Fishy Babbelfish revisited

[cviller]

Well, I completed my version of the babbelfish a few months ago and took it for a small road tour to visit friends and family. Comparing the sonics to mid-end amps was just such a blast!
My brother wanted me to build him one, so I did. However in between I finished the F4 and was surprised how little noise it produced. It got me thinking and also the layout published in the service manual gave me a few pointers on how to better my design.
GRollins has also given many useful pointers on using jfets and I have tried to absorb some of that information into my

Changes:
- The input seemed very sensitive to fiddling with cables so I lowered the resistor values in the input and feedback.

- I removed the decoupling capacitors because I had a hunch they only provided noise to my signal ground.

- The input ccs was changed to aleph style with irf9610 and zener.

- And a few other small changes to make it more like aleph30.

- Source resistors on the 2sj109 input pair was reduced to 4R7 to get better bass

I started soldering Friday and delivered it Saturday, so I had little time to testing and comparing it to my other amps.

In overall it turned out pretty good. The bass is definitely louder and noise is greatly reduced. The turn off thump is also removed. I suspect the ac gain might be slightly too high, but I didn't have time to check it.

As mentioned, I didn't have time to thoroughly compare it to my own babbelfish, but to my ears it sounds better. A very nice amp indeed!

I have attached the schematics.

[cviller]

Inside

[cviller]

Front. Chassis is from www.hifi2000.it - very nice to work with.

[Magura]

Hey, you're gaining in on me and Steenoe....we only make like 4 amps a year....you seem to run a factory at home

Nice work.

Magura

[JC Fardo]

Hello Cviller

Thanks for share pics and schematics.

What PCB did you use and where did you get 2sj109 devices?

Your amp uses 4 output IRF240 while Zen-mod's uses 2 IRF150N, I think . Is there others Babbelfish versions? I couldn´t find where this project starts from on this forum.

Sorry. perhaps these are too basic questions. Any way, thanks for commens and assistance

[cviller]

I made layout and etched the myself. The layout is double layered, but I don't mind sending it if you want it.

To get the 2sj109's I had to sell my soul to the ... haha, no I got them from a friend.
Those things are almost impossible to get, you might get some pointers in the alephx-j thread.

You are correct I have used 4 output devices to spread the load and make it more like AlephJ and easier to drive my 4ohm speakers. My project started in the babbelfish pcb somewhere, but unfortunately, I spend most of the time debugging some hum problems. You can see some stuff from my first build here:

http://viller.org/audio/2007jan_jfish/

I actually call it jfish or FishAmp instead of babbelfish, since it is more fish and less babbel.

And Magura, thanks for your comments!
No, I'm not running a factory, but it is so much fun building amps - I cannot stop!

[JC Fardo]

Thanks cviller

How much power do you get with 2 IRF 150N output devices? I need to source and size heatsinks.

Luckly will find 2sj or rip from my Borbelys...

Regards

[cviller]

How much power do you get with 2 IRF 150N output devices? I need to source and size heatsinks.

I think Zen Mod ran quite a lot of current through his 150 devices. He must have had around 400-500mV across a .22 or .33 source resistor, which amounts to something in the range of 1.2-2.3A... with 22V rails, you are looking at a dissipation of approximately 26-50W per device.

I used 4 irfp240 per channel with 0.47ohm source resistors, resulting in approximately 1A each, just like aleph 3. With 22V rails this is... 22W.

You have to think about what kind of speakers you are trying to drive and at what volume level.

[cviller]

Yesterday I built another one of these fishamps and hooked it up on a piece of heat sink so I could do some listening tests - I was not completely satisfied how the bottom end turned out on the one I built for my brother. But I was in a rush to complete his amp and didn't have time to compare it to my old amp.

Now I have done that and found that it sounded very mellow in comparison. The problem turned out to be R131 a drain resistor on the negative input resistor. When I decided to include it I was only concerned with easing the voltage on 2sj109, but it turned out that it seriously changed the sonics. Now I have shorted it and the amp sounds wonderful!

It does not reach the detail and control offered from my F4, but it still is a very nice amp indeed!

[cviller]

The heat sink is 30x25x5 cm and it needs a small fan to avoid getting too hot.