Aleph J illustrated build guide

OK so I tried the bulb test. On just the power supply the light bult does go off after a second or less. This is a 60 watt light bulb. Now when I do this test with the amp boards connected the ligth stays bright. I tried each amp circuit seperately and it did the same on both sides. Is this normal. What size light bulb should I be using? Thanks guys, I did look over the boards and they seem good with nothing touching.
 
Thanks 6L6. I was freaking out thinking it should go out. I pluged it in and everything seems to be OK. I check the DC offset and set it to 0 and now the bias is set at 0.400V. This is with the light bulb out of the circuit. I don't have all the sheetmetal done yet so can't do the final step in your build guide. I like to thank all you guys for the help.
John
 
Try adjusting the DC offset with the bulb still connected. If you can get it close to zero, everything is probably working ok and you can try full power.

Also, both you guys owe us some photos... :D :D :D

Thank you Jim! Your reply just comes in on time! SUPERB! I'm able to adjust the DC offset close to 0.098 V with bulb connected! Will try full power now!

Yes, Will upload some photos tonight once everything finished! I'm almost at the finish line with this BEAST!

Thank you so much for the help Jim. I owned you big time!
 

6L6

Moderator
Joined 2010
Paid Member
The biggest reason to check offset at this point is to see if there is a gross wiring error or something like a cold solder joint. If the Offset is ok (and this can be tested with the bulb in place) that's a pretty good indication that the wiring is good.

Now go to full power and re-check offset and set bias once it's warmed up. If good, disconnect that channel and do the other. If that's ok, then connect both channels, fire it up, double check bias and offset, grab a beer, coffee, wine, etc... and put into the system.

Then be absolutely amazed at how incredible this amp really is. :)
 
hi Jim,

Please see the images.
For some reasons, when i connect full power, i smell something funky right away. Visually, i saw the Resistors at the PSU board change color to yellow. Maybe, it's heated up too much.

I'm using Transformer 400 VA 20-0-20. Before connecting the power, it reads -27.5V and +27.5 at Pos and Neg rails. Not sure if it's too much for the amp.







 
Help needed to finish my Aleph J amp!

Dear Jim and all the experienced AJ builders,

I need a little help here.
Thanks to Jim for pointing out, Q2, Q3, Q4 ZTX transistors are all backward on both channels.

After fixing Q2-Q4 polarities on both channels, I'm able to bias both channels at 0.4 V with DC offset at 0.002 V and 0.004V respectively. Letting the amp warms up for about 1 hour the bias does not drift much. It's only 0.018V drift after warming up. Readjust bias/offset. Connecting AJ amp to the system, I only get the music to play very clean in 1 channel (no humming/buzzing very clean sound). The other channel is dead silent.

I need your inputs and whatever help/insight/experience that you can offer will be greatly appreciated! Below are the steps that I did for the debug of the other silent channel.

0. Checking connectivity from RCA inputs to PCB inputs and Speaker +/- connectors to PCB outputs. All connectivity are good b/w input and output of PCB to speakers connectors and RCA connectors
1. Checking power supplies V+ = 24.25V and V- = -24.25V into both channels
2. Both LEDs are lit up on both PCBs
4. Hearing soft humming noise from transformer. Jim told me that it is normal for certain transformers. My transformers shield cable is connected to the chassis GND together with earth gnd. I also install a metal EMI transformer shield as seen in my previous post photo
3. Both heatsinks are very warm on the channel that plays music and channel that does not
4. Swap speakers and input cables for Left and Right channels to make sure it's not related to cables/speakers/preamp. Confirms that the channel that is silent is still silent after cable swaps
5. Checking Voltage at Q2, Q3, Q4 for both channels.
- Q2 and Q3 Vb, Ve, Vc are the same for both channels
- Q4 is different
- Q4 voltage for the working channel:
* Vc = 4.54
* Vb =0.338
* Ve = 0
- Q4 voltage for the non-working channel
* Vc = 4.65
* Vb = - 3.59 V
* Ve = 0

6. There's a big difference in Voltage at base for Q4 b/w the working and non-working channel
7. I checked Q4 (NPN ZTX450) at the non-working channel and confirms that PN junction = 0.688V. Meaning Q4 Vbe = 0.688V, Vbc = 0.687V. It proves the Q4 transistor itself on the non-working chan is functional
8. Checking continuity on DMM at the Base of Q4 to bottom leg of R27B, R27 and R15, it's all connected

9. Tracing backward Q4 Vb = -3.59, VR27B(bottom leg) = -3.59, VR27(bottom leg) = -3.59V, VR15(connection b/w R15 & R27) = -3.59V

10. Changing value of R27. It's able to change Q4 Vb = 0.33 as the working channel. However, by doing this, bias voltage at R18 changes to 0.489V on the non-working channel. This experiment also do not get the music to play on this channel

11. Checking voltages at Q5 (big Nmos transistor). Both channel have the same voltages Vg = 4.633, Vd = 24.25, Vs = 0.408

At this point, i run out of idea to understand why music does not play on 1 channel vs the other. Most of the number measured looks legit on both channels except for Q4 Vbase and biasing combination b/w 2 channels.

At the moment, I do not have oscilloscope at home. I only have DMM. If there's a need to use it for debug, I will find the way to use one.

I know it is a long reply. I sincerely thank you for your effort and help in advance.

Best regards,
Tom
 
Last edited:
Also, both you guys owe us some photos... :D :D :D

It's alive!
I let it play for a few hours yesterday. I think I can turn up the bias on it. The heat sinks were at 110F - 113F after a few hours. It sounds real good and is quiet. I put my ear up to the speakers and did not hear any hum or buzz. Thank you everyone for help and guidance. Here are some pics.

URL]


URL]


URL]


URL]
 
Thanks guys!
For those wondering about the clear brace on the caps. I think it was my fault for not pushing the caps down enough but once soldered they seemed a little flimsy sitting on those two little pins. So to take the stress off the pins I made a 8 pack brace out of Plexiglas to hold them together to stiffen them up a little.
 
I also figured out why the other channel is not playing music. After an extensive debug and trace back all the way from the input signal with the oscope, I figured out R2 and R4 was wrong. It was 221 ohm instead of 221k as in schematic and the other working channel.

I only play music through my cheap test speakers for now. The music is very clean no buzz or hum from soft to the loudest volume. There is no thump on start but there's a slight/soft thump on switch off. Other than that, I consider this is a success for my first DIY monster amp project. I currently let the amp warms up and will post some pictures of the finished product later.

Thank you Jim again for helping and pointing out some of the things I did not do right for my first DIY monster amp.

Btw, Very nice and beautiful build, Kazoo. Well done!

Regards,
Tom
 
Last edited:
that's too much +/-1V5

however , without any cables on input and without temp equilibrium (for that , case must be finished and lid on) it's hard to expect total stability

again - Iq and DC offset setting is iterative process , top lid on , as condition that amp gut is on steady tempreature
Well, after a weekend of tests. No progress.
I finished the assembly and i tryed to tune R7 and R27. Bias was OK but offset drived me crazy. No stability, even after a hour of heating. I measured a 1.2 Khz signal across output jacks with +-0.5V DC range and peaks to 1 or 2 V.
First measurement at cold start was -20 V ! and it slowly increased to nearly 0.
Some pictures attached
 

Attachments

  • IMG_0148 (1457 x 1092).jpg
    IMG_0148 (1457 x 1092).jpg
    397.9 KB · Views: 512
  • IMG_0149 (1457 x 1092).jpg
    IMG_0149 (1457 x 1092).jpg
    489.9 KB · Views: 323