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As General of the computer sound card if the total effect is generally not very good, often wear headphones to listen to a lot of strange sounds, if you want to do-it-yourself USB DAC to make best results, a USB PCM2702 DAC chip, such as the PCM2706 and ...

I had the choice of PCM 2706PJT, the use of its flexible than the PCM2702, and SPDIF output can I2S, IT is a monster, was the only word regarded as a fundamental element of the PCM2706 to say whether the voice of their own if Otherwise, leave a fiberglass production that we have received and then the GC-CAD V2.0 are very good. I want to strengthen the function, right! Try it! However, as a result of recent time is not enough, I do not have the full demand Zhanyou added, only the strengthening of the next.

1.Plus BNC coaxial output, the Council received a suspension of the BNC.

2.An increase in external power options, USB-General CAD is the use of USB directly to 5V power supply, but by the power of PC audio equipment may not always have the desired effect, I 'I am therefore of its external power supply, 3.3 V for the group 2 Power Supplies, a group of analog circuits for power, a group of digital circuits for power. COUNCIL PC and the lay-out discussion about the separation and a broken left on the hole, if you do not need external power, provided that it is broken, you can lower the volume.

The following are my last revised circuit:

The use of an external power L1117-3, the LDO 3V (voltage regulator IC), which is characterized by a low pressure difference, but only the best input voltage in the range of 4.8 to 6V, or I would during the process , The use of 12V DC adapter, power burn-L1117 at 3.3 V, burned on the exchange, burnt 7, the station is really great articles I bars.

The use of internal or external USB power to the circuit board to select Jumper, connect an external power supply for the employment of 1, 2, 2, 3 inserted in the internal use of USB power.

External power supply circuit left socket adapter, I had to stay 2 position, which one of you must also use their own elections in this direction for inserting the plug.

Fiber output can be used for the first TOTX178, 179,173, etc., fiber or compatible output of the first, I let you all types of electronic circuits in the first fiber-optic pin-compatible.

BNC BNC coaxial output is not directly in the main LAYOUT circuit board, I went to 2-pin, and then to people who can put on the chassis from outside the BNC or RCA Block.

As for the PCM2706 own production, I used the usual 3.5 mm headphone jack, if the direct use of computer speakers would be more practical, but it would be better received their best amplifiers.

Parts list is as follows:
R1, R2 ................................................ 15 Ω
R3, R4 ................................................ 22 Ω
R5, R6, R7, R8 ........................................ 3.3K
R9 .................................................... 1M
R10, R11 .............................................. 1.5K
R12, R13 .............................................. 330 Ω
R14 ................................................... 100 Ω

C1, C2, C3, C4 ........................................ 1uF/16V
C5,C6 C5, C6 .......................................... 47uF/16V
C7, C8 ................................................ 0.022uF (223)
C9, C10 ............................................... 100uF/16V
C11, C12 .............................................. 27P
C13 ................................................... 0.1uF grass-roots

U1 .................................................... PCM2706PJT
U2 .................................................... TOTX178 or compatible, and so on

LED ................................................... 3mmLED
L1, L2 ................................................ BEAD (core)
S1 ~ S7 ............................................... Small button switch
J1 .................................................... 3.5MM stereo headphone jack
J2 .................................................... USB-B-type outlet
CON1 .................................................. 2PIN pin Block
XTAL1 ................................................. Crystal 12Mhz
JP1, JP2 .............................................. 3PIN pin Block

Parts of the following non-necessary items, the use of an external power supply when the need for the following parts:
C14, C16, C18 ......................................... 100uF/16V
C15, C17 .............................................. 0.1uF grass-roots
P1 .................................................... 2.0mmDC Power Block
U3, U4 ................................................ L1117-3.3V

The following is a Upon completion of the photo:
The first test done PCM2706 USB DAC
Then do the PCM2706 USB DAC

Due to the use of two-panel design, so even if you have to DIY circuit board, to be careful on the hole well, in the welding must also pay attention to board up and down side through the hole to connect, it is necessary to carefully, one by one spot , The top hole through the use of the welding I am fine copper (from the general removed the suspicious wire to the more than OK fine line), the first place through the hole and then welding, if there are places that hole capacitor, such as the outlet can not be double-sided The welding parts, but also to use such a lead through the first, in front of the hole to find places to foil next to the weld can not play other parts had to hole-blocking, if that hole is the resistance, the switch , And so on .. core, it can be a double-sided welding. If the plant is the system board, then of course there will be no hole through the problem.

In fact, such a small cost to achieve External computer audio, CP is a very high value, do not want to spend a lot of money, you want to burn the little DIY, can be said to be a good choice.

If you download the PDF file is in the next few pages, you can see the film circuit board files, printed automatically canceled when the zoom function to print 1:1.

Download PDF version: GC-PCM2706USBDAC-FL.pdf
Film file to download: PCM2706D-BL.pdf

Superb Power Amplifier using TDA7250

This 2-channel hybrid IC is normally configured with TIP142/147 power darlingtons for its' output. For those who prefer to use power transistors instead, the TDA7250 can easily be converted. All that is required are a few transistors, 4 additional resistors and some rewiring.

This conversion centers mainly on changing the output section to a Sziklai.

Sziklai Output

In our IA502 on the right, drivers Q1,Q2 are 2SC2238 and 2SA968, and outputs Q5,Q6 are 2SA1216 and 2SC2922 respectively.

No instability problems were encountered from this conversion. After a period of run-in, the amplifier remained thermally stable.

Is this version worth the extra cost and effort?

If one is only interested in something basic, the TIP version would be sufficient. But if one is after sonic performance, I would recommend this version.

2SC2922/2SA1216 hardwired

the TDA7250 ic

2SJ113/2SK399 SEPP AB-40W stereo power amplifier, no feedback, the DC system

MJ wireless experiment in 1992 and announced in June

MOS-FET power output stage, a simple voltage・Miller called the NFB minor loops in multiplied by a powerful, and put on overalls with the NFB, has achieved very low output impedance, the natural sound of the amplifier.

Lead chassis S4 (300 × 200 × 60) is used. Both sides in the handmade SHIMASHITA wood paneling.
Block on the chassis are amplified voltage capacitors and a small stage for those who for the power transformer and the radiator and looks imposing, but the real thing is compact and lightweight.
Input terminals and output terminals to a lot of effort SUPATORON.
At the bottom of the radiator board配SHI MOS-FET power output stage and to shorten the wiring, the gate入RENAKU series resistance does not even oscillation.
Just change a little wiring, the source follower circuit voltage circuits in the mirror can be changed.
Miller-voltage operating conditions of the basic design is satisfactory, the source follower to change to get high-quality sound.

Miller-voltage circuit

Miller-voltage circuit and, as shown in Figure 1, MOS-FET source follower circuit and facing each other, the zero-bias operation to add J-FET, multiplied by the output stage to return to the local circuit.

[Figure 1] The output stage of the library
J-FET drain side of the drive and a collector of Tr-stage gate MOS-FET, so it is high impedance.
Pch Nch of the J-FET drain and between the MOS-FET INBIDANSU low bias power are combined with V B.

Therefore, the drive signal from the current stage, I S, J-FET to the source of the flow resistance R S, J-FET source of the signal voltage V S to occur, MOS-FET to the source of power equal to V S V O voltage can be obtained.

J-FET drain side of the higher impedance Z D, the output impedance of Z O will be reduced, MOS-FET input capacity of Cis (all seen from the side of the gate capacity, and will include feedback capacity) to I see a higher frequency and lower Z D, Z O increases.

MOS-FET gate - source voltage V GS, at a maximum and not more than V B, the maximum drain current I D is limited in quantity, so the effect of preventing excessive current may have up to two out of The current limit action in the clip must be designed to SHIMAWANAI.
The MOS-FET, the threshold voltage V GS (th) g m and the highest transconductance is desirable.
Fortunately, switching for the rich in power MOS-FET, but the request was consistent with many.

The design of this machine

MOS-FET used in Hitachi 2SJ113/2SK399 to.
Figure 2 shows the transmission characteristics.

1A and the idling current I O and Figure 2 and V GS is the extent to 5V, V B of the V GS is about twice the 10V.

[Figure 2] 2SJ113/2SK399 V GS-I D characteristics of
V GS to take a maximum of 2SJ113/2SK399 the aforementioned principles of the V B is less than 10V.

V GS in the case of a 9V about 9A So I D, 2Ω load resistance of the output voltage is also available in 18V, low enough to bear the load impedance.

For the basic design of the circuit is shown in Figure 3.

[Figure 3] The basic design of this machine

Power transformer, the tango TOROIDARUTORANSU using the RS-3101, the output stage supply voltage V DD is about 32V.

I O V B significantly higher if you set it, I D at the current clip can be larger, while the MOS-FET to increase the amount of heat, P CH channels of loss over the amount of allowable because This machine, and I O is 1A.

[Figure 4] heat dissipation design

Table 1 from the standard table P CH = 100W (Ta = 25 ℃), T CH = 150 ℃, so

Heat inside the θ i resistors θ i = (T CH - T a) / P CH = (150 ℃ - 25 ℃) / 100W = 1.25 ℃ / W.

DENKA TO-3P heat sheet using the MOS-FET and the thermal resistance between the radiator, Contact thermal resistance thermal insulation resistance θ c + θ s = 0.75 ℃ / W.

Below is a circuit diagram of the heat conduction.

P CH = V DD I C = 32V × 1A = 32W, so Radiator will be allowed to seek maximum temperature T f,

T f = T CH - P CHics =150℃ -32W×(1.25℃/W +0.75℃/W ) = 86℃

Ta ambient temperature of the radiator in the case of 50 ℃, The maximum permissible radiator heat resistance,

θ f = ( T f - T a )/ P CH = ( 86℃-50℃ )/32W =1.125℃/W

Figure 4 design radiating from the radiator to keep the temperature must be below 86 ℃.
Therefore, the radiator of a flexible TF1212 (122x120 × 40) in four pieces, MOS-FET is attached by a single, open-style chassis and put on.

Bias circuit as shown in Figure 5, V B less than 1 ~ 2V zener diode voltage and low anti-adjustable instrument (VR) has been able to adjust.

[Figure 5] Bias Circuit

The circuit and cause a bad contact VR, I O is on the rise as a dangerous, VR is reliable in use. CRD Diode, SEMITEC Japan = E102 0.88 - 1.32 mA, 10V

The constant voltage bias circuitry to operate a minimum of about 2mA current I L.

Miller-voltage circuits used in the local feedback 2SJl08/2SK370 of the J-FET I DSS 5.5mA is ranked GR, g m and the same amount if I DSS, and other forms of J-FET is also available.

The output stage for a full swing to V S necessary, to afford to ± 30V, R S at the time that I S 2.2kΩ is in full swing is ± 14mA.
When you, 2SJl08/2SK370 current flowing through the gate area covered Tr, is the gate to the low-impedance does not affect operation.

Tr stage of the drive for the operating current I S I S I SO that is half the 7mA, drive circuit and locally Biasing stage of the J-FET feedback circuitry necessary to operate because of the current sources of supply, drive stage Tr I DO idling current of the

I DO > I L + I DSS + I SO I DO> I L + I DSS + I SO
= 2mA+5.5mA+7mA = 2mA +5.5 mA +7 mA
=14.5mA = 14.5mA

'91 Of the amplify circuit voltage in the February issue of its MOS-FET DARINTONANPU INBATEDDO as well as two-stage amplification of the no-return.

FET first dan level of the output stage with zero bias 2SJ108/2SK370 behavior is the same.

Figure 3 is a constant,
I DO = ( R DI DSS - V BE ) / R E I DO = (R D I DSS - V BE) / R E
=(1kΩ×5.5mA-0.6V)/0.27kΩ = (1kΩ × 5.5mA-0.6V) / 0.27kΩ
=18mA = 18mA
Thus, the above conditions are satisfied.

If I DSS is a small increase in R S and will need constant change.

In addition, R S of the increase can be, if滅RASHITA Conversely, 1.8kΩ below the oscillator to the output stage.
NFB also put to the Ministry of voltage amplification, or as the output stage of the oscillation Darlington to make it easier to connect.
Such circuits, in order to prevent oscillation, MOS-FET and the gate necessary to insert a resistance in series there.

The circuit of the machine

All of the library circuit is shown in Figure 6.

[Figure 6] The circuit of the machine

Amp circuit parts

Change of source follower

Part of the power circuit

The amplification of the first dan level voltage, FET to cover the cascode-voltage connection was made.

To amplify the power of the voltage, the power to reduce noise and crosstalk, CR put filters.

To prevent oscillation, MOS-FET's drain and capacitor ground connection between the wiring to a minimum.
This type of capacitor used in a significant impact on the stability of this machine 1μF use of multilayer ceramic capacitors, in a square wave output waveform was able to reduce ringing.

In making this standard to guarantee performance, Tr KONPURIMENTARIPEA and keep FET using a commercially available, and no resistance to the 5 percent level used in the selection.
A pair of strict screening device, and using high-precision resistance, to get the balance of push-pull, you can further reduce distortion.

The machines used in the standard device is shown in Table 1.

In addition, the unit of the standard elements of a possible substitute.

[Table 1] FET, Tr standards

Maximum Ratings (Ta = 25 ℃, * Tc = 25 ℃)

Electrical Characteristics (Ta = 25 ℃)




T j


g m

C is

Electrodes connected
Model name












-2.6~ -20














* P CH


V GS(th)

g m

C is












-2~ -5















T j

f T

C ob




h FE























T j

f T

C ob




h FE




















The production of this aircraft

A4-size chassis lead the S4 (300 × 200 × 60).

Impossible without wiring and components acrobatics on the use of the mounting, as long as stylized as a result of how the parts are in place, but not from the beginning rather than in accordance with such style, the best components and circuitry It is thought to want a place. High-current circuit in order to shorten the wiring, 22000μF blocks of storage capacitors on the inside of the chassis.

Processing of the chassis, radiator and cooling radiator for the better part of the mounting, to increase stiffness of thick reinforced with aluminum angle.

YASURI chassis in the welding marks from flat paint and Trim can be

Decoration on the front of the word processor in a black plastic sheeting was printed in gold ribbon stickers on their own.

For the board, copper foil for printed circuit board wiring can not be used as a vapor.
As a result of the library board, as in Figure 7, the bull's-eye of the copper foil substrate in the etching solution to remove the lead wire through a hole in the expansion of 2mm in diameter, and bring out the wiring in place of a single wire fault of 0.8mm thickness Strange.

[Figure 7] of the library board

The upper parts of the board layout

zu7.gif (24134 bytes)

Place the bottom part of the board

Change of source follower

zu7u.gif (23743 bytes)zu7s.gif (12518 bytes)
MOS-FET from the board to speed up the wiring, the board placed part of the mounting position, I sent a particular concern.

Tr two-stage during the drive, angled aluminum heat sinks are attached to the tie, the heat of the earth plate connected to the substrate, and the chassis may not have any contact.

FET complementary characteristics , so the thermal drift, it is binding, so the heat on this machine is not binding.

Upper and lower parts of the substrate is mounted on both sides, and are cross-wired to the stereo, not making a mistake when you have good circuit diagram and to see that match.

Power supply circuit, the capacitor blocks from the terminal Rch Lch and wiring into two strains, and 100Ω power supply voltage amplifier attached to the plate to lag, the output of the idling current stage of the resistance to check the terminal block 0.47Ω Mounted on.

The output signal Q8, Q9 and the gate of 2.2kΩ extracted from the Earth's is a logical.
Therefore, Q10, Q11 from the source of Q8, Q9 Hye-wiring of the gate, which are then wired to the output pins.

But from the supply side of the Earth Hye 2.2kΩ, and the output pins and wiring.

Rectifier diode from the wiring to emit intense RIPPURUNOIZU other引KI回SHIMASU do not interfere with wiring.

MOS-FET gate of the current-carrying wires and open and the input capacity is in charge of the gate voltage to drain excessive current to flow, so beware of destruction.

Adjustment of the machine

Before the adjustment of the resistance VR 1 and VR 2 to leave the minimum value.

Turn the first time, in case of emergency drain and power MOS-FET 10Ω10W between the need to connect to the resistance.

Turn the output within ± 2V DC voltage, 10Ω peers verify voltage is less than 10V.

10Ω would remove the anomaly, the wiring back to normal.

The first adjustment, and idling for 1A current, VR 2 to adjust the voltage of 0.47V at both ends 0.47Ω.

If the VR 2, it is up to 0.47V If the VR 2 in the series with less than 1 ~ 2kΩ resistance in the case, contrary to 0.47V as VR 2 more than the minimum if the HZ-HZ-9L zener diode 7L exchange.

After idling 0.47Ω current settings and leave a short circuit.

DC output voltage to 0V and then to adjust the VR 1, but the power of the state暖MAっcold and heat until a stable condition change DC voltage output to 0V in any state. The machines fluctuation band around the center of the 0V.

Turn the VR 1 to increase output if the DC voltage, Q 1 source of 390Ω

After more than a measurement of adjustment, and later was able to get the property.

Changes to the source follower circuit

Lower SOSUFO If you compare the change in voltage that Miller was going to show excellence, excellence is fundamental to the circuit, the source follower of the great qualities who is also my best MASHITA.

Miller FOROWAHE voltage changes from the source, Figure 6, Figure 7, as shown in the return of local resistance to remove the FET switching can be a simple, so one can enjoy as much of the amplifier.

After the changes increase Idling a little current, so the re-adjustment is required.

In addition, changes to the circuit in the switch is no more acceptable.

The longer the oscillation circuit will be easier if the switch is running a poor contact and damage the cause of switching from the speakers.

In addition, a source follower of the voltage amplifier if you want to change the mirror, mirror voltage as the above-mentioned constraints must be met.

The characteristics of this machine

Figure 8 characteristics and the frequency of the Figure 9 crosstalk characteristics of the source and the voltage follower without a difference in the mirror, and accepted the good characteristics of the vocal cord is in the region.

RESUBONSU the high-growing region because of the high-frequency signals of the MOS-FET input current capacity can be passed through the gates - the source of signal voltage between the decrease in cost.

[Figure 8] frequency characteristics.
zu8.gif (14832 bytes)

[Figure 9] characterization of crosstalk
zu9.gif (17063 bytes)

Figure 10 is characteristic of the distortion, and frequency for each individual to move parallel to the low-voltage Mirror, low-frequency effects of a localized because of the high return rate is a low distortion.

[Figure 10] distortion characteristics
zu10.gif (21832 bytes)

Figure 11・damping factor characteristic of the low-frequency BORUTE JIMIRA If there are more than 1,000 from 600Hz to 100kHz while much is falling in a straight line.
The cause, MOS-FET input will increase capacity and frequency for the local decrease in the amount of feedback.
Meanwhile, the case source follower, about 20 in the regional auditory zone is nearly constant. This is like a personality characteristics of each other's differences, which divide the sound quality is a factor.

[Figure 11] damping factor characteristics・
zu11.gif (18643 bytes)

Then resist Load by 10kHz square wave output waveform of the load and capacity are shown in the photos.

Enlarge to rise again to display the waveform, the ringing is legible.

10kHz square wave output waveform Photo
SOSU・FOROWA Miller voltage・

8Ω load 4Vp-p

8Ω load 4Vp-p

sf8.gif (34662 bytes)vm8.gif (46892 bytes)

0.1μF load

0.1μF load

sf01.gif (35640 bytes)vm01.gif (36468 bytes)

0.47μF load

0.47μF load

sf047.gif (38284 bytes)vm047.gif (35653 bytes)

8Ω +0.1 μF load 4Vp-p

8Ω load 55Vp-p

sf801.gif (36849 bytes)vm55.gif (34460 bytes)
Miller-source voltage follower and stability in both high-capacity load is not on the oscillation.
High stability and the improvement of property ambivalent relationship with, is a difficult balance.

The high-range aircraft to more than necessary that the property did not extend to higher depreciation was available taxis.

ON-OFF at the time of supply shocks 0.5Vp-p less noise and lower the residual noise Rch 140μV, Lch, and it also reduces the 130μV, and silence the cry of power transformer in the extra care.

The temperature of the radiator, but if you do not mind the location of the ventilation, can not be touched by hand and the heat is not enough.

The sound quality of the natural voltage moist Miller faction, the source follower and a faction a spectacular reduction of the thick, and to insist on individuality, both of which are difficult to discard, the悩MIMASU choice, but only if producers Can enjoy luxury.

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