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DAC/Pre-amp for JBL 305m MKIIs

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SK123

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I admit to not having read every post in this thread, but, just in case it may help:
What have you set the input sensitivity switch to on the 305p? For balanced inputs, it should be at +4dBu, but for single ended input (i.e. RCA to XLR) it should be at -10dBV.
If it is set incorrectly, (+4dBu with a single ended source) the output volume will very likely be lower than expected. Changing to the -10dBV setting might be a very straightforward fix for the "low volume" issue.

I am glad you mentioned the -10/+4 dbu, just completely forgot these. I had these on -10 because I was using RCA connection. I switched to the +4 now, and it didn't fix the volume issue. But volume issue doesn't really bother me, it just feels like these don't sound as rich as before. Also, the gameplay on these ain't all that satisfying either (in fact pretty disappointing particularly bf5).
 
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Burn in with speakers isn't really a thing, it's a myth. I don't know enough about how the HD400 works to describe if it will reduce sound quality or not. The loss of volume is a bit disturbing, on the surface, but I don't know if that is expected or not.

Ya, just that I was horrified in the beginning, and couldn't believe all the positive reviews for the speakers. Most likely its my audio software I was going back and forth trying to figure out whether 2 channels sound better or 8 channels.

Dont know if it's just my imagination or for real but it took ~20 hrs of audio for me to feel the 'wow factor' in these speakers and didn't have all these different variations of sound stage. May be because I left it on 2 channels and didn't bother playing with the software anymore fixed the unusual sound issue for me.
 

AnalogSteph

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But I do feel that wiring though the HD400, the richness of the speakers is quite reduced, and they sort of sound like when I got them first (like the burn-in time required). Also, the overall volume is reduced to like 1/4th which is not a big deal, but I do hope my speakers will back again begin to sound how they were sounding before wiring this product, hopefully within couple of hrs of playing.
Honestly, that doesn't sound normal. I'd say something is quite definitely not right there, in either your wiring or the HD400 clone.

You should not be seeing any substantial loss in level unless the output impedance of your source is super high. I conducted some measurements on my original HD400 a while back, and I don't think insertion loss came out to more than 1-2 dB using a 22 ohm SB Audigy FX output and I think ~22 kOhm recording input. The only thing it really didn't like was being plugged into a (consumer) microphone input with DC bias supply. That sent the transformers into saturation, with the low end completely gone and distortion off the charts.

To me your description almost sounds like a lost ground connection on the unbalanced side, or perhaps even the balanced side outputting a signal between T+R in parallel and S. Sounds like a case worth investigating with the trusty multimeter.

Here's another test:
Use the tone generator in Audacity to generator a sine. 440 Hz @ 0.3 is fine.
First play in mono.
Duplicate the track twice. Assign one of the new tracks to the left channel, the other to the right channel.
Select your right channel audio and apply the "invert" effect. Now you've got a test tone with both channels out of phase.
Mute your original mono test track.
Play back.

Normally both should play at the same volume, the out-of-phase one will just sound super weird. If there's a major difference something is in fact wrong.

I cannot seem to find any pictures of what the innards of a HD400 should normally look like, but I imagine it would be two small either toroidal or more conventional EI (e.g. Tamura) transformers mounted on a circuit board.
 
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Honestly, that doesn't sound normal. I'd say something is quite definitely not right there, in either your wiring or the HD400 clone.

You should not be seeing any substantial loss in level unless the output impedance of your source is super high. I conducted some measurements on my original HD400 a while back, and I don't think insertion loss came out to more than 1-2 dB using a 22 ohm SB Audigy FX output and I think ~22 kOhm recording input. The only thing it really didn't like was being plugged into a (consumer) microphone input with DC bias supply. That sent the transformers into saturation, with the low end completely gone and distortion off the charts.

To me your description almost sounds like a lost ground connection on the unbalanced side, or perhaps even the balanced side outputting a signal between T+R in parallel and S. Sounds like a case worth investigating with the trusty multimeter.

Here's another test:
Use the tone generator in Audacity to generator a sine. 440 Hz @ 0.3 is fine.
First play in mono.
Duplicate the track twice. Assign one of the new tracks to the left channel, the other to the right channel.
Select your right channel audio and apply the "invert" effect. Now you've got a test tone with both channels out of phase.
Mute your original mono test track.
Play back.

Normally both should play at the same volume, the out-of-phase one will just sound super weird. If there's a major difference something is in fact wrong.

I cannot seem to find any pictures of what the innards of a HD400 should normally look like, but I imagine it would be two small either toroidal or more conventional EI (e.g. Tamura) transformers mounted on a circuit board.

Hey Steph how are you doing!!
Thank you for detailed reply. Pls check my attached file, I hope I followed the instructions correctly. I 'select' on the third recording and put the invert effect for that track. I don't hear any weird sounds, just the same tone on all three.

Also, on Aliexpress, one of the reviews for the product says they only get half the signals: https://www.aliexpress.com/item/4000087053010.html?spm=a2g0s.9042311.0.0.52234c4ddjBIBc

I dont know if my clone HD400 really is faulty.

Also, weirdly enough, I maxed out the volume to 100 in one of the games, and it still was sort of "low" and didn't bother my ears. Before for music, 10 was the super high, now at 40 it still feels a bit lower than previously 10.
 

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Something's really wrong with the volume stuff, it's actually much less that 1/4th. I increased music vol to 70 and it sounded like how it used to sound at 10-12 before connecting to hd400. Than I reduced back to 40 vol and it was really low. And it still didn't sound as rich and detailed.

Is it possible TS to RCA cables could be promoting downgrade of signals? I should have asked before why TS to RCA instead of TRS to RCA?
 
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AnalogSteph

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Something's really wrong with the volume stuff, it's actually much less that 1/4th. I increased music vol to 70 and it sounded like how it used to sound at 10-12 before connecting to hd400. Than I reduced back to 40 vol and it was really low. And it still didn't sound as rich and detailed.
That's like a lot. Around these parts, the difference between 11% and 70% is about 28 dB.

This honestly sounds like what you're hearing may be (normally unwanted) common-mode coupling, i.e. you're inadvertantly conducting a CMRR test on the HD400. 28 dB sounds roughly like the right ballpark for that in a SE-SE scenario (I would expect more running into a balanced input).
Is it possible TS to RCA cables could be promoting downgrade of signals? I should have asked before why TS to RCA instead of TRS to RCA?
It actually shouldn't matter - RCA to TRS would bridge R and S anyway, one way or another.

All I can think of is that you should probably try to dig up (buy/beg/borrow/steal) a multimeter and verify continuity on your cables. (If you have never used one, YT tutorials FTW.)
RCA to TS should be signal --> tip, shield --> sleeve.
TRS to XLR should be T --> 2, R --> 3, S --> 1.

Also, if you could borrow an XLR to TRS to test the HD400 clone with the multimeter, you should be finding a connection (transformer winding) between T and R (2 and 3), S (1) not being connected. That's for both input and output side. (Mine actually gave better distortion figures when used in reverse, but had an ultrasonic peak in frequency response. I'm guessing they put in some sort of parallel load resistor just on the output side to keep the peaking at bay.)
 
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That's like a lot. Around these parts, the difference between 11% and 70% is about 28 dB.

This honestly sounds like what you're hearing may be (normally unwanted) common-mode coupling, i.e. you're inadvertantly conducting a CMRR test on the HD400. 28 dB sounds roughly like the right ballpark for that in a SE-SE scenario (I would expect more running into a balanced input).

It actually shouldn't matter - RCA to TRS would bridge R and S anyway, one way or another.

All I can think of is that you should probably try to dig up (buy/beg/borrow/steal) a multimeter and verify continuity on your cables. (If you have never used one, YT tutorials FTW.)
RCA to TS should be signal --> tip, shield --> sleeve.
TRS to XLR should be T --> 2, R --> 3, S --> 1.

Also, if you could borrow an XLR to TRS to test the HD400 clone with the multimeter, you should be finding a connection (transformer winding) between T and R (2 and 3), S (1) not being connected. That's for both input and output side. (Mine actually gave better distortion figures when used in reverse, but had an ultrasonic peak in frequency response. I'm guessing they put in some sort of parallel load resistor just on the output side to keep the peaking at bay.)
Thanks for the suggestions again. I dont have any friends that are into electrical stuff so it would be difficult to acquire multimeter. I am thinking of buying an actual Behringer HD400 and comparing it with the clone one. I will update you guys whenever I am able to test both products side by side.
 
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I wasn't implying a fancy multimeter - you can get some half-decent ones in the 20-30$ range already (even if it may not be EEVBlog approved), and your nearest home improvement store might have one. They're quite handy to have around.
Ok, I'll look into it. For the Brngr hd400, only one of the four major store-chains near my home has it, and i cant return an opened box product, only exchange. lol.
 
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So I got the Behringer HD400, and my speakers are back again to being boomy and awesome. Can't believe the crap they sold as the clone.

That being said, my volume is still about 1/3 than it used to be. E.g. it sounds at 30 what it used to sound at 10-12 at unbalanced connection. With the clone model, even at 100 it wouldn't sound as good and rich as it sounds now. Ironically though, the clone is built exact quality as the original one, it would suck to recycle this. If any of the inner parts can be changed, that'd be awesome.
20200824_163810529_iOS.jpg
20200824_164125605_iOS.jpg
 

AnalogSteph

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So I got the Behringer HD400, and my speakers are back again to being boomy and awesome. Can't believe the crap they sold as the clone.
Yay! :cool:
That being said, my volume is still about 1/3 than it used to be. E.g. it sounds at 30 what it used to sound at 10-12 at unbalanced connection.
Huh. I can't shake the feeling that there's still something amiss here. It sounds for all the world like super high output impedance.

What did you say you're using for a soundcard again? Xonar STX? Have you ever messed with the swappable opamp business?

In case of onboard audio I'd be wary of any 1-piece 3.5 mm to RCA adapters, these can be really dodgy.

Input sensitivity and volume knob are definitely set like they were before? There's a 12 dB difference between -10dBV and +4 dBu alone.

I would suggest you recheck levels by temporarily plugging one of the HD400 input cables directly into the speaker again - it would be silly to find that we're chasing ghosts here.
With the clone model, even at 100 it wouldn't sound as good and rich as it sounds now. Ironically though, the clone is built exact quality as the original one, it would suck to recycle this. If any of the inner parts can be changed, that'd be awesome.
Unless the circuit board contains some gross miswiring, it could pretty much only be the transformers. These 600 ohm jobs are normally used in landline telephone and fax applications; I suppose the folks at Behringer identified a type that was good for rather more than just that, while the clone may be using a more modest type that doesn't have much to offer in the bass department - telephony doesn't require much below 300 Hz after all.

Here's more than you probably wanted to know about transformers like these:
https://www.onallbands.com/non-linear-xformer-behavior/
 
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Asus Essence Stx II is my soundcard. Never messed with the swapable opamps though, but I was really itching to do, than got busy in other things.

Volume knobs are on full as before but i changed the sensitivity to +4 from -10 because of the balanced connections. If I'm not mistaken, this should increase the volume even more rather than going down? I wish my speakers were set on my tiny desk, would have been so much easier than picking them up off the floor (placed on yoga blocks :)) every time needs to tweek something...

Edit: Ok so for one of my speakers, I ran them using the input cable, and the volume was the same. Than I changed the sensitivity back to -10 for RCA connection and the volume shot up back again, like it used to be.

I was under the impression that +4 dbu would mean higher volume..

If volume decrease doesnt translate to lower sound quality than I guess I am happy with playing them at 24-30 at+4dbu, instead of 8-12 at -10dbv?
 

AnalogSteph

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Good to know that the mystery has finally been solved.

I was under the impression that +4 dbu would mean higher volume..
Actually, no, as you found out.

What you are setting is input sensitivity, i.e. input level required for a given output level (@ volume = max), 92 dB SPL @ 1 m in this case. At -10 dBV (300 mVrms), you will need 12 dB less than at +4 dBu (1.228 Vrms). So -10 dBV is in fact the quieter setting.

According to specs, the -10 dBV setting will accept levels up to +6 dBV = 2 Vrms or typical consumer DAC output level (including your STX II's line out), vs. up to +20.3 dBu (8 Vrms) for the +4 dBu setting.
If volume decrease doesnt translate to lower sound quality than I guess I am happy with playing them at 24-30 at+4dbu, instead of 8-12 at -10dbv?
It would certainly still seem adequate to me. Here (Xonar D1) 24-30% would translate to -21.6 dB to -18.2 dB, so you'd still have about the recommended 20 dB of headroom.

However, it would be better if you arrived at this input sensitivity by choosing -10 dBV and turning down the volume dial instead. I am very much assuming that the input sensitivity switch alters analog input stage gain to give input ADC full-scale input at either 2 Vrms or 8 Vrms, and the volume dial is just controlling internal digital level adjustment. A consumer line-level output combined with the +4 dBu setting would thus result in the top 12 dB of ADC dynamic range being wasted, and if memory serves that's only around 100 dB to begin with. In return, ADC noise would be brought up. So you may be seeing higher noise than necessary, and as we all know the JBLs aren't exactly setting any records in this regard to begin with.

For reference, I am using the same range of soundcard output volumes with
* ReplayGain enabled (album gain, avoid clipping), pre-gain = -3.2 dB, WASAPI (shared mode) output (just as loud as DirectSound, but I figured it would be one less abstraction layer as DS sits on top of WASAPI in the sound stack anyway)
* YouTube volume = 50%

(BTW, get XonarSwitch if you don't have it, the tool has proven quite handy for its ability to set presets alone - I've got ones for 44.1, 48, 96 and 192 kHz @ 24 bit each. Note, if you ever need to set system and card sample rate different from one another, go with card > system. While hardware upsampling is very good, attempting to downsample has resulted in terrible quality for me.)
 
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As always, thank you so much for the great, detailed explanation. I did switch back to -10 dbv yesterday and feel better about my speakers :)
I will play now with XonarSwitch and see what it does for me.
 
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