System Design

2018/11/24 created
2018/11/24 updated

Design Targets

The primary target of Gaudi II's system design is eliminating the shortcomings of Gaudi. I believe that for achievement of the best sound quality it's better way to solve problems one by one than to employ outstanding circuits and/or mechanisms.
Unsolved problems in Gaudi

In addition, the following items are set as priority targets.

  • To improve convenience
    Maintenance free, remote control, low power consumption
  • To improve affinity with visual components
    Pure audio system to A/V system
  • To enhance immunity
    Not affected by power supply voltage fluctuation and noises from outside

Gaudi was also used like an A/V system, and I'm planning to further enhance Gaudi II's function and performance as an A/V system while giving top priority to sound quality.
If I'll have energy to spare, I also want to challenge the 4-channel stereo system like Sansui QS4, which was the rage in 1970s. I have more than a dozen of vinyl discs that are compatible with QS4. Some of them are recorded by artists who ingeniously utilized the surround effect for their music. I want to listen to their recordings with the sounds they intended to make.

For Gaudi system, I stuck to designing and building all the components, but I've decided to use commercial products, except for components for which I can make use of my own ideas.

Better yet, you also have an option of composing the system with commercial products only. However, in that case, you will use components that do not fully match the system design. Commercial products are those designed by professional, but because they are not designed according to your order, they could cause some problems.
Especially,it is obvious that custom design is more advantageous for loudspeakers and power amplifiers. Because the size of the room and the quality of the room acoustics have a great influence on the loudspeaker design, and the loudspeaker design has a great influence on the power amplifier design.

It will be the choice of which to choose between ready-made products designed by professionals and custom components designed/built by an amateur. In the latter case, the result depends greatly on the level of knowledge, techniques and skills of himself.
I chose the latter. The more you brush yourself up, the better the sound quality of Gaudi II. It looks like a mirror reflecting yourself. Also, depending on your own hard work, there is a possibility to realize sound quality exceeding the manufacturer's high-end system. Just thinking so excites me.


Specifications

The specifications of the whole system is as follows:

Input source
Analog disc ... LP, EP, also SP if possible (main source)
Music files ... DSDIFF, DSF, WAV, FLAC , AIFF, ALAC, WMA, MP3 (DSD up to 5.6M, PCM up to 192kHz/24bit)
Internet radio (FM, AM radio)
CD, DVD, Blu-ray Disc
TV (cable TV set top box (STB))
Other ... Smartphone, portable music player etc.
Inputs
PHONO: For AD player ... RCA Jack
DAP: For digital audio player (music files, CD, DVD, BD & net radio) ... balanced, XLR jack
AUX: Auxiliary input (for STB or other sources) ... unbalanced, RCA jack
Outputs
EQ OUT: Phono EQ output ... balanced (XLR jack)
PRE OUT: Preamplifier output ... balanced (XLR jack)
PHONES: Headphone jack ... 3P standard jack
Frequency response
25Hz-40kHz (+/-6dB)
Distortion ratio
THD+N: Less than 0.01% (except loudspeaker)
<< THD (total harmonic distortion) does not reflect sound quality so much. What kind of indicator best reflects the sound quality, currently under study >>
Max SPL
110dB (L+R, at the listening position)
Power dissipation
Less than 100W (when playing an analog disc)
Convenience
Wireless remote-controlled selector and volume
Wireless remote-controlled music play (except analog disc)
Others
The potential of the frame ground (FG) is the same as earth.
Even if there is a difference in ground potentials of devises, not to impair sound quality.
Each device is to be designed so as to enhance immunity for AC line noise (under consideration of quantification)

For details on how I fixed the specifications, please see the following PDF.
Details on System Specifications

I put my opinion on the sound quality of the vinyl disc on another PDF. Please click on the button on the right.


Configuration

System Configuration Ver.2.2

Like Gaudi system, Gaudi II is a triamplified system (3-way multi-amplifier system). The reason for sticking to the multi-amplifier system is that it is obvious that distortion will occur unless the power amplifier and the LS unit (loudspeaker unit) are directly connected in principle.
The LS unit is a transducer that outputs sound pressure proportional to voltage. Also, the impedance of the LS unit fluctuates greatly. Therefore, it is necessary to drive with stabilized voltage. It is necessary to minimize the output impedance of the amplifier and the cable impedance. However, in the case of a multiway speaker with built-in network, some impedance will be placed between the amplifier and the LS unit, causing distortion inevitably. Even if you use an amplifier or cable with low impedance, the distortion still occurs.

If there were true full-range LS units (having flat response between 20Hz and 20kHz with very low distortion), the single amplifier system could be a hi-fi system. But as long as I know, there exists no such LS unit.

Every amplifier is a semiconductor amplifier. I won't use vacuum tubes, because they have instability factors such as aged deterioration, and pick up microphonic noise. Compared to vacuum tube power amplifiers, the semiconductor power amplifier has lower output impedance, so it can bring out the advantages of multi-amplifier system more.

Considering to make the phono EQ (phono equalizer amp) independent from the preamp, I've decided to place the phono EQ within the preamplifier, bacause I've decided the analog disc is the main source also in Gaudi II.
I also considered embedding the crossover network in the preamplifier, but I gave up the idea. Because the preamp should be placed near the players and the network should be near the power amps, and the power amps should be placed close to the loudspeakers and the players should be far from the loudspeakers as long as possible. If the network is embeded in the preamp, the six LINE cables have to be much longer.

The biggest difference between Gaudi and Gaudi II is the volume control. In Gaudi II, the volume control itself is not included in the preamp. Six mono volume units are embedded in each power amp, and they are controlled by the MCU (micro controller unit) in the preamp. The MCU receives signals from the volume knob (rotary encoder) of the front panel or an infra-red remote, and sends control signal to each power amp.

The MCU also controls the power-on/off sequence. After the preamp is powered on, the MCU turns on the crossover network, and then the power amps. The power-off sequence executes in the reverse order: power amps => network => preamp.

Components

The record player (ADP) is Technics SL-1200GR, and the cartridge is Audio Technica AT33PTG/II. As for the cartridge, I will consider replacing it with another one, when the stylus reaches its end of life. As a result of examination, I may choose AT33PTG/II again.

To the extent that emphasis is placed on analog discs, there may be those who feel a sense of incompatibility in that ADP is neither my original nor a luxury one.
For me, I believe that the most important part in analog disc playback is the cartridge. Since cartridges can be freely selected even with commercially available ADP, I don't think it's necessary to build my original ADP.
I'm satisfied with a tonearm that has the ability to enable the cartridge to trace a high sound quality record. I don't think further performance is required. If the turntable has less than 0.1% wow/flutter and no vibration nor electric noise is generated, it is OK with me. Some high-end ADPs have prices exceeding 10 million yen ($110k), but I don't think that such a luxury player is necessary for Gaudi II.
Actually using SL-1200GR, I judged that it has the necessary performance as Gaudi II's ADP. The good point of the SL-1200GR is that it is well vibration-proof. It may be said that it is the most important performance for ADP.

PC is used as digital audio player (DAP). The PC must be specialized for audio use; no cooling fans, SSD for the main drive, only DAP apps installed, etc. Such PCs are available these days.
I'm using Sony HAP-Z1ES now, but I am not satisfied with its sound quality. And, the PC excels the HDD player in expandability. I've decided to replace HAP-Z1ES. For details of HAP-Z1ES, see this page.

All the amplifiers are to be newly designed and built, because the amplifiers in Gaudi do not meet the requirements of Gaudi II.

Category Maker Model # Outline specifications Note
Analog disc player Technics SL-1200GR Direct drive turntable
33/45/78 rpm
Statically balanced tonearm
[reasons for selection]
Cartridge Audio Technica AT33PTG/II MC type, Microlinear stylus
Output: 0.3mV, F-range: 15-50,000Hz
[reasons for selection]
Replacement to be considered
when the stylus reaches its end
of life
Digital audio player (TBD) (TBD) 1TB SSD, CPU clock >3GHz, RAM: 16GB
No cooling fan, high-quality PSU
[reasons for selection]
Preamplifier NOBODY PA-217 Diversity
(tentative)
Open-loop type phono EQ,
Gain=66dB (MC only)
Embedded MCU
Flat stage: Gain=0dB
2 LINE inputs, EQ OUT, PRE OUT
PHONES OUT, Infra-red remote
[details]
Crossover network
(channel divider)
NOBODY CD-2XX Cross points: 800Hz, 6,800Hz
24dB/oct analog filters
Time alighment adjuster
[details]
May be substituted by a manufacturer product
Power amplifier
for tweeter/squawker
NOBODY MA-2XX Tweeter: FET discrete 10W mono
Squawker: TI LM3886 20W mono
[details]
Power amplifier
for woofer
NOBODY MA-2XX Class-D 80W mono [details]
May be substituted by a manufacturer product
Loudspeaker NOBODY SS-309B 3-way speaker system
Tweeter: Fostex T925A
Squawker: Fostex D1405+H400
Woofer: Fostex FW305
[details]
D1405 might be replaced
Audio rack NOBODY AR-416 Air Granite stone base
5-story wood rack
vibration-proof
[details]
Cable TV STB (released from the cable TV station) TZ-HDW611P
(tentative)
Terrestrial, BS, CS, double tuners
Recording feature, 500GB HDD
(tentative)
[reasons for selection]
To be replaced in the near future
TV/display (TBD) (TBD) 43 in. flat display, 4K
HDMI x3 or more
[reasons for selection]

Maximam Output and Gain

For Gaudi system, I decided the maximum output of each amplifier with a rough estimate. As for the gains, I decided them with little consideration.
For Gaudi II, I set appropriate values ​​under certain grounds. For details, please see the following PDF.
[Max output and gain]

Maximam output voltages of preamplifier & crossover network
2V (RMS)
(There is a possibility of making it 2.8V (+3dB))
Maximam output power of power amplifiers
For tweeter: 5W
For squawker: 10W
For woofer: 80W
Gains of amplifier stages
Please see the following system block and level diagrams. (Click to enlarge)
Note that the master volume in both figures is actually built in each power amplifier.Gaudi II block diagramGaudi II level diagram

Layout

I don't know how to calculate the optimum value of the loudspeaker position or the listening position, since I haven't studied the acoustic design yet.
In the future, I'd like to learn the know-how of acoustic design and calculate the optimal positions.
However, since the room where Gaudi II is installed is not a dedicated listening room but a living room, I must also consider the aspect of living space. It is actually difficult to make major changes from the present situation.
The following system layout diagrams are provisional.

Gaudi II system layout (top view)Gaudi II system layout (side view)

 

 

 

 

 

 

 

 

 

Gaudi II component layout diagram

You can determine the component placement on the audio rack and the TV rack on firm grounds.
Arrange it so that the cables become as short as possible. In particular, a lengthy speaker cable has a high degree of adverse effect on sound quality, so place the power amplifiers just next to the loudspeakers.
Please see the component layout diagram on the right. (Click to enlarge)

In the component layout diagram, the tweeter/squawker amps are placed on the TV rack, but I am considering placing it on the woofer boxes.



Cabling

I don't care much about cables. From my experience with Gaudi, I know that even inexpensive cables are good in sound quality.
Especially, expensive cables for maniacs tend to have a thick character, I feel (It might be my wrong impression since I haven't tried out so many cables). I think that a cable with a simple structure is better than expensive ones.
I don't care much about the materials of the cable, either. But OFC is used even for a cheap cable these days, so I will use a cable using OFC or better material. I think the material of the coating is more influential in sound qulity than the material of the core wire of the cable, but for now, it's not a firm belief.

Regardless of the balance type or unbalanced type, 2-core shielded cable are used for the line cables in order to prevent external noises from coming into the signal as much as possible.
For a connection with a manufacturer product, if it has balanced input/output, a balanced cable is used. Using the balanced cable is expected to avoid problems caused by ground potential difference and ground looping in the system.

The loudspeaker cables should be as short as possible. In order to take advantage of the features of the multi-amplifier system, it is necessary to make the impedance between the amplifier and the LS unit as close as possible to zero. For that, shorter cables are desirable. Thick cables have low impedance too, but they tend to be expensive and not user-friendly. I prefer short and a little thick cables.
The NOBODY power amplifiers don't have output terminals. The cables are connected directly to the output transistors with soldering or crimping.

The cables used by Gaudi II is shown in the table below.

Connection Wire Length Sender end Receiver end Cable type
ADP --> Preamp Low capacitance
Unbalanced wire
0.7m RCA plug RCA plug
Neutrik NYS373-0
SL-1200GR's original cable modified
to meet Gaudi II's requirement
Stereo pair w/ earth wire
DAP (PC) --> Preamp OFC balanced wire
BELDEN 8412
1.5m RCA plug
w/ teflon insulator
RCA plug
w/ teflon insulator
Balanced type
Stereo pair
STB --> Preamp OFC balanced wire
NEGLEX 2549
3m RCA plug
Neutrik NYS373-0
RCA plug
Neutrik NYS373-0
Unbalanced type
Stereo pair
Preamp -->
Crossover network
OFC balanced wire
NEGLEX 2549
3m XLR jack XLR plug Balanced type
Stereo pair
Crossover network
--> Tweeter/
squawker amp
OFC balanced wire
NEGLEX 2549
1.2m XLR jack RCA plug
Neutrik NYS373-0
Unbalanced type
HF-MF pair x2
Crossover network
--> Woofer amp
OFC balanced wire
NEGLEX 2549
1.2m XLR jack RCA plug
Neutrik NYS373-0
Unbalanced type
Mono x2
Tweeter/squawker amp
--> Tweeter
0.7mm gold-plated
OFC wire
Amtrans GW-T-0.7Of
0.7m
(0.3m)
Soldered Bound on post
Titian oil applied
When placing the amplifier
on the Woofer Box,
the length shall be 0.3m.
Tweeter/squawker amp
--> Squawker
0.7mm gold-plated
OFC wire
Amtrans GW-T-0.7Of
0.7m
(0.3m)
Soldered Bound on post
Titian oil applied
When placing the amplifier
on the Woofer Box,
the length shall be 0.3m.
Woofer amp
--> Woofer
OFC quad wire
Canare 4S6
0.7m Bound on post
Titian oil applied
Bound on post
Titian oil applied
The cable length is the length
from amp's terminal
to woofer's terminal.

 


AC Power Line

Outlet
Gaudi II Mains Connection Ver.2.2

The AC power is taken from the wall outlets dedicated to Gaudi II.
Since many devices require power supply, some power strips are used.
Please see the right AC power connection diagram. (Click to enlarge)

There are three wall outlets; the two are 100V and the other one is 200V. They are positioned behind the audio rack and the TV rack.
The 100V outlet is dual type, and 200V outlet is single type.
Each outlet is directly connected to a dedicated breaker in the switchboard. It is not shared with other outlets and lighting fixtures.
VVF 2.0 cables are used for wiring in the wall. They have been routed so that the lengths of the cables are as short as possible.

All the sockets used in the wall outlets and the power strip are for medical use (hospital grade).
The medical socket has the contact resistance of 1/3 of the normal socket.
100V: Panasonic Electric Works WN 1318
200V: Panasonic Electric Works WN 11122

Power cable

As for the power cable, I am not selective. I don't think the power cable is so influential to sound quality. I'd like highly reliable cables rather than audio grade cables.
For home-built amplifiers, I always use a 3-wire cable (with a ground wire). The plug is also 3P type. For manufacturer products, I use the supplied cable as it is.


Room Acoustics

As for acoustic design, I am still studying now, so I don't have a specific plan yet.

Gaudi II is installed in a room where the acoustics is too live (the reverberation time is too long).
In addition, the material of the inner wall and floor is so thin that they could be resonated. And, I know standing waves occur between the left and right walls.

During the Gaudi era, I installed sound absorbing materials and sound absorbing panels here in the room. But I decided with a sense of intuition what kind of sound absorbing material to use and the places where they were installed. Some have great effect, others are not.

In the near future, I'd like to do acoustic design based on theory and actual measurement data.
In addition to installing the sound absorbing panel, I'd like to implement all necessary measures to improve the sound quality, such as optimizing the installation position of the loudspeakers and reinforcing the floor and walls.


Supression of vibration

There are two kinds of anti-vibration (suppression of vibration) methods.
The first one is to prevent vibration generated from the loudspeakers from being propagated to the other components (suppression of acoustic feedback). The second one is to prevent resonance of the floor, walls, furniture, etc (deadening).

Suppression of acoustic feedback

A special vibration-proof audio rack is used so that vibration from the loudspeakers will not be propagated to the components on the audio rack. Since the record player is vulnerable to vibrations in particular, I actually measured the vibrations by using the pickup of the record player, and confirmed the performance of the audio rack, AR-416 Air. AR-416 is my original audio rack. It was completed in June, 2017, and is used in Gaudi II.

Deadening

Since the floor and walls of the room where Gaudi II is installed are thin, reinforcement is necessary.

I put carpet tiles, which are made of thick rubber and relatively thin carpeting material, on the floor near the loudspeakers. That is effective to suppress resonance.

I'm still seeking for other effective measures.