Aleph J circuit question

[Wang1]

Could someone expalin the purpose of R7 and R8 trimmers and if the original 1k r7 and r8 are left in place or jumped.

The same goes for R27.

The reason for asking is the original design has no trim pots, where these added by NP at a lter date?

Thanks

 

[Zen Mod]

you're speaking of which exact iteration of Aleph J?

present one from Store?

 

[Wang1]

This one I assume is the current one

 

[Ben Mah]

R7 and R27:

https://www.diyaudio.com/community/threads/aleph-j-illustrated-build-guide.241729/post-3615473

https://www.diyaudio.com/community/threads/aleph-j-illustrated-build-guide.241729/post-3615479

Pots in R7 and R27, jumper in vertical R27.

R8:

https://www.diyaudio.com/community/threads/aleph-j-illustrated-build-guide.241729/post-4988127

https://www.diyaudio.com/community/threads/aleph-j-illustrated-build-guide.241729/post-4989203

1K in R8, and no pot.

 

[Ben Mah]

More info:

https://diyalephj.blogspot.com/2020/10/building-amp-boards.html

 

[Wang1]

Thanks, but just to be clear:

R7- Is the fixed 1k resistor removed in place of the pot? Then once the offset is fixed is the pot replaced with a fixed resistor of the required value? (Same question R27 re bias)
R27 - is R27B sill in the circuit?

 

[Zen Mod]

R8 1K populated, no pot populated
R6 jumper ( short) populated

R7' pot populated, no R7 populated - DC Offset setting point

R27A jumper (short) populated , R27B no populated, R27 pot populated - Iq setting point

 

[Ben Mah]

Leave pots in place after bias and offset adjustment. No need to replace with fixed resistors.

 

[Wang1]

thanks all for you assistance

 

[Zen Mod]

proper list is in post #7

set, close, enjoy

as Ben said - no fiddling with fixed resistors instead of trimpots

proper OCD needs to be pointed in Books direction, and only when one is able to construct its own ( even if damn single stage with BC109 is in question) then fiddle with all tricks

prior to that, leave it as original

and Papa's J is good original.... Boyz just got carried off ( way off) wanting to make more versatile package

Been there, done that ...... and probably will sin again .......

 

[Extreme_Boky]

Could someone expalin the purpose of R7 and R8 trimmers and if the original 1k r7 and r8 are left in place or jumped.

The same goes for R27.

The reason for asking is the original design has no trim pots, where these added by NP at a lter date?

Thanks

 

[Zen Mod]

no

R8 need to be fixed, 1K

 

[Extreme_Boky]

no

R8 need to be fixed, 1K

 

[Zen Mod]

now you're just missing 68K in series with 100K trimpot

 

[Extreme_Boky]

you mean parallel?

 

[Wang1]

Sorry, but i have another point for clarification, on the original schematic R13 is connected to R18 and source Q7, yet on the current schematic above R13 is connected instead to R19 and source Q8, ???

 

[Ben Mah]

Q7 and Q8 are identical and matched, and connected with their source resistor in parallel, as are Q5 and Q6. Connecting R13 to either Q7 or Q8 behaves the same electrically and the same goes with R15 connecting to either Q5 or Q6.

 

[Wang1]

Thanks for the clarification, all is clear now 🙂