Aleph J illustrated build guide

[BobEllis]

^exactly

 

[Zen Mod]

I know one guy with Golden ears ( hands and brain , too ) who's saying that his J2 ( FW origigi ) is better sounding when -in is fed , while +in is grounded

I didn't pursue that further , asking about absolute phase in his system .......

 

[BobEllis]

Remember the inverting chip amp craze? I think we called you Choky way back then.

 

[Zen Mod]

yup

 

[Seavan]

Interesting, I assumed that you do not want the amp to invert. Does it suggest that maybe your other equipment inverts too?

 

[Zen Mod]

invert or not , that's just matter of absolute phase of entire system

plenty of that written and accessible on web ; easy to change as flipping speaker cables is simple ...... or in preamp ....... super easy if balanced one is in question , just exchanging place of +/- phases

 

[Bones13]

Can you help me with what input I should ground for RCA? Is it IN- that goes to ground and IN+ is an actual input? Thank you!

I am not the expert, but I used IN+ from the RCA middle connector, and the shield to ground. Along those lines, I grounded the IN- for use with the RCA connector. I use a switch on the back panel. I send all three (IN+, IN-, and ground) to the XLR plug. I connected the IN+ and ground to the RCA plug, and the switch grounds the IN- when the switch points at the RCA jack.

 

[Seavan]

I am not the expert, but I used IN+ from the RCA middle connector, and the shield to ground. Along those lines, I grounded the IN- for use with the RCA connector. I use a switch on the back panel. I send all three (IN+, IN-, and ground) to the XLR plug. I connected the IN+ and ground to the RCA plug, and the switch grounds the IN- when the switch points at the RCA jack.

I was thinking about something like this with using an XLR shorting plug if I can find one.

 

[Seavan]

Zen Mod, do you mean that the AJ may sound better with -in compared to +in assuming that the phase is not inverted in both cases?

 

[Zen Mod]

I didn't tried ; I just wrote , for your amusement , what a man of respect said once .

it's easy to try - send hot from RCA to amp neg leg input , ground its pos leg

 

[Seavan]

Thank you! I will try it when I finish building. I can also change the phase on my DAC to keep it consistent.

 

[Seavan]

So, I finally powered up one channel. I was able to set 0 out. However, the voltage on the output resistor at 68k R27 was 580mV. I had to rotate R27 almost to the end to read 350mV.

Also, I read about 20mV more on the other resistor, so, it's like 5% difference.

Is it all normal?

BTW, I am using 5U chassis and it does not seem to get too hot at 400mV.

 

[Zen Mod]

if you can't set intended Iq ( voltage across one source resistor - either R18 or R19 ) , increase value of resistor connected in series with R27 trimpot ; do not use R27B

then - if you can't set 0 output offset , and offset is positive - either increase R7 or use just R7- trimpot (without R7)

all that referring to sch in #179 ........ I can't find better one here

whatever - be more specific , mentioning voltages and positions ; it always helps to keep things clear

 

[Seavan]

Zen Mod, thank you for clarification. I can set voltages. My concern is that 1) With R27 at 68k I get about 600mV, and to set 350mV I need to set R27 almost at its end position. 2) that voltage on R18/R19 differs by about 20mV (400mV, 420mV). I am just not sure if this is normal at all, but from your response it seems that it should be normal. BTW, I am using 6L6 kit of parts.

What is sch #179?

 

[Zen Mod]

sch from post #179

if you can't set low enough Iq (voltage across R18 or R19 ) - decrease value of resistor (R27A) connected directly in series with R27 trimpot

difference in voltage across two neighbor source resitors is OK if is in 5%

 

[6L6]

Remember that R27 actually set the AC current gain of the Aleph CCS. That it also effects bias is just a lucky happenstance.

If your heatsinks are up to it, (and with a 5U you should have little issue...) just set the 'bias' as high as you can until you A) can no longer zero the DC offset or B) have 65C at pin 2 of any Mosfet and 55C heatsinks.

 

[BobEllis]

Jim, I don't see how R27 affects AC gain. The way I read the various articles, AC gain is set by the ratios of R15 to R24 and R16//R17 to R20//R21//R22//R23 (meaning the parallel values of the grouped resistors.) Usually we adjust only R15 to vary AC gain.

 

[Zen Mod]

it affects , of course , but not so much as R15 itself and ratio of resistor groups you mentioned

and that is applicable for waste range of Iq , meaning waste range of R27 value

 

[ahne]

Hi

First at all Thanks
I just finish solder the PCB , the 74bl i ve got from Spencer with 11mA .
Can i use from my Aleph 2 the IRFP240 there are stickers on it from
30-140 which are the best for the J ?

Cheers Manuel

 

[Zen Mod]

regarding IRFP240 : you need to ask a guy from whom you bought them , for meaning of stickers

I presume/resume that , whoever was that , he sent you them clearly grouped by matching

that's only thing important - matching ....... class of Ugs is irrelevant

upper ones need to be matched together

lower ones need to be matched together

no need to match them up to down