rlackey
Member
Hello! This is my first post in this forum, so hopefully I've done my research well enough and this post will make some sense to someone.
I am designing a modular in-line 8 buss valve console, each input channel needs to have a valve mic preamp and eq stage. The EQ doesn't have to be fully parametric, but I need more control over the mids than the standard Pultec curcuit affords.
I plan to build modified versions of both a "Gyratec IX" mic pre amp, and the SRPP Pultec passive EQ. The starting point for both of these are the standard schematics available from Jakob's website.
This is all well and good, but I am not very good at leaving things well enough alone so I want to add the MEQ filter stages into the Pultec EQ.
Now, I've read through a very helpful thread on this subject here. "Pultec filter section question" - http://www.groupdiy.com/index.php?topic=2534
It seems that much progress was made and resulted in some very useful schematics that I have also printed out.
I have a couple of unresolved questions, which I am sure would be answered by studying NewYorkDave's EQ, however I totally understand his reasons for taking down the schematics.
The first question is, due to the 50-some dB drop that results, how best can I modify the gain stage to compensate? I seem to remember JC commenting on two possible solutions, splitting the filter sections, each with it's own amplifier, or putting an amplifier before and after the passive filter.
This also links into my second question.
I have been in contact with Per Lundahl about ordering suitable transformers, as I was unsure that the LL5402 called for on the input of the Pultec was correct. The LL5402 is actually a output transformer, and Per noted to me that it was in fact unsuitable for use as a input. He recommended a LL1531, LL1540 or LL1527. He also recommended the LL1538 as a mic input transformer for the mic pre amp rather than the LL1528 which is on the schematic.
This lead me to find another thread entitled "Pultec IN/OUT transformer impedance, in which the use of a higher impedance input transformer was discussed, and Jakob commented himself that the Pultec requires a low z input transformer because it can load down to 75ohms (in a worse case scenario). Is the Gyratec IX likely to handle this situation?
Ok, to summarize both of my questions into one (long) sentence.
Can anyone help me understand how to implement the extra filter sections with either of the options JC mentioned? (i.e. a gain stage before and after the filter sections, or separate the filter sections, each with its own amplifier... I picture the options kind of like running them either in serial or parallel).
Both of these options also leave me a bit lost when it comes to choosing suitable input and output and transformers.
Please also let me know and correct my interpretations of these two options if I am wrong.
I hope I'm not asking questions that have been asked a million times before.
Thanks!
Rich Lackey :grin:
I am designing a modular in-line 8 buss valve console, each input channel needs to have a valve mic preamp and eq stage. The EQ doesn't have to be fully parametric, but I need more control over the mids than the standard Pultec curcuit affords.
I plan to build modified versions of both a "Gyratec IX" mic pre amp, and the SRPP Pultec passive EQ. The starting point for both of these are the standard schematics available from Jakob's website.
This is all well and good, but I am not very good at leaving things well enough alone so I want to add the MEQ filter stages into the Pultec EQ.
Now, I've read through a very helpful thread on this subject here. "Pultec filter section question" - http://www.groupdiy.com/index.php?topic=2534
It seems that much progress was made and resulted in some very useful schematics that I have also printed out.
I have a couple of unresolved questions, which I am sure would be answered by studying NewYorkDave's EQ, however I totally understand his reasons for taking down the schematics.
The first question is, due to the 50-some dB drop that results, how best can I modify the gain stage to compensate? I seem to remember JC commenting on two possible solutions, splitting the filter sections, each with it's own amplifier, or putting an amplifier before and after the passive filter.
This also links into my second question.
I have been in contact with Per Lundahl about ordering suitable transformers, as I was unsure that the LL5402 called for on the input of the Pultec was correct. The LL5402 is actually a output transformer, and Per noted to me that it was in fact unsuitable for use as a input. He recommended a LL1531, LL1540 or LL1527. He also recommended the LL1538 as a mic input transformer for the mic pre amp rather than the LL1528 which is on the schematic.
This lead me to find another thread entitled "Pultec IN/OUT transformer impedance, in which the use of a higher impedance input transformer was discussed, and Jakob commented himself that the Pultec requires a low z input transformer because it can load down to 75ohms (in a worse case scenario). Is the Gyratec IX likely to handle this situation?
Ok, to summarize both of my questions into one (long) sentence.
Can anyone help me understand how to implement the extra filter sections with either of the options JC mentioned? (i.e. a gain stage before and after the filter sections, or separate the filter sections, each with its own amplifier... I picture the options kind of like running them either in serial or parallel).
Both of these options also leave me a bit lost when it comes to choosing suitable input and output and transformers.
Please also let me know and correct my interpretations of these two options if I am wrong.
I hope I'm not asking questions that have been asked a million times before.
Thanks!
Rich Lackey :grin: