Gyraf Pultec without output trafo???

[jeroddumas]

Is it possible to do the pultec without the output trafo???

 

[CJ]

yes.

 

[jeroddumas]

How will it affect the unit besides the sound??

 

[CJ]

it will be cheaper.

 

[Bjorn Zetterlund]

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]

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

 

[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?

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]

[quote author="martthie_08"]
Having a quick look at the Gyraf Pultec Schematic - where did Jakob leave the interstage transformer?[/quote]

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 author="martthie_08"]
Seeing that the input trafo is optional as well, does it mean you build it totally without audio signal transformers?[/quote]

Yes.

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

Jakob E.

 

[chrissugar]

[quote author="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?
[/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 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 author="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?[/quote]

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

 

[martthie_08]

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]

from Chris:

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]

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]

yes...

 

[snaper]

yes...

News of the day for me, thank you !!!

 

[calvinjosephalex]

Hey there!
I'm kinda new to electronics and I'm trying to build the gyraff pultec. I've got all the parts except for the 2 power supply transformers. I thought of winding them from a friend. What are the specifications I need to tell him. What kind of transformers are those (step up or step down) Someone please help. I really want to make this. This has been my dream for such a long time now.

 

[solkatten]

Its very practical solution to build only the filter in passive unbalanced box. Inductors are very prone to pick up noise.

I have build a passive stereo Pultec to freind of mine it works great in DI or line in connection.

 

[calvinjosephalex]

Its very practical solution to build only the filter in passive unbalanced box. Inductors are very prone to pick up noise.

What should I use for the transformers. I mean the power supply. Do you have any idea???

 

[solkatten]

What should I use for the transformers. I mean the power supply. Do you have any idea???

Hi you have schematics gyraf.dk
Its 2 standard pri: 230v sek: 12 v toroidal power Trafos

 

[solkatten]

Hi you have schematics gyraf.dk
Its 2 standard pri: 230v sek: 12 v toroidal power Trafos

If your freind is goding to Wind a trafo. Primary voltage depends on where you live secondary voltage 230v and 12v. Power rating 30VA

 

[calvinjosephalex]

Ohhhh but should we use toroidal transformers. Is there any problem if we use 2 ordinary transformers. 230: 12 and 12: 230 as specified in the circuit