a impedance of 300ohm.
I remember to have seen something like this, but it definitely was for higher impedance headphones, more like 600 ohms.

Quote:
Is this a good idea?
I donīt think so, I am afraid. The pentode section of ECL82 in a CF will not be able to drive anything near 300 ohms, since even considerably stronger tubes like f.e EL86 in CF have a hard time to do so.

Quote:
The pentode of ECL82 is very similar of the EL84...
Not really. The closest to EL84 you can get with a pentode contained in a compound tube is ECL86, which is quite close to a power-derated EL84, indeed. I doubt as CF it will be able to drive 300 ohms headphones either.

Regards,

Tom
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Old 8th April 2007, 09:11 AM   #3
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I have a headphone amp using the ECL82. It uses 12V mains toroidals as output transformers. I use parafeed to drive the transformer and has both loop negative feedback, and plate to plate feedback to smooth out the response.
The ECL82 pentode sounds a bit thin at 105V and 25mA, but with 40mA of current it fills out a lot. I have a pair of 8ohm headphones which sound great, and a pair of 32ohm SENNHEISER which sound a bit thin.

I can drag out the schematic if you are interested.

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Old 8th April 2007, 09:51 AM   #4
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Parafeed designed for ECL86, easily modded for the 82.
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Old 8th April 2007, 04:47 PM   #5
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Geek,

Can the transformer of the PARAFEED be a 220 - 12v transformer? What is these transformer?

Shoog,

Mine Sennheiser have a Impedance of 300ohm...

Best Regards,
Felipe
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Old 8th April 2007, 05:22 PM   #6
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Geek,

The circuit will be so so it here.

http://web.comhem.se/illuwatar//Tube...schematics.gif
But with a pentode instead 6as7 to use a ECL82...

Like the circuit in here. But I don't know who I connect a pentode and who I design this circuit with a pentode.

Can anybody help me?

Best Regards,
Felipe
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Old 8th April 2007, 06:28 PM   #7
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I'd try inverted triode connecting the pentode of the ECL82 - see steve bench's site for more information on inverted triode operation.

Its not a new technique, but does enable a 'normal' tube to drive low required loads relatively easily.

However, as the grid takes the strain, the output power available is lower than the normal ratings - but should be plenty for the 30 or 40 mW you'll need, and he's used it to drive an 8R speaker..! so the load wont be an issue.

http://members.aol.com/sbench102/inverted.html

Just some thoughts


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Old 8th April 2007, 10:02 PM   #8
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Hi Felipe,

Quote:
Originally posted by mod_evil
Can the transformer of the PARAFEED be a 220 - 12v transformer? What is these transformer?
Sure, it's not that critical.

I've found the parafed arrangement is the least critical configuration for output transformers.

I custom wound mine. The second set of transformers I made, I used a pair of el-cheapo chokes from China and unwound them. They had exactly 1500 turns of wire on each. So I layed down one secondary winding, put the 1500 turns back on, layed a second secondary and paralleled the secondaries and have a fabulous little OPT for $2


Quote:
Originally posted by mod_evil
Geek,

The circuit will be so so it here.

http://web.comhem.se/illuwatar//Tube...schematics.gif
But with a pentode instead 6as7 to use a ECL82...

Like the circuit in here. But I don't know who I connect a pentode and who I design this circuit with a pentode.

Ok, a 6AS7 *can* do this. Low mu+low Rp is good for this. A little pentode unfortunately can not unless connected triode, making a super high Gm triode unit.

ECL82 won't cut it I'm afraid, at least not for 300 ohms, as mentioned elewhere. However, the 7KY6 trioded would probably do you fine for what you want. Rp is high, but it has Gm like no tomorrow!
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Old 8th April 2007, 10:14 PM   #9
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Geek,

I have some problems to make transformers... I live on Brazil, I haven't El-Cheapo transformers here, and the transformers in here is so critical to make/buy.

I have other choice... I can make a SRPP to make a gain, and a buffer with transistors to make the buffer to connect the Headphone to the tubes =D

What do you think about this idea?

Best Regards,
Felipe Navarro
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Old 8th April 2007, 10:31 PM   #10
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Hi,

Quote:
Originally posted by mod_evil
I have other choice... I can make a SRPP to make a gain, and a buffer with transistors to make the buffer to connect the Headphone to the tubes =D

What do you think about this idea?
I'd say go for it. I like totem poles

Here's one I did based on a White CF actually:

http://geek.scorpiorising.ca/HeadphoneAmp.html
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