jeroddumas

Gyraf Pultec without output trafo???
« on: July 07, 2005, 04:46:31 PM »
Is it possible to do the pultec without the output trafo???
genius is the highest level of insanity


CJ

Gyraf Pultec without output trafo???
« Reply #1 on: July 07, 2005, 05:39:22 PM »
yes.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

jeroddumas

Gyraf Pultec without output trafo???
« Reply #2 on: July 07, 2005, 05:44:39 PM »
How will it affect the unit besides the sound??
genius is the highest level of insanity

CJ

Gyraf Pultec without output trafo???
« Reply #3 on: July 07, 2005, 06:13:47 PM »
it will be cheaper.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Bjorn Zetterlund

Gyraf Pultec without output trafo???
« Reply #4 on: July 07, 2005, 06:42:37 PM »
You get more output level, but less drive capability since you don't have the 2:1 'gearbox' that is the output transformer (assuming you mean the gyraf version of the pultec?).  You could still make it a ground compensated output and it would probably do just fine into 10k loads.

Bjorn

chrissugar

Gyraf Pultec without output trafo???
« Reply #5 on: July 08, 2005, 04:41:56 AM »
All my Pultecs (the stereo mastering one and the three mono ones) have transformer and transformerless output. They work fine at the transformerless out, the only restriction is that you can't load them with low impedances. If the next stage has 10K input Z it will work perfectly.
Just don't try to load it with some wintage 600 ohm input Z gear.

chrissugar
Christian Mike Sugar
        CMS-LAB

martthie_08

Gyraf Pultec without output trafo???
« Reply #6 on: July 08, 2005, 05:43:54 AM »
chrissugar, that is really interesting, how do you wire it for trafoless output, do you just grab the signal before it hits the output trannie?

Having a quick look at the Gyraf Pultec Schematic - where did Jakob leave the interstage transformer? Seeing that the input trafo is optional as well, does it mean you build it totally without audio signal transformers?

gyraf

Gyraf Pultec without output trafo???
« Reply #7 on: July 08, 2005, 06:47:27 AM »
Quote from: "martthie_08"

Having a quick look at the Gyraf Pultec Schematic - where did Jakob leave the interstage transformer?


Not needed if you don't run the push-pull stage anyway. Interstage trafo was originally a simple way of doing a phase splitter for output stage:

http://www.gyraf.dk/gy_pd/pultec/pultech.gif

Quote from: "martthie_08"

Seeing that the input trafo is optional as well, does it mean you build it totally without audio signal transformers?


Yes.

Or you could build the filter stage only, and use anything that has some 20dB gain to up the level..

Jakob E.
..note to self: don't let Harman run your company..

chrissugar

Gyraf Pultec without output trafo???
« Reply #8 on: July 08, 2005, 09:18:58 AM »
Quote from: "martthie_08"
chrissugar, that is really interesting, how do you wire it for trafoless output, do you just grab the signal before it hits the output trannie?


I take the signal after the output condenser. It is a good idea to add a 50 ohm resistor (between capacitor and output jack) to isolate the output from the capacitive load of the cable. It is also a good solution to use a jack with switch to disconect the transformer when you use the transformerless output.
I remember I read an interview with Tim de Paravicini (designer of EAR high end equipment) where he said that he don't use input transformer in he's Pultec eq. Signal goes directly into the passive network.

Quote from: "martthie_08"
Having a quick look at the Gyraf Pultec Schematic - where did Jakob leave the interstage transformer? Seeing that the input trafo is optional as well, does it mean you build it totally without audio signal transformers?


Jakob's Pultec is not a clone of the real thing. The filter is exactly like the real Pultec but the makeup gain circuit is a smarter, cleaner and simpler one. You can do what Jakob sugested, build only the filter part and use any circuit (tube, fet, transistor) for makeup gain.

chrissugar
Christian Mike Sugar
        CMS-LAB

martthie_08

Gyraf Pultec without output trafo???
« Reply #9 on: July 08, 2005, 09:50:01 AM »
thanks guys, I think I will build the tube stage anyways, the srpp design  looks interesting, although I will have to do some more reading to fully understand it. At least now it is clear to me, as to why there is no interstage transformer.
How important to sound / stability is the particular model of ecc88 in this circuit? I was planning on going for a E88CC JJ Red Label, I have had great success using JJ's current production 6V6GT in my guitar amps and they are not as expensive as NOS...


clintrubber

Gyraf Pultec without output trafo???
« Reply #10 on: July 08, 2005, 10:40:26 AM »
from Chris:
Quote
I take the signal after the output condenser. It is a good idea to add a 50 ohm resistor (between capacitor and output jack) to isolate the output from the capacitive load of the cable. It is also a good solution to use a jack with switch to disconect the transformer when you use the transformerless output.


I thought I've seen you mentioning this as well for some other circuits (JFP ? API... ?).
Looks like a nice solution, that switched jack.

But that 50 Ohm is then still in the signal path when you use the TX-out, right ? Or do you use one of those output-jacks with 'isolated' switching from the TRS-pins (so that you can short the 50 Ohms when going TX) ?
I figure that 50 Ohm resistor won't matter with a big TX, but for lesser TX, how fast would it become in influence ?

Regards,

  Peter

snaper

Re: Gyraf Pultec without output trafo???
« Reply #11 on: March 18, 2015, 10:56:57 AM »
Old topic sorry about revivification, but was just playing the transformless pultec idea with a simple opamp gain stage.

Am I correct if Im thinking about something like this :


gyraf

Re: Gyraf Pultec without output trafo???
« Reply #12 on: March 19, 2015, 01:52:48 AM »
yes...

..note to self: don't let Harman run your company..

snaper

Re: Gyraf Pultec without output trafo???
« Reply #13 on: March 19, 2015, 03:01:36 AM »
yes...
News of the day for me, thank you !!!


 

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