Noir, a two transistor headphone amp: class-A, single ended, 150mA bias

Jump to Latest
#121
It is obviously distorted/clipping at less than half of the pot level with the HE-4xx's which is to me a moderate listening level. It's a bad combination for whatever reason. Now that being said I have never been impressed with the HE-4xx's and I don't rule out that there is something wrong with them.

Now I do love the T60RP's with the NOIR, this combination brings a different presentation than the SMSL THD amp that I have been listening to for a while now. There is more pace to the mid base to mid range. Kick drums impact are articulated, bass guitar was more accounted for in comparison. When I listened to Mondo Cane I could hear more room reverb, no check that I could hear the room reverb which I compleatelly missed with the SMSL combo. I've heard other parts of this recording that jump out, and it is great but I have babbled enough about my tin ears. Oh one more thing I have turned up the T60RP/NOIR combo to 11 for no longer than 3 seconds and no obvious distortion / clipping at all, just too loud to listen to.

I do find it weird that two cans that are at least similar electrically on paper give such drastically different presentation. I really do not consider the MassDrop HE-4xx a reference at all.
 
#122
Is sensitivity much different for the two headphones? On paper they should be fairly close.

I would suggest taking the multimeter to the HE-4xx and measuring DC resistance at the plug. Maybe there's something silly like a sneaky short. Speaking of which, visually compare the plugs of both cans as well - sometimes a non-ideal plug/jack combination can give you a bad day as well. At times adapting back and forth between different sizes can resolve such issues.
 
#123
I didn't look at paper until I posted but the T60RP's are 50 ohm with sensitivity of 92db/mw. The HE-4xx are 35 ohm at 93db/mw.

DCR for the T60RP is 49.4 tip to ground, 49 ring to ground, 98 tip to ring
HE-4xx 41.6 tip to ground, 41.7 ring to ground, 83 tip to ring
Grado SR60 is 32.3 tip to ground, 31.8 ring to ground, 64 tip to ring

I have tried different adapters for the He-4xx's both listening and measuring with no difference worth mentioning. It confuses me more with measuring the DCR higher than expected on the HE-4xx, I bet money its sensitivity is much lower than advertised.
 
#125
How critical are the values of the power fuse on the power supply input (RXEF050)? Mouser doesn't have these in stock and they've been back ordered for months. Can I simply use an inline .5amp slow blow fuse or a lower value (.5 amp versions are in stock) ?
 
#131
Restricted Availability, screen capture image below.

It appears that DigiKey UK does not have the same restriction (???), call them on the telephone to verify this point.

Example

_
 

Attachments

  • screeng.png
    screeng.png
    66.8 KB · Views: 868
#134
Do you have an unused Ethernet cable? It’s a great source for wire for projects such as this. I used a strand of wire from such a cable in mine, not sure if it was 28ga specifically, as it’s not particularly critical.
 
#137
Last edited:
#138
Stuck at home because the Gouv issued a request for everyone to stay home unless you need to go to the grocery store, I did my own version of the Noir, an intriguing very nice HP amp. Tom of Neurochrome did a detailled analysis of the amp and he identified a few areas where the original design may be improved such as the power supply noise floor, channel separation and a slight oscillation under certain load. I don't pretend to be able to improve an already mature design, but I may try. I still used the same circuit topology but I also added a few twists of my own. No need to mention that it is a private project, just for me. The official project is still on diyaudio store. Here is what I did:

I like integrated power supply, so I added a 24V SMPS power supply, with CLC filter (same as my version of the B1 preamp), followed by one common and then two dual CRC filters (one final RC stage per channel) to try to reduce the noise floor, added two possible ALPS volume pots on the same pcb, reroute the input traces up to the pot to separate them with gnd traces and split VCC layers per channel to try to improve channel separation, added a chassis Ground lifter for the audio ground, reversed the VCC on the positive side, and the gnd as I prefer. Finally I also added a snubber network at the output, apparently the original circuit can oscillate a little depending on the load. The snubber exact values (if they are needed) are still not determined... It still fits into the same enclosure, but it doesn't work with the store included front panel. No problem I'll do my own... Here a picture of the concept.
 

Attachments

  • Actual PCB.JPG
    Actual PCB.JPG
    278 KB · Views: 633
Last edited:
#139
For those who are interested, here are 3 different gain versions of Noir in LTSpice. 6dB (stock), 9dB and 12dB. Only R75 - 78 values are changed. The 12dB version waveform clips asymetrically. I'm planning on building the "hot-rod" 9dB version to see how much it might improve performance on my planar magnetic cans.
 

Attachments

#140
Algar_emi said:
but I also added a few twists of my own. No need to mention that it is a private project, just for me.
Click to expand...

Fantastic! I'm glad you're experimenting and I hope you have tons of fun with it.

You might be forced to choose the next-bigger Galaxy 1U chassis (230 mm deep instead of stock Noir's 170 mm deep chassis) in order to create enough room for an IEC mains inlet. If so then you can select an IEC inlet with integrated fuse; that will allow the user to replace a fuse from the outside, without having to open the cabinet and fiddle with the PCB. It also allows you to select an IEC inlet with both an integrated fuse and a mains power switch. I don't see any flywire / external I/O terminals for an on-off switch on your PCB layout. Since Noir consumes 8 watts thanks to class-A operation, you might want to turn it off when you're not actively listening.
 
You must log in or register to reply here.
Top Bottom