New PassDIY Headphone Amp (now available)

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Yes, it's a meanwell PD-25.

Regarding ground loops: I've tested with a laptop and a phone - both produce the same result which is a quiet but still audible hum. Since neither a laptop nor my phone were connected to mains during the test I'm thinking I may have a ground loop somewhere internally then.

The amp produces quite a lot of noise when no input is connected - is it normal?

I know I may be fighting an uphill battle here with a SMPS but I'm willing to spend time to debug this one and add some more filtering if necessary.

I'll try to draw all my ground connections later today so that you guys can have a look and tell me if I'm missing something here.
 
No volume pot for now, feeding it straight from the source. I will try to unplug some redundant ground connections and see what happens.

EDIT: I think I solved it. I wired the headphone jack in the wrong order ;) I'm testing the amp right now with HD600s and it's super quiet. I need to wait till I go back home to test with my IEMs as they are more sensitive.
 
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It looks from your photo (a nicely detailed one too) that the 0v grounds for each channel are common together on the power supply output terminals, then go each amp (with it's own input ground/shield) and you have taken a separate ground wire output and commoned up these on the headphone socket - try removing one from the amplifier output terminal and see what happens - I use the 4 pins wiring system these days to avoid this possible complication

I remember somewhere that a resistor was sometimes inserted in the signal ground wire but can't remember if this is practical/suitable here

Check the Meanwell ground/0volt scheme - You could also make up a metal mesh cage to cover the PR2525 and fasten it to the chassis

On the Neurochrome amplifier switch-mode power supplies, Tom uses a choke and a cap on the output of the switcher supplies - I don't know the values (a proprietary design) but it illustrates that it might be worth looking at this later on.

It is worth persevering with
 
Yeah, I missed that too

I have an idea that altho the circuit isn't totally new or unique, it'll provide no end of variations - I got a couple of the single Burson V6 ICs (still a couple available here in the FS section) to expand the chip selection and playing with different power supplies too

I didn't realise that Nisbeth had boards available and had one designed -
're-invented the wheel', so to speak - and I got some boards from china - similar layout - could have saved the trouble, damnit!

I once used a 'shorting' jack plug on a headamp - a silly mistake and caused no end of trouble
 
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My own version with super regulator and the Burson classic.
 
Thanks Nisbeth,

I pretty much followed your layout with just a few 'tweeks' here and there, so it's still your and Wayne's design - thank you

I'm playing around with some different components and there's some minor changes to the sound altho it does seem to reflect differences in the power supply with a much higher bias current, plus the input IC

Like 'chat', I'm currently using the Burson Classis V6s and it's a pretty good overall result but as this is so subjective, it's hard to describe as it's directly dependent on the headphones - I'm using the Massdtop version of the HiFiman HE 400s (the HE-4XX) with an aftermarket cable instead of my old k701s - works very well indeed.
 
Curiously, I set my Salas shunt reg up to drive the DAO headamp but found the results less than satisfactory - even when the supply was passing 350mA for the amps 250mA consumption, it just didn't seem to work well - I tried all sorts of different things but never did find out why - with that amp, I just went back to using an over-designed but simple CMx supply - hope you get a better result

With this HPA, I'm trialing thru some different supplies like Shunt regs, AMB Regs, TeddyRegs, and the simple KMx circuit -

I'm actually rather curious about the TPS7A4700/3301 regs but not so easy to find the pcbs - I found the Aune guys in Taiwan but can't work out how to order a couple of pairs of fully assembled boards that they have on their website
 
This is a follow up review of several of the DIY headphone amps presented in the past months through several brands of headphones.
My original post on the Salas DCG3 build is #2131, for the XRK971 build is #1229 and the Pass DIY build is #820 for anyone wanting to read my first thoughts.
Since that posting, I have purchased through a MassDrop buy, a set of Sennheiser HD6XX phones, which I believe are actually HD650 cans. New additions on the headphone amp side include one of Pete Millet's Korg Nutube headphone amps and a desktop (AC) version of XRK971 PCA. This amp is biased at 120ma, running larger Panasonic caps on the output and very large caps (15000uf) on the power input than a battery operated version of the PCA. The Nutube amp also has a pair of Burson V6i opamps in place of the recommended OPA551 opamps. The Pass DIY by Wayne has a Sparkoslab SS3602 in place of the AD823.
Play back is now through a SMSL M8A DAC with a clean outboard 5vdc supply. Also inline is an Uptone USB Regen. The audio file is a .FLAC. All systems are given a minimum of 24hrs at room temperature before listening.
Last time I used a live performance of Dave Brubeck's "Take Five". This time I am using a Pink Floyd song from their 1973 album "Dark Side of the Moon". That song is " The Great Gig in the Sky". The instruments are a piano, Hammond organ, pedal steel guitar, bass, and drums. The main vocals are supplied in an almost orgasmic way by Clare Torry. Her wailing reveals much about the amps and headphones!!

Salas DCG3
Sennheiser HD6XX
Wide soundstage with drums and Torry appear in the center. Cymbals are clear and crisp sounding. Organ far left, piano front in right ear. Vocals soar with no obvious distortion. The piano is well defined.
HiFi 400i
Similar wide stage as the Sennheiser cans, spoken voice clear. The cymbals and Torry's vocals are not as clear as with the Sennheiser phones. Bass is very defined. For the second set of vocals Torry is slightly overpowered by the piano. Piano and bass are clearly defined.
Thinkd Sound ON-2
Soundstage appears lower and more separated. Cymbals are clear and defined. Vocals are centered and also well defined. Drums and cymbals crisp sounding. There is a better balance with the piano and Torry. Piano crisp with nice overtones.
OB1
Nice base definition. Good soundstage, though drums and cymbals are masked somewhat by the organ and piano. Torry vocals are a bit muddy sounding. In her second set of vocals the sound is more subdued as well the piano is less defined. Overall a more muted sound not as defined, though not unpleasant to listen to.
Ultrasone Pro 750
Piano sounds slightly smeared with a bright sound. Drums and cymbals have very clear sizzle to their sound. Hammond organ very dominate in left ear. Torry's 2nd vocals are clean sounding the piano sound is rounded, with the bass somewhat subdued.
Sony 7506
Piano is thin sounding, with the bass rounded and full sounding. Drums and cymbals are prominent and defined. Torry's vocals are the most upfront sounding of the headphones I have. In her 2nd set of vocals the bass is very dominate with the piano still sounding thin, not as defined.
Audio Technica ATH-M50
A very detailed piano, with good bass, nice wide soundstage. The drums are distinct with the cymbals having a clear sizzle to their sound. Torry's vocals clearly defined. The Hammond organ has a nice mellow sound. Torry's 2nd vocals are still defined and the bass is very present. However she appears to sound more in the background with the bass and piano up front.

XKR971 desktop Pocket Headphone Amp
Ultrasone Pro 750
Piano smeared somewhat, not as distinct. Drums are clear and the cymbals have a nice sizzle sound to them. Hammond organ sounds muddy, not as clear. Torry's vocals are bright. In the 2nd part the piano is still a bit muddy sounding, though there is a nice balance with vocals, piano and bass.
Audio Technica ATH-M50
Piano clean sounding with a wide soundstage. Hammond organ is distinct. Drums and bass are more pronounced. The vocals are not as clear and defined.
Sony 7506
Vocal very clear. Pedal steel and organ are clean and clear sounding. Drum and cymbals are well defined. The bass is very pronounced. In 2nd set Torry's vocals are a bit shrill sounding, but clear. Individual piano notes are clear. For this amp and song this headphones really are nice.
HiFi 400i
Wide soundstage with a clear organ and piano. Nice airy vocals with the drums and cymbals crisp. Hammond organ is distinct with a good balance on vocals and rest of the instruments. Torry's 2nd vocals really soar and the piano is nice and round with distinct overtones.
OB1
Wide soundstage with defined bass and clear pedal steel. A good blend of organ, drums, vocals and piano. Smooth clear 2nd vocals and piano. There is a nice balance with good depth in the soundstage.
Think Sound ON2
Slightly bright piano. The pedal steel sound smooth, with nice drums and cymbals sizzle. The organ is clean and defined. The bass is very solid along with clean, clear vocals. Torry's 2nd vocals and overall sound are nicely balanced. The piano and bass are balanced with the piano not as bright. Her vocals are very light and smooth.
Sennheiser HD6XX
Piano very natural sounding, with the pedal steel smooth and rounded. A wide soundstage with the drums somewhat muted and cymbals not as crisp sounding. The vocals are further in the background. Her 2nd vocals are distinct and soaring. The piano is very nice with the bass sounding further back, not as dominate. Overall a good balance.

Pete Millet Korg headphone amp.
HiFi 400i
Nice wide soundstage with a natural sounding piano. Clear pedal steel and crisp sounding drums and cymbals. The Hammond organ is nice and distinct, with Torry's vocals being more centered and clear. In the 2nd there is a good balance between the vocal, piano, and bass. Torry's voice seems to float above it all.

Audio Technica ATH-M50
Good bass with a wide soundstage. Pedal steel is not as distinct. The drums are more forward, additionally the organ and drums seem to overpower the vocals a bit. Her second vocals are better sounding balance with the instruments. They also are brighter and pushed back in the soundstage. The bass is very prominent.
Sennheiser HD6XX
Another wide soundstage with the pedal steel and vocals clear. The Hammond organ is distinct. Drums have a nice balance with the crisp cymbals coming through. Overall good balance between the vocal and instruments. Torry's vocals just seem to float and soar in this 2nd bit, with the piano notes clear and distinct. The bass appears at a slightly lower level.
Sony 7506
Defined piano and bass on a wide soundstage. The pedal steel is distinct with the drums sounding upfront, though a bit over powering. Torry's vocals are clear and distinct as is the Hammond organ. In the second part she is heard a bit more forward in depth and every bit as clear. Piano and bass are well defined.
Think Sound ON2
Rounded bass and pedal steel with the piano not as defined. A nice wide soundstage. The Hammond organ and vocals are defined. The cymbal really has nice sizzle and the drums are very forward. Torry's vocals in the second part seem pushed back, but still distinct. The piano and bass dominate in this section.
OB-1
A wide soundstage, with a forward sounding piano. Pedal steel not as distinct, with the overall sound not as defined. The organ, drums, piano are blending together more. Vocal is also muddy sounding. Same for the 2nd bit, vocals sound muted, with the piano not as defined. However the balance of the piano, bass and vocals is ok.
Ultrasone Pro750
Another wide soundstage. Overall a bit light sounding, not in your face. The pedal steel and Hammond organ are clear and defined. Piano though sounds muddy. The cymbals sound almost a bit artificial sounding. Torry's vocals are clear. The bass and piano have a nice balance in this second bit with her vocals centered though a little muddy sounding.

Wayne's Pass Headphone Amp
Audio Technica ATH-M50
Wide soundstage, with a clear pedal steel and full sounding bass. Upfront Hammond organ, with distinct drum and cymbal sounds. Vocals appear pushed back, but very distinct sounding. In the second bit, piano and vocals have a nice balance and still are clear and distinct. The bass seems a bit upfront.
Sony 7506
Piano and pedal steel are distinct and clear. Vocals are more forward and clear. Same with Hammond organ and piano. The bass is dominate. For the 2nd bit vocals are airy and distinct with a nice balance against the piano. Bass is at an even level, not too forward.
HiFi 400i
Piano, bass, and pedal steel are distinct on a nice wide soundstage, with a nice balance. The cymbals are a bit down and sound slightly muted. The vocals and Hammond organ not as clear. In the second, Torry's vocals seem a bit smeared sounding and not as bright. The piano and bass are nice sounding with good imaging. The vocals sound more forward.
Think Sound ON-2
Nice balance on the piano and pedal steel. The organ and Torry's vocals are distinct and a bit more forward. Drums and cymbals have a clear sound with nice sizzle. In the second bit, the bass, piano and vocals still maintain a nice balance, plus the vocal are still distinct. The bass is not as dominate. Overall a very smooth rounded sound.
OB-1
Piano, pedal steel and bass are nicely balanced on a wide soundstage. Cymbals are crisp and distinct. Vocals are not as clear, with the bass and Hammond organ dominate. For the 2nd bit the bass still dominates, the piano is distinct. The vocals have some smear but are more forwad in the soundstage.
Sennheiser HD6XX
Needs more drive from this headphone amp. Bass not so forward, with the pedal steel and piano nice and rounded. The drums and vocals seem a bit pushed back, with the cymbals sounding very natural. The organ is clear and distinct. Nice overtones in the second bit with Torry's vocals more prominent. Piano and bass have a nice balance.

Ultrasone Pro 750
A wide soundstage, with the cymbals lacking some sizzle. Organ and vocals sound slightly muddy. For the second part the piano and Torry's vocals are distinct. Both appear centered in the soundstage with the piano slightly more forward. The bass is nicely matched with the piano and vocals.

This posting is just one person's thoughts on how some of the DIY headphone amps and various headphones sound. Your listening results will certainly differ from mine.
For me it is a lot about the build and then the enjoyment of listening to something I have built. Thanks to the many out there that can design these amps and are willing to share with the rest of us.
David
 
My "Whammy" - one step before completion..still missing some parts and alps RK27 pot not yet been received..."The caveman" diy PCBs + non-polar caps instead electrolytic ones source resistors will be 5R (two 10R parallel) for approx. 100mA bias. BB OPA 2604 + IRFs
 

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