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Old 28th November 2017, 11:26 PM   #101
cspirou is offline cspirou  United States
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Interested in making a guitar preamp with this. Anyone know of any interesting 6p1 guitar circuits?
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Old 29th November 2017, 01:29 AM   #102
drpro is offline drpro  United States
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Location: Nashvegas
Korg NuTube is now available online
Pete, I bought one of your Korg HP amp boards recently. Finally got around to building it last night, took about two hours. Your attention to detail was appreciated. Reminded me of when I built Heathkits back in the day.
Applied power and everything works. I have been enjoying listening to it this past hours. Yours is great, a nice addition to several other class A headphone amps I now have.

Thank you again for your skills and time.

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Old 29th November 2017, 09:03 AM   #103
Koifarm is offline Koifarm  Netherlands
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Originally Posted by impuls60 View Post
How does this nutube compare to a regular triode? I would like to hear some listening opinions of it I wonder if this would make a good fit with the tpa3255 I own?? I have a pentode tube amp that does voices and instruments really good, but it doesn't have the power that the tpa3255 has. Therefore I'm looking into making a hybrid amp with the tpa3255. With the lifetime of the nutube and the clean tpa3255 it could be an interesting mix.
Look at post 28.
For just line signal remove output IC LME49600 of my schematic.
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Old 4th December 2017, 09:19 PM   #104
Chul is offline Chul  South Korea
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Join Date: May 2003
Location: Pusan Korea
Default Balanced linstage with Nutube..?

I am attracted by the possibility of DHT balanced line stage with battery power.
What would the gain and output impedance be, in this circuit?

Chul from Korea
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Old 5th December 2017, 05:37 PM   #105
Algar_emi is offline Algar_emi  Canada
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Korg NuTube is now available online
Very interesting, just bought the pcb + tube from Pete. Thanks
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Old 16th December 2017, 01:36 AM   #106
Walter H is offline Walter H
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Pete, I purchased the Korg Nutube evaluation board from you (not sure of my soldering chops) and I'm awaiting delivery. I have no doubts that your kit is significantly better, that said how does the eval board sound? Is the sonic character similar? I look forward to putting it in an enclosure and enjoying it. It sounds like I'll be able to adjust the bias and dial in more tube goodness if I want.
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Old 8th January 2018, 09:30 PM   #107
arild is offline arild  Norway
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Join Date: Mar 2006
Location: New Castle Colorado
Pete Buffer question
I got one of your buffers up and running and i am noticing the buffer has developed a strong hissing sound on one channel the other channel hisses as well but not so much. I don't have an oscilloscope right now so i can't see the noise as i set the bias. I set the bias at 2V over C4 and C10 is this the correct measuring point? and what is your recommended setting. I am using a battery 12.7V
I don't recall having this strong hiss when i first listened to the buffer, it was there for sure but not as much.
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Old 8th January 2018, 09:35 PM   #108
pmillett is offline pmillett  United States
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It might be oscillating. If you used a FET for the input buffers (2N7000) as opposed to a bipolar (2N3904) - it can break into oscillation when driven from a low impedance source.

If so... you can fix it by adding a ~1k resistor in series with the gate, or by swapping the FET for a bipolar.

Usually I set the bias by measuring the voltages on the Nutube plates, and setting them to be about 1/2 the supply voltage.

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Old 9th January 2018, 12:12 AM   #109
arild is offline arild  Norway
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Location: New Castle Colorado
Thank you Peter
I tried putting in a 1.5k resistor at the input, that's all I had didn't help. I was looking at your schematic R8,9 should be 330K for 12V that i am running not 475k that I have there now.
I will order the 330K resistors and some 1K just in case and the input buffers 2N3904 to see if that works, I hope I didn't break it.

Last edited by arild; 9th January 2018 at 12:14 AM.
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Old 11th January 2018, 04:27 AM   #110
arild is offline arild  Norway
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Location: New Castle Colorado
man this Buffer sounds terrific very happy!
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