Sunday, March 15, 2009

Indeed 6N11 Tube Class A Headphone Amplifier Vs. Qinpu Q1 + Indeed L-top 6N3 Buffer Amplifier.

Prior to launching into the review, I will state that I have no connection with either manufacturer and certain photos and diagrams which I have reproduced here I have obtained permission from Mr. Paul Cheung of Indeed Hi Fi Labs which would be used for information purposes only.

Introduction of the contenders:

Indeed Hi Fi Labs 6N11 Tube Class A Headphone Amplifier:

The review is a double review between the Indeed 6N11 Tube Class A Headphone Amplifier Versus the Qinpu Q1 + Indeed L-top 6N3 Buffer Amplifier combo. First off the Indeed Hi Fi Labs 6N11 Headphone amplifier is a Hybrid amplifier using a Chinese military grade class tube, if you see a J on any Chinese tube it means that this is military grade. The indeed amplifier is a combo of the 6N11 tube and the IRF63o Mosfet. There are no op. amps in the chain. Regulation is accomplished by way of a LM317 and what immediately comes to mind is the replacement of this item with a higher grade equivalent from Linear Technologies (a possible note for upgrade in the future). The design is a cute design and what I would call an open board, with only two clear acrylic covers for the top and bottom. The workmanship of the boards is very good and the class of components used is also good employing nichicon caps and dale resistors.

Below is the circuit of the 6N11 tube amplifier (with permission from Indeed):

The power supply for the 6N11 tbe amplifier is a seperate switching supply supply with an output of 24 Volts rated at 2A and a ferrite choke on the output cable for removal of noise. During operation of the amplifier, the supply ran warm but was not hot. The power cord is detachable, so those who like to play around with power cords can do so, I did not change the power cord for the purpose of this evaluation since the power cord on the Qinpu Q1 is fixed and not detachable which is a pity! The mini audio pot appears to be either a alps or matsushita audio grade pot and I did not detect any imbalances to channels at various levels.

The circuit diagram resembles one drawn by Sijosae, first shown by this Korean on headwize/zerosoft some time ago.

The outlook of the Indeed 6N11 is quite cute and in some ways reminds me of the Earmax although the outlook is different, the size is somewhat similar. It would be nice to have a review of the Indeed versus the Earmax but this is not possible as I do not have the latter anymore. But from my memory, the Earmax would probably still win hands down.

Okay, here are the general manufacturer's specs.:

In Put Power: DC24V 400mA
Input Sensitivity:50mV
Input Impedance: 100KOhm
Out-Put Impedance:16~600 Ohm
Dynamic range: 84.6dBA((300 ohm) 89.8dBA(33 ohm)

Frequency response:10Hz-60KHz +/- 0.25dB
Minimum THD: 0.016%(300 ohm) 0.45%(13 ohm)
Signal/Noise Ratio >90dB
RCA 2CH Input X1
6.3mm 2CH Output X1

Shipping Weight: 1kg

Transformers AC100V ~AC240V\50~60Hz 1.8A
Dimension:80mm (D) X 80mm (W) X 48mm (H)

The manufacturer's photo of the 6N11 amplifier layout (used with permission):

As for tube rolling, 6DJ8/6922/ECC88 are fully suitable for replacement for differences in musical taste. The JAN-Sylvania 6DJ8 is an very nice tube with good sonic capabilities and would be a nice candidate for this tube amplifier for tube rolling. A version of this 6N11 tube is also produced in the Russia under the designator 6N23P (Russian: 6Н23П).

So what do you get with the 6N11 headphone amplifier:
  1. 1 x Headphone Amplifier
  2. 1 x New Peking 6N11 tube Class
  3. 1 x 1.5M AC power cord
  4. 1 x Switching Power Supply Universal AC 100V-240V~2A / 50~60Hz to 24V DC 2A out put
    (Auto-Detect Internationally Compatible)
  5. 1 x 1.5M Audio cable (3.5mm earphone plug to RCA)
  6. 1 x 6.3mm to 3.5mm Gold coat earphone Jack adapter.
Above: The indeed 6N11 Class A Headphone Amplifier in my own listening environment.

The impressions between the 6N11 and the Q1 will listed below in the evaluations, this section is primarily on the outline of the products under review.

The 6N11 Class A Tube Headphone Amplifier is available from Indeed Hi Fi Labs on eBay, Indeed have a website: Indeed Hi Fi Labs but the headphone amp and the 6N3 Tube Buffer Amplifier cannot be found on their website. You could also send and email to Mr. Paul Cheung of Indeed.

Qinpu Q1 Headphone Amplifier + Indeed Hi Fi Labs L-top 6N3 Tube Buffer Amplifier:

The Qinpu Q1 came via Head Direct. It is a solid state design unlike the Q2 which is a tube amplifier. The Q1 packs allot of value for money as it also has speaker outputs for speaker connection and packs into the package a stereo FM tuner which is not at all bad. Whereas the 6N11 is just the stand alone bare bones amplifier.

There is not much available information on the circuit employed inside the Q1 and no attempt will be made to open up as this will null and void the warranty. It weighs approx. 1.1 kg and is almost the same weight as the 6N11 together with power supply.

The manufacturer's general specifications for the Q1 are as follows:

Aluminum Chassis serves as heat sink, integrated amplifier with FM tuner
Output Power: 2 x 2 W ( 8 ohms¸ RMS)
Frequency Response: 100Hz-20kHz
THD: < or =" 0.5%">
S/N Ratio: > or = to60dB(A Weighted)
Crosstalk Attenuation: > or = to 50dB
Input Sensitivity: < or =" to">
Overloading Level: > or = to 10V
Input Impedance: 20k ohms
Power Supply: 220V-240 50Hz 8W
Net Weight: 1.1KG/pcs
Dimension:135mm x 170mm x 71mm

The Q1 is of substantial build quality and the appearance vis-a-vis the price value is quite hard to beat since it also includes a built in FM tuner. The a.c. transformer is housed in a red casing which protrudes the top of the amplifier casing, this is the same for the tube version Q2. During the listening tests the Q1 ran cool all the time. There is no information on what type of class amplifier this is in the manufacturer's details and I highly suspect that it is a class AB design.

Above is the Qinpu Q1 and Indeed L-top 6N3 Buffer Amplifier in my listening environment.

The additional FM tuner is handy and neat, although there is no frequency display making it impossible to know what frequency you are listening to, a display would be a nice addition. Tuning is made by way of scan buttons located (up/down) in front of the red transformer housing and scanning / lock on to stations is very quick. I found with the use of the supplied wire antenna that I was able to pickup most stations that I usually listen to. No sensitivity and selectivity details are given at all for the FM tuner front end section by the manufacturer. There is no noise and hiss between scanning of stations and this suggests that a auto squelch (quieting) circuit is employed which is good.

Qinpu has a website but the information given is very limited: Qinpu Q1

These are available from Head Direct. Both the Indeed 6N11 and the Qinpu Q1 are of Chinese origin.

I have connected an Indeed Hi Fi Labs L-top 6N3 Tube Buffer Amplifier to the input of the Qinpu Q1, and I will give you reasons for this later on in the review.

Indeed Hi Fi Labs L-top 6N3 Tube Buffer Amplifier:

The Indeed Hi Fi Labs L-top 6N3 Tube Buffer Amplifier comes in a neat little aluminium box with part of the 6N3 tube protruding from the top, which is good for cooling purposes. Buffer Amplifiers are used primarily on the output of a CD player and between the amplifier input. They are also used in the tape loop of an integrated amplifier, between a pre and power amp if there is a length of cable, between your Phono Stage and your Preamp.

Below is a photo of the L-top 6N3 Tube Buffer in it's listening environment of my home:

The tube employed is s Sino 6N3 class J tube which is a military grade tube. There are now a number of amplifiers using the 6N3 and 6N11 tubes. Primarily because these are readily available in China and their cost is cheap and audio quality of the class J tubes is fairly decent. If one is thinking about tube rolling with this buffer to obtain other sonic signatures, 5670/2C51/6CC42 tubes are all compatible with this buffer stage amplifier.

So you may ask what the benefits of a buffer amplifier are? With a buffer amplifier such as this, it would provide high input impedance and therefore should not offer any loading to the source CD player and as a result it gives in theory the best possible performance. On the output side ideally it should have a low output impedance making it easy to drive any amplifier easily and ensuring virtually perfect linearity. It should also offer low noise, low distortion, a large overload margin and wide bandwidth presenting an extremely clean sound with huge dynamic range. In the end minute audio details should become more apparent and the sound more liquid. Normally buffer amps. do not add amplification and are unity gain, however there are a few other models on the market which have OdB, +2dB and +4dB gain settings, but such buffer stages are at many more times the price then this amplifier - for example the Sound Space Buffer Amplifier.

Another photo of my L-top 6N3 Tube Buffer Amplifier.

So the manufacturer's claimed specs. quoted are:

In Put Power: AC17V 500mA 50/60Hz;

Input Sensitivity:0-5V;

Input Impedance: 100kOhm;

Out-Put Impedance:>200 Ohm;


Frequency response:10Hz-25KHz

Minimum THD >0.025%

Signal/Noise Ratio >97dB

RCA Input X1

RCA Output X1


Power On/Off switch

Fully Non-magnetic Aluminum Cabinet

AC 220V or 110V to AC 17V 1000mA Adaptor built with USA plug Only.

Other audio gear used in the evaluation:


Headphile Darth Beyer V3 Lepoardwood;
Audio Technica ATH-ESW9 Le Luxe Wood Headphones (Hokkaido Cherry Wood);
M-Audio Q40 Studiophile Dynamic Headphones;
Goldring DR-150 (Open Back Dynamic).


Oregon Scientific Music Element CD Player.

Inset photo is the Oregon Scientific Music Element CD Player that I used for the source -

Some basic tube data about the 6N3 and 6N11 Sino tubes:

As mentioned before, the J designation on these tubes means that they were produced in China specifically for military applications and thus would be of higher grade then normal tubes without such designation.

6N3: Data Page

6N11: Chinese PDF Data Sheet


1. The Indeed 6N11 Tube Class A Headphone Amplifier:

The 6N11 tube amplifier has been allowed to burn in for a 6 day period (5 hours per day) before any actual listening was undertaken.

It is apparent why Indeed Hi Fi Labs made this amp. an open design with the acrylic top and bottom plates. The little amp ran quite warm and the open design allowed cooling quickly, an enclosure I think would have cooked the parts quickly to well done without proper ventillation.

As outlined above the amplifier was tested with a number of different headphones and one primary CD source. Even though the amount of burn in time has been rather limited the first impression I received listening to the amplifier was that is was warm and very musical. I suspect that replacing this with a JAN-Sylvania 6DJ8 would further improve the amplifier and these can be had for $15 - 30. The music was very fluid and it was very airy.

It was also quite articulate and tonal balance was quite good also. Bass extension was quite good but I would not call really deep and impact was above moderate. It did not seem laid back or forward. listening at different levels I did not hear any channel imbalances, but at high volumes one would expect to pick up on low level tube noise.

Attack and decay are both quite well balanced. Resolution was above average and some of the most delicate details on some tracks I did not notice with other equipment actually came through. Overall depth and sound stage was well prestented as fairly deep and wide but not the best encountered, this may be a limitation of the tube with low burn in hours and again may yet improve with a tube such aas the JAN-Sylvania 6DJ8. Focus was also fairly decent, the sound overall is quite open.

This is a fairly decent little headphone amplifier.

I did not detect much in the way of noise during quiet passages and the music again was quite fluid and open. I did not detect any sibilance, the M-Audio Q-40 headphones with their in your face characteristics would have quickly detected this.

Even with the bass heavy Darth Beyer V3's I did not experience over bearing bass, the punch was good and nicely controlled and tight without muddiness. I would describe the overall sound as sweet.

2. The Qinpu Q1 + Indeed L-top 6N3 Tube Buffer Amplifier:

I first listened to the Qinpu Q1 by itself after the same number of burn in hours, whilst the detail and resolution was good and I did not detect any harshness, it was a very wee bit sibilant. There was something about it, it did not seem as spacious as the 6N11, but would this improve further with burn in still remains to be seen.

Pace, Rhythm and Timing was actually on par with some more expensive amps. But there seemed something lacking - realness and naturalness seemed to be amiss. It was also a tab bit grainy and imagery and focus whilst good was slightly below that of the 6N11. On the two tracks -"Didn't know I was looking for love" by Everything But The Girl as well as "Ancient" by Jeanne Newhall, I did not feel the fluid flow of the music as much as I did with the 6N11. I felt the music to be a bit on the dry side and not to my liking.

There was also one annoying issue with the Qinpu Q1, the volume pot was noisy and scratchy and this I felt was a no-no since it is a new piece of equipment and should be using an audio grade pot? Whilst I have not looked inside the Q1, I suspect that this pot may not be of audiophile grade and may need cleaning with a contact cleaner or possibly changing to a better quality alps or matsushita audiophile grade pot as I suspect it may be a low grade pot. I did not notice any imbalances at low or high listening levels. The scratchy pot was most annoying though! This aspect I do take strong issue with and give the Qinpu Q1 a big thumbs down.

Bass extension and impact were fair but not as good as the 6N11, control was however tight. The depth and sound stage although apparent were not as deep and well defined and overall imaging was stronger with the 6N11.

In a nutshell, what was a good sounding amp previously was dwarfed by the sonics of the Class A 6N11.

So what to do, enter the 6N3 buffer amplifier from Indeed. I connected this between source and input of the Qinpu Q1 and let it burn in for the same number of hours before taking a another listen.

It became immediately apparent that after connecting the 6N3 that the highs were more crisp, definition appeared to be better, bass extension and impact seemed better. Depth and sound stage were better defined, deeper and wider. Imaging was also better. So now for a further A-B with the 6N11. After about an hour listening between the two sets, it was still obvious that the Class A 6N11 was still ahead and better sounding but not by such a large margin as before when the Qinpu Q1 was standing alone by itself. The Qinpu was not as dull and became much more musical but I still like the definition, clarity and imaging produced by the 6N11.


In this A-B shoot out, my own opinion is that the 6N11 Class A Headphone Amplifier from Indeed is the winner and I like it's musical qualities. There is plenty of room for experimentation including:

  • Changing the 317 regulator to a better grade equivalent from Linear Technologies;
  • Tube rolling - change to a JAN-Sylvania 6DJ8 or a Telefunken equivalent (expensive but if you have one around it would be nice to see and hear the difference);
  • Experimentation with battery power as a power supply source, this is already slated as a project I will look into;
  • Possibily the change of the resistors to some other types like Tokyo Ko-on or RMG types with gold plated OFC leads;
  • Change of the electro. caps to some Black Gates or Elna Cerafine etc.
  • Can play around with different AC cables on the switching power supply.
The down side of the 6N11 is it is open on the sides and you have to be careful with what you are doing! You need to put some rubber pads on the bottom or it tends to slide about on the desk top. It does tend to run warm.

The Qinpu Q1 - Nice chassis, well bult like a tank. Sound is good but not near the 6N11. The FM tuner is an added plus to the package. It does have speaker outputs so you can hook up to a pair of small speakers if you wish. Runs cool. When connected to the L-top 6N3, the combination yielded much better results then with just the stand alone Qinpu Q1.

The downside of the Q1 - AC cord is not detachable like that on the switching supply of the 6N11, cannot play around with AC cables. Mine had a noisy volume pot - a big no-no ( I will need to look inside at some stage on the construction and components used and cannot comment on the circuit build quality at this stage), I recommend to add an additional buffer amplifier like the L-top 6N3 to open up the sonics.

In conclusion I like the Indeed 6N11 Tube Class A Headphone Amplifier.

Price Reference: (Postage Extra)

  1. Indeed Hi Fi Labs 6N11 Class A Headphone Amplifier US$79.99
  2. Indeed Hi Fi Labs L-top 6N3 Tube Buffer Amplifier US$42.00
  3. Qinpu Q1 Headphone Amplifier from Head Direct US$39.00 (Sale Price!)
Reviewing CD and Tracks: Custom made by ripping songs to FLAC than normalized/burnt via Nero9.

CD Tracks: Esteban - Norwegian Wood; Everything But The Girl - I didn't know I was looking for love; The Corrs - Runaway; Acoustic Alchemy - Mr. Chow; The Verve - Bittersweet Symphony; Willie & Lobo - Amsterdam; Tim Weisberg - Party of One; Sleep Station - There She goes; Seattle Symphony Orchestra - Beethoven's Symphony No. 9 (Scherzo); Sim Riney - What was I to you; Rebecca Pidgeon - Spanish Harlem; Pink Floyd - Dark Side Of The Moon; Mike Oldfield - Tubular Bells.

Additional CD's for auditioning:
1. "The Sound of Analog is Back" From Mark Levinson (Red Rose Music);
2. "CD Master I - Direct Master Cut Vinyl CD" Mastering by Mark Levinson;
3. "CD Master II - Direct Master Cut Vinyl CD" Mastering by Mark Levinson;
4. "The Purest Sound-City Folk Songs-Vili" TIS Hong Kong;
5. "Dido" SRS + WIZOR Mastering CD;
6. "The Police" SRS + WIZOR Mastering CD;
7. "Avril Lavigne" SRS + WIZOR Mastering CD;
8. Jeanne Newhall - "Wild Blue";
9. Andrew Lloyd Webber - "Variations"


  1. Cable used were all copper OFC cables - home made with gold plated RCA plugs;
  2. Will listen and compare also using Silver cables at some stage;
  3. If someone has a Qinpu Q2 and the Indeed 6N11 headphone amp, it would be nice if if they also did an A-B test since the Q2 is a tube amp and such an evaluation would be closer to home;
  4. Boomy on Head fi will be doing an A-B evaluation between the Head Direct EF-1 Headphone Amp. and the Indeed 6N11 and it would be interesting to see his evaluations and comments.
  5. The writer has no connections with Indeed or Qinpu whatsoever and the evaluations and based on the writer's own observations and opinions.
Below are some more of my photographs:

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