1081 Project Errata

[Tekay]

Since I think that the BA440 heatsink will be a problem for some DIY'rs and to myself I tested the circuit with BD139/140 as output pair instead and it's working just fine!
The bias is a little higher but I can't measure any distorsion difference!

My test setup is an original BA489 board stuffed with BA438/440 and wired like the pre-section in the 1081 complete with in/out transformers!
Without any signal the original setup draw 36mA and the modified 40mA (there's a led VU connected to the psu also)

Hope this is to any help? :grin:

 

[rafafredd]

What do you mean by "modified"? Running the output in class A?

Can you share more?

 

[thestudio]

What are people using for BC type transistors BC441, BC441-6, BC461, BC461-6????? which are prefered over other???


Who was the original manufacture, are they still available in small dark corners of the world? :roll:

 

[Tekay]

With modified I ment with changed output pair!

 

[tommypiper]

Hi Tekay!

What are the BD139 you used? Do they require heatsinks? Don't you think modern heatsinks will work with the original transistors?

cheers,
tommypiper!

 

[Tekay]

I used BD139/140 as output pair, bended the legs so I could use a heatsink mounted on top like the original.

 

[tommypiper]

Tekay,

I thought you were using different transistors to use a different heatsink?

What options are known for running the 1081 in class A? Would that require a different output amp?

 

[rafafredd]

I think it can be done by changing just one resistor on the amps. Should get hoter...

 

[tommypiper]

Which resistor...?

 

[Infernal_Death]

OK since the gain switch group order is on it's way i try to start to finish this project. There are still many questions unanswered but right now i have two questions.
1. I don't know the orientation of the inductors. I got a set from the group order and they are marked with a white dot on one side but i don't know how the dot is orientated on the board and i couldn't find the info anywhere
2. What is the value of R22 ? (the one resistor on the far left side of the board which is marked as R? )

As always thanks ! :thumb:

Flo

 

[orson whitfield]

Please let me know who's doing that switch order I have money waiting to be sent to him via paypal but I erased all my emails by acciedent.

 

[Infernal_Death]

The switch order is done by Tommypiper (look at the post above mine)

Flo

 

[tommypiper]

Flo, I asked the same question about the inductors in another 1081 thread here somewhere, can't find it now. I think Gus was in the thread. I think we figured out one of the inductors, but I can't remember. I think Tekay may have replied... Ask Peter Purpose, he has a couple partially built ones already (not with Tommytone's boards, but would be the same orientation) and let us know. :grin:

Orson, I'm doing gain switch order. Jonathan is doing EQ switch order. I just sent you PM. The gain switch order is about to close soon.

:guinness:

 

[Infernal_Death]

Hey Tom

Thanks for the infos. I did a search and must have missed your question.
Anyway i just wrote a pm to Peter Purpose and as soon as i get some infos i of course will let you know.

I figure since the gain switch order is coming around there should be quite some people in the near future be ready to finish this project so i guess it's good to answer all those questions (and i have to say i already found many things which aren't clear to me).

Flo

 

[Infernal_Death]

I received an answer from Peter who was kind enough to send me a pic of his board, Peter thanks for that !

Looking at it it has the white dot on the left inductor in the upper left corner so i guess it's the same way with the Tommytones boards. Can anybody confirm this ?

Flo

 

[Infernal_Death]

I still would like to know the value of R22 which is marked as "R?" on the board. Anybody ?

Flo

 

[Family Hoof]

Has anyone else noticed this? I apologize if it's it been mentioned but I couldn't find any.

On the parts list for the BA340:

The emitter resistors on the output pair (I think Tommy calls them R1 and R2) should be 1.5 ohms, not 100k ohms. I was having a really hard time trying to figure out how it could push enough current through those. :roll:

Also R12 should be 36k, not 3k6, and R11, 13 should be 47k, not 4k7.

 

[Infernal_Death]

Wow, thanks for pointing this out. Didn't know this. I guess i need to pull the B340 out of the motherboard and replace those resistors as i stuffed the boards while looking at the parts list.

Thanks :thumb:

Flo

 

[Infernal_Death]

Bump. Anybody knows what R? is ?

I am really surprised that there is so little interest in this project. After all, all the group orders should be reaching the end and people should have all the parts so i think there should be some new talk about the 1081 project ? But seems like i am wrong ?

Flo

 

[Gus]

Flo

I think there is a lot of interest in this project. I think we are waiting to see someone finish one with all the notes needed to build it correctly. This project is not as easy as the others and the good switches needed cost a good amount of money.