Help wanted: Jfet front-end for Aleph 2

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Official Court Jester
Joined 2003
Paid Member
maybe you can dream about this one , later

regarding pcb - all you need is some pcb raw material , good alcohol based marker , and ..... google for hydrogen peroxide pcb etching

or just make it on universal pcb - those ones with matrix of little dots
 

Attachments

  • Babelfish Aleph 2.pdf
    43.7 KB · Views: 302
Last edited:
maybe you can dream about this one , later

regarding pcb - all you need is some pcb raw material , good alcohol based marker , and ..... google for hydrogen peroxide pcb etching

or just make it on universal pcb - those ones with matrix of little dots


I'm currently looking for different sources for the PCB, I'm waiting for a quote from a local & overseas suppliers.

Wow!!, Babelfish Aleph 2 version utilize just two 2sj74. Why BC556A?, there are a lot of similar models BC556BTA, BC556ATA, BC556BTF, BC556BTFR, BC556ABU, BC556BG, with the exception of last one all appears to have similar parameters.

What is your impression of Babelfish Aleph 2 sound?, I know I’m expecting a subjective answer that may represent your taste, but it’s important to me. I like mids and a good bass but not excessive to move my entire house. I use to listen Jazz from digital and analog sources.

I was making plans to in a near future build the AlephJ-X using the Graeme schema, but the Babelfish Aleph 2 could be a good alternative too, I'm already have the transformers and power supplies for that voltage.

Another question, in the standard Aleph 2 the MPSA18 can be replaced by a ZTX450 as in Aleph 4, 30 and 60.


Regards,
Alejandro
 
I would stay with your original Aleph 2J plan. Zen did say that his recommendation was for later.

In case you didn't know, member Wayne who made the recommendation earlier in your thread is one of the partners in Pass Labs. So consider your original project to be blessed.

Any of the BC556 transistors will work as a cascode here.

Stay with two 2SJ74BL transistors on each side. At 5ma each they are working hard already and the total current at 10ma in each leg of the diff pair is the same as the original Aleph 2. If you start changing things too much then you may start creating design issues that are too difficult to resolve. Take things slowly and one small step at a time.

Graeme
 
Official Court Jester
Joined 2003
Paid Member
BC556A or MPSA or ZTX - that's all the same , considering their role in circuit

Babelfish Aleph 2 - I didn't tried it as drawn , but I don't have reason to doubt it ;) - I drew that for someone asking how to put JFets in Aleph 2 , few months ago

sound - you heard one Aleph , you heard them all ....... scaling up just for power you need for task

I'm expecting that implementing cascoded bjt buffer between JFet input LTP is clearing sound for step more , referring to change from mosfet LTP to JFet one ....... but - will that please your ears , that's completely on you

I know , when I tried buffer there few years ago , in my Babelfish J prototype , I found efforts well paid of

and - once more - all these small bjts - you can consider them as universal types .... sort of

edit - as gl pointed - stay with already made plan , for start ; so - 2+2 JFet LTP , instead of IRF LTP
 
Thank you ZM. That clarifies your recommendation nicely.

Can someone explain why R71 is present in this schematic. It's present on the Aleph-J schematic from the DIYA store too. In Alejandro's schematic the only purpose I can see is to reduce the power dissipated by the CCS transistor. But the existing IRF9610 in the Aleph 2 is already handling that just fine.

Graeme
 
I would stay with your original Aleph 2J plan. Zen did say that his recommendation was for later.

In case you didn't know, member Wayne who made the recommendation earlier in your thread is one of the partners in Pass Labs. So consider your original project to be blessed.

Any of the BC556 transistors will work as a cascode here.

Stay with two 2SJ74BL transistors on each side. At 5ma each they are working hard already and the total current at 10ma in each leg of the diff pair is the same as the original Aleph 2. If you start changing things too much then you may start creating design issues that are too difficult to resolve. Take things slowly and one small step at a time.

Graeme


I'm really honored by the help received from Zen Mod, Wayne Colburn and you, I had read thousands of posts of each one in the past 8 months and perfectly knows what have done each one in the last ten or more years.

I will keep things as stated on the last diagrams.


Regards,
Alejandro
 
I wish i had the parts, i'd drop this into one of my A2 monoblocks tonight!

a nice way to experiment, without destroying the original front end...

A JFET, A JFET, my Aleph 2s for a JFET!!! (matched pairs please) :cool:



Now i'm wondering how it would effect the sound... maybe help the top end of the A2?
maybe give it a bit more air? -i'm thinking subtle effects here...
 
Hi Bob,

By my calculations the cascode transistors have about 25 volts or so across them and 5 ma of current flowing. That gives 125mw of dissipation. Seems safe to me without a heat sink. I used the ON SEMI data sheet off Digikey. Seems well within the SOA.

Graeme
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.