Finally got the "other" channel converted to bufferless and there is additional clarity.
Also, replaced the 6.8K resistor on those reg boards with 1K - just thought I should do that and since I did both at the same time I have no idea if it makes a sonic difference. Certainly helps quell the audionervosa that always ensues after a good direction is given. Cannot remember if I need to thank metaphile or William for this - so I will thank them both. I was not hearing any noise before. Now I can assure myself I am not hearing any noise.
No question - it always sounds better when both channels are the same. Obvious, of course.
Will replace the same resistors on the left channel this evening.
I do not have any gain difference between bass channels after all. Who knows what was making that appear to be the case. Went through the EQ process YET again and all is equal.
I had somehow manged to destroy my right hand CD so when installing the replacement I added the "phase plug" (an illegal copy - please do not tell anyone) if there could be anything more generic looking than this phase plug which is not a phase plug. Mr. Delgado came up with it for the K402 domestic edition he calls JUBILEE UBER ALLES or something like that.
I do think it makes the high frequencies less directional.
Found that stuffing the box of an MEH loudspeaker with reticulated foam makes the best stuffing I have heard. Probably would be advantageous with any large sealed box. Doesn't take up much space due to its open cell construction but seems to do an excellent job of confusing and diffusing the back wave. I think the left speaker not having this treatment initially made it sound and measure with lower sensitivity. I know that sounds kooky.
I have completely filled the rear cavity with this foam - I mean the foam itself being open cell does not take up space like a closed cell foam would.
Sorry for the digressions.
Also, replaced the 6.8K resistor on those reg boards with 1K - just thought I should do that and since I did both at the same time I have no idea if it makes a sonic difference. Certainly helps quell the audionervosa that always ensues after a good direction is given. Cannot remember if I need to thank metaphile or William for this - so I will thank them both. I was not hearing any noise before. Now I can assure myself I am not hearing any noise.
No question - it always sounds better when both channels are the same. Obvious, of course.
Will replace the same resistors on the left channel this evening.
I do not have any gain difference between bass channels after all. Who knows what was making that appear to be the case. Went through the EQ process YET again and all is equal.
I had somehow manged to destroy my right hand CD so when installing the replacement I added the "phase plug" (an illegal copy - please do not tell anyone) if there could be anything more generic looking than this phase plug which is not a phase plug. Mr. Delgado came up with it for the K402 domestic edition he calls JUBILEE UBER ALLES or something like that.
I do think it makes the high frequencies less directional.
Found that stuffing the box of an MEH loudspeaker with reticulated foam makes the best stuffing I have heard. Probably would be advantageous with any large sealed box. Doesn't take up much space due to its open cell construction but seems to do an excellent job of confusing and diffusing the back wave. I think the left speaker not having this treatment initially made it sound and measure with lower sensitivity. I know that sounds kooky.
I have completely filled the rear cavity with this foam - I mean the foam itself being open cell does not take up space like a closed cell foam would.
Sorry for the digressions.
You know what sucks about this level of accomplishment?
It feels like the end of a journey and the end of audio DIY for quite a while.
I now have all the headphones amplifiers anyone should ever want and I have an amazing preamp.
Goodbye bench, I may never see you again!
It feels like the end of a journey and the end of audio DIY for quite a while.
I now have all the headphones amplifiers anyone should ever want and I have an amazing preamp.
Goodbye bench, I may never see you again!
Have you considered building a DAC? How about speakers? 
Nah, I am not a believer in DACs. Topping, SMSL, Gustard do it better than I ever could.
That’s as far as I will go. I am not a woodworker and speakers are too high in voodoo. And I think commercial options cannot be easily surpassed.
Those speakers look cool! Are those 15” dual concentric?
My experience with DACs is that the new ones are not worthy of even shining the pins of the TDA1541. Or maybe they lack proper implementation. Maybe others like @Vunce who have built many know better. For me, the TDA1541 simply puts me in touch with the music. But yeah, DACs are a deep hole. Miro’s boards have made it accessible but then if you start talking to Mark, Marcel, and others, one can be working on it a long time.
My experience with DACs is that the new ones are not worthy of even shining the pins of the TDA1541. Or maybe they lack proper implementation. Maybe others like @Vunce who have built many know better. For me, the TDA1541 simply puts me in touch with the music. But yeah, DACs are a deep hole. Miro’s boards have made it accessible but then if you start talking to Mark, Marcel, and others, one can be working on it a long time.
An all-JFET headphones buffer… 😵💫😵💫😵💫
I read that. But I tried R2R, listened to various IanCanada arrangements, old DACs in CD players, PS2, etc. I couldn’t hear a large difference and I couldn’t tell if it was better or simply different.
Not saying there isn’t something there, it’s probably my ears are not good enough.
If I went that route, it would definitely have to be some kind of well proven kit.
Did you guys build DACs that you think mop the floor with AKM or ESS-based commercial offerings?
I know Rahul said Miro.
I know Rahul said Miro.
Yes, but I don't particularly like the sound of the commercial ESS offerings I've heard - too ethereal for my tastes, not enough body. I think Miro AD1862 sounds great.
Had some time on the bench tonight to tweak the regulated power supply to try to get higher output voltage and lower noise.
It worked!
Here are the details of my setup; 50VAC transformer. Zener string of 20 + 20 + 20 + 15. Only had 7.1V across R6. At this voltage output, with a 6k8 resistor I was getting noise from the Zener string (only around 1mA of current). Aimed for 5mA of current and swapped R6 with 1k36 of resistance. Problem solved.
Earlier when I noticed this noise, before I realized the reason for it, I lowered the output voltage by swapping the 15V Z4 with a 6.2V Z4, and it went away. What I didn't realize at the time was that the reason the noise was gone was that I had 2mA of current through the zener string, because now R6 was dropping 15V instead of 7.1V. In other words, increasing the output of the supply by raising the voltage by 9V also roughly halved the current through the string. Now that I have lowered the value of R6 I can get the output voltage I want without the noise.
Problem solved. Thanks @ElArte, @william2001 and @ra7 for all the great information - I learned a lot.
It worked!
Here are the details of my setup; 50VAC transformer. Zener string of 20 + 20 + 20 + 15. Only had 7.1V across R6. At this voltage output, with a 6k8 resistor I was getting noise from the Zener string (only around 1mA of current). Aimed for 5mA of current and swapped R6 with 1k36 of resistance. Problem solved.
Earlier when I noticed this noise, before I realized the reason for it, I lowered the output voltage by swapping the 15V Z4 with a 6.2V Z4, and it went away. What I didn't realize at the time was that the reason the noise was gone was that I had 2mA of current through the zener string, because now R6 was dropping 15V instead of 7.1V. In other words, increasing the output of the supply by raising the voltage by 9V also roughly halved the current through the string. Now that I have lowered the value of R6 I can get the output voltage I want without the noise.
Problem solved. Thanks @ElArte, @william2001 and @ra7 for all the great information - I learned a lot.
Lovely! Glad it worked.
I’ll post the updated buffer this weekend and we can round out the build.
I’ll post the updated buffer this weekend and we can round out the build.
I've got a gain of 8.2x, which is going to be a little low in my system if I'm throwing away my tube pre and current front ends in the amp and trusting the SCG to provide all the voltage gain for that DHT goodness. Can Rg1 be safely lowered here without making a mess of things?
Yes, it can be lowered, or Rsch can be increased. Might have to readjust the voltage at the output after the change.
Here's the updated buffer. It replaces J175 with a resistor. This makes it a single-ended buffer and the whole preamp is now single-ended. I have measured three channels with this change with repeatable results, so it should work in your builds as well. If you intend to use the buffer, this is what you should go with.
The 4k7 resistor together with a voltage at the bottom of R107 of about 40V should give a little less than 10 mA of current through Q105. There is some flexibility with the 4k7 (R108) resistor. You can go lower to get more current but be sure that you are not exceeding 400 mW of dissipation on Q105. For example, if your supply is 65V and you have 40V at R107, then the current through Q105 is 40/4k7 = 8.5 mA, and voltage across Q105 is 65-40 = 35V, making the dissipation about 300 mW.
The sound is a bit more authoritative with the buffer in place driving my Lateral FET MOFO. Driving an F4, it makes no real difference.
Thanks for your patience with these changes. This should wrap it up for the SCG JFET Pre. I will post updated gerbers and BOMs this weekend.
The 4k7 resistor together with a voltage at the bottom of R107 of about 40V should give a little less than 10 mA of current through Q105. There is some flexibility with the 4k7 (R108) resistor. You can go lower to get more current but be sure that you are not exceeding 400 mW of dissipation on Q105. For example, if your supply is 65V and you have 40V at R107, then the current through Q105 is 40/4k7 = 8.5 mA, and voltage across Q105 is 65-40 = 35V, making the dissipation about 300 mW.
The sound is a bit more authoritative with the buffer in place driving my Lateral FET MOFO. Driving an F4, it makes no real difference.
Thanks for your patience with these changes. This should wrap it up for the SCG JFET Pre. I will post updated gerbers and BOMs this weekend.
I don't have a 'scope at home but the equipment I do have says this thing should be ready to make some noise, hopefully the good kind. Gain is 12.5x with Rg1 @500 ohms. Good timing on the final buffer so I have that installed as instructed.. hot off the press... Final assembly will take some time, I'm kinda slow usually.
