BA-3 As Preamp

[Zen Mod]

according to sim , stock is close to 20db

dunno , didn't check in vivo , have too small number of Toshiba mosfet critters in drawer

 

[nashbap]

just use simple proportion calculus , to know what value of R13 you need for desired gain

Thanks ZM, AndrewT and Hikari1 for your comments.

If I understand my ZM speak correctly, increase R10 and decrease R13 by similar percentages from schematic values to get the desired voltage gain/db reduction?

Hikari1 my question about db for the BA-3 is because I plan on building an F6 and may need a preamp. I am presently using my F5TV3 with 27db gain and an AVC (thanks ZM for this:AVC & Input Selector for Papa's Koan M2) and at very loud volume I use -9db attenuation.

BTW, F5TV3 with Toshiba Mosfets and an AVC sounds very, very good indeed.

Nash

 

[Zen Mod]

leave R10 (and R11) as is , load those output buggers , decreasing R13

 

[Russellc]

I'd be careful here...I built the BA-3 w/stock gain and it was way less than I expected. Feels/sounds more like 15db gain to me, stock. Which is kind of what Zen Mod is saying. I find it perfect w/the F5 at stock gain. Not noisy and when cranked up loud I use 80% of the volume dial.

I find stock gain, whatever it is fine as well.

Russellc

 

[nashbap]

leave R10 (and R11) as is , load those output buggers , decreasing R13

Thanks. Will then decrease only R13 if gain is too much, leaving all else same as in schematic.

Nash

 

[Hikari1]

I think the F6 as less gain than the F5. You will probably need all the gain the ba3 has...unless you have really efficient speakers or a small room.

 

[gior]

...

I just put your values in LTS sim of BA3 FE I already had

...

Would somebody have the spice models of the toshiba Mosfets. I found one for the N channel once but couldn't find the P channel one.

Thanks

 

[Zen Mod]

extract this and replace standard.mos file in LTSpice cmp directory

you can rename old one (say oldstandard.mos) to keep it , just in case

I got models from Generg , just put them on end of file

 

[gior]

Thanks.
I'll try it this evening.

 

[AndrewT]

How do we open a .mos file?

 

[Stopher]

just open it directly with ltspice or replace the original in the lib/cmp dir like zm was saying. im pretty sure its essentially just a text file..

edit: thanks btw, I've been looking for the 2sk2013/2sj313 models for a while now 😀

 

[AndrewT]

OK, I moved the .mos file to lib sub directory, in Andrew. Not in LTspice because my PC won't let me work in LTspice. Access not permitted.

 

[gior]

It works for me too.
Thanks again

 

[JLOP]

Hi all

Little question about output offset : shouldnt It be measured accross R13 instead R12 as stated ? I got only 1 mV accross R12 ?

 

[Zen Mod]

ref. to which schm. exactly ?

 

[JLOP]

Nelson's schematic ZM
http://www.diyaudio.com/forums/diyaudio-com-articles/194809-burning-amplifier-ba-3-a.html

"as stated" is in SL6 build guide

 

[Zen Mod]

Hi all

Little question about output offset : shouldnt It be measured accross R13 instead R12 as stated ? I got only 1 mV accross R12 ?

across R13 , or R12-R13 node and gnd

gnd is what's important in equation

 

[JLOP]

OK Thanks ZM, you are reassuring me. I will suggest SL6 to update his excellent build guide for newbies (;-)

 

[Zen Mod]

whatever

practically , either across R13 or between any end of R12 and gnd

 

[gcolnaghi]

Today i completed my build. Sound is very promising .... 😱😱😱
Here few pics.

Best regards Gio