Aleph P v1.7 Build from Wisconsin

Oh no, not another “from Wisconsin” build!

This time I will be documenting my build of the Aleph P v1.7 from Jim’s Audio in HK. Now before you start giving me grief for this (as some no doubt may be so inclined), let me lay down some groundwork.

I first learned about the Aleph P during a preamp discussion in which I was curious about a variety of technologies. Specifically, I was intrigued by the multiple “flavor” options of the Schiit Freya+. Mr. Pass suggested I look at the Aleph L which has both a passive and active component depending upon the position of the volume control knob. While researching that product, I ran across another conversation that discussed the Aleph P. Similarly intrigued, I kept reading about that one and Mr. Pass made comments that he preferred the sound of the P over the L (paraphrased). Given that I have built an Aleph J amp -- and it is a balanced device -- it seemed natural that the balanced nature of the Aleph P would be a good companion to it. So off I went on a mission to learn as much about the Aleph P as possible.

Search revealed several folks who had built and provided board sets for this design once upon a time, but at the current time there aren’t any folks in this community who do so. A web search revealed Jim’s Audio had a design as well as matched semis for it, so I placed an order.

Disclaimer: New to DIY, I was unaware of the conflict that brewed within the community for those who develop products based on Pass designs who are not members of DIYA or aim to make a profit off of his work. That's not lost on me. So call me ignorant for not making the connection. I’ve already had the IP discussion with others in the community, so no need to bring it up again. I did attempt to contact Mr. Pass through a couple of channels to discuss the status of this design, but it’s possible my message didn’t reach him. I realize he’s a busy man with hundreds of emails to go through daily, so no hurt feelings on my part. There are no other options for purchasing boards for this design, this version of the product is available, I bought it, and it’s my goal to complete it. This is the tale of that project and is meant as an educational experience. I don’t expect assistance from community members who are opposed to this particular version of the Aleph P preamp, only humbly ask that they allow others to follow along with the build. If I fail (or it fails), then that’s on me and I take responsibility for my actions.

So let’s get the show on the road, shall we?
 
Last edited:
The Jim’s Audio (JA) version of the Aleph P v1.7 (AP) is a combo board that contains the amplifier stage and an onboard power supply. Each board supports one channel of audio and therefore requires two boards for stereo. After analyzing the JA schematics and comparing them to the official service manual for the AP, I found that the amplifier stage was the same as designed in the service manual. There is an addition of two 50-ohm variable resistors (VR2, VR3) on the drains of the CCS FETs, parallel to the 22-ohm drain resistors (LR2, LR3 on the JA boards – R44, R59 on official), used to compensate for biasing differences between each side of the amp. According to the folks at JA, the following was stated about them:

“VR2 and VR3 are to adjust the biasing current on the mosfets. When power up, measure the voltage across LR2 and LR3 respectively. If the voltages are almost the same, then no adjustment is needed. If the voltage differs by over 20%, then adjust these two VRs so that the voltage are close to each other. It is not necessary to make the two voltages the same though as there is always a tiny difference. Normally a small adjustment of the VRs can do.“

In addition, JA chose to not use the switches to offer selectable change of gain with the AP, opting to fix the gain at its lowest setting of 1.3dB. It may be a blessing in disguise, however. With the AP having a max gain setting of 15dB and the Aleph J having 20dB gain, it’s a lot of gain. Perhaps potentially too much for the AJ inputs. So I’ll go with this configuration first. If I need more gain, I’ll add/remove/short resistors as needed.

attachment.php


attachment.php


The Power Supply section of the JA AP contains the rectifier, storage caps, zeners, and power FET with supporting circuitry. Because there are no input switches, there is no need for the relay power supply section, nor is there any accommodation for the mute circuits. The only difference I noted between the JA PSU and official is the two 1000uF caps after the bridge were combined into a single 2000uF cap for compactness. The shaded area below is what's included on the board.

attachment.php
 

Attachments

  • Amp Schematic.jpg
    Amp Schematic.jpg
    648 KB · Views: 2,195
  • PSU Schematic.png
    PSU Schematic.png
    163.4 KB · Views: 1,883
  • IMG_4626.jpg
    IMG_4626.jpg
    1 MB · Views: 1,413
Last edited:
Starting with the usual low-profile components, I started with the resistors and diodes, followed by small capacitors and potentiometers (set to center prior to install), and then large capacitors. I opted for the WIMA caps because they fit the spot, the sound nice in my AJ (to me – I don’t know the difference yet), and they aren’t horribly expensive at a few bucks apiece. And the red just looks cool. :D I finished up with the small transistors up in the CCS.
 

Attachments

  • IMG_4663.jpg
    IMG_4663.jpg
    707.4 KB · Views: 144
  • IMG_4664.jpg
    IMG_4664.jpg
    817.3 KB · Views: 112
  • IMG_4660.jpg
    IMG_4660.jpg
    979.6 KB · Views: 104
  • IMG_4661.jpg
    IMG_4661.jpg
    869.6 KB · Views: 85
  • IMG_4662.jpg
    IMG_4662.jpg
    841.8 KB · Views: 93
  • IMG_4665.jpg
    IMG_4665.jpg
    813 KB · Views: 101
  • IMG_4666.jpg
    IMG_4666.jpg
    712.4 KB · Views: 95
  • IMG_4667.jpg
    IMG_4667.jpg
    872.6 KB · Views: 142
  • IMG_4676.jpg
    IMG_4676.jpg
    988.7 KB · Views: 206
Last edited:
Next step are the amplifier and CCS FETs. These were matched at JA and sold as a set. After installing and aligning them, I installed these really cool low-profile heatsinks on the FETs. The nice thing is they have friction/pressure clips on them that keep the devices pressed tightly against the heatsink. They have lots of cooling area, but they’re not so big they get in the way of components around them. Many of the AP creations that I’ve seen have a piece of L-shaped aluminum stock screwed to them. This is a lot sexier in my opinion. A dab of compound on the back of each FET, slide the heatsink over the top, clip it in place. The heatsinks had locating pins at the bottom, but since there are no holes in the PCB to support them, I removed them and allowed the bottom of the heatsink to rest on the board held up by the FETs they cool. It’s a solid mounting arrangement.

Heatsinks (Mouser):
567-OMNI220-18-25-1C
567-OMNI220-18-50-2C
567-OMNI-220C
 

Attachments

  • IMG_4678.jpg
    IMG_4678.jpg
    778.3 KB · Views: 244
  • IMG_4679.jpg
    IMG_4679.jpg
    902.7 KB · Views: 204
  • IMG_4684.jpg
    IMG_4684.jpg
    797.3 KB · Views: 234
  • IMG_4686.jpg
    IMG_4686.jpg
    704.4 KB · Views: 233
Last edited:
Installed the capacitor bank with Panasonic 1000uF electrolytics. The open position is for the 2000uF cap noted a couple posts up. At the time I ordered parts I was having trouble finding 2000uF caps at 100V. I’ve since located them (Nichicon 2200uF caps) and they’re on order.

I ordered a 100VA, 40V(x2) transformer from Antek to provide the 80VAC juice required on the input and should be able to test out the board when it and the larger PSU caps arrive. This preamp will be used in conjunction with the Muses volume control project in my other build discussion, so I have to coordinate the testing of this and Muses as well (which I also have transformers coming in for).
 

Attachments

  • IMG_4696.jpg
    IMG_4696.jpg
    881.8 KB · Views: 230
The one and only
Joined 2001
Paid Member
As it.is my practice to answer all emails, it is possible that yours got lost.

So you understand, I don't get upset about diy cloning for several reasons:

1. It's DIY

2. I don't need the money.

3. Could be worse - they could be cloning someone else.

:snail:
 
  • Like
Reactions: 1 user
Thank you for your reply. I'm appreciative of your consideration and your designs. Sorry we didn't connect, but very happy to have the opportunity to bring another of your devices to life. I'm truly looking forward to listening to it.

Respectfully,
Chris

As it.is my practice to answer all emails, it is possible that yours got lost.

So you understand, I don't get upset about diy cloning for several reasons:

1. It's DIY

2. I don't need the money.

3. Could be worse - they could be cloning someone else.

:snail:
 
Thanks! There are a lot of great choices out there in this community. This is the direction I chose, but there are others that fit the bill as well. Looking forward to seeing where this one goes. I chose it because it's unique and doesn't follow the "usual path". :)

Beautiful as usual Chris, eagerly waiting for next steps as I am building my J2 so the balanced preamp is in my mind ;)
 
Member
Joined 2004
Paid Member
Great work Chris! Super clean and tidy once again and well documented.

On the transformer - 80VAC (40 + 40) is going to be too high. If I remember correctly, you want to aim for about 60VAC (30+30) which will give you the 80VDC or so after rectification and the zener string will regulate that down to about 63V.

Cheers :cheers:
Stephen
 
Perfect. :cheers:

Thanks for that feedback. I wondered the same. The service manual shows a 40x2 transformer so I chose one of those. But I'd probably be better off with a 30x2. I should have stock in Antek! :)

Great work Chris! Super clean and tidy once again and well documented.

On the transformer - 80VAC (40 + 40) is going to be too high. If I remember correctly, you want to aim for about 60VAC (30+30) which will give you the 80VDC or so after rectification and the zener string will regulate that down to about 63V.

Cheers :cheers:
Stephen
 
Last edited:
Ah, yes. After a second look, you're right. I don't know where my brain was when I ordered that transformer then. :spin: Correct device is on the way.

Now I have to look for something to build with +/-50V rails. :p

The schematic in the service manual shows an Avel D4007, which is a 30+30.

Here are the Avel specs:
Transformers and Power Converters From Avel Lindberg, Inc.

You might be looking at the "80V UNREG", which is the DC voltage.
 
Last edited:
I finished populating the boards, adding a 2200uF cap and a power connector (thanks @dBel84). Time to burn in the first board. I spun up the variac to 60VAC to provide the ~80VDC unregulated. No smoke, so life is good!

I checked the drain resistors' voltages. Out of the box they were quite close, so I probably didn't need to do much according to JA. However, in an earlier post a few years back on the topic, Mighty ZM suggested that the voltage here be adjusted to 400-450mV. So I gave the VRs a few turns and ran them up to 400mV. They're sitting nice and steady. I checked the temps of the drive FETs and power FET and they're sitting nice and steady as well.

After they have a chance to burn in for a while longer, I'll check the offset on the output and see if there is any significance. The 2K pot that sits between the +/- stages reads "rightgain" on the schematics, so I'm not too sure what to do with that one. The service manual doesn't much discuss its purpose. I presume it's a gain balance adjustment to find the zero spot, but it's unclear to me. It may be referenced in one of the reference docs in the Pass circuit library, so I'll have to do some research. I'll be gentle with it and see what happens when adjusted (currently centered 1K-1K). If anyone has insight on this one, I'm happy to hear about it.
 

Attachments

  • IMG_4734.jpg
    IMG_4734.jpg
    845.9 KB · Views: 310
  • IMG_4720.jpg
    IMG_4720.jpg
    805.4 KB · Views: 282
  • IMG_4721.jpg
    IMG_4721.jpg
    837 KB · Views: 251
  • IMG_4724.jpg
    IMG_4724.jpg
    726.2 KB · Views: 254
  • IMG_4723.jpg
    IMG_4723.jpg
    642.7 KB · Views: 241
  • IMG_4725.jpg
    IMG_4725.jpg
    636.9 KB · Views: 133
  • IMG_4726.jpg
    IMG_4726.jpg
    644.6 KB · Views: 130
  • IMG_4728.jpg
    IMG_4728.jpg
    562.5 KB · Views: 173
Official Court Jester
Joined 2003
Paid Member
in case that that horizontal resistance (2K trimpot and 2 resistors) is 0 Ohm , you have pure LTP, and gain is highest possible

if you introduce resistance there, it acts as degeneration path, decreasing tracking/AC current mirroring between left and right half of LTP, thus gain is smaller

set by your needs, that's it
 
And now cooking board #2. Adjusted the drain resistances to read 400mV as the previous set.

I'm not sure yet how I'm going to tweak the horizontal resistance between the circuit halves just yet. I don't know that any static resistance measurement is going to predict how the circuit will react. So once I get them broken in a bit, I'll inject a signal into the inputs and adjust the resistance accordingly. I hypothesize that I should be able to adjust it such that I'll see 1.3dB gain as the circuit suggests for this input voltage divider configuration. Let's see if I'm right. :)

I appreciate the clarity on the circuit operation, ZM :cheers:
 

Attachments

  • IMG_4743.jpg
    IMG_4743.jpg
    877.1 KB · Views: 135
  • IMG_4741.jpg
    IMG_4741.jpg
    852.8 KB · Views: 124
  • IMG_4742.jpg
    IMG_4742.jpg
    956.3 KB · Views: 99
Last edited: