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

[Jonkan]

I guess i have to try it and see if i like it!
Thanks.
/J

 

[emrr]

Thanks Joe, you stated all the bits I was wondering about. Everyone have a look back at page 6 if you missed it.

 

[khstudio]

UPDATE

The JLM Hybrid is AWESOME on the input!

It took a while, but I hand wired 1 Hybrid with a switch to test the Class A & A/B, also a jumper to turn the Servo ON/OFF.

Joe was right... I did NOT need the Servo or any Caps.
Offset was like .1 mv
& with the Servo it was -.3 mv

I also tested with & without the 620 ohm resistor:
It sounded better without it. The difference was slight but was there.
It also had no major effect on the level or the way the controls worked.

I should mention that I took out the Cinemag 15k:15k TX's & set up 1 channel with "correct" 600:600 TX (& 620 Secondary Load) & the 2nd channel with the Hybrid (NO Load).

BOTH channels are cool... but I have to say that I keep favoring the Hybrid. It's just plain nice & almost perfect sounding & feeling. It's cleaner & more defined but not harsh & sterile. It is just more tight & accurate & if I decide to keep the Hybrid, it is COMPLETELY UNIVERSAL & I don't have to worry about what I'm connecting it to. :green:

CLASS "A" Mode was the best to my ears.
The Hybrid is set up for UNITY GAIN, just like I posted (Joe's Email)

Joe's description of the sound also matched what I heard when comparing the TX to the Hybrid input.

Thank You EVERYONE :!:
For your patients & advise. :thumb:

 

[khstudio]

After getting some rest, I did a few more hours of testing & listening I really like both the Hybrid & 600:600 TX on the input.
The Hybrid just works EVERYWHERE... Driven by my Pre's, Unbalanced 10k inserts & will probably help my MAIN Outputs (still untested) - which are driven by 5532's (Unbalanced)

On the other hand... the 600:600 TX on the input with the 620 load has a nice flavor... distortion or not it's pleasant & IS more interactive feeling & sounding than the Hybrid. Lows have a little more Umph & Growl, & the Highs are more colored & smooth.

For now, I've only been able to test the TX Input by driving it with my Mic Pre's & DA Converter... which seem to handle the Pultec's load.
I didn't want to do anything with the "Buffers" yet until I decided on the Hybrid (which will serve ALL my needs & connectivity)

OK...
So I have these nice Cinemag 1:1, 15k:15k Line input transformers.

I'd like to try them in front of the Hybrid but once again... I could use some advise. I'm curious if it will give me a little more "Flavor" along with the versatility when combined with the Hybrid... I'm sure the CMRR will improve.

Below is how I have the Hybrid wired now.

Can I just add the Cinemags to what's draw or should it be changed to work correctly or even improve what I have now.

I did find this from JENSEN (thanks JC)
http://www.jensen-transformers.com/as/as003.pdf
But in the NOTES it mentions the Damping & 10k...
I'm not sure what to do with regards to this?
Should I load the secondary or leave it open when connecting to the Hybrid (As drawn above) ???

Once again, Thanks for helping. :grin:

 

[ioaudio]

hi kevin,

i f i may suggest something:

use the 15k:15k as an interstage transformer, after the filter section, before the make up amplifier, just like in a real (tube) pultec.

http://www.purpleaudio.com/pdflib/PultecEQP.pdf

-max

edit:schematic link

 

[drpat]

Hi Max,

Just to avoid further confusion, the schematic link that you posted is not for a real Pultec. Actually, Kevin's unit would be closer to a real Pultec "without" the interstage transformer, as the solid state units didn't require one...

 

[ioaudio]

thanks pat,

i edited the link. what i meant was the tube unit eqp-1a.
i thought kevin was looking for a use of his interstage transformer, and this would be a further thing to try. (galvanic isolation for the filter section)

-max

 

[khstudio]

Somehow I managed to blow up one or both of my BD139 & 140's. :sad:

Since I just wired it by hand I think I got a short somehow when moving it around & testing. Sadly I only had 1 pair... but I do have some BD135 & BD136's... Will these work OK in the Hybrid amp circuit ???

I do plan on buying some from JLM but wanted to finish testing first.

I could also still use some advise on connecting my Cinemag 15K:15K Input TX's in front of the Hybrid. The main thing is I'd like to have (& hear) the TX's doing the De-balancing but I think the way I wired it (posted earlier) may not work correctly. If I'm right, that wiring is set up for the IC to De-Balance (& for Unity Gain which I still want).

Could someone PLEASE help me out on this? :green:

 

[rodabod]

[quote author="khstudio"]
I could also still use some advise on connecting my Cinemag 15K:15K Input TX's in front of the Hybrid. The main thing is I'd like to have (& hear) the TX's doing the De-balancing[/quote]

Wire the 15K:15K at the input so that your gear plugs straight into the primary. Wire the secondary to the hybrid opamp configured as a voltage follower (very simple) with the top of the secondary going into the opamp, and the bottom tied to ground. Attach 10K across the secondary of transformer to reflect back a suitable impedance. Search for "voltage follower" if you are not sure how these are wired.

 

[khstudio]

Thanks Rob... I'll do a search on the Voltage Follower info.

I just need to get my Hybrid circuit working again.

Do you know if the BD135 & 136's will work in place of the 139 & 140?

 

[rodabod]

[quote author="khstudio"]
Do you know if the BD135 & 136's will work in place of the 139 & 140?[/quote]

I honestly couldn't say as I don't know the circuit that well, nor do I know about various transistor types. Maybe see if you can find what the differences are. Or just try it.

 

[Harpo]

BD135/137/139 and complimentary BD136/138/140 only differ in Vceo 45, 60, 80V and Vcbo 45, 60, 100V in prementioned order. For usual op-amp supply voltages (dunno your schemo) all should be suitable.

 

[khstudio]

[quote author="Harpo"]BD135/137/139 and complimentary BD136/138/140 only differ in Vceo 45, 60, 80V and Vcbo 45, 60, 100V in prementioned order. For usual op-amp supply voltages (dunno your schemo) all should be suitable.[/quote]

Here's the Circuit:

http://jlmaudio.com/JLM Hybrid Opamp circuit.pdf

 

[khstudio]

[quote author="rodabod"][quote author="khstudio"]
Do you know if the BD135 & 136's will work in place of the 139 & 140?[/quote]

I honestly couldn't say as I don't know the circuit that well, nor do I know about various transistor types. Maybe see if you can find what the differences are. Or just try it.[/quote]

I did try it (because I remembered people interchanging them in the Gyraf 1176) ... just wasn't sure if the Hybrid circuit had certain NEED's for the 139 & 140.

Anyway, after the swap to the 135 & 136's & a new 2604, it still didn't work. I'm still looking it over but can't seem to find the problem... but I don't give up to easily.

 

[khstudio]

Found it... the most microscopic solder bridge I've ever seen

You can't rule anything out but damn... I rechecked everything for HOURS... O well.

Anywho... for some reason... the 135 & 136's in installed don't seem as nice as I remembered the 139 & 140's being.

I'm gonna put the 139 & 140's back (hopefully they are OK & it was the solder bridge) Then move on to adding the Cinemag, to see if it sweetens things up a bit more.

 

[rafafredd]

I see you were using some 2520's for the gain in the pultecs. Well, 2520's would work great in front of it as well. You could go cinemag to 2520 (yes, they work at unity gain, and also, they were MEANT to drive 75 ohms optimally on the original API circuits) then filter, then 2520's again then the tamuras. this way, you keep it the same api color on the input.

 

[khstudio]

[quote author="rafafredd"]I see you were using some 2520's for the gain in the pultecs. Well, 2520's would work great in front of it as well. You could go cinemag to 2520 (yes, they work at unity gain, and also, they were MEANT to drive 75 ohms optimally on the original API circuits) then filter, then 2520's again then the tamuras. this way, you keep it the same api color on the input.[/quote]

I wish I had enough to do that but they're all spoken for.

 

[khstudio]

[quote author="khstudio"]Found it... the most microscopic solder bridge I've ever seen

You can't rule anything out but damn... I rechecked everything for HOURS... O well.

Anywho... for some reason... the 135 & 136's in installed don't seem as nice as I remembered the 139 & 140's being.

I'm gonna put the 139 & 140's back (hopefully they are OK & it was the solder bridge) Then move on to adding the Cinemag, to see if it sweetens things up a bit more.[/quote]

I put the 139 & 140's back in + a NEW 2604 & it sounds MUCH "Sweater".
The Hybrid must like the 139 & 140's best. :idea: So they didn't blow. :green:

I've got a mix up from last nights session that sounds great already... so I'm gonna dump down a few mixes with & without my new Dual Pultec to see what it can do.

 

[drpat]

OK, so to get things straight, you ended up with the following configuration, right?

Cinemag 15k:15k -> JLM Hybrid -> Pultec filter -> Pultec SS amp -> Tamura 250:600(?)

 

[khstudio]

[quote author="drpat"]OK, so to get things straight, you ended up with the following configuration, right?

Cinemag 15k:15k -> JLM Hybrid -> Pultec filter -> Pultec SS amp -> Tamura 250:600(?)[/quote]

Didn't get to the Cinemag 15k:15k yet... just got the Hybrids working & I've spent the last few hours listening to the output caps.
I've had Tants installed (Like the original SS Pultec) but damn... they ALL sound different when trying to get a matching pair for a Stereo Unit.

So far, I liked the Tants, FC's (pretty close to open, no cap) & PW's... a little warmer & nice.

I'm wondering what the "Original" Military ($25) Tants would sound like. :?:
How consistent are they Pat?

The Tants (When I found good sounding ones) have a nice, cool shape, Punch & cut. Out of the 4 new ones I bought, only 2 sound good... 1 is Great & the other close but probably not close enough for Stereo. :sad:

I DO like it totally bypassed (No Cap) but the DC is about -144mv - FABIO's 2520's

Now... I've been thru this before but I have to ask, how much is too much DC??? These are FABIO's 2520's from the LAST batch.
The TAMURA Output TX's are 600:600 STEEL CORE & are slightly larger than what's used in an API 312. (Which also does NOT use a Cap)

It's nice to finally have it completely up & running so I can do these final "Shaping tweaks" Like everyone says - It's ALL about the AMP & the sum of all parts... What a huge impact the Output cap has on the whole thing.

Decisions Decisions.

I am going to leave the Hybrid on the input & try it for a while before messing with the front end anymore + it doesn't create any loading issues no matter what I plug into it.