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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 14 Feb 2017, 20:26 
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maresaldeflota wrote:
One new question, where i put multimeter to measure the bias?

This post should walk you through the process: viewtopic.php?p=14346#p14346

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PostPosted: 17 Feb 2017, 05:35 
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Joined: 13 May 2016, 02:02
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Location: Javea, Spain
Hi Everyone,
About a year ago I built this headphone amp and put it in a nondescript box. It was an exercise to see if I could follow a schematic and test out my ancient soldering skills (I was a bench wireman many, many years ago). I also wanted a low voltage project to play around with before I attempted something high voltage. As a first project it was perfect. To this day I think the sound is really something else. I can listen through an inexpensive set of AKG headphones for hours whereas after a short amount of time listening to a budget stereo system I get listening fatigue.
I've gone on to build a high voltage valve amp and built the speakers to go with it, Matt Renauds' 6EM7 Vertical Amp, a pair of Fostex Bass Reflex Speakers and a Dayton Audio Subwoofer. It just goes to show what an excellent site this is.
A couple of weeks ago I decided the headphone amp really deserved a nice case, so I built one to match the speaker cabinets.
I've suddenly got a desire to play around with this great little headphone amp again. Using my desktop audio out though a Fiio DAC I find I only use a small amount of the volume available. My headphones are 30 ohms, is it possible to drive some fostex high efficiency speakers in series (32 ohms for one channel) with the headphone amp? If driving speakers is possible, what are the lowest impedance speakers I could use per channel? The Fiio DAC does allow for a gain of 6 or 12 dB to be switched in if required. I've never used it but it's there if I need it. Any advice, negative or positive with an explanation would help toward me understanding more, I'm learning all the time. Thanks in advance.


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PostPosted: 17 Feb 2017, 11:26 
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Hello, i have only one problem now, a terrible hum in the sound, i use 470 uf and a 100 uf + uf 3.3 what can I do to remove it?


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PostPosted: 17 Feb 2017, 17:51 
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maresaldeflota wrote:
Hello, i have only one problem now, a terrible hum in the sound, i use 470 uf and a 100 uf + uf 3.3 what can I do to remove it?


explain how you've connected these caps ?, is it caps in the powersupply or do you referring to those caps in the amplifier ? ( drawing please or pictures )

if the hum comes from your power supply a good filter is needed to suppress hum. easy way ( CRC ), lets say 1000 uF - (x) ohm - 1000 uF at least, bigger is better. (x) depends of how much voltage you've got from your rectified supply.

you can read about different filter methods here: http://www.daenotes.com/electronics/dev ... r-circuits


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PostPosted: 17 Feb 2017, 23:30 
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john55 wrote:
My headphones are 30 ohms, is it possible to drive some fostex high efficiency speakers in series (32 ohms for one channel) with the headphone amp? If driving speakers is possible, what are the lowest impedance speakers I could use per channel?


Hi John - nice work. This headamp uses a mosfet output statge and can drive an 8 ohm speaker. Close to 1W so it will work with your fostex speakers.

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PostPosted: 18 Feb 2017, 07:23 
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Thanks for the quick reply. I hooked up a pair of speakers this morning, and provided I cut back the output from the desktop a little it sounded really good. I like the idea of using this amp both ways in the main living room of the house, background music through the speakers, or headphones if my better half is watching something on T.V. that doesn't appeal to me. As I mentioned the AKG headphones are 30 ohms, I fancy a pair of high impedance headphones and I have another set of speakers rated at 4 ohms. Can the mosfet output stage cover such a wide range of impedences and will I have heat problems. At present I don't use heatsinks as I read that a 24 hour heat test in a sealed box went well without any problems.


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PostPosted: 19 Feb 2017, 12:29 
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If you are gonna try drive speakers, you should add heatsinks to the mosfest. While you are at it, also add heatsinks to the regulators. This way you can also increase the current through the regulator and that should help with driving speaker loads.

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PostPosted: 19 Feb 2017, 12:35 
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i have driven speakers with it
and i have to say this mini amp sounds lovely
even trough crappy speakers (how better the speakers how better it sounds)


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PostPosted: 19 Feb 2017, 13:55 
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note this build is a current amplifier and not a combinated current and voltage amplifier. the reason is output is taken from source. if output was taken from drain it would both amplify voltage and current.

see illustration.


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PostPosted: 19 Feb 2017, 16:11 
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KrammeAcoustics wrote:
note this build is a current amplifier and not a combinated current and voltage amplifier. the reason is output is taken from source. if output was taken from drain it would both amplify voltage and current.

see illustration.


If the current output is close to 1 watt at the current configuration, how much more power increase will there be if the output is taken from the drain into 8 ohm (efficient) speaker load? Would replacing the FET withe the 2N3055 from the MCA make any difference? I kind of liken the idea of having the option to switch between headphone and high volume of speaker.


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