"single ic and input trafo preamp"...

[oragall]

Hi, today finish my 2 first green pres and  in few days more i upload photos ....


Now i like continue in a new proyect using  transformers, i thing in  312 preamp or others , but here in my conuntry not sell the apropiates transformers.

I looking the internet and found a jensen shematic based in one transformer with ratio 1:4  and one NE5534 IC, this preamp see easy.
this is the link of the proyect.

http://www.jensen-transformers.com/as/as017.pdf]http://www.jensen-transformers.com/as/as017.pdf


Now work this preamp with any 1:5 transformer with ajusting the zobel network ?
and any prove if the preamp work well and the sound its good?




pd: the green preamp work increible (incredible).

 

[3nity]

Yes.

 

[skipwave]

[quote author="oragall"]Now work this preamp with any 1:5 transformer with ajusting the zobel network ?[/quote]

Yes, the transformer's datasheet will provide appropriate zobel network values.

[quote author="oragall"]and any prove if the preamp work well and the sound its good?[/quote]

The proof is in the building. Because it is from Jensen you can be sure the design is good and adequately overdesigned to make their transformers look good. After all, what good would it do them to post a design that made their product perform poorly? (For the peanut gallery, I know this logic does not always hold true; Buyer Beware)

By the way, if you aren't into perfboard or veroboard, this design would be very easy to build on JLM Baby Animal PCB:
http://jlmaudio.com/Baby_Animal_Mic_Pre.htm

 

[oragall]

tnx...
i dont decide to the next proyect... if i do this, need make de pcb, good for me because ner diy a pcb. Now hve only two options of transformer, the first and the best is a OEP transformer, and the second is a Neutrik NTE4.

 

[oragall]

i study this proyect and write some lines with samples of the idea.....

the trafo :

OEP262A3C  1:6.45


the formule of gain its
gain : 20 log (15K/150ohm) + trafo gain  ?????

if is thrue the gain of this shem. is 57 db. i need ajust to 60db....

what do toy thing... its a good proyecto to relize??? work or not work????

 

[PRR]

> OEP262A3C    1:6.45
> trafo gain  ??

Use the same formula as the amplifier gain.

> the formule of gain its  gain : 20 log (15K/150ohm) + ....

The amplifier voltage gain is the ratio of the two resistors, 15K/150= 100.

The transformer voltage gain is the turns-ratio, 1:6.45

The total gain is 100 * 6.45 or 645.

Then do the "20 log" conversion to dB numbers: 56dB

> if is thrue the gain of this shem. is 57 db.

So you knew how to compute transformer gain. 

> i need ajust to 60db....

A) "No you do not." You rarely need 60dB gain in modern audio. When you do "need" 60dB gain, 56dB or 57dB will work just as well. You can make any final level adjustments in the mixing.

B) You still say you want 60dB. OK. You want gain of 1,000. You have transformer gain of 6.45. 1000/6.45 = 155, the gain needed in the amplifier. If 15K/150 gave gain of 100, then 15K/98 will give gain of 155 in the amplifier and 1,000 or 60dB overall.

----------------

If you are recording harpsichord with ribbon mikes, you may need 60dB or more. Pop music on dynamics uses more like 35dB-45dB. Rock music on large condensers may be 15dB-25dB, or less.

"(15K/150ohm)" - The real formula is (15K+150)/150ohm, or 15,150/150, or gain of 101. We don't care 100 or 101. But if you change 150 to 15K, to use for loud rock, the gain is not 15K/15K=1, but (15K+15K)/15K= 2, which is different enough to matter.

 

[oragall]

tnx prr ... now its clear how to calcule the gain... you have reazon and not change the gain of the idea.


the shem. see good or maybe have problems?? the idea is copy the shem to pcb and then diy a good preamp.

 

[PRR]

> the shem. see good or maybe have problems??

Medium ratio transformer into a NE5534 was good enough for many-many broadcast and recording consoles. Nothing wrong with the basic idea.

The NE5534 must have power pin decoupling capacitors to ground very close to each power pin. Someone else may have more experience. In general, I would put two 10uFd 25V caps from power pins to power ground within 1 inch (2.5cm) of the chip, and also two 100uFd 25V caps where power comes onto the board, unless your power supply (which has big caps) is within 6 inches 15cm of the board.

I would not use the diodes. YES, I once lost a good hand-built analyzer because my helper put the batteries in backward. But here you only have one $2 chip. Be careful when you connect power. Use two 47 ohm resistors between the chip+10uFd caps and the 100uFd caps.

 

[oragall]

tnx again prr... now im going to traslate the pen to pc shematic and then do the pcb.




The idea of this preamp is do and "invent" my preamp study the operation of that thinking in old consoles with a coloured sound of transformer.
Other idea of this preamp its do a good proyect of low price and easy to do with good sound to record guitars, bass, and o ther instruments with microphone.

 

[oragall]

First impresion of PCB... include the phantom swish....


looks good? any comment??
how to determine the tipo of potenciometer to use??? log, rev log, linear.? or use a lorlin swish to change the db?

 

[oragall]

Actualized 3.0 ... corrected some things of the anterior pcb now i thing  is ok the pcb.

 

[PRR]

Reverse Audio.

 

[Arno]

as prr and the jensen notes say you need 10K Reverse Log potmeter.

This is probably the hardest part to find for your project.

You can get them from http://www.omeg.co.uk/
But that seems a little far from your location.

There's a description at http://www.gyraf.dk/gy_pd/calreq/magnus_j/rebuilding_pot.htm
You can build a mono rev log pot from a stereo log pot and a mono log/lin pot by replacing the right tracks.
The rear track on a log pot is actually a reverse log track because it's mirrored.


gr
arno

 

[oragall]

need change the pcb its no 100% good... un few hours more ...


Tnx fot the reply.

Yes is thrue, the part more hardest its the pot, here no sell in my country but, the more ease to obtain the rev. here in chile is change a  log pot with the gyraf metod.



But if I use a lorlin 12 potitions with a determinated resistor ???? Work or nor work good?

 

[3nity]

you can get them from Small Bear Electronics in the states..

 

[Arno]

But if I use a lorlin 12 potitions with a determinated resistor ???? Work or nor work good?

I think lorlins are non shorting.
The jensen paper says to use shorting switches.
Though I don't really know if there would be a big difference.
I think the reason to use shorting switches is to avoid the loud "plop" you'd hear when changing gain.
(someone correct if this is wrong  ???)

You'll have to recalculate the resistor values if you use a 11 position switch too.

gr
arno

 

[gyraf]

Lorlin switches are available in both shorting and non-shorting.

Jakob E.

 

[maxwall]

Is it possible to take a regular 10K log and reverse the connections on the pots solder lugs so when the pot is turned clockwise direction the resistance will decrease instead of increase ? Hence reversing the taper direction to obtain your reverse log pot ...

 

[oragall]

now actualized the pcb with corrected errors.

Tnx all ... and the date of smallbear its exelent... maybe i can obtain some of this



now i buying some components....

the idea go!   

 

[oragall]

now i put the list of component.. now im  developing the pre.



In the zobel network... how its better 820pf or 680pf... ???? in the forum recomend 800pf to oep a3e, but only have the numbers of capaciors before mencioned.