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Salas DCG3 preamp (line & headphone)
Salas DCG3 preamp (line & headphone)
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Old 19th September 2017, 02:55 AM   #2131
drpro is offline drpro  United States
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Salas DCG3 preamp (line & headphone)
Background:

One person's observations on three different class A headphone amps and six different manufactures headphones. The listening observations were made over a period of several days. At age 65 with mild tinnitus and definite high frequency hearing loss these observations should be taken with these facts in mind.

The class A headphone amps are the diy Pass Headphone amp by Wayne (wizard's assistant) at Pass Labs, XRK971's Pocket class A amp, and Salas's DCG3 line and headphone preamp. All three amps where built to the designers BOM. In the PCA by XRK some builders suggested some capacitor changes on the input, output and supply rails I made the changes.

All three of these headphone amps are described on the DIYaudio.com site, so if you want more details seek out those threads.
The source music is "Take Five" by Paul Desmond and Dave Brubeck. It is from the 1982 album "Concord on a Summer Night" (live). It was ripped as a Flac and played directly from a Dell computer using that device's output. No outboard DAC was used.

The six headphones I used are the Sony MDR-7506, Audio Technica ATH-M50, Ultrasone Pro 750, ThinkSound ON2, HiFiman HE400i, and Status Audio OB-1. Cost of these headphones ranges from 60-400usd. Certainly not high end, but reasonable in price.

Listening note, for each set of headphones listened too I would replace the 9v batteries used in the PCA with fully charged ones.

XRK971 PCA headphone amp

OB1 - bass a little muffled, mids clear not hyped, sound stage reasonable front to back, cymbals muted sounding, no zing. decent sound stage width, not overly bright, clarinet sounds clean and clear.

ON2 - bass more clear, solid, clarinet seems more neutral/natural, more sizzle on cymbals. there is more separation of instruments, nice sound stage, drums are more defined than OB1 phones

HE400i - needs more gain than ON2 or OB1 phones, bass not as much in your face, clarinet and piano are more natural, nice sound stage, piano solo very wide, drum solo is like you were there.

Ultrasone 750 - piano sounds more treble, clarinet also lost some presence, good separation on individual instruments, sound stage not as wide, piano solo not as deep, seems like I am not hearing in overtones, some loss of sizzle on cymbals

MDR7506 - narrow sound stage, bass hyped and muffled sounding, clarinet muffled and close feeling. cymbals muddy, no sizzle. piano sounds constrained. overall feeling is muddy and lack of separation including audience clapping

ATH-M50 - clarinet sounds constrained, bass heavy, lots of it, clarinet feels lost in bass, during lower notes on piano sounds nice and clean, sharp, clear, sound stage wider during piano solo, drum solo wider with nice front to rear depth. sizzle on cymbals, clarinet loses some clarity

Pass DIY headphone amp

HE400i - needs more gain to match over headphones, nice wide sound stage, instruments are placed well with good depth, nice balance and separation, the piano sounds like you are there with overtones and decay, nothing sounds hyped

ON2 - a bit more bass sound, clarinet sounds tighter and appears farther back on stage, nice balance between, piano, drums, bass with sizzle on cymbals, piano brighter than HE400i phones, nice detail on drum solo

Ultrasone 750 - narrow sound stage, piano is constrained sounding, clarinet centered, lacks depth, piano lacks luster with solo in front, drum solo is nice and clear with cymbal clean

OB2 - clarinet muffled somewhat muddy, sound stage lacks depth, lack of clarity in the high notes, drum solo muffled sounding with no sizzle on cymbals, ok sound stage width, crispness lacking in drum solo

ATM-M50 - sound stage feels closed in, bass more present with good depth, clarinet has more range, piano notes more rounded, sound stage improves during piano solo, hand claps sound natural, drum solo opening sounding, real very lifelike

MDR7506 - bass hyped, clarinet and piano slightly muffled, decent width on sound stage, bass overwhelming at times, nice sizzle on cymbals, lack of depth in sound stage, drums lack some midrange.

Salas DCG3 headphone amp

HE400i - wide sound stage, good balance of instruments, clarinet really soars, audience clapping sounds natural, piano has nice tonal balance, a little light on drum solo, nice staging on drum solo. overall a very nice tonal balance

ON2 - bass a bit more pronounced, clarinet brighter sounds closer to listening in person, very good width of sound stage, piano also brighter sounding, drum solo more in your face as if you are present in the audience

Ultrasone 750 - nice balance of instruments, clarinet a little muddy sounding, nice wide sound stage along with nice depth, piano solo a touch bright sounding, drum solo has nice imaging, nice sizzle on cymbals

OB1 - nice separation of instruments, clarinet a little bright, bass slightly pronounced and muffled, wide soundstage, piano seems realistic, though there is some loss of clarity during the drum solo

ATM-M50 - bass has more presence overshadowing the other instruments, sound stage not as wide, bass too dominate during piano solo, piano solo tight, slightly artificial sounding, not melodic, good depth and width on sound stage during drum solo with nice sizzle on cymbals

MDR7506 - narrow soundstage, bass dominates, clarinet sounds natural, piano solo thin sounding, strident, strained, crisp drum sounds with nice sizzle on cymbals.

Observations:

Depending on your requirements any of these three headphone amps sound very good, excluding cases these amps are very affordable, using new parts in my situation costs range from about 50usd to 300usd. Also boards and some parts are included from each of the three designers making the build very easy.

As to the various headphones, the top two for me are the HE400i and ON2. Third would be the OB1. At 60usd a steal. Some of the folks on the PCA/XRK971 thread have created an eq file for those phones that improves the listening pleasure. Bottom of my list are the Sony's. These are going away for me.

I am a fan and user of Massdrop. The Thinksound ON2 came from there at a really nice price. I participated in the Sennheiser HD650 drop and I am looking forward to receiving them in December, I believe that 20000 people participated. Great deal.

Obviously everybody hears differently and has different requirements. Any of these headphone amps would be a delight to own and I thank the designers for their skills and willingness to make them available to the audio masses.

YEMV (your ears may vary)

David
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Old 19th September 2017, 06:57 AM   #2132
Salas is offline Salas  Greece
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Salas DCG3 preamp (line & headphone)
Hello David, thanks for letting us know about all those headphones subjective behavior on three different preamps. From those I had the opportunity to listen on Sony MDR-V6 via the DCG3. Its supposed to be a very close model to the MDR-7506. Generally I agree with your overall impressions on the Sony except noting that the V6 seemed bit different in overall tilt. Didn't let its bloated side dominate -although it was there- but appears relatively cleaner, though in a trebly and bit mid recessed kind of a way. In their case I preferred the Grado SR60 overall as smoother although mid forward but such headphones can't be comparable in ergonomics and function at all except in price range. The Sony has much superior mechanical design and its closed back. Also the Grado sits on the ears and the Sony is circumaural although not roomy enough.

You can measure the hp output impedance of your preamps. By matching them amps for Zo the headphone comparisons could be more level. DCG3 gives you the arbitrary Rz pcb position but you could add series resistors at the hp output socket alternatively. By setting a measured level, say 1V 300Hz, on a high resistor load like 10k and then measuring voltage value again across a low resistor, say 27R, you could derive Zo by leaving the R1 box empty and putting the other values in a divider utility like this one: Voltage Divider Calculator

Having myself the HD600 I guess you will be happy with the HD650 drop. Friends who have both tell me that the newer years production 650 is silently improved for clarity than previous 650s (includes the new 6XX drop I suppose). Described as less tonally precise than the 600 I got by bit more mid-bass and bit less treble but noticeably less grainy with bad recordings and that helps its all-round compatibility with available music files and discs.

I am sure that the members would be interested on your findings about pairing the DCG3 as a line preamp with several known DIY amps too.

Regards
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Old 19th September 2017, 08:37 AM   #2133
RCruz is offline RCruz  Switzerland
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Salas DCG3 preamp (line & headphone)
Quote:
Originally Posted by Salas View Post
If also you need to have both relays engaged the Leds can reliably support up to their own nominal current (check the spec sheet of the ones you got vs your two relays needs). But usually its one or the other, not line output to amp and speakers playing while listening to headphones.

You don't need to double up on drive circuits. R1 C1 could be common timing delay and you could pull the relays through Q1 using a switch for which one's coil you prefer to engage. A two way for phones/speakers or a three way switch for phones/speakers/both if you must.

The Zener is to create a threshold voltage for Q1's base to open at as the RC is reaching it charging up.
Thank you Salas, I am redrawing the circuit and placing the switch just between the leds and the two coils driven by the same BC. Perfect

so the zener speeds up turn on right ?
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Old 19th September 2017, 08:54 AM   #2134
Salas is offline Salas  Greece
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The Zener fixes a level that the RC has to reach but that also stands comfortably lower than the remaining B+ after the coil's drop to contain enough voltage space for the transistor to operate. I don't have a sim to post you voltages on nodes because I just put it together on the breadboard back then, made it work, then complemented it to the main circuit.
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Old 19th September 2017, 03:54 PM   #2135
drpro is offline drpro  United States
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Salas DCG3 preamp (line & headphone)
Thank you Salas for those words. Since I listened to these phones I have received a SMSL M8A from another Massdrop purchase and will be using that for future listening sessions. The Dell is an older desktop unit.
As time permits I will audition the DCG3 with the two versions of Pass amps I have built.
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Old 19th September 2017, 03:59 PM   #2136
Salas is offline Salas  Greece
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Nice. Keep us posted.
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Old 19th September 2017, 04:19 PM   #2137
Salas is offline Salas  Greece
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BTW a good usb dac will give you surprisingly more insight to source material quality vs just the Dell pc and those amps are capable to pass it. I wish your SMSL purchase will prove a success to your liking.
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Old 27th September 2017, 10:22 PM   #2138
Algar_emi is offline Algar_emi  Canada
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Salas DCG3 preamp (line & headphone)
Hi Salas. For the DCG3 J3 BF256B JFET there is no special note for it. Do we need to select it for a specific IDSS? Thanks
Sb
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Old 27th September 2017, 10:59 PM   #2139
Salas is offline Salas  Greece
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Hi Sb. My original 20 samples bought from EU were averaging around 10mA IDSS but its a 4 to 5 mA in circuit bias current result we look for in combination with R3's degeneration effect. Read post #452 on how to test before assembly for the adequate resistor value no matter if your BFs will significantly differ from mine or between them in IDSS or pinch off voltage.
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Old 28th September 2017, 02:13 AM   #2140
Algar_emi is offline Algar_emi  Canada
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Thanks! SB
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