DIY Preamp using Khozmo Attenuator

JayT

JayT

Member
Joined
Feb 10, 2019
Messages
83
Location
Oregon
With the recent discussions about the Hattor preamps, I thought I'd post some photos of a handbuilt preamp I recently completely which uses a relay-based input selector and shunt attenuator from Khozmo. I'm using a fully balanced attenuator (four channels of attenuation for stereo), which then feeds a buffer board with both balanced and single-ended outputs.

The Khozmo is built using Takman REY shunt resistors and Vishay Z-foils for the series resistors. All the rest of the signal path resistors are also Vishay Z-foils. All wiring is solid-core silver with teflon insulation.

I have two balanced outputs - one directly from the buffer, and the other with series MiFlex KPCU copper-foil caps. This second output rolls off the bottom couple octaves. Depending on the input impedance of the amp, the -3db point is between 40Hz and 80Hz. My speaker system uses an active servo-controlled open baffle subwoofer for each channel which can handle up to about 200Hz, so having the passive roll-off for the upper frequencies puts a bit less stress on the speakers and amp.

I am thrilled with the sound - by far my most successful DIY electronics project so far. My Parasound JC2-BP that you see sitting below my new preamp in the photos is now for sale.
 

Attachments

  • preamp in rack 1024.jpg
    preamp in rack 1024.jpg
    154 KB · Views: 83
  • Preamp1 1024.jpg
    Preamp1 1024.jpg
    234.6 KB · Views: 82
  • preamp back 1024.jpg
    preamp back 1024.jpg
    86.8 KB · Views: 82
That is awesome. Nice job! You should be very proud of that pre-amp.

Arek offers some dam fine equipment, either fully built or for the DIY community.
 
Thanks Randy.

Yes, Arek was a pleasure to work with and makes some great kit. Highly recommended.
 
Dang, I would have a very hard time trying to decide what parts are needed even :). Looking at the Khozmo site and it is like, ok, what does each of these do even :).

It looks like you did a great job figuring it all out and putting it all together.
 
It looks professional compared to some of the spaghetti wiring passive line stages that people have posted pictures of.
 
Arek was a big help there. I explained what I was trying to accomplish and he's the one that suggested the product I ended up using. I think the attenuator I am using is fairly new and isn't shown on their website yet.

From the start of my email dialog with him until I had the attenuator in my hands was 3 1/2 weeks. And that was with some custom programming for my "logo" on the OLED and engraving of the remote. Can't complain about that!
 
MEP is right, it looks like a professional job!

Arek has been great to deal with. The only thing that delayed my Tube Stage was that he was out of the custom made transformers that he uses. After these arrived he had it out right away. It amazes me how fast things arrive from Poland.

Definitely can't complain about the custom programming. I hadn't noticed the remote engraving until you mentioned it. It looks way cool! BTW, the display is nicer than the one that comes with his top Hattor.
 
Neat layout and wiring. Looks great. I bet it sounds awesome. Is that a Modushop chassis ?
 
Thanks guys. No relation to the company that makes the CD transports. Just my first name. :D

Yes, this is the Modushop Slimline 2U purchased through the DIY Audio store. They've been great to work with as well. I also used their cases for a pair of small monoblocks, and have another pair on the way now for a pair of Purifi-based class D monoblocks that I'm building with a 1500VA linear power supply for each channel. I hope to have them done by Christmas (at least version 1 - I'm planning to experiment a bit with different buffer designs).
 
I thought the Purifi is only for OEM. Are they now selling to DIY as well ? It's been a while I have looked at them. Interesting you choose to build with the linear ps, not many does. I think powering the buffer board with a good power supply is critical in the way the amp module will sound. Will you be using the Purify buffer as well ?
 
JayT said:
Thanks guys. No relation to the company that makes the CD transports. Just my first name. :D

Yes, this is the Modushop Slimline 2U purchased through the DIY Audio store. They've been great to work with as well. I also used their cases for a pair of small monoblocks, and have another pair on the way now for a pair of Purifi-based class D monoblocks that I'm building with a 1500VA linear power supply for each channel. I hope to have them done by Christmas (at least version 1 - I'm planning to experiment a bit with different buffer designs).
Click to expand...

Thank you JayT.

* Jay's Audio also makes a Dac-2 Signature and several Linear Power Supplies.
 
Purifi is now offering their 1ET400A module for DIY. I am not using their EVAL input buffer for a number of reasons. First, it is for stereo and I'm building monoblocks, but it also incorporates the connectors on the board, so this makes it harder to experiment with other buffers.

I've designed the chassis so that it has enough room for a 130mm x 85mm input buffer, which should give me enough space to experiment with several different approaches. I'm going to use the Neurochrome buffer board to start with since I think this is a well designed op-amp based board that uses op-amps with enough drive to do a decent job. But I have plans to design and build a few more options to see how they affect the sound. I'm planning a discrete single-ended class A design and a triode-based design, among others.

I chose to use a linear power supply for a few reasons. First, I wanted to design the power supply myself instead of use an off-the-shelf SMPS which is what most of the class D vendors use, and I've never designed a SMPS myself so didn't want to try to tackle this. I also think that a good linear PS can respond faster to changes in current demands and delivery more peak current than something like a Hypex SMPS1200A700 that is commonly used. Many of the top rated class D amps use linear power supplies, so I think there is something to this. But we'll see how it sounds when I'm done.

I mostly do DIY because I enjoy the challenge and satisfaction of building it myself - at least as much as the end result. But it's always nice to end up something I can enjoy and be proud of.
 
Devg said:
Don't think so. Jay's audio builds some of the best Redbook CD players and based out of China.

Srajan's glowing review on 6moon:

6moons audioreviews: Jay's Audio CDT2 MkII
Click to expand...

That's a very nice top loading Redbook CD transport, built like a high-end jelwery Swiss (China) watch.

It too has an OLED display ... cool. ... And good review too; "glowing" just like you've said.

35.jpg
 
Thanks. I debated with myself on how to do the grounding and did a bunch of online research to get ideas. What I ended up with seems to work really well. No audible hum or hissing coming from the speakers. The heavy copper plates are probably overkill, but hey, that's what diy is all about. I'm there only one I have to please :D
 
That is very nice work, congratulations. Nothing like the satisfaction of building it yourself.
 
Thanks stereogeek. Particularly when it it sounds good :D

My first DIY electronics project this year was a set of FirstWatt F5 Turbo monoblocks, and I have to say I was disappointed with the sound. I was expecting them to sound fabulous, but they really didn't come close to my Parasound JC5, particularly in the detail they presented.

I later built another pair of monoblocks based on a Neurochrome chip amp design, which I'm pretty happy with. It doesn't have the effortless power that the JC5 has, but everything else about it sounds excellent.

I'm looking forward to finishing the class D monoblocks I mentioned earlier in this thread. Hopefully by the end of the month.
 
You must log in or register to reply here.
Back
Top