The 100ohm output resistors on the Korg are not attenuation. To create attenuation you need a divider to ground.
The 100 ohm resistors on the output are prevent interaction with the power amp. The 33K to ground on output is just there for safety to provide a path to ground if the RCA cable is disconnected. It is too large a value to effect attenuation.
If you wanted to create attenuation it would be like 3K parallel/5K to ground. But the output impedance will become like 3K or so instead of 100R. Check if this is friendly for your power amp.
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When I built my B1-Korg, I had this same concern about a preamp that adds gain to power amps that really don't need a gain stage in front of them. I was expecting there to be problems. In practice, this has turned out to be a non-issue for me. I just run with the volume know a little lower 
No issues at all!
No issues at all!When I built my B1-Korg, I had this same concern about a preamp that adds gain to power amps that really don't need a gain stage in front of them. I was expecting there to be problems. In practice, this has turned out to be a non-issue for me. I just run with the volume know a little lower
Ah, the voice of reason!
Thank you.I feel like I got this off in a negative direction with my question about the resistors at the Korg output. Surely this can be done with a simple adjustment somewhere, perhaps with a little compromise?
Just looking at the Korg schematic, the volume control is a simple 50K resistor. If reducing the audio output of the preamp to allow greater travel of the volume control pot is the goal, why cannot the 50K volume pot be replaced with a combined resistor in series in front of a smaller value pot so that the total resistance is still about 50K? Then, full travel of the pot would constitute only a fraction of the range of the standard 50K pot?
On the other hand I understand that the Korg has a considerable turn on/off thump and an adjustment at the volume control will have no effect on that. Is this thump serious enough that speaker damage could result given the amplifier & speaker circumstances described above? I guess it would depend. Haven't built mine yet so don't know what that thump is like.
My purpose in building the Korg is to insert some "musicality" into my rather dry system, and one thing I considered was to place the Korg as a simple buffer right at the power amplifier and continue to use my passive LDR volume control. Had I chosen to go this route (and I still may do so), probably I would have replaced the potentiometer with fixed-value resistors to deliver approximately unity gain. I think my speakers can handle practically any thump I throw at them.
Separate from volume control travel, that's been addressed.
It may have been mentioned, but just in case...
Turn on your pre-amp before you turn on your amp. Turn off your amp before you turn off your pre-amp. No turn-on, turn-off thump. No worries for your loudspeakers. Also, it's just good practice.
Although some of these solutions will work, the easiest, simplest, and best answer is merely adjust the volume knob to where it works in your system and listen to music.
Noted! Thanks for all the input. Always helps to learn about the effects of different options. I'll plan to build it as directed and cross that bridge if I need to.
This is the exact reason why you should build the Korg. Musicality. If it doesn't work for you after you build it stock then worry about the volume control. Adding the LDR in from of the Korg doesn't accomplish a lot except saves you the cost of the volume pot. Save the LDR for systems that need it. I have built all the Pass B1s and have used many different buffers. I prefer the Korg B1 even if no additional gain is needed.
Unfortunately that actually doesn't work for me -- this LDR arrangement is my design and build, and I wrote the software for the programmable chips so I have an emotional attachment. One fellow who runs them tested their tracking and found that the channels were within 0.1dB of each other and the log curve. In addition to the unusual LDR-centric features, the display also shows all the main preamp information like volume, balance, selected input, etc. Considering the time and effort I put into it, I really want it to be always part of any system I build.
And, remembering back to when I first got it working, the improvement in sound that the LDRs made in my system was totally worth the effort. I think the Korg and the LDRs will make an awesome preamp. It won't fit in the standard Korg chassis so after this build with the Academy Audio volume control with IR, I'll do a custom chassis with enough room for everything.
I would be interested in how you hook this up when you get it. I just puchased this and the DC/DC converter for my Korg. I am just a beginner diy'er so my knowledge is limited on how to integrate this in. So any help is welcome.
I'm about to buy the MUSES volume control and I don't like the idea of powering it from the B1 power supply. What about using a 15 volt wall wort to power it? I have a few of the PO89ZB boards which a generous DIYAudio member gave to me and I was thinking of putting one of these boards in front of the volume control wall wort...anyone care to comment on this plan?
Thanks.
Thanks.
The muse chips require a bipolar supply. Korg B1 is single.
Muses probably don’t care about the quality of the supply I would imagine.
Hi, a question about phase. Per the B1K article, "Remember that the preamp is phase-inverting. In order to get the correct absolute phase coming out of the speaker you must invert the phase after the preamp. The easiest place to do this is at the loudspeaker. Of course if you prefer it out of phase, that's fine with [papa]."
So, set at the recommended 9.5V bias, as I understand it the B1K output will be positive phase 2nd harmonic. Now put into an ACA, which is also phase-inverting, what happens to the phase, is it now negative phase at the ACA output? But with v1.8 wiring, the outputs of the ACA are phase-inverted, so back to positive phase 2nd harmonic? Please help!
So, set at the recommended 9.5V bias, as I understand it the B1K output will be positive phase 2nd harmonic. Now put into an ACA, which is also phase-inverting, what happens to the phase, is it now negative phase at the ACA output? But with v1.8 wiring, the outputs of the ACA are phase-inverted, so back to positive phase 2nd harmonic? Please help!
