Aleph 5 based on BrianGT boards

[Nohabla]

Hi,

A long time ago i bought one set of aleph boards from Chipamp. I am now in the process of finishing them.

I have populated the boards as per the "Brians PCB Aleph - parts list" see attachment. I cannot remember where i got the parts list, perhaps from Chipamp.com before it closed..

It is a dual mono config with 2x25vac Toriods.

These are my findings when power voltage is +/-34 vdc from PS:
The output transistors does not heat up, just 2,2mv across R40 and even less on R39.

Q1, 2, 3 does heat up.

Voltage over z5 = 9V
Voltage over R8 = 5,2V
Voltage over R18 =3,3V
Q5 Gate to source =1,6mV
DC on output = 96mV

Any thoughts?
Appreciate all input

 

[Zen Mod]

schm, pics

pretty please

 

[Dennis Hui]

Can you link/post a schematics for your board?

Edit: Mighty Zen Mod beat me to it.

 

[Nohabla]

Her's a schematic i picked up in another thread and pics.

Thanks for looking

 

[Dennis Hui]

Your voltage across R18 looks low. Are your Q1, Q3 IRF9610 devices matched?

 

[Nohabla]

Yes they are matched, or at least supposed to be, but perhaps i have managed to mix them up. I will take them out and do a rematching.
Does the BOM look right to you, for a A5?

 

[Nohabla]

The input 9610's (Q1-3) and even the ztx450 (Q4-5) are matched. Both cards shows the same values under test. I have populated the cards as per the BOM posted.
If there is an error i must have made it on both cards.
I have checked the cards and it looks like the parts are installed in the right places

Any sugestions to what to look for?

 

[Zen Mod]

3 wires going to lower group of mosfets , but 4 wires going to upper group of mosfets ?

that additional is sense for Aleph CCS

 

[Bfpca]

I just looked up the Vgs for a batch of 9610s I matched for a Group buy. 3.8volts would be pretty typical for. Looks like 23.5ma total current but only 8.4m across r18. 3.8volts is not enough to turn on the output fet. I see a lot of resistors are TBD. Do you have the recommended values in place? If you can’t find any problems you could try a 1k pot in place of R18. Start with it at 0 ohms and adjust it for the correct bias current.

 

[Nohabla]

4 wirres goes to each side, the black was probably hard to see in the first pic's.

 

[Nohabla]

Hi, Yes the TBD: R12 is 453r, R13 is 221k and R17 is 75r. R6 is optional, for closer matching of Q1 and Q2. I have left it out.

I will try your tip about 1k pot at R18, starting at 0 ohm.

 

[Nohabla]

Hmm, well it's like the amp readjust it self when i get past 3,3v across R18, no matter how much i turn the pot after i get past 3,3v it will not increase for more than a secound or so. The magic point looks to be 142 ohm at R18.

 

[Zen Mod]

inputs shorted , no load , while setting

 

[Bfpca]

Could Q4 be conducting and preventing the voltage from going higher? Check Q4 orientation to make sure it’s the correct pin out. Also check Vbe to see if it’s conducting.

 

[Nohabla]

inputs shorted , no load , while setting

Hi, have tried both shorted and not, theres no difference, the amp acts the same. Also no load on spk output.

 

[Nohabla]

Could Q4 be conducting and preventing the voltage from going higher? Check Q4 orientation to make sure it’s the correct pin out. Also check Vbe to see if it’s conducting.

Hi, yes i'm starting to suspect that. Q4 arrangement is some kind of limiter/protection circuit? Bussy at home to day, havn't had time to look at this, will try to morrow.

 

[Zen Mod]

take a look in also active Aleph 5 thread

my posts about trimpots

remove Q4