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

[khstudio]

Keep in mind that both of these chips have +6dB of gain...

Really... I missed that part & don't think I like the idea too much :sad:

can they be set up for "Unity Gain"?

Damn, always a hitch with this stuff.... I REALLY need a drink, it's been 2 months. :guinness: :guinness: :guinness: :guinness: :guinness: :guinness: :razz:

 

[Greg]

Kevin:

You are much farther along in this project than I am, but originally I am just going to set mine up with a 600:600 input.

For interfacing with modern gear, I'm thinking the 10K:600 input transformers and adding more makeup gain seems logical to me. I will continue to stew over the options. Adding solid state components does not seem like the best option here for me.

 

[Greg]

Gotcha... to drive the pultec.

 

[clintrubber]

Hey Kevin, why do you keep asking for stuff when the answers are already given ? :?
You're of course not obliged in any way to go that PRR/Tori-route,
but I took the small trouble of getting that info back together and then it's a bit :evil: to see
you're still asking for info when a possible & suited unity gain solution was already given.

If it doesn't suit you then it's a small trouble for you to indicate why it isn't suited I'd say, we can think further then and possibly adapt. Like it went now Tori felt ignored and PRRs dog deserves(/d) better than that.

BTW, those mentioned driver chips will be fine I guess but I have no idea down to which loads these could drive. Down to that 75 ?
The unwanted 6dB gain in these is obviously easy 'remedied' by a resistive divider in front of them.

 

[okgb]

[quote author="drpat"]To drive the Pultec, and many other devices...


[quote author="okgb"]but resisters on the outputs of pultecs
[ and some neve modules ] has been one of those secrets for a long time[/quote]

I've been told that by many people, however, in practice, a 620Ω loading resistor on the output of a Pultec only gets you a drop in signal, added noise and a roll off on both the high and low end.

Trust me... been there... done that...[/quote]

Must be some people in some cases , [ what's on the other side ? ]
but you have the goods , so i trust your opinion , do you think it is more
of a myth ?

I think Kev's last quoted approch to build them as normal , if you add both
the Xfmr & unbal i/o will give you options with the interfaces , possibly
wiring a few different types but not stuck or committed to them .

So a couple of driving circuits have been mentioned , seems like good place to start , I can see wanting to , from others experience get the best
start [ like not going down a bad path, i feel your pain ]

Good luck & skill , you have the ears and you're on your way !

 

[okgb]

Sorry double post , stupid computer , i should have more patience

 

[khstudio]

[quote author="clintrubber"]Hey Kevin, why do you keep asking for stuff when the answers are already given ? :?
[/quote]

1 - I appreciate your help.

2 - I'm here to learn & like the fact that there are "Options" to choose from to fit my needs.

3 - I'm not the only one that's reading this thread & my needs & parts I have in stock here may be different from someone else's.

 

[clintrubber]

[quote author="drpat"]Clintrubber,
Those chips have a stated output impedance of 50Ω...[/quote]
OK that's the source impedance, but are they happy driving a 75 Ohms load ?

The datasheet for the SSM2142 for instance goes down to 600.. 300 load, but doesn't tell much about below that.
Perhaps the other types are more sturdy, but I'd say the '2142 won't do it right by the book.... which might mean nothing in practice of course, and that 75 is worst case, but I thought we were after a 'safe on all accounts'-solution here.


IIRIC a 990 happily does 75, so here we have another 'valid' option.

 

[rodabod]

[quote author="clintrubber"]
OK that's the source impedance, but are they happy driving a 75 Ohms load ?

The datasheet for the SSM2142 goes down to 600.. 300 load, but doesn't tell much about below that.

IIRIC a 990 happily does 75, so here we have another option.[/quote]

Exactly what I was thinking... You need a driving stage which can deliver into 75 Ohms without significant distortion. Yes, you could probably ask a typical chip like a 5534 to do so, but teh distortion figures in the low-end will be crap.

So, is it correct that the Pultec filter section needs to see a 600 Ohm output impedance feeding into it? That was my understanding. In this case, yes, a simple chip that can drive 75 Ohms should be good.

 

[khstudio]

All good info here. :thumb:

I can't try all the options yet because I don't have all the parts here.

I have the parts in stock right now to try 2 of these options:

Also,
In DRPat's defense... he HAS already built & used the SSM Line driver option & has several (About 12-16) that he patches thru & said it drives his Pultec's & other 600 ohm gear, No Problem & sounds great.

I also did read about the buffering & input impedance OF the "Line Drivers" in the data sheets... this is why I asked Pat again if he added anything else to the SSM's.

... just got an email from Joe Malone:

HI Kevin
You just need to use the Hybrid opamp in the standard balanced in
opamp arrangement with 4 x 10k resistors and 2 x 47pF caps.

Thanks
Joe Malone

I'm going to try this today but I'm not exactly sure where to put the resistors. I'm getting pretty good at this stuff but still need help.
NOTE: This is the option that would replace the input TX!!!

The only thing Joe never mentioned is the 600 ohm resistor from + to GND, right before the High Boost Pot... should I add it or leave it off after the JLM Hybrid :?:

The 2nd option I'm going to wire up today is JC's...
It's basically the output stage of the GSSL with a few resistor changes & Unity Gain. It also reminds me of Steffens input on his solid state Pultec but this goes BEFORE the Input TX, not replacing it.
This Option will go from my Un-Balanced 10k gear to the 600:600 TX on my Pultec.

The line drivers are cheap enough & I will be trying them too (when I get them)

 

[khstudio]

I forgot to mention that my Dual Pultec sounds KILLER!

It even sounded great BEFORE I loaded the input correctly but it really woke up after... which is the reason for this thread.

I want a rack of these things. It completely blows away any EQ I own or have heard.

Here's some LARGER PICs:::::::::::
http://www.twin-x.com/groupdiy/thumbnails.php?album=243

 

[rodabod]

[quote author="khstudio"]
... just got an email from Joe Malone:

HI Kevin
You just need to use the Hybrid opamp in the standard balanced in
opamp arrangement with 4 x 10k resistors and 2 x 47pF caps.

Thanks
Joe Malone

I'm going to try this today but I'm not exactly sure where to put the resistors. I'm getting pretty good at this stuff but still need help.
NOTE: This is the option that would replace the input TX!!!
[/quote]

Kevin, I mentioned this already here. Maybe you didn't read it.

Roddy

 

[clintrubber]

[quote author="rodabod"]Kevin, I mentioned this already here. Maybe you didn't read it.

Roddy[/quote]
That's the thing with Kevin, he seems a nice, quick-responding & hardworking guy but can be a bit busy with various new questions & experiments that he doesn't notice things have already been answered :wink:

All fine, enjoy those EQs,

Peter

 

[syn]

see dingo schematic on the jlm site...

 

[khstudio]

[quote author="rodabod"]

Kevin, I mentioned this already here. Maybe you didn't read it.

Roddy[/quote]

Oh no...
I read it & it was ALWAYS on the top of my list of things to try.
I was just waiting for Matt or Joe's feedback on how to wire it "Correctly"
To the Pultec!!!...That's all.

What if I hooked it up wrong & it sounded like crap... then I'd totally disregard it as a valid option... not good.

 

[khstudio]

[quote author="syn"]see dingo schematic on the jlm site...[/quote]

Hey thanks... i totally forgot about that.

The DINGO is what I saw hooked up to the JLM Pultec Kit (that's not available yet)

Still wondering about that 620 ohm load resistor from + to GND :?:
Joe never said if they used it or not... oh well... me try it & listen/sweep. :green:

 

[Greg]

Nice work, Kevin!

But I was thinking this was using tubes.

 

[khstudio]

OK,
I just looked at the DINGO Schematic & it just confused me more... sorry :sad:

http://jlmaudio.com/JLM dINgO complete schematic.pdf

Joe's email said:

HI Kevin
You just need to use the Hybrid opamp in the standard balanced in
opamp arrangement with 4 x 10k resistors and 2 x 47pF caps.

Thanks

Joe Malone

 

[khstudio]

[quote author="Greg"]Nice work, Kevin!

But I was thinking this was using tubes.[/quote]

Thanks Greg. :thumb:

No tubes, I used the 2520's & Patrick's advise & schematic of the real Solid State Pultec 1A3's output stage that he posted.

Tamura 600:600 TX on output
Still have to change the Cinemag 15k:15k's on the input to 600:600
Cinemag inductors
(but I didn't follow the schematic that's floating around for that... it is a little off in my opinion... will explain that later)
The Real Solid State Pultec's amp stage is unique:\
No Feedback cap, 150k to GND, 10pf after it to GND, TANT 150uf/6v output cap & a 1uf/100v mylar between the Filter & Amp.
(I used Sprague Vitamin Q's on mine)

 

[Greg]

I saw your previous post... I will draw it for you.