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

[khstudio]

[quote author="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.[/quote]

Greg #1... thanks for helping. :thumb:

#2... I see NO connection with those 2 statements... you definitely read it wrong... sorry bro.

Once again,
when I measured the DC offset (In My SS Pultec circuit - using the 2520's) it scared me BECAUSE I thought it was the 2520's causing it. I new it was high & I was concerned about my 8 channel API 312 I just finishing up - & didn't plan on or want to use output caps. Nor did I want to send THAT much DC thru the OT's & especially, Damage my new 2520's that I waited almost a YEAR to get!!!

I hope this makes sense.

The SS Pultec circuit (Draw by PAT) DOES require an output cap & I have no problem using one. It does sound very good as is but that doesn't mean I won't revisit possible changes to the output amp or setup down the road.

Like I said, I still have a long way to go with learning about electronics but I've come a long way & I'm no dummy or lazy.
Some of you guys have a lot of background & knowledge & sometimes take for granted, things that seem easy to you are not so for others.
But that doesn't mean we can't learn.

My ultimate goal is to have great sounding gear & an understanding of it so I can make great music!
I'm a Musician & Engineer 1st... then a tech.

I'm also a cool & sharing dude... despite what some might think.

 

[khstudio]

Well I finally finished my Pultecs... check um out:
My 3 DUAL PULTECs - EQP-1a3 - Solid State
http://www.groupdiy.com/index.php?topic=359989

I just want to thank EVERYONE who took the time to help me out :thumb:
:guinness: :sam: :guinness:
(Weather I used your idea's or not... I still learned a lot & ended up with some KILLER sounding Pultecs.)

 

[emrr]

Due to space constraints, I had need to put an active buffer/driver in front of a Pultec style mid-EQ filter, so I put a THAT1246 in front of a THAT1646 in this configuration.  It's working very well, and not breaking a sweat at any filter setting.    I had two of this filter temporarily running with no buffer, single ended, just a 620 ohm input shunt as is normally found on the secondary of a 600:600 transformer.  Ear comparisons with the passive input variation revealed no fingerprints from the 1246/1646, and filter action remains essentially the same.  If there's any additional 1st filter gain range, it's very tiny.    I don't see any need to use build-out R between 1646 and filter at all.  I put them on those handy little Rat Shack 1.5"x1.5" IC perf boards, and floated them above the main board on a longer stand-off.  Space was so tight I had to cut the Rat Shack boards down as much as possible to make this happen. 

 

[mikeyB]

Sorry if this should be a new thread (but moderators - feel free to move if required), but i,ve had the drive problems that Kevin had in the first post, so i think it would be useful to continue here!

Built 2 dual channel  pultecs using ioaudio inductors and initially the NE5532 drive and makeup stage over at NRG,s site.
My units work good at low boost/cut settings but seem to crap out at higher settings. Not been too much of an issue for my mastering engineer,s unit as he uses just to tweak final mixes but for both of us a pain in mixing at higher settings.
Recently had the fortune of repairing a langl*vin single channel unit (hi boost switch had died - not the first grayhill i`ve had to replace! - really had to chop it up to preserve the circuit board!). Anyhow - replaced the switch and proceeded to do an a/b comparison of the lang against my unit. Wow! - the lang just totally pi**ed over my unit - much more solid and aggressive but sweet at higher settings!!!

So - what was at fault? - the filter or interfacing, or both?

Broke into the lang with a toggle switch so that i could A/B the filter circuits using the lang interfacing and BANG! - the filters were incredibly similar, albeit a bit of frequency jumping due to absolute cap/inductor values in the high boost section - more than chuffed with the filter sections!

So - onwards!
My mastering man wants to proceed with solid state( he,s got plenty of valve flavour i built him) so will probably proceed with the jlm hybid opamp solution as outlined in the previous posts.

For my unit, however, i would like to make this a valve pultec.
Now, as i understand it - the drive required for 600R input is pretty hard for a lot of modern gear and i`ve seen the recommendations to ease the input load with a step down input tx. Seen a 10k to 600R mentioned but the gyraf SRPP would struggle to make up the difference.

I`m considering two options:
1) Use a 2k4/600 input tx and gyraf SRPP output makeup and match the in circuit/bypass(still through the in tx and srpp) resulting in an overall reduction of signal level through the unit.
or
2)Use either 10k/600 or 2k4/600 input and a set G9 make up amp - hopefully keeping the same overall level through the device. Would input at the DI jack pre 1st stage.

Any thoughts aprreciated - thankyou!

 

[mitsos]

No idea on your problems, but if the filter is working properly, then it could only be the in or out amps.  FWIW, member PPA has done a solid state I/O PCB for use with passive EQs.  For input, the simplest is a 600:600 trafo, HS56 or similar.

for another tube output option, check the 6n6p line stage Kingston posted a while back. 

in this thread:
http://www.groupdiy.com/index.php?topic=39842.0

 

[mikeyB]

Well I finally finished my Pultecs... check um out:
My 3 DUAL PULTECs - EQP-1a3 - Solid State
http://www.groupdiy.com/index.php?topic=359989

I just want to thank EVERYONE who took the time to help me out :thumb:
:guinness:  :sam:  :guinness:
(Weather I used your idea's or not... I still learned a lot & ended up with some KILLER sounding Pultecs.)

Hi Kevin, just tried the link but dead - do you have a final schematic of the pultec - want to know what the best flavour for the output amp?

 

[JW]

hey MikeyB

I just got done pulling out my Gyraf srpp amps to replace with 2520 amps per the SS pultec schematic posted here at some point. I don't know exactly which schematic you have but I can send the one I have for you to compare.

After some listening, I found I preferred the SS pultec amp to the SRPP amp. Seemed a little more open to me. I'm using a cinemag CMOQ-2s on the outputs, and the Sowter 3603 (I think?) on the inputs.

But I really wanted to build up the original valve circuit. Probably will at some point.

This is just heresay, but it seems like I've heard a few folks say the the EQP-1A and EQP-1A3 can sound pretty similar. I wonder if that's true.

 

[mikeyB]

hey MikeyB

I just got done pulling out my Gyraf srpp amps to replace with 2520 amps per the SS pultec schematic posted here at some point. I don't know exactly which schematic you have but I can send the one I have for you to compare.

After some listening, I found I preferred the SS pultec amp to the SRPP amp. Seemed a little more open to me. I'm using a cinemag CMOQ-2s on the outputs, and the Sowter 3603 (I think?) on the inputs.

But I really wanted to build up the original valve circuit. Probably will at some point.

This is just heresay, but it seems like I've heard a few folks say the the EQP-1A and EQP-1A3 can sound pretty similar. I wonder if that's true.

Hi JW - can't find the ss pultec schematic - dead links - could you please pm me the schem?
Thanks
Mike

 

[frans]

BTW I wanted to say THANK YOU for everyone contributing - I'm gathering information for my solidstate Pultec and appreciate all your efforts.