Introducing the MAGMA front end for BA-2 and F4

[generg]

Sorry, Mr. Pass when the question was inadequate ........😱

 

[generg]

I bought two Lundahls 1674, connected primary and secondary windings to an autoformer and use them with a pair of modified F4.🙂

The sound has not the charm of the Semisouth solutions concerning the voices but in the sum it is a very very good solution!
It is a detailed, yet relaxed sound with much atmosphere.....🙂🙂🙂

 

[generg]

I followed Nelson recommendation to try different transformers...😎

This time I tried Jack Ellianos PVA2-N from his Electra Print...

He recommends it as a transformer pre with a 10k pot

Electra-Print.com PVA Passive Audio Pre-Amplifier

I put it the crippled F4 as a gain stage, wired it as an auto former and......

I like it much more than the Lundahl 1674.......😀

and it costs only the half .....! (Lundahls 200.-€/ElectraPrint 120$)😀

So if you want to have a try I recommend you to start with Electra Print!

 

[albertNL]

B1 - trans/autoformer - F4?

As I was reading this thread, I could not stop wondering if positioning a trans/autoformer between a stock B1 and a stock F4 would give you a "B1 with gain" (or an "F4 with gain" depending on how you look at it)?

Would this work?

 

[Zen Mod]

yeah
especially if you use F4 (side) without Jfet buffer
thread is exactly about something like that and it's mentioned already as "crippled F4"

 

[Nelson Pass]

You mean liberated F4 don't you?

😎

 

[Zen Mod]

it can be liberated when you do this , but when ZM is in case ....... it can only be crippled .....

 

[generg]

ha, ha....

really two different points of view....!😀😀

 

[generg]

yeah
especially if you use F4 (side) without Jfet buffer
thread is exactly about something like that and it's mentioned already as "crippled F4"

or if you need a higher input impedance put it between the buffer and the output stage.... that should work at least with the bootstrapped F4....



and thanks to audiorob again...!

 

[Zen Mod]

ha, ha....

really two different points of view....!😀😀

there are just two groups here ;

one is Greedy Boyz group ;

other one is Papa group ;

considering that Papa group contains just one member , conclusion is simple - where Mighty ZM belongs .....

I call that some distinction ..... and that's why is there other one , regarding liberation and crippling

 

[albertNL]

yeah
especially if you use F4 (side) without Jfet buffer
thread is exactly about something like that and it's mentioned already as "crippled F4"

Thanks for the reply Zen Mod.
I had a look at the M2 manual and see that the arrangement is B-T-O (B=buffer, T-transformer, O=output stage). I understand that the output of T is enough to drive O.

Still a few questions though (sorry, I have an inquisitive mind).

1.
In the F5 the first stage performs voltage gain as well as impedance conversion (I assume). Not so in the F4. There it only does the latter.
In the F5 the input impedance in 100KOhm. I asume this to be due to the characteristics of the 1st stage. Is that correct?

2.
The B1 performs 3 functions:
- impedance conversion
- volume control
- input selection

Would a simple passive source-selector and passive volume control be better than a B1 as a front-end for an F5 (or any other poweramp with high input impedance)?

I guess the questions is:

is the output of a 25K or 50K pot (or equivalent circuit) too small to drive an F5?
​

Thanks,

Albert

 

[generg]

I can contribute that the transformer makes voltage gain in M2 but no current gain, current even goes down.... but this seems to be no problem for the following stage.

 

[Zen Mod]

I time when thread started , I posted a smile as post #2 ...... but completely forgot to post about my play with Papa's Koan , about 6-7 months earlier :
http://www.diyaudio.com/forums/pass-labs/174674-papas-koan-papas-surprise-2.html#post2356057

and yes - my GE Generg remind me few moments ago about this thread 😉