PULTEC - Input Options -Buffers- Imp - TX - JLM Hybrid opamp

[martthie_08]

good stuff, keep it coming, I'll be playing around with my two pultec clones in the near future (when I get my 2520's). I wasn't all too thrilled with the sound of my units, ok the bottom end is killer, but the top could be sweeter. It always bugged me that I have a "solid state" housing and tubes on the inside, maybe I'll set things right, with the help of all the hard work you've put into studying and testing. Thanks! Marten

 

[drpat]

Marten,

Don't cry too soon. The original EQP-1A3 was all tube, and they used the same gain knobs as you have on your unit. Get that top end rockin' it's well worth it when it's right...

 

[khstudio]

Marten,

If you don't like the Hi Boost... TRY swapping the Cap/Inductor ORDER!!!
It's 2 wires... EASY! :wink: At least worth a listen.

Believe me... it makes a difference. I listened to it back & forth for a few hours.
With the Caps first (coming out of the 10k wiper) the sound is more open & clearer.

When you hit the Inductor FIRST, it sounds slightly more compressed & more Vintage... also a hair more focussed.

It seems that some models & different companies that make Pultec clones change this order too. YES, the original "Pultec" was = Caps first BUT... it's POSSIBLE the LANG EQ didn't... Still waiting for Pat to look into his crystal ball to see. :razz:
I had a TUBE TECH EQ-1B (or C, I forget) & IT had the Inductor first... so it made me want to try it with mine to hear what it does.

I like the 2 options so much I'm installing a switch to have the option.

I wasn't going to mention this until I posted my "Completed Dual Pultec" thread but....

 

[martthie_08]

that's some great infos, thanks guys! I think I'll investigate the input impedance/driving issue first, then check out some different film caps for the HF section (currently WIMA FKP2 IIRC) and look into replacing the inductor (currently Toko's).

I'm on a Gyraf board at the moment, so changing the order of inductors/caps will not be trivial, but that's interesting stuff. I have a feeling that some of the voodoo associated with the Pultecs is being cleared out, at least for me, very good

oh, and what manufacturer potentiometers are you guys using, I have a feeling they might have an effect on the sound as well :roll: I think I have Bourns conductive plastic on my unit.

 

[drpat]

Marten,

I used Allen Bradley carbon composition pots, and stuck with the same part numbers as the original. My original units all have the same pots that were in there from 40 years ago, so, I figured that was a decent track record. I cleaned all of the pots on all of my Pultecs when I purchased them and have had absolutely zero issues with them since...

I've never tried the plastic pots in this circuit, but I'll assume that the difference would be the same as using carbon comp resistors vs metal film.

Another thing about the pots on a Pultec that many people dont seem to know, is that they rotate past the "10" position by a couple of notches. So, when a Pultec knob is fully clockwise, the knob indicator line is pointing straight down (past "10"). This is the easiest way to tell a fake Pultec from a real one...

Sorry to jack your threads Kevin...

 

[rodabod]

[quote author="martthie_08"]the top could be sweeter.[/quote]

Marten, I'd maybe look at the bigger picture if you think that there is something "missing" as far as the top-end is concerned. I agree that it's good to use quality components, but I doubt changing something such as the potentiometers is suddenly going to improve the unit dramatically.

Out of interest, what are you driving it with? And is it configured for 10K input impedance or 600 Ohms?

Roddy

 

[martthie_08]

thanks for the help, this may be a point, I got a 600:600 UTC at the input with a 10k resistor as per Gyraf, coming directly out of a RME or Motu DA. But I'll probably do some more testing and start a new thread of my own, this little takeover was rather a "note to self" and a "thumbs up" to Kevin...

 

[rodabod]

Marten, if it is easy enough to do, I would maybe try removing the 10K to see how changing the source impedance affects the performance. I'm just wondering after what Roger was saying earlier on about driving the pultec directly from a de-balancing stage. Note that your RME or Motu may not be very happy driving this load though. You may need to check some specs.

 

[khstudio]

[quote author="martthie_08"]thanks for the help, this may be a point, I got a 600:600 UTC at the input with a 10k resistor as per Gyraf, coming directly out of a RME or Motu DA. But I'll probably do some more testing and start a new thread of my own, this little takeover was rather a "note to self" and a "thumbs up" to Kevin...[/quote]

No need to start a new thread... I don't mind.

I bet that 10k is part of your problem.

 

[okgb]

I advocate this all the time , to give yourself the options
of bal/unbal , especially on micpre outputs , or i/o things
that may be used in inserts

 

[rodabod]

[quote author="RogerFoote"][quote author="rodabod"]Marten, if it is easy enough to do, I would maybe try removing the 10K to see how changing the source impedance affects the performance. I'm just wondering after what Roger was saying earlier on about driving the pultec directly from a de-balancing stage. Note that your RME or Motu may not be very happy driving this load though. You may need to check some specs.[/quote]

It has been years since I cracked open a MOTU converter box, but IIRC the 1224 has SSM2142s on the outputs. If so, you can use a TS cable (shorting ring to gnd at the 2142) and try driving the EQ filter directly, unbalanced through a 600R.
[/quote]

Cool.

Marten, I'm inclined to say, swap the 10K secondary load resistor on your Pultec to ~ 600 Ohms and then compare to how it was with the original 10K. It sounds as if the Motu can probably drive it reasonably (maybe not perfectly at some settings). The RME may well drive it ok at 600 Ohms too seeing as they are professional-grade, but I'm not sure.

Roddy

 

[khstudio]

I'm using the RME converters here.

Also, if you read back earlier, I WAS using a 10k on the secondary... when I changed it (even with the Cinemag 15k:15; input TX's) the sound changed a LOT.
It's not like it was bad before the change... it just seemed to get Fatter & Tighter & the controls were more responsive... it's hard to explain but I'm trying.

BTW, I've been using my Dual Pultec with the JLM Hybid in the input & it sound pretty good BUT I can't seem to drive into it like I could before OR it is driving into the filter section too hard. Like when I was tracking bass yesterday... I had to be real careful with the input levels.

It may possibly be a little too clean but I have to spend some time with it, then I'm going to put the 600:600 back on the input & try some of the "Buffer" idea".

The circuit seems to like the 620 ohm... so I'd get that right first - then, don't be afraid to try changing the order of the Cap/Inductor. :wink:

EVERY part I swapped had an effect on the sound & feel.

Good Luck.

 

[khstudio]

[quote author="drpat"]

Sorry to jack your threads Kevin...[/quote]

Jack away... i love all the input. :green:

I REALLY should change the TITLE of the thread... but to what?

 

[khstudio]

[quote author="drpat"][quote author="khstudio"]I REALLY should change the TITLE of the thread... but to what?[/quote]

:green: "50 ways to make a Pultec sound like a Manley" :green:[/quote]

You B@stard!!!!!!!!!

:razz: :razz: :razz: :razz: :razz:

I know... i deserve it.

But be honest... how many of you learned SOMETHING from this thread :?:

 

[khstudio]

I Copied this from another thread because I feel it belongs here to:
http://www.groupdiy.com/index.php?topic=26913

[quote author="Greg"]hey Kevin:

Re-read PRRs post. Take a look at your bias resistor... i.e. the one hanging off the non-inverting terminal as a way to reduce your DC offset. I believe PRR feels it is too high for a BJT input decive... like the 2520. Perhaps reducing that value with help (not eliminate) your DC offset.

Also, considering you are using a fixed gain stage, I would lean more towards an inverting configuration (yours in non-inverting) with a DC trim resistor. This might yield better results. Then flip the polarity back with your output transformer.[/quote]

Greg,
Thanks. I was talking to Pat last night about setting up my Make-up amp differently. The schematic IS exactly how Pultec did it on their SS model but that doesn't mean it's the BEST option. Although people like the SS Pultec as is, Pat did mention that when this was designed, the test equipment wasn't as advanced back then & it's possible they just used their ears & liked this setup's sound... who knows.

The bottom line is, I'm not stuck to using it... & thought about trying other things (like your idea) or just set up an API 325 Line Amp, etc...
When I etched the PCB's, I made them "Universal" so I could do anything I want.

Right now... BOTH channels "Match" very well... so changing 1 channel & comparing will not be hard. (this was not the case a week ago. They didn't match)

About the HYBRID:
It still sound good but after further use (during sessions & tracking) I found it seems to "Clip" pretty easily. I didn't seem to have or notice this problem with the TX on the input.
I feel this is because the 600:600 input TX, loaded with the 620r drops the gain (I think, aprox. 6dB ?) but when using the HYBRID, there is NO drop at the input because it's set up for UNITY Gain. This will cause the signal to "Bang" into the 2520 (make-up amp) harder.

So I'm going back to plan "A" with the input TX (Stock Setup)
I've already made a few different 'Buffer" options to try, test & listen to.

After I settle on the input. I will tackle the Make-up amp.

 

[Greg]

[quote author="khstudio"]The schematic IS exactly how Pultec did it on their SS model but that doesn't mean it's the BEST option.[/quote]
I am not familiar with the solid state Pultec. Do you have an original schematic or a link or two I can read?

 

[khstudio]

[quote author="Greg"][quote author="khstudio"]The schematic IS exactly how Pultec did it on their SS model but that doesn't mean it's the BEST option.[/quote]
I am not familiar with the solid state Pultec. Do you have an original schematic or a link or two I can read?[/quote]

It's already been posted several times.

The filter section is just like the Tube unit's... but the AMP is a 2520 & TX's are HS56

This is as close as your going to get to seeing a real SS Schematic:

 

[Greg]

These are the two quotes I was referecing, perhaps I read them wrong:

[quote author="khstudio"]The schematic IS exactly how Pultec did it on their SS model but that doesn't mean it's the BEST option.[/quote]
[quote author="khstudio"]Now, the SS Pultec isn't set up exactly like the 312 but I wouldn't think it would cause the offset to change. :idea: :?:[/quote]

Anyway... I think you should look at changing your bias resistor or use an inverting configuration with a DC trim resistor. Both of these could lower your DC offset. I don't think you will be able to eliminate the need for a coupling cap, but lowering the DC offset should allow you to use a lower cap value resulting in less "smearing" of the audio.

 

[drpat]

That schematic was drawn by me, it's not an original one, but it was done while I had one of mine cracked open for a few days. I used it while I built my solid state equalizer because I couldn't find an original schematic. Obviously it's not set up like an API preamp, but, it does sound good "as is".

 

[khstudio]

Another UPDATE:

I had to mix down a song for a band this week & had a chance to run some thru my new Dual Pultec. I did a few my standard way then a few thru the Pultec, taking notes & pictures of the settings so I could go back & listen.

Everyone in the band liked ALL my standard mixes but ended up choosing the Pultec one. :green: It was just more defined, had a nice, none offensive flavor to it & tightened up the bottom end (which is the hardest part to get right when mixing). We all love bass but it can kill or make a mix. The Pultec seemed to move it into an upper low range and control the "loose" SUBs.

While the mix was up & after the band left, I decided to install the 600:600 Input Trannys to have a listen & run test.
The TX was also cool but did have a hair dirtier highs... but the lows were nice & I think I could hear the better CMRR, especially in the holes of the mix & especially in the lows & definition of them.

But in the end, the band chose the HYBRID Version of the mix over all the others (which BTW got sent out today to go on a Compilation CD with other pro bands) I could have picked a few different mixes myself... even ones without the Pultec at all but I did like it a lot.

So, the HYBRID it is :grin:
It's universal & can happily marry with whatever I plug into it & it sounds great!

Now... my final test is to try my Cinemag in front of the HYBRID.
I still have the same mix set up & untouched, also all the setting on the Pultec have not moved from the favorite/Best settings we picked for the mix.

I'm going to try this... & most likely mount the transformers in my patch bay so I can use them with other units as well.
NOTE: ALL of my output (main & inserts) are unbalanced on my console.
After reading the info from JENSEN... it seem that adding the input TX can significantly improve CMRR, among other things.
Also, I'm not using the Jensen, I'm using Cinemags equivalent CMLI 15/15B.
MY HYBRID IS SET UP EXACTLY LIKE THE "PRO TYPE INPUT" shown in the diagram - Unity Gain.
(Original PDF)
http://www.jensen-transformers.com/an/an003.pdf

Hopefully some of you guys are getting something out of this thread...
If so... please let me know. I'm doing my best to learn, test & share what I can.

& once again, thanks to all who have helped.

Kevin