I found the JFETs to be tough little buggers. They are good with 50V or so amd about half a Watt. So they might survive an accident but I wouldn’t put them through that on a constant basis. Hope you got it fixed Rick.
Looks like the buffer is going to change again. But it’s the same devices. So if you bought some you’re good.
Looks like the buffer is going to change again. But it’s the same devices. So if you bought some you’re good.
Well, they might measure as "good" but after this abuse they sound very bad.
Got the gain right - one of my two 20K resistors for the Schade resistor had a broken lead!
But the buzz is still there though slightly less intrusive. Will keep searching.
Got the gain right - one of my two 20K resistors for the Schade resistor had a broken lead!
But the buzz is still there though slightly less intrusive. Will keep searching.
I had buzz early on in my build. I abandoned the thermistor/cap combo, tied the RCA shields together and to ground, then made sure both my DAC and preamp were plugged into the same power strip.
No more noise since.
Thanks for your advice - El Arte.
Unfortunately I have done all of that. What is weird it is only on the left side (two stages for one channel in a bi-amp setup).
All signal grounds are tied together for each line stage and all components are plugged into the same socket.
I use two of my hotrod power strips - one for amps and line stages and the other for dacs, etc - but both plug into the same outlet. There is no connection to house ground. I have tried connecting house ground to the amplifier heatsink and to the case of the DAC (none of my DIY components are in a box so nothing to connect house ground to other than the heatsink for the amplifiers) with no effect at all.
The offending channel is close to my music computer (low power) but when it is off the noise is still there. Same with my DSP box, and my dante stuff (REDNET and Cisco router) - when they are turned off the noise is still there.
There does seem to be some kind of bad synergy between the two stages - with just the one channel (treble or bass) on the noise is almost non-existent but when both are on it is much too noticeable. There is no noise with the DAC off but I know it is not the fault of the DAC since I have used other DACs in the position and the noise remains.
It just occurred to me to plug the DAC that drives this channel to another outlet with house ground and hear what happens.
I will find it eventually - though suggestions of where to look are WELCOMED.
I usually make my own cables. I am using AUDIO ENVY cables between DAC and line stage. I need to make up a test cable and make sure the cable is not the problem. I, also, wonder if my old input coupling caps could be the problem. TRT DYNAMICAPs I bought to use for speaker crossovers twenty years ago. I have some AURICAPs due on Saturday. I would not mind at all of these cure the problem.
Problems do introduce opportunities to learn something. And since I have much to learn I never get upset about this.
Unfortunately I have done all of that. What is weird it is only on the left side (two stages for one channel in a bi-amp setup).
All signal grounds are tied together for each line stage and all components are plugged into the same socket.
I use two of my hotrod power strips - one for amps and line stages and the other for dacs, etc - but both plug into the same outlet. There is no connection to house ground. I have tried connecting house ground to the amplifier heatsink and to the case of the DAC (none of my DIY components are in a box so nothing to connect house ground to other than the heatsink for the amplifiers) with no effect at all.
The offending channel is close to my music computer (low power) but when it is off the noise is still there. Same with my DSP box, and my dante stuff (REDNET and Cisco router) - when they are turned off the noise is still there.
There does seem to be some kind of bad synergy between the two stages - with just the one channel (treble or bass) on the noise is almost non-existent but when both are on it is much too noticeable. There is no noise with the DAC off but I know it is not the fault of the DAC since I have used other DACs in the position and the noise remains.
It just occurred to me to plug the DAC that drives this channel to another outlet with house ground and hear what happens.
I will find it eventually - though suggestions of where to look are WELCOMED.
I usually make my own cables. I am using AUDIO ENVY cables between DAC and line stage. I need to make up a test cable and make sure the cable is not the problem. I, also, wonder if my old input coupling caps could be the problem. TRT DYNAMICAPs I bought to use for speaker crossovers twenty years ago. I have some AURICAPs due on Saturday. I would not mind at all of these cure the problem.
Problems do introduce opportunities to learn something. And since I have much to learn I never get upset about this.
Check your trimmers. I have had trouble with those in the past. Scratchy ones in specific sweep ranges. One would say faulty ones.
That is good advice but I am in the process of replacing resistors with VISHAY metal foil trimmers which are close to perfect in that regard.
what is strange is that each channel is silent if running alone but the noise begins with both being on.
In the process of going over the offending bass channel. Maybe this will make it go away.
THANKS for your suggestions.
Take care,
what is strange is that each channel is silent if running alone but the noise begins with both being on.
In the process of going over the offending bass channel. Maybe this will make it go away.
THANKS for your suggestions.
Take care,
That would typically make me suspect a ground loop, but since you have both grounds connected together, it’s not possible. Maybe a device didn’t like an excess of voltage/current. All bets are off.
One of the reasons I never got a DCA75 is that they cannot test in-circuit, which is what I always seem to need.
after all these mods, and jfet instead of mosfet, it would be useful for me if you could post an updated schematics of what sounds best for you ra7?
I am sure he much prefers the sound of FET version. From messages it is clear he loves what the circuit is doing with these close to throwaway devices.
If you are going to use the CCS with the J113 I found that it is best to buy 100 of them and sort. I think this version of the CCS offers a little more of what is good about SCG.
You need to get a batch of J175 but the J111s in the group of 100 I got were far more alike than the other two so pot luck might be just fine there.
I am not using the buffer - my SCGs are next to the amplifiers and even though these are THF51 followers they seem to drive the amps effortlessly - who knows if that has any meaning at all? Works very well as far as I can tell.
I have tried the various versions of the circuit as he proposed them and there is no doubt what he has done, so far, it the best of them all. I was initially skeptical of those tiny things being able to drive my amplifier. He assured me there would not be a problem and he was right. I have got used to Rahul being right. One thing i like about this project is that Rahul continues to work with the circuit. This is a living project.
This circuit is so simple that it does make a difference using the best components for each position as you can. Not to say it did not always sound good - I started out with DALE RN resistors and as time has gone by substituted silly parts I had in my collection - SHINKOH resistors for J175 gate stopper and a 2 watt one for the Schade resistor. Caddock MK132 in the bias circuit and the CCS. These have the advantage of allowing tighter layouts. My raw supply is choke input followed by an LR filter and then to the board with the original two caps (I choose 1mF) with a 1R resistor in between. Rahul's revised supply has more RC filtering stages using smaller capacitors. I will never know how the two compare. Too lazy to try that. I am suing a film cap instead of the elctrolytic in the "regulator". I had some of the good WIMAs in 0.22uF so I used them - they are quite large. All of Rahul's suggested changes have been for the good.
If you use a J113 with a Vp of 1.67/1.68 you can always get the 15mA easily using a 20R trimmer. I have already mentioned this but it makes things so much easier - I was trying to do it with resistors and that did not work well at all. If you use a J113 with 1.5 to 1.54 Vp you can probably use something like a 100R pot and then more easiy find a resistor combo to replace.
If you are going to use the CCS with the J113 I found that it is best to buy 100 of them and sort. I think this version of the CCS offers a little more of what is good about SCG.
You need to get a batch of J175 but the J111s in the group of 100 I got were far more alike than the other two so pot luck might be just fine there.
I am not using the buffer - my SCGs are next to the amplifiers and even though these are THF51 followers they seem to drive the amps effortlessly - who knows if that has any meaning at all? Works very well as far as I can tell.
I have tried the various versions of the circuit as he proposed them and there is no doubt what he has done, so far, it the best of them all. I was initially skeptical of those tiny things being able to drive my amplifier. He assured me there would not be a problem and he was right. I have got used to Rahul being right. One thing i like about this project is that Rahul continues to work with the circuit. This is a living project.
This circuit is so simple that it does make a difference using the best components for each position as you can. Not to say it did not always sound good - I started out with DALE RN resistors and as time has gone by substituted silly parts I had in my collection - SHINKOH resistors for J175 gate stopper and a 2 watt one for the Schade resistor. Caddock MK132 in the bias circuit and the CCS. These have the advantage of allowing tighter layouts. My raw supply is choke input followed by an LR filter and then to the board with the original two caps (I choose 1mF) with a 1R resistor in between. Rahul's revised supply has more RC filtering stages using smaller capacitors. I will never know how the two compare. Too lazy to try that. I am suing a film cap instead of the elctrolytic in the "regulator". I had some of the good WIMAs in 0.22uF so I used them - they are quite large. All of Rahul's suggested changes have been for the good.
If you use a J113 with a Vp of 1.67/1.68 you can always get the 15mA easily using a 20R trimmer. I have already mentioned this but it makes things so much easier - I was trying to do it with resistors and that did not work well at all. If you use a J113 with 1.5 to 1.54 Vp you can probably use something like a 100R pot and then more easiy find a resistor combo to replace.
El Arte - I assume you went to Percy's website?
Know which J113s (for Vp) you will use before you select your trimmer resistance.
I use a 5K in the bias circuit but augmented with resistors.
These are a pleasure to use. Once set they stay set. And I think they are sonically invisible.
Know which J113s (for Vp) you will use before you select your trimmer resistance.
I use a 5K in the bias circuit but augmented with resistors.
These are a pleasure to use. Once set they stay set. And I think they are sonically invisible.
Yes, I do like the JFET version very much. The final will be very close to this one: https://www.diyaudio.com/community/threads/schade-common-gate-scg-preamp.380487/page-67#post-7733582
The buffer has been updated, so it won't look like that, but otherwise it is pretty close. Also, in this post you can see the steps to update the existing PCB to the JFET design:
https://www.diyaudio.com/community/threads/schade-common-gate-scg-preamp.380487/page-68#post-7759725
Hoping to post final soon.
In my pursuit to reaching QUIET for my left channel I returned to the CINEMAG transformer on the bass channel - needed the extra gain and now the noise is gone. No ground connection at all between SCG and DAC. Left the tweeter channel single ended. I installed the transformer on the left woofer channel, too. I do think, in this case, the transformer is better due to the extra voltage.
THEN I noticed the left tweeter channel was still noisy. Funny how removing a noise will allow another noise the notice it has been wanting. Figured I had a noisy J175 so I thought I would replace it with 2SJ74. The noise is now gone but what is interesting: it is no quieter than the J175 in the other channel and does not seem sound any different. So in my case the holy TOSHIBA brings nothing you cannot get from a good J175.
Got a pair of the TOPPING D90 Discrete DACs and they are better than the D90III. Much better in fact. Wish I could afford two silly DACs but these seem to be pretty interesting for the money.
THEN I noticed the left tweeter channel was still noisy. Funny how removing a noise will allow another noise the notice it has been wanting. Figured I had a noisy J175 so I thought I would replace it with 2SJ74. The noise is now gone but what is interesting: it is no quieter than the J175 in the other channel and does not seem sound any different. So in my case the holy TOSHIBA brings nothing you cannot get from a good J175.
Got a pair of the TOPPING D90 Discrete DACs and they are better than the D90III. Much better in fact. Wish I could afford two silly DACs but these seem to be pretty interesting for the money.
Glad to hear J175 sounds just as good as a J74 here. My observation was that it sounds a bit more dry than J175 and at large swings it gets more edgy than J175. Nothing wrong with a J74 used in the right place though--there is no doubt that it is a fantastic part.
For DACs, use an AD844 as the IV. I think there are similar newer chips that have low impedance inputs that suit current out DACs. But nothing sounds like an AD844 used the right way. See here for example. The Zen IV uses a similar principle. I don't say this lightly: using AD844 without feedback was the most impactful change to digital audio in my system since I started building.
I have been distracted by BAF planning, but also making slow progress on PCBs. I'm just going to post the gerbers here and not go through the pain of managing a group buy.
For DACs, use an AD844 as the IV. I think there are similar newer chips that have low impedance inputs that suit current out DACs. But nothing sounds like an AD844 used the right way. See here for example. The Zen IV uses a similar principle. I don't say this lightly: using AD844 without feedback was the most impactful change to digital audio in my system since I started building.
I have been distracted by BAF planning, but also making slow progress on PCBs. I'm just going to post the gerbers here and not go through the pain of managing a group buy.
Yes, I agree with your assessment but did not know how to express it.
Instead of converting the other channel to 2SJ74 I will find another quiet J175. Which will not be difficult.
There are so many easy ways of getting pcbs and you have plenty of things to do that are far more important. You have made a good decision.
Take care,
Instead of converting the other channel to 2SJ74 I will find another quiet J175. Which will not be difficult.
There are so many easy ways of getting pcbs and you have plenty of things to do that are far more important. You have made a good decision.
Take care,
Have no idea where to begin with making my own DAC - other than using ADS844 in I/V!
It would take all of my time trying to decide with chip to use!
I will stick with simple stuff! Thanks for the encouragement - I wish I had the courage ...
It would take all of my time trying to decide with chip to use!
I will stick with simple stuff! Thanks for the encouragement - I wish I had the courage ...