Philip_BlueFX
Active member
Greetings folks.
I decided to have a swing at the G9 project since there where so many information about it around, especially from the gyraf guide.
I went a little over this and etched my own boards based on my own designs and I am currently trying to implement an electronically balanced input instead of the transformer (which I don't own, hence the lack of comparing of the two).
Let me take you through this, so I can get to the point. The point being that this thing is not silent enough (I get 50Hz and 100Hz hum with their harmonics).
First off, You will notice a 3rd toroid which is one providing the balanced circuit voltage @30V approx. It's my attempt (that still lives in my troubled future) to implement a 1176 style compressor into this preamp, but please let's leave this out of THIS discussion. So yeah, the 30V PSU is taken from the 1176 Rev.G schematic.
About the grounding scheme, I wanted to have an as clean as possible wiring, so I decided to split the ground into two busses, being one for the PSU and one for the audio. So the audio ground is the big copper wire connecting the in-out xlrs and all preamp-gain-volume-output.trafo grounds are connected on it. The PSU ground is connected again with a solid copper wire to the IEC socket and all mains-psu-heater.common-smoothing.caps grounds are connected on it. The chassis is grounded on the input xlr but I have tried doing so with a screw next to the IEC socket instead, which made no difference.
All my signal cables are single-side shielded on a near ground connection and I tried to twist all my power wires with a ground wire to minimize inteference.
Also, all regulators are isolated with silicon pads from the chassis on which they are mounted for heat dissipation. This decision was made to save some space and it seems to be working but it makes the chassis way too hot on the spot so I am considering of getting a big heat sink. This move also lives in my troubled future unless I understand that that's where my problems lie.
Now to the noise issues. From a poor spectrum analysis (output xlr to my presonus interface with interface gain at minimum) from Studio One I see a high noise floor, a 50Hz spike and it's harmonics.
This is with AND without the unbalancing circuit in the front. I found out that if I ground the input (without the unbalancing circuit) the hum disappears.
It took me sometime struggling with the TL783 (HT ripple was about 30mVpp) but I replaced it and the filter caps (I believe it was the 783 though) but it didn't make any difference noisewise (ripple is about 6-10mVpp now). So I figure it must be something else... I am struggling with this because I fear it must be my wiring that is off, or the grounding scheme, so I would love some feedback on this. The two ground busses idea came to me after I looked at many many designs of other tube amp enthusiasts and it seemed like a real solid solution. Also it makes sense to my inexperienced hollow skull.
I also fear that this is an issue that a transformer would potentially solve. Thing is, I am trying to save the money for a trafo and furthemore I am too interested in making this unbalancing circuit to work (which is not my design either, of course). The aforementioned circuit is taken from Moxtone's take on the 1176 Rev.G and is more or less the same as the original 1176. I took the liberty to step up the gain to much the 1:5 transformer's gain (and try to boost my signal over the noise).
So, any thoughts?
This whole process is for learning purposes, experience, suffering and desperation that may lead to the loathing of one's self.
Wish you all the best.
And here are some pictures of my unit at this moment. Unbalanced circuit is on the breadboard.
https://ibb.co/k3nKBGRhttps://ibb.co/526NbyNhttps://ibb.co/gvVbvtghttps://ibb.co/yktmxP7https://ibb.co/7J8mRvMhttps://ibb.co/3R8Gjkphttps://ibb.co/PTcX18jhttps://ibb.co/HnhtGVH
I decided to have a swing at the G9 project since there where so many information about it around, especially from the gyraf guide.
I went a little over this and etched my own boards based on my own designs and I am currently trying to implement an electronically balanced input instead of the transformer (which I don't own, hence the lack of comparing of the two).
Let me take you through this, so I can get to the point. The point being that this thing is not silent enough (I get 50Hz and 100Hz hum with their harmonics).
First off, You will notice a 3rd toroid which is one providing the balanced circuit voltage @30V approx. It's my attempt (that still lives in my troubled future) to implement a 1176 style compressor into this preamp, but please let's leave this out of THIS discussion. So yeah, the 30V PSU is taken from the 1176 Rev.G schematic.
About the grounding scheme, I wanted to have an as clean as possible wiring, so I decided to split the ground into two busses, being one for the PSU and one for the audio. So the audio ground is the big copper wire connecting the in-out xlrs and all preamp-gain-volume-output.trafo grounds are connected on it. The PSU ground is connected again with a solid copper wire to the IEC socket and all mains-psu-heater.common-smoothing.caps grounds are connected on it. The chassis is grounded on the input xlr but I have tried doing so with a screw next to the IEC socket instead, which made no difference.
All my signal cables are single-side shielded on a near ground connection and I tried to twist all my power wires with a ground wire to minimize inteference.
Also, all regulators are isolated with silicon pads from the chassis on which they are mounted for heat dissipation. This decision was made to save some space and it seems to be working but it makes the chassis way too hot on the spot so I am considering of getting a big heat sink. This move also lives in my troubled future unless I understand that that's where my problems lie.
Now to the noise issues. From a poor spectrum analysis (output xlr to my presonus interface with interface gain at minimum) from Studio One I see a high noise floor, a 50Hz spike and it's harmonics.
This is with AND without the unbalancing circuit in the front. I found out that if I ground the input (without the unbalancing circuit) the hum disappears.
It took me sometime struggling with the TL783 (HT ripple was about 30mVpp) but I replaced it and the filter caps (I believe it was the 783 though) but it didn't make any difference noisewise (ripple is about 6-10mVpp now). So I figure it must be something else... I am struggling with this because I fear it must be my wiring that is off, or the grounding scheme, so I would love some feedback on this. The two ground busses idea came to me after I looked at many many designs of other tube amp enthusiasts and it seemed like a real solid solution. Also it makes sense to my inexperienced hollow skull.
I also fear that this is an issue that a transformer would potentially solve. Thing is, I am trying to save the money for a trafo and furthemore I am too interested in making this unbalancing circuit to work (which is not my design either, of course). The aforementioned circuit is taken from Moxtone's take on the 1176 Rev.G and is more or less the same as the original 1176. I took the liberty to step up the gain to much the 1:5 transformer's gain (and try to boost my signal over the noise).
So, any thoughts?
This whole process is for learning purposes, experience, suffering and desperation that may lead to the loathing of one's self.
Wish you all the best.
And here are some pictures of my unit at this moment. Unbalanced circuit is on the breadboard.
https://ibb.co/k3nKBGRhttps://ibb.co/526NbyNhttps://ibb.co/gvVbvtghttps://ibb.co/yktmxP7https://ibb.co/7J8mRvMhttps://ibb.co/3R8Gjkphttps://ibb.co/PTcX18jhttps://ibb.co/HnhtGVH