B1 with Korg Triode

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#2,101
Just a quick shout out to say the B1-Korg was sounding very good with a Twisted Pear three terminal regulator. Then I switched to a TP shunt regulator, one of the older ones. The sonics took a good leap up in refinement. 🙂

The B1-Korg frontends an F4 clone.
 
#2,102
cubicincher said:
Hello Meper,


nice to hear from you again!
The adjustment pots are connected. I did not use the pots on the pcb. I wired it
to the backplate pots to adjust also if the case is closed. The wires are underside of the pcb.

I used BOURNS 10kohm precision trimpots (10 turns). Makes exact adjustments easy. But I forgot to make a connection from T7/T8 to the outside of the case.
So, to measure I have to open the case again. Or I have to count the amount of
turns (sure not that exact).
In my combination at the moment with the BA-3 poweramp - the B1 Nutube drives the BA-3 with ease.
But I use a easy to drive loudspeaker (4 Ohm, 91dB/W/m, 2-way d'appolito) and
my BA-3 is running close to the edge (+/-34.9V rail voltage, BA-3 gain stage and BA-3 complementary output board). In the gain stage I use original TOSHIBA JFETs from punkydawgs. They run hot!).
Greets
Dirk
Click to expand...

Hi Dirk,
What wire and connectors did you use for the Nutube? I find them very flimsy and they can bend out of shape easily.
 
#2,103
Perfect! My speakers are probably around 97db, so shouldn't have any problems.


Nelson Pass said:
Depends on the speakers as well as how loud you want it.

Me, I listen at moderate levels to 95 dB loudspeakers. A scope on the
amp triggered for peaks shows about 2 watt peaks unless I am trying
to impress someone. 😉

2 watts is 4 volts peak, which requires about 1 volt from the Korg.

The Korg will reasonably deliver a 3 volt peak before the 2nd harmonic
starts owning the dance floor, and the resulting 12V peak coming
out of the amplifier is about 18 watts.

This would give you the same level I listen to but with an 85 dB speaker.

I think you'll be OK.

😛
Click to expand...
 
#2,104
6L6 said:
I'm building up a store version PCB, here's the part numbers (Mouser) I'm using if anybody is interested -


10ohm 3W 603-FMP300JT-73-10R
221ohm 71-RN55C-F-221/R
270ohm 3W 594-5093NW270R0J
475ohm 71-RN55D4750F/R
1K 71-RN55D-F-1.0K
7.5K 71-RN55C7501F/R
33.2K 71-RN55D-F-33.2K
332K 71-RN55D-F-332K

10K trimmer 652-3386F-1-103LF

10uF 647-UFG1K100MEM
1000uF 647-UKW1E102MPD

9.1v Zener 512-1N4739A

Remember that R1 and the transistors are included with the PCB





NuTube_PCBtransistors_-_No_Version_1024x1024.jpg
Click to expand...

Hi Jim, what size are the R1 resistors included in the store kit? Also, what are the 221 ohm resistors for in your BOM? They aren't in the B1 Korg pdf on the FirstWatt BOM.

Thanks!
 
#2,106
For the Christmas Korg and Toshiba JFETs measured by Papa 100 ohm resistors are used and as there are no 100 R's in the list they are probably 221 R for J113....as mentioned by Nelson.

I decided to dampen the chassis a bit using bitumen. There was some mechanical ringing when I knocked on the chassis. Now it is "dead" and I think it is an improvement. I had some spikes around 6 kHz when knocking at the chassis using the Focusrite and Arta software. So now I sleep a bit better. It is also nicer feeling lifting the Korg……..
 

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#2,107
Nelson Pass said:
...they are the Source-to-ground resistors for the current sources.

These vary by fet selection, and set the current sources to 6 mA or so.
Click to expand...

(Emphasis mine.)

Store PCB are using Fairchild Jfets.

Also, when Nelson says 'these vary by fet selection" that means those particular jfets in that particular bag included with that particular PCB.

MEPER said:
... as there are no 100 R's in the list they are probably 221 R for J113....as mentioned by Nelson.
Click to expand...

Doesn't matter. The "R1" resistors are supplied with the PCBs and mated to those particular transistors.
 
#2,110
I made the same experiment as Nelson with Korg to check how much output voltage is needed when playing at normal listening level. I would say the listening level was quite loud. I would never play louder. I played classical music. I used Korg with MoFo and I measured output of MoFo which should be identical to Korg output (MoFo has no voltage gain). I used a DMM set to AC to measure average RMS and then set to Peak hold max. to measure peak voltage. As can be seen average RMS is about 0.5 V and peak 4-5 V. I am surprised that average RMS is not more. Speakers are TG OBL-15. They have a sensitivity of about 94 dB. Room is 30 m2 and distance to speakers are about 3m. So Korg works fine with MoFo if speakers are relative sensitive.
 

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#2,112
OBL-15 works in quite small rooms. My "HiFi friends" are surprised how loud they can play using small amps like ACA or 7W 300B SET. I wonder if manufactures "cheat" a little bit with how sensitive their speakers are as it is a sales parameter...….
Troels Gravesen warns about "Tinnitus" using these speakers.
 
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