New DIY Phono Pre
- Thread starter dnewma04
- Start date
dnewma04
The Healer
Douglas, thanks for the compliments and for the heads up on the UTC transformers, they have a couple of models with 5-6 primaries and a 50k secondary that I have watched and a few seem to go under the radar a bit. In the meantime, I picked up some inexpensive Beyer moving coil mic transformers that have been used by others effectively as a MC transformer with a 15:1 step up. I'll play with those and continue to search for a pair of nicer models with more flexibility. We have a working phono now and already do have some improvements planned for future models. 40H chokes to replace the 20H, better sheilding, minor layout changes, and possibly some other things.
As Ed said, it's wonderful to get compliments from anyone, but especially so from established DIYers. I have the chassis picked out for my DaRIAAs and hope to get to it by years end, with any luck.
As Ed said, it's wonderful to get compliments from anyone, but especially so from established DIYers. I have the chassis picked out for my DaRIAAs and hope to get to it by years end, with any luck.
jaymanaa
RIP 1961-2018
I was fortunate enough to hear this on the modified Cornies and Ray's homebrew transmission lines.
These guys do first rate work and it sounded excellent. I find the talk about the power supply especially interesting.:scratch2: Keep having fun and turning out 1st rate custom gear guys.:thmbsp:
These guys do first rate work and it sounded excellent. I find the talk about the power supply especially interesting.:scratch2: Keep having fun and turning out 1st rate custom gear guys.:thmbsp:#17 #18
Hello, thanks for your replies.
I downloaded the 6SL7 schematic and the data sheet of the 6SL7.
In this schematic ro ≈ R1 thus the first stage isn't well insulated
from the RIAA low pass. I'd like to see ro<<R1. See fig.4.4.2
You have strong negative current feedback caused by the cathode resistor
R15 and R17, this eliminates desired triode characteristics.
Why not making a triode design that points out triode characteristics?
Kind regards,
Darius
Hello, thanks for your replies.
I downloaded the 6SL7 schematic and the data sheet of the 6SL7.
In this schematic ro ≈ R1 thus the first stage isn't well insulated
from the RIAA low pass. I'd like to see ro<<R1. See fig.4.4.2
You have strong negative current feedback caused by the cathode resistor
R15 and R17, this eliminates desired triode characteristics.
Why not making a triode design that points out triode characteristics?
Kind regards,
Darius
This is not the problem, I know a lot of excellent solid state RIAA preamps.
And I am sure this one is excellent too, no question. But no triode sound.
Try out triode sound.
Kind regards,
Darius
Triode amp does not mean triode sound.
This depends in the circuit design.
A triode has both characteristics, you can operate them pentode/transistor like
and triode like. It is in your hand which characteristic you want to point out.
It is not much work to make the discussed circuit triode like,
ok we need some #26 "techno-babble".
Kind regards,
Darius
Darius,
If you could make a suggestion on how to modify the Octal Cornet circuit so that it'd be more of a triode sound, I would certainly like to try it. Unfortunately I am not as experienced in circuits as I'd like to be, so it might have to be a specific suggestion like "replace R15 and R17 with such and such value of resistor".
I assume that your direct coupled approach has the triode sound? We will be trying it out eventually.
If you could make a suggestion on how to modify the Octal Cornet circuit so that it'd be more of a triode sound, I would certainly like to try it. Unfortunately I am not as experienced in circuits as I'd like to be, so it might have to be a specific suggestion like "replace R15 and R17 with such and such value of resistor".
I assume that your direct coupled approach has the triode sound? We will be trying it out eventually.
jmathers
Super Member
And a related question to Darius (for those of us interested in purchasing the Cornet 2 board from Jim Hagerman):
Is the plain old Cornet 2 schematic "triode-like" or "transistor-like?"
Here 'tis:
http://www.hagtech.com/images/cornet2schem.gif
Jeff
Is the plain old Cornet 2 schematic "triode-like" or "transistor-like?"
Here 'tis:
http://www.hagtech.com/images/cornet2schem.gif
Jeff
currituckco
Super Member
Great thread! Keep the power supply discussion going...I've got a 6SN7 homebrew preamp I was working on that the power supply isn't right yet either. Can you go into more detail about what isn't working right in yours and what you plan to do about it? Thanks!
dnewma04
The Healer
Currituckco,
Basically, we underestimated the current in the circuit by a good deal. Because of this, it appeared that the 20H choke in L1 had high enough to reach critical inductance. What is actually being drawn is approximately 10ma (maybe a bit less) and with that low of current, the models in PSUDII were thrown off. What we need is closer to 40H in the first choke position to reach critical inductance.
What we needed to do was add a resistor to create a current sink, that raised the current draw that created enough draw to make 20H adequate in the first position. On the second rendition, our plan is to bump up to the first choke high enough to allow us to remove the current sink "band-aid".
Basically, we underestimated the current in the circuit by a good deal. Because of this, it appeared that the 20H choke in L1 had high enough to reach critical inductance. What is actually being drawn is approximately 10ma (maybe a bit less) and with that low of current, the models in PSUDII were thrown off. What we need is closer to 40H in the first choke position to reach critical inductance.
What we needed to do was add a resistor to create a current sink, that raised the current draw that created enough draw to make 20H adequate in the first position. On the second rendition, our plan is to bump up to the first choke high enough to allow us to remove the current sink "band-aid".
triode design rule:
I think in a good triode circuit design this factor should be more than four.
Ra/(µRk+ri) >4
See green text:
http://rl12t15.blogspot.com/2007/11/ecc83-als-treiber-fr-die-300b.html
Kind regards,
Darius
PS: This is no "purchase information". The factor gives no information about
"how it sounds". It is just "techno-babble" #26.
I think in a good triode circuit design this factor should be more than four.
Ra/(µRk+ri) >4
See green text:
http://rl12t15.blogspot.com/2007/11/ecc83-als-treiber-fr-die-300b.html
Kind regards,
Darius
PS: This is no "purchase information". The factor gives no information about
"how it sounds". It is just "techno-babble" #26.
currituckco
Super Member
dnewma04 - thanks for the run down. i need to unpack that a little bit - i have a but of work to do to understand the behavior of current, and what too much or two little does to a choke - and so your example will help me, so thanks. So to be clear, there was more current than you expected? And what did this do to the operation of the circuit? How did you diagnose the problem?
and again, congratulations, it looks like an awesome piece. i'm jealous. nice work!
and again, congratulations, it looks like an awesome piece. i'm jealous. nice work!
dnewma04
The Healer
Actually, there was less current than we expected. Because of that, the 20H choke in the first position did not have high enough inductance to act as an input choke. The result was voltage that was significantly higher than PSUD2 predicted. Instead of 325v like we expected, we were seeing upwards of 400v. By adding the current sink, we basically put a 25-30mA load on the power transformer and that was enough to make the 20H input choke see enough current to work like it predicted.
Do you have PSUDII? If so, I you send me your email address, I can send you our PSU and you can take a look.
One thing I should point out is that I am calling it an input choke, but we do have a very small cap as the input that allows us to tune for various changes we might encounter at the outlets of different homes.
Thanks again for the kind words. I was happy with the chassis work and how it turned out, but Ed's work underneath is really what stands out in the design.
Do you have PSUDII? If so, I you send me your email address, I can send you our PSU and you can take a look.
One thing I should point out is that I am calling it an input choke, but we do have a very small cap as the input that allows us to tune for various changes we might encounter at the outlets of different homes.
Thanks again for the kind words. I was happy with the chassis work and how it turned out, but Ed's work underneath is really what stands out in the design.
PakProtector
AK member
hey-Hey!!!,
There is no issue with sticking in another choke. The 15 Hy/75 mA U-frame would be one to try. There are advantages to two inductors in series too, things like breaking up winding capacitance improves the high frequency filtering. If you need to consume a bit of current and would also like an 'ON' indicator, consider the orange 0A3. Rig the dropping resistor to deliver 10-15 mA of current...
cheers,
Douglas
There is no issue with sticking in another choke. The 15 Hy/75 mA U-frame would be one to try. There are advantages to two inductors in series too, things like breaking up winding capacitance improves the high frequency filtering. If you need to consume a bit of current and would also like an 'ON' indicator, consider the orange 0A3. Rig the dropping resistor to deliver 10-15 mA of current...
cheers,
Douglas
