I fear plastic ends to the case will let the hum in...
Perhaps add a ground terminal to the metal part of the case and ensure the two halves are in electrical contact (anodized finish is an insulator).
Perhaps add a ground terminal to the metal part of the case and ensure the two halves are in electrical contact (anodized finish is an insulator).
Good catch, both halves of the enclosure are electrically bonded, and I added a ground terminal. I also removed the anodizing at contact points to ensure continuity.
Only if they are a truly random sample, whatever that is, but most will never order very many new parts at one time.
Often there is a clear bias toward smaller uF values, though you may get one or two dead-on parts out of a group of 10-20.
Since many thoughtful ideas and questions have come up in this thread, I’ve gathered the key materials for anyone who wants to take a closer look or replicate the build.
Here is the original Altium Designer project, which includes the schematic and PCB layout exactly as used to fabricate the boards. All layers are included and the output jobs are set up so you can directly generate Gerbers for production if needed. And also a 12-page PDF that documents the project in detail, covering circuit theory, attenuation structure, simulation results, layout photos, BOM, mechanical design, and final assembly.
The goal of sharing these is to make the design transparent and reusable, whether for direct use or as a starting point for your own variation. It’s not a commercial project, just a personal tool developed for precise phono stage testing, but if it’s useful to others, all the better.
Download links:
Altium project – ready for PCB fabrication
Project documentation PDF – full design and build notes
Here is the original Altium Designer project, which includes the schematic and PCB layout exactly as used to fabricate the boards. All layers are included and the output jobs are set up so you can directly generate Gerbers for production if needed. And also a 12-page PDF that documents the project in detail, covering circuit theory, attenuation structure, simulation results, layout photos, BOM, mechanical design, and final assembly.
The goal of sharing these is to make the design transparent and reusable, whether for direct use or as a starting point for your own variation. It’s not a commercial project, just a personal tool developed for precise phono stage testing, but if it’s useful to others, all the better.
Download links:
Altium project – ready for PCB fabrication
Project documentation PDF – full design and build notes
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I'm only half joking.
In spite of the full cast alu box, I have a hard time finding THE sweet spot on my bench where hum is not too intrusive.
I get that، sometimes it feels like hum has a mind of its own. Glad I’m not the only one playing 'find the hum-free zone' 👍
Good to have a reverse riaa.
I use this one for decades.
Never used enclosure, no humm.
Selected parts by hand from big batch.
Build several phonostages with good respons. See measurements below.
My generator has 50 ohm output impedance.
Recap, good to have your own reverse RIAA.
This one is build by hundreds DIY's.
Cost just a view euro,s.
I use this one for decades.
Never used enclosure, no humm.
Selected parts by hand from big batch.
Build several phonostages with good respons. See measurements below.
My generator has 50 ohm output impedance.
Recap, good to have your own reverse RIAA.
This one is build by hundreds DIY's.
Cost just a view euro,s.
Sit the unit in back or on top of the preamp, and use very short cables between them.
Regarding hum, aluminium or copper enclosures don't shield low-frequency magnetic fields well unless they are much thicker than the skin depth, which is of the order of 1 centimetre in copper at the usual mains frequencies. They do shield low-frequency electric fields well. To reduce the sensitivity to low-frequency magnetic fields, you can try to keep loop areas as small as possible, particularly the loop from resistors 13...20 in post #4 to the output connector and back.
There's accurate and there's pretty. Some people have time to build both but I just needed to git 'er done.
Great to see your version. Selecting parts by hand from a large batch really shows in the response. That’s a true DIY spirit right there. Also the variety of approaches is what makes DIY so interesting.
Thanks for sharing your build and results 🙏
It's interesting how surprisingly deep the skin depth is at 50/60 Hz.
I tried to keep return paths tight and loop areas minimal, especially around R13–R20 and the output jacks. I’ll revisit that area again to double-check for possible improvements.
Appreciate the practical reminder👍
Hi,
interestingly regarding hum I typically can see large hum peaks when measuring with the QA401.
So far nothing helped, no moving positions, no switching lights of, no different connections, resp. cables etc.
The only option I see left seems a powered USB cable for the QA401, though nothing changed when I supplied it through an laptop instead of the PC.
I don´t see those big peaks with he DAAS32.
Connected in a listening setup its immideately obvious, that the phono-stages are not the source of the hum.
So if You measure through the inverseRIAA take the resullts with a grain of salt.
If large hum artefacts show up, it might not necessarily be audible hum, but just inverseRIAA related.
jauu
Calvin
interestingly regarding hum I typically can see large hum peaks when measuring with the QA401.
So far nothing helped, no moving positions, no switching lights of, no different connections, resp. cables etc.
The only option I see left seems a powered USB cable for the QA401, though nothing changed when I supplied it through an laptop instead of the PC.
I don´t see those big peaks with he DAAS32.
Connected in a listening setup its immideately obvious, that the phono-stages are not the source of the hum.
So if You measure through the inverseRIAA take the resullts with a grain of salt.
If large hum artefacts show up, it might not necessarily be audible hum, but just inverseRIAA related.
jauu
Calvin
Sometimes just getting it finished matters more than anything, especially when the circuit works as it should.
Your build definitely gets the job done.
Personally, I’ve found that inverse RIAA filters are best reserved for checking frequency response and crosstalk. Once we start analyzing noise, THD, or intermodulation, things can get unreliable pretty quickly, too many variables introduced by passive loading, grounding, and even loop area effects.
I see the IRN more as a tool for linearity tests than full spectrum analysis. Still incredibly useful, just within its sweet spot.
Hi nice buildings.
I am using Jim Hagerman inverse riaa net for measurements.
http://www.hagtech.com/pdf/iriaa2.pdf
https://cdn.shopify.com/s/files/1/0433/2441/files/riaa.pdf
cheers
I am using Jim Hagerman inverse riaa net for measurements.
http://www.hagtech.com/pdf/iriaa2.pdf
https://cdn.shopify.com/s/files/1/0433/2441/files/riaa.pdf
cheers