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HeadAmp Gilmore Lite Mk2 Review (headphone amp)

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#21
sssn: I had the same thought at first about a beefier power supply, but it would only be helpful for low impedance headphones. The 600 Ohm load shows it hard clipping at about 5 Volts, so that's a strict limit regardless of the current. With 125 mA on tap for each channel, you can in theory go all the way down to 40 Ohms without clipping at 5V before you run out of current; in practice it's not perfectly efficient so you'll lose a bit along the way. This is reflected in the multi-graph where the 50 Ohm load still tracks closely to the higher impedance loads, but lower than that it falls off quickly.

As pma noted, the main dashboard does seem to be 100 kOhm here which is unusual for a headphone amp; previous reviews are 600 Ohm. Agree that it shouldn't make a difference, but the multiple impedance plot (which I also like, please keep) shows a SINAD of 90dB for 600 Ohm vs the 87dB on the dashboard so there's definitely something creeping in at a higher impedance load unless another variable was changed as well.
 

RickSanchez

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#23
Good, but you must know that legends of your graphics are still #@#!. They would not pass any quality peer review journal.
I could be wrong but I don't think Amir has control over the legends. Those are generated by the software on his AP analyzer.
 

Svperstar

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#24
OMG finally! I have debated sending in my Mk2 to be reviewed. I have it as my daily driver for my office laptop for work from home, currently driving my Sennheiser HD580 the first "real" amp I got back in 2004 was the original Gilmore Lite so I wanted the mk2 as soon as I saw it:

GilmoreLitemk2.jpg


My personal laptop has the SMSL SP200, I can't really hear a big difference besides the SP200 gets a lot louder.
 
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Svperstar

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#25
But like Amirm said, if you have one of these there's nothing really to be gained in terms of sound quality by replacing it with a newer product that measures better, unless you are trying to drive difficult low-impedance 'phones.
I always had the suspicion my Audeze LCD-2 were being held back by the GL mk2, with the SP200 they do get much louder and the bass sounds cleaner but this could be placebo because the THX amps are know to have a clean signal. I like my mk2 and have no plans to sell it. Listening to it on my work computer right now.
 

Svperstar

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#26
Another tough sell. I don’t understand manufacturers who don’t look around to see who they’re competing against.
As someone who bought one as soon as they became available I was already well aware I could get something cheaper that measured just as good if not better. It was about the nostalgia and coming "full circle" after buying then selling the original Gilmore Lite. I've debated buying an old early 2000s Gilmore Lite, they pop up on ebay pretty regularly.
 
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acbarn

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#27
As someone who bought one as soon as they became available I was already well aware I could get something cheaper that measured just as good if not better. It was about the nostalgia and coming "full circle" after buying then selling the original Gilmore Lite. I've debated buying and old early 2000s Gilmore Lite, they pop up on ebay pretty regularly.
That's a good reason to buy one!
 

Svperstar

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#28
sssn: I had the same thought at first about a beefier power supply, but it would only be helpful for low impedance headphones.
Just FYI but Headamp has a history of releasing beefier power supplies for their amps. Back in the day you would get a Gilmore Lite and drop $200 more dollars on a DPS(Dedicated Power Supply) which supposedly increase sound quality. When the original Gilmore Lite was my daily driver I never bothered with it. I just got a nice power conditioner and called it good.

Supposedly Justin(Headamp) was going to release a beefier power supply for the mk2 in 2020 but I can imagine with COVID and things he has more important stuff to worry about.

Its still listed on the site as shipping Summer 2020:

https://www.headamp.com/products/gilmore-lite-mk2

EDIT: I checked on Head-Fi and there IS a shipping "Golden Reference Discrete Regulated Power Supply" for the mk2 now
glmk2ps.jpg
 
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Svperstar

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#29
Here is the original Gilmore Lite with the DPS, I assume it would be similarly bulky with the mk2 considering how much bigger it is.

623735-4889ab78-headamp_glite_gilmore_lite_headphone_amplifier_with_dps[1].jpg
 

MZKM

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#30
I have a new test which shows the output voltage at a number of impedances. You can convert them to watts using the formula power = Voltage * Voltage/Load resistance:



Nice to see that it can handle even 12 ohm load but distortion rise as the load impedance reduces is quite significant.
Is this 1kHz? If so, is the bandwidth different? Because I can’t see where the 87dB SINAD would come from (especially if the impedance of the test load for the SINAD is 20 ohm).
 

PeteL

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#32
Is this 1kHz? If so, is the bandwidth different? Because I can’t see where the 87dB SINAD would come from (especially if the impedance of the test load for the SINAD is 20 ohm).
I doubt the choice of load for SINAD would be 20 ohms, it’s should be an easy load, high enough to be considered an unloaded measurment, but I’ll let it to @amirm for the specific number. as the graph with thd+N curves at various impedance, I think that many here are trying to read too much into it. they are simply the same as the curves to determine max power, but expressed in volts, allowing to see with the same metric if if the amp can supply the same voltage before clipping as the load gets harder. or in other words, if there is a voltage drop, it means we have a limitation in current supply.
 
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Francis Vaughan

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#33
Some late observations.
Ages ago I remember reading a commentary from Kevin Gilmore about his design philosophy. He seems to be one of the low global feedback adherents. Looking at a photo of the PCB, one can get a pretty good feel for the design, and this is confirmed by some of the description made about the circuit on the HeadFi web site. It is a dual differential pair design, using JFETs in the differential pairs. One can see the pairs glued back to back, the current sources (which appear to be biased by LEDs). There is some confusing commentary about a servo current source, which would be the op-amp present on the PCB. I can't see how this would be running the current source, but it could well be a DC offset servo. Then four voltage amplifier transistors in a symmetric setup (probably emitter followers) and then the four pairs of paralleled output devices. So a conventional push-pull class-A output stage. This is a high performing setup, but perhaps the choice of lower feedback is the reason for medium THD. The web site's claimed performance almost exactly matches Amir's.

But, more pertinent, a lower feedback class-A design is not very robust to power supply issues. A less noisy PS may well improve the result. The new PS is $300. Given the Topping A90 already wipes the floor with this amp for $500, I'm not convinced spending more money on the PS is good value, and $800 for the amp/PS combination looks very poor value as a new purchase.

A hidden question with any class-A output stage is the bias current. No class-A output can stay class-A forever. One the delivered current exceeds the bias current operation ceases to be class-A. A single ended class-A will just clip. A push-pull class-A will revert to class-AB. This is why impedance of the load is important. Any class-A amp really should include a minimum load impedance in the specs to indicate the load when it no longer operates in class-A at full swing. Luckily many low impedance headphones are also high sensitivity, so they don't need large voltage swings, and may remain class-A in normal use. But a low impedance, low sensitivity headphone may well find itself taking the amplifier out of class-A operation.

Most amplifiers will simply linearise the output with global feedback as they transition through the A to AB crossover point. A low global feedback design will tend to show more distortion as the amplifier does this. One suspects that is part of what we see here in the measurements of distortion versus voltage swing and load. There are a number of break points on each curve, and these likely represent different transitions of the output stage operation as it swings.

This isn't to say that class-A is deficient, indeed it is ubiquitous in such circuits, but one needs to be clear about its limitations. In the best of worlds it always provides superior performance, but the limitations of its application must be taken into consideration. (I note that the much higher priced Gilmore amps use what appears to be the same building block, but with added heat sinking, so I wonder if they push the bias current up.)
 
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#34
this amplifier was one of the very first amps that have a dc servo that is outside the audio feedback loop.
the opamp controls the front end current sources.
 

Francis Vaughan

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#35
this amplifier was one of the very first amps that have a dc servo that is outside the audio feedback loop.
the opamp controls the front end current sources.
Ah, I wondered that, but given the LEDs right next to the current sources, I wasn't sure what was going on. Nice idea.
 

Svperstar

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#37
Neat to see this - I built a mains powered DIY version of the original that still functions. As noted in this review, not a good value today, but it made my HD580 cans "come alive" compared to the anemic circuitry built into motherboards of the day (circa 2003?).

https://headwizememorial.wordpress.com/2018/03/11/a-pure-class-a-dynamic-headphone-amplifier/
The Gilmore Lite -> Sennheiser HD580 was my first "real" setup. Very nice improvement over my Pocket Amp V2 -> Sennheiser HD595.

The PAV2 was battery powered and you could hear scratching when you turned the volume knob.
 

Francis Vaughan

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#38
The PAV2 was battery powered and you could hear scratching when you turned the volume knob.
I have an ageing Headroom Bithead somewhere. It was explicitly designed with no DC blocking capacitor ahead of the volume control. The explanation being that the possible scratchy sound when moving the volume was a small price for eliminating the cap. Mine never scratched much anyway. The logic of removing the cap is perhaps open to debate, but there is at least method to the madness.
 

Svperstar

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#39
I have an ageing Headroom Bithead somewhere. It was explicitly designed with no DC blocking capacitor ahead of the volume control. The explanation being that the possible scratchy sound when moving the volume was a small price for eliminating the cap. Mine never scratched much anyway. The logic of removing the cap is perhaps open to debate, but there is at least method to the madness.
The Pocket Amp V2 was the first amp I ever owned when I stumbled into this hobby on accident. Price was right at $50. Very portable. When you turned the volume knob all the way up could hear buzzing on all headphones, probably doesn't measure well but liked it for its time.

http://electric-avenues.com/
 

Tortie

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#40
Seeing this overpriced amp get taken to the woodshed by Amir has me smiling because Kevin Gilmore is such a unpleasant curmudgeon online. He constantly disses competitors on the little backwater audio forum Head-case.org where he's considered the resident guru. Look at the SiNAND! Hilarious. And for $500? lol
 
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