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Connecting 50 ohm headphones to 16 ohm tap?

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Posted on December 27, 2014 at 17:30:14
kuramura
Audiophile

Posts: 30
Location: Chicago
Joined: December 31, 2010
 Hi I have LCD-2 headphones connected to Bottleahead 2A3 Paramour amp. 8 ohm speaker output. Headphones are 50 ohm so I have 10 ohm resistor parallel with headphones to lower resistance to 8.3 ohm. I've asked on Magnequest forum if there is a better way for connecting that and someone suggested to try 16 ohm tap directly to BH-5 Full Nickel Output transformers. Should I try it or will it damage the amp?

 

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RE: Connecting 50 ohm headphones to 16 ohm tap?, posted on December 27, 2014 at 17:46:20
Paul Joppa
Industry Professional

Posts: 7295
Location: Seattle, WA
Joined: April 23, 2001
 Triode amps with no feedback, such as the Stereomour, are perfectly stable into any load - there is no risk.

It is pentode amps with feedback which risk instability when unloaded. The reason is they are transconductance amps whose open-loop gain becomes very large when unloaded, exceeding the stability margin at high frequencies.

 

RE: Connecting 50 ohm headphones to 16 ohm tap?, posted on December 27, 2014 at 17:48:14
Garg0yle
Audiophile

Posts: 859
Joined: December 1, 2014
 I don't think you will damage the amplifier.

FWIW typically in that situation power and distortion will drop, as the transformer reflects a higher impedance back to the tube.
(50 ohm phones on a 16 ohm tap.)


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RE: Connecting 50 ohm headphones to 16 ohm tap?, posted on December 27, 2014 at 19:11:44
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 Along with PJ's comments, I'd suggest trying all the taps and using whichever one you like the most.

Going to the 4 Ohm tap will lower the available power (shouldn't matter for your headphones IMO), but will decrease the noise floor, decrease the distortion (maybe marginally in your case), and increase damping.

Going up to the higher impedance taps will increase available power while also increasing the noise floor and decreasing damping.

It's not clear whether you already have the Magnequest iron in your Paramours or the stock iron provided. There is a massive performance upgrade to be had by upgrading to the latest factory spec iron or getting some Magnequest iron. (The old Paramour transformers are made by Speco, and easily recognized by the yellow bobbin tape. The stock plate choke will be a unit from Triad with two black wires coming out. The Magnequest iron will be in brass channel frames, which is easy to see, and the new production Bottlehead iron will have black, red, and blue wires on the plate choke, and solder terminals on the output transformers)

 

RE: Connecting 50 ohm headphones to 16 ohm tap?, posted on December 28, 2014 at 07:33:49
kuramura
Audiophile

Posts: 30
Location: Chicago
Joined: December 31, 2010
 Thanks everyone for responses. I have BH-5 Full Nickel Outputs and BH-6 Plate Chokes along with 10uf (Mundorf 3.3 Silver oil parallel with Obbligato 6.8 film oil)

 

RE: Connecting 50 ohm headphones to 16 ohm tap?, posted on December 28, 2014 at 11:57:25
Triode_Kingdom
Audiophile

Posts: 10044
Location: Central Texas
Joined: September 24, 2006
 I use a parallel resistor across an 8 ohm output *plus* a series resistor to my 32 ohm Grados. Without the latter, my 6BQ5 SETs would bust my eardrums!

 

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