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Tube DAC 3.5B
Assembly Manual
February 10, 1997
SHELDON D. STOKES 103 Windy Cove Apt I Hampton VA 23666 [email protected] http://www.clarkson.edu/~stokessd
Table Of Contenets:
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 3 Theory Of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 3 Board Etching Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 6 Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 7 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 10 Component Outlines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 12 Ground Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 13 Signal Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 14 Wiring the Circuit Board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 15 Digital Filter Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 16 Customizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 16 Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 17
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Introduction: The purpose of this manual is to be a guide to the proper assembly and maintenance of your Tube DAC. The board has been carefully laid out and constructed to make assembly easy and straightforward. The DAC itself has been designed to be very robust and to give years of trouble free service. Theory of Operation: This DAC consists of four separate parts, the decoder, the digital filter, the digital to analog conversion, and analog gain and buffering. The first part, is the decoder. The digital audio data enters the DAC via a coaxial input BNC connector. It uses the standard SPDIF standard 75 input impedance, but the DAC uses a BNC connector rather than an RCA jack. The data stream is capacitively coupled to a pulse transformer. The pulse transformer reduces common mode noise dramatically, and improves the performance of the input circuitry. The output of the pulse transformer goes to the input pins of the decoder chip. It also has a 75 resistor in parallel with the chip to set the input impedance. The decoder chip reconstructs the various clocks from the serial data stream. This chip uses a PLL (phase locked loop) to generate the clocks from the data stream. Sampling and status information are also extracted from the data stream. The data and clocks then go to the digital filter. This filter removes any information from the data stream that is greater than half the sampling rate. The data coming out of this chip is oversampled by 8 times. This means that there are now 8 samples in the time that there was one going into the chip. This will be very useful because it will move the quantization noise generated by the DAC chip 8 times farther away from the audible band. The data and clocks then go to the DAC chips. This is the heart of the DAC. The DAC chip used here are 20 bit models, that actually have two DAC chips inside each physical chip. They are operating in a complimentary "push-pull" fashion. The DAC chips output a very small current that is proportional to the number input. The analog stage must take that current output and convert it into a voltage, amplify it if necessary, and buffer the signal so it can be sent to the pre-amplifier without serious degradation. The first task is to convert that very small (micro to millivolt) current into a voltage. There have been a myriad of schemes to convert that current to a voltage in other commercial DAC's. Very fast op-amps are popular, as are a variety of very clever discrete schemes. The problem with these "active" current to voltage conversion (I/V) schemes is that they typically require many elements. In the case of an op-amp, there may be 40 transistors and a bunch of bulk silicon resistors and capacitors as well as a large amount of feedback involved in the process. And if that wasn't enough, the current value changes very rapidly, so if the I/V stage isn't designed perfectly, it can produce slewing induced distortion. This DAC uses a much more simple scheme (thanks to Peter Campbell for this one). A small value resistor is placed from the output of the DAC to ground. Thus, via Ohm's law (V=IR), a voltage proportional to the current is produced. There is only one user selected, passive element in the signal path. There is no risk of slewing induced distortion, and the signal path is as short as possible. There is a downside to this approach. The DAC chip was designed to have it's output pin always at ground potential. And it has a pair of diodes inside the chip to protect the output from any extraneous voltage on it. So that if the output rises to around 0.7 volts, the diodes start to con-
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duct. This has the nasty side effect of clipping the signal. So the thing to do is keep the voltage generated across the I/V resistor as low as possible. But if the voltage is too low the signal to noise ratio will be compromised, because the signal will require too much gain. So there is a trade off. It turns out that the PCM-63 DAC chips from Burr Brown work very well using this resistor I/V scheme. There is also a "Bipolar offset pin" on the PCM-63 DAC chip. This subtracts 2 mA of current from the output pin when it is connected to it. The reason they provide this feature is that a zero signal audio condition really is half scale in digital number terms (the audio signal must swing negative as well as positive). So the BPO pin sucks off half of the total possible output current. So the zero signal current with the BPO pin attached is zero. This may seem like a great idea, but it has a downside too. The current source is also made up of a bunch of transistors and bulk silicon resistors and capacitors. These things are best left out of the audio path. So the BPO pin is shorted to ground where it pulls 2 mA of current off the ground plane. This means that the zero signal current is now 2 mA and it can be as high as 4 mA. So the resistor value must be lower than it normally would have been if the BPO pin was used. This zero signal current is not a problem because the analog stage is capacitively coupled, and a DC offset on the input is filtered out. A FFT analyzer was used to determine the resistance value for the I/V converter where the signal starts being clipped by the diodes. It turned out that a resistor larger than 116 caused harmonics to start to be generated from a pure tone. This design uses a 100 value. This provides a healthy 2 mV signal for amplification. The signal to noise ratio is not as high as it could be, it is very good all the same. With a good pair of tubes the DAC is dead quiet. The small voltage must now be amplified and buffered. This is done with a SRPP (series regulated push pull) vacuum tube stage. The SRPP stage can be thought of as a standard resistance coupled triode gain stage, but instead of a large plate resistor, a constant current source is inserted between the power supply and the plate. This acts to make the gain stage much more linear, lowers the harmonic distortion, and provides a much lower output impedance than a single gain stage would have. This SRPP stage uses one half of a dual triode for the current source and the other half for gain. The output is capacitively coupled to the output jacks. The signal from the DAC is coupled to the grid of the gain tube via small resistor. This resistor reduces the likelihood of high frequency instability in the analog section by forming an RC filter with the input capacitance. As was stated earlier, the output current changes very quickly, and that creates high frequency energy (quantization noise). The continuous audio signal is essentially made up of steps. Most commercial DAC's filter this energy out. Many different filter topologies were tried, and they have all colored the sound and reduced the performance of the DAC in some way. So the analog stage was left unfiltered. The downstream audio components then act as a filter. Many people have balked at this approach, bringing up the potential for subharmonics being generated in the audio band and such. Those effects haven't been noticed to date. And those who have listened to this topology have really liked the sound, many say it's better than any other digital component they have heard. If some filtering is desired, a few pF of capacitance can be added between that plate and the grid of the signal tube. This will act to reduce the bandwidth of the tube, and roll off that high frequency energy. But try listening to the DAC unfiltered first. Due to the 8 times oversampling digital filter, this noise is at and above 352.8 KHz, which is very far above anything that is audible. The combination of a passive I/V converter resistor and a simple unfiltered tube stage make this one of the simplest and shortest analog sections on the market today. It's a belief of the
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designer that a short clean signal path is the best way to get the closest to the music. These various DAC stages all need to be powered. And this is an area that simplicity doesn't always pay. This DAC uses 4 raw supplies and 8 separate regulation stages. It uses a totally separate transformer for the digital and analog sides as well. The DAC also has a split ground plane that is connected at a point near the mixed mode decoder chip. The digital side of the DAC requires two voltages. Most of the chips require 5 volts, but the DAC chips with their push-pull architecture, also require -5 volts. These voltages come from a full wave rectified supply that feeds a pair of adjustable regulators, with their adjust pins heavily decoupled. Adjustable regulators were chosen over fixed regulators because they are much better at keeping digital noise from being fed back out of them and back into the power line, only to come into the analog stage. The analog stage requires several voltages. The DAC chips analog section also requires plus and minus 5 volts. There is another full wave bridge supply feeding four adjustable regulators, thus each DAC chip has a dedicated regulator pair feeding it plus and minus power. The tube stage requires two power supplies as well. First the tubes require heater power. The heaters also have a regulated DC supply. An adjustable regulator is also used here as well, so the filament voltage can be changed by simply changing a resistor. The heater supply actually floats about 85 volts above ground, so the heater to cathode voltage is not exceeded in the tubes. The final power supply is the high voltage for the tubes. There are many opinions out there on that is the best way to supply power to tubes. One school of thought is to use passive filtering via RC and inductive filters. This can be very musically satisfying, but creates a power supply that has a high impedance. This high impedance supply actually degrades the performance of the constant current source portion of the SRPP stage. Regulated supplies typically have amazingly low output impedances, but they can be electrically noisy (especially on transient demands), and some folks complain that they lack musicality. A semi-regulated power supply design was chosen, this gives the advantages of a regulated supply, with the quietness and musicality of a passive RC supply. First the high voltage from the transformer is full wave rectified and filtered. A string of zener diodes is biased via a resistor from this voltage. A capacitor is placed across the zener string to maintain the voltage precisely during varying loads, and the capacitor also filters out any diode noise. A pass transistor is referenced from the zener string. The drain of the transistor is attached to the raw supply. The gate is attached to the top of the zener string. The source is then sitting at the zener potential. This arrangement can provide much more regulated power than the analog stage could ever use. The output of the transistor then goes through a pair of small resistors and is filtered with a big pair of filtering caps. This final RC stage gives additional noise filtering and reserve power for the analog stage. All the rectifiers are solid state. Many people seem to prefer tube rectification. Tube rectification produces much less electrical and RFI hash than solid state rectifiers. But tube rectifiers are very limited in how much capacitance can be used after them. And they generally make higher impedance supplies than solid state rectifiers. So what would be ideal is to have a solid state rectifier that wouldn't produce all that electrical hash. Well the secret is to absorb that hash with ceramic capacitors hung across each leg of the diode bridge. Each rectifier bridge has 4 ceramic caps to absorb that diode hash. There are also capacitor power supply bypass caps right next to each chip where the power enters. The digital side uses tantalum capacitors, and the analog side uses film capacitors. The final capacitors in the high voltage supply also are bypassed with film caps.
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Board Etching Tips: The artwork is printed onto transparency film from a laser printer, print it three times. Cut out two of the prints with about a quarter inch of clear space around the circuit board image. Then carefully tape these two copies to the uncut one after carefully aligning the traces of the overlay to the uncut sheet's traces. When finished, there should be three perfectly stacked copies. This increases the contrast of the final image. When a transparency is printed with a laser printer, there are usually holes in the black printed parts. And the blacks aren't all that black when it is held up to the light. Overlaying makes the blacks much more black, and gets rid of the holes. Now the artwork is ready to use. This method uses GC® positive sensitized boards and developer. The FR-4 fiberglass 1 Oz. grade board works very well (they can be gotten local electronics stores). The board emulsion is sensitive to UV light, A good source of UV to expose the board is a GE® sunlamp. The sunlamp is hung so the bottom of the bulb is about 12" above the board. The exposure time is 9 minutes. With a yellow incandescent bug light-bulb on, pull the protective coating off the board and carefully align the artwork on top of the board. Then cover the artwork with a piece of glass to hold the artwork against the board (just like making a contact print in photography). Then turn the sun lamp on for 9 min. If a sunlamp is unavailable, the sun at noontime (on a clear day) can be used exposing the board for about 20 minutes. The exposed board gets dumped into the developer which has been mixed up beforehand. The developer says to use a 1:9 concentration of developer to water, but a 1:5 mix can be used, which works faster and can yield slightly better results. However the timing is more tricky, so it is not recommended for the first time. Submerge the board into the developer (A photography developer tray works very well), and rock the solution back and forth over the board. The exposed parts with start to dissolve. The emulsion is green and it will wash away exposing the copper underneath. This is the tricky part. The board must be removed when all the emulsion is off the exposed areas. If the board is removed too soon, the emulsion won't be completely dissolved off the exposed areas and it won't etch, if the board is in the developer too long all the emulsion dissolves and all that is left is a bare board. With the 1:9 solution this time window is about a minute, with a 1:5 solution it's about 20 seconds. The board is removed from the developer and washed off with room temperature water, then scrape at a an exposed area and see of there is any emulsion left there. if there is, place the board back in the developer for a few seconds. Repeat this as necessary until the exposed areas clear. With a little practice, it's pretty obvious when it's time to pull the board out. Do all the developing using the yellow bug light. When the board is done, wash it off and let it dry. Be careful of the emulsion, it's easily scratched, especially when fresh from the developer. Next, drop the board into an etching solution. Ferric Chloride is available from the same electronic outlets where the GC® boards and developer are purchased or from Radio Shack®. Ferric Chloride is a nasty smelling, iodine looking, serious staining stuff. Pour out the developer from the tray, wash it out and add the etchant. Then put the board into the etchant and rock gently back and forth for about a half hour or so, until all the exposed areas are clear. Then remove the board and wash it clean. The emulsion can then be removed with acetone or alcohol. Then all the holes need to be drilled in the board. A Dremel® moto tool works well for drilling the small holes, a small drill press would also work.
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Parts List: The following parts list is just a recommendation. many other parts will work as well or better than the ones specified here. Many people have substituted high grade resistors in the analog stage. Sprague Orange Drop polypropylene capacitors also work quite well as output caps. There isn't much to be gained by swapping out parts in the digital section however. The RCA jacks specified in the parts list are not very good quality, but it's hard to find decent RCA jacks for sale in electronics catalogs. If you would like a better grade of RCA plug, check with a high quality audio parts supplier. The part numbers listed are internal Digikey part numbers, except for the two power transformers, which are Toroid Corp. part numbers. The transformers specified are very high quality torroidial designs, however they are very expensive. Other brands of less expensive transformers will also work quite well. The transformers and tubes can be purchased from Antique Electronics Supply. The digital filter must be purchased from Seponix (the sole US importer). The Decoder chip can be purchased from your local Crystal Semiconductor representative, call or write to Crystal to find the dealer in your area. Here are the addresses and numbers for the parts suppliers:
Antique Electronic Supply 6221 South Maple Avenue Tempe, AZ 85283 Voice: (602) 820-5411 Fax: (602) 820-4643 http://tubesandmore.com
Crystal Semiconductor PO Box 17847 4210 S. Industrial Dr. Austin TX 78744 Voice: (800) 888-5016 Voice: (512) 445-7222 Fax: (512) 445-7581 http://www.crystal.com
Digi-Key Corporation 701 Brooks Ave. South Thief River Falls, MN 56701 Voice: (800) DIGIKEY Voice: (218) 681-6674 Fax: (218) 681-3380 http://www.digikey.com
Seponix Corporation 2151 O'Toole Ave. Suite L San Jose, CA 95131 Voice: (800) 237-4590 Voice: (408) 922-0133 Fax: (408) 922-0137 http://www.seponix.com/
Toroid Corporation Of Maryland 2020 Northwood Dr. Salisbury, MD 21801 Voice: (410) 860-0300 Fax: (410) 860-0302 http://www.toroid.com
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Part # TR1 TR2 TR3 U0 U1 U2 U3 U4 U5 U6 U7 U8 U9 U10 U11 U12 U7' U8' U9' U10' U11' U12' C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 C37 C38 C39 C40 C41 C42 C43 C44 C45 C46 C47 C48 C49 C51 C52 C53 C54 C55 C100 C101 C102 C103 C104 C105 C106 C107 C108 C109
Desription Toroid Transformer Toroid (W/ Custom Winding) Pulse Transformer Adjustable Regulator Adjustable Regulator Adjustable Regulator Adjustable Regulator Adjustable Regulator Adjustable Regulator Adjustable Regulator Decoder Chip Digital Filter XOR Chip Hex Inverter 20 Bit DAC Chip 20 Bit DAC Chip Chip Socket (machined pin) Chip Socket (machined pin) Chip Socket (machined pin) Chip Socket (machined pin) Chip Socket (machined pin) Chip Socket (machined pin) Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Ceramic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Film Capacitor Electrolytic Capacitor Film Capacitor Electrolytic Capacitor Film Capacitor Electrolytic Capacitor Electrolytic Capacitor Electrolytic Capacitor Film Capacitor Electrolytic Capacitor Film Capacitor Electrolytic Capacitor Film Capacitor Electrolytic Capacitor Film Capacitor Electrolytic Capacitor Film Capacitor Electrolytic Capacitor Tantalum Capacitor Film Capacitor Tantalum Capacitor Film Capacitor Tantalum Capacitor Tantalum Capacitor Film Capacitor Film Capacitor Electrolytic Capacitor Tantalum Capacitor Tantalum Capacitor Film Capacitor Film Capacitor Electrolytic Capacitor Film Capacitor Film Capacitor
Value 57 VA 54 VA "1:1" LM337T LM317T LM317T LM317T LM317T LM337T LM337T CS8412-CP NPC5843A 7486 7404 PCM63P-K PCM63P-K 28 Pin 28 Pin 14 Pin 14 Pin 28 Pin 28 Pin 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 820 pF 68 uF 4700 uF 3300 uF 3300 uF 4700 uF 100 uF 4700 uF 4700 uF 4700 uF 100 uF 4700 uF 100 uF 10 uF 100 uF 1 uF 3300 uF 0.1 uF 100 uF 1 uF 100 uF 100 uF 4700 uF 0.1 uF 4700 uF 0.1 uF 4700 uF 0.1 uF 4700 uF 0.1 uF 100 uF 0.22 uF 100 uF 47 uF 0.047 uF 47 uF 0.1 uF 47 uF 47 uF 0.1 uF 0.1 uF 1000 uF 47 uF 47 uF 1 uF 0.1 uF 1000 uF 1 uF 2.2 uF
Voltage
Part Number 707.082 5651 257-1015-ND LM337T-ND LM317T-ND LM317T-ND LM317T-ND LM317T-ND LM337T-ND LM337T-ND
Page
Manufacturer
Price
p p p p p p p
? 122 122 122 122 122 122 122
1K V 1K V 1K V 1K V 1K V 1K V 1K V 1K V 1K V 1K V 1K V 1K V 1K V 1K V 1K V 1K V 450. V 16. V 25. V 25. V 16. V 6.3 V 16. V 16. V 16. V 6.3 V 16. V 6.3 V 450. V 400. V 400. V 25. V 250 V 400. V 400. V 6.3 V 6.3 V 16. V 100. V 16. V 100. V 16. V 100. V 16. V 100. V 6.3 V 100 V 6.3 V 6.3 V 250. V 6.3 V 100. V 6.3 V 6.3 V 100. V 100. V 10. V 6.3 V 6.3 V 100. V 100. V 10. V 100. V 400. V
DM74LS86N-ND DM74LS04N-ND PCM63P-K-ND PCM63P-K-ND AE7228-ND AE7228-ND AE7214-ND AE7214-ND AE7228-ND AE7228-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P4127-ND P6439-ND P6234-ND P6245-ND P6245-ND P6234-ND P6201-ND P6234-ND P6234-ND P6234-ND P6201-ND P6234-ND P6201-ND P6197-ND P6433-ND E4105-ND P6245-ND E2104-ND P6433-ND E4105-ND P6201-ND P6201-ND P6234-ND E1104-ND P6234-ND E1104-ND P6234-ND E1104-ND P6234-ND E1104-ND P6201-ND E1224-ND P6201-ND P2017-ND E2473-ND P2017-ND E1104-ND P2017-ND P2017-ND E1104-ND E1104-ND P5643-ND P2017-ND P2017-ND E1105-ND E1104-ND P5643-ND E1105-ND E4225-ND
p 113 p 113 p 127 p 127 p 97 p 97 p 97 p 97 p 97 p 97 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 274 p 242 p 227 p 227 p 227 p 227 p 227 p 227 p 227 p 227 p 227 p 227 p 227 p 227 p 242 p 267 p 227 p 267 p 242 p 267 p 227 p 227 p 227 p 267 p 227 p 267 p 227 p 267 p 227 p 267 p 227 p 267 p 227 p 255 p 267 p 255 p 267 p 255 p 255 p 267 p 267 p 236 p 255 p 255 p 267 p 267 p 236 p 267 p 267
Toriod Corp. Of Md $ 39.95 Toriod Corp. Of Md $ 170.00 Schott $ 9.61 $ 2.17 National Semiconductor National Semiconductor $ 1.30 $ 1.30 National Semiconductor $ 1.30 National Semiconductor $ 1.30 National Semiconductor $ 2.17 National Semiconductor $ 2.17 National Semiconductor Crystal Semiconductor $ 30.00 NPC $ 23.50 $ 0.70 National Semiconductor $ 0.53 National Semiconductor Burr-Brown $ 41.50 Burr-Brown $ 41.50 Assman $ 1.48 Assman $ 1.48 Assman $ 0.74 Assman $ 0.74 Assman $ 1.48 Assman $ 1.48 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic ECK-series $ 0.28 Panasonic TS-Series $ 4.12 Panasonic SU-Series $ 1.72 Panasonic SU-Series $ 1.85 Panasonic SU-Series $ 1.85 Panasonic SU-Series $ 1.72 Panasonic SU-Series $ 0.09 Panasonic SU-Series $ 1.72 Panasonic SU-Series $ 1.72 Panasonic SU-Series $ 1.72 Panasonic SU-Series $ 0.09 Panasonic SU-Series $ 1.72 Panasonic SU-Series $ 0.09 Panasonic SU-Series $ 1.14 Panasonic TS-Series $ 4.04 Panasonic E-series $ 1.42 Panasonic SU-Series $ 1.85 Panasonic E-series $ 0.26 Panasonic TS-Series $ 4.04 Panasonic E-series $ 1.42 Panasonic SU-Series $ 0.09 Panasonic SU-Series $ 0.09 Panasonic SU-Series $ 1.72 Panasonic E-series $ 0.29 Panasonic SU-Series $ 1.72 Panasonic E-series $ 0.29 Panasonic SU-Series $ 1.72 Panasonic E-series $ 0.29 Panasonic SU-Series $ 1.72 Panasonic E-series $ 0.29 Panasonic SU-Series $ 0.09 Panasonic E-series $ 0.35 Panasonic SU-Series $ 0.09 Panasonic EF-series $ 0.83 Panasonic E-series $ 0.22 Panasonic EF-series $ 0.83 Panasonic E-series $ 0.29 Panasonic EF-series $ 0.83 Panasonic EF-series $ 0.83 Panasonic E-series $ 0.29 Panasonic E-series $ 0.29 Panasonic HFQ-series $ 0.75 Panasonic EF-series $ 0.83 Panasonic EF-series $ 0.83 Panasonic E-series $ 0.73 Panasonic E-series $ 0.29 Panasonic HFQ-series $ 0.75 Panasonic E-series $ 0.73 Panasonic E-series $ 2.92
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C110 C150 C151 C152 C153 C154 C155 C156 C157 C158 D1 D5 D9 D13 D17 D18 D19 D20 D21 D22 D23 ZD1a ZD1b ZD1c ZD1d R1 R2 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R20 R21 R22 R24 R25 R26 R27 R28 R29 R30 R30a R31 R32 R33 R34 R35 R81 R82 R83 R84 R85 Q1 Q2 Q3 SB1 LED1 LED2 PWR V1
S1
Film Capacitor Film Capacitor Film Capacitor Electrolytic Capacitor Tantalum Capacitor Tantalum Capacitor Film Capacitor Film Capacitor Electrolytic Capacitor Film Capacitor Diode Bridge Diode Bridge Diode Bridge Diode Bridge Diode Diode Diode Diode Diode Diode Diode Zener Diode Zener Diode Zener Diode Zener Diode Metal Film Resistor (2W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Carbon Film Resistor (1/4 W) Carbon Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) Metal Film Resistor (1/4 W) N Channel MOSFET NPN Transistor NPN Transistor Dip Switch Array (4 switches) Red LED (error) Yellow LED (De-emph) Green LED (power) Heat Sinks (10 Pack) 6DJ8/6922 Dual Triode 6DJ8/6922 Dual Triode BNC connector Power Entry Module RCA Jack RCA Jack SPST toggle switch
2.2 uF 0.1 uF 0.1 uF 1000 uF 47 uF 47 uF 1 uF 0.1 uF 1000 uF 1 uF 1.5A 1000V 1.5A 1000V 1.5A 1000V 1.5A 1000V 1A 1000 volt 1A 1000 volt 1A 1000 volt 1A 1000 volt 1A 1000 volt 1A 1000 volt 1A 1000 volt 62 V 62 V 62 V 62 V 47 K Ohm 100 Ohm 100 Ohm 499 Ohm 2 K Ohm 665 Ohm 2K Ohm 665 Ohm 2K Ohm 665 Ohm 2K Ohm 665 Ohm 2K Ohm 665 Ohm 2K Ohm 665 Ohm 2K Ohm 75 Ohm 10 K Ohm 1 K Ohm 10 K Ohm 1M Ohm 2.4M Ohm 4.7 K Ohm 332 Ohm 2 K Ohm 332 Ohm 332 Ohm 33.2 Ohm 680 Ohm 680 Ohm 1 M Ohm 100 Ohm 33.2 Ohm 680 Ohm 680 Ohm 1 M Ohm 100 Ohm IRF740 4401 4401 (10 pack) (10 pack) (10 pack)
400. V 100. V 100. V 10. V 6.3 V 6.3 V 100. V 100. V 10. V 100. V
400V
E4225-ND E1104-ND E1104-ND P5643-ND P2017-ND P2017-ND E1105-ND E1104-ND P5643-ND E1105-ND W10G-ND W10G-ND W10G-ND W10G-ND 1N4007GI-ND 1N4007GI-ND 1N4007GI-ND 1N4007GI-ND 1N4007GI-ND 1N4007GI-ND 1N4007GI-ND 1N4759ACT-ND 1N4759ACT-ND 1N4759ACT-ND 1N4759ACT-ND 47KW-2-ND 100X-ND 100X-ND 499X-ND 2.00KX-ND 665X-ND 2.00KX-ND 665X-ND 2.00KX-ND 665X-ND 2.00KX-ND 665X-ND 2.00KX-ND 665X-ND 2.00KX-ND 665X-ND 2.00KX-ND 75.0KX-ND 10.0KX-ND 1.OOKX-ND 10.0KX-ND 1.0MH-ND 2.4MH-ND 4.75KX-ND 332X-ND 2.00KX-ND 332X-ND 332X-ND 33.2X-ND 680X-ND 680X-ND 1.00MX-ND 100X-ND 33.2X-ND 680X-ND 680X-ND 1.00MX-ND 100X-ND IRF740-ND 2N4401-ND 2N4401-ND A5304-ND P300-ND P306-ND P303-ND HS132-ND
p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p
267 267 267 236 255 255 267 267 236 267 162 162 162 162 162 162 162 162 162 162 162 173 173 173 173 290 289 289 289 289 289 289 289 289 289 289 289 289 289 289 289 289 289 289 289 289 288 288 289 289 289 289 289 289 289 289 289 289 289 289 289 289 289 186 158 158 342 466 466 466 101
Panasonic E-series Panasonic E-series Panasonic E-series Panasonic HFQ-series Panasonic EF-series Panasonic EF-series Panasonic E-series Panasonic E-series Panasonic HFQ-series Panasonic E-series General Instrument General Instrument General Instrument General Instrument General Instrument General Instrument General Instrument General Instrument General Instrument General Instrument General Instrument Diodes Inc. (ITT) Diodes Inc. (ITT) Diodes Inc. (ITT) Diodes Inc. (ITT) Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo Yageo International Rectifier National Semiconductor National Semiconductor Amp Panasonic Panasonic Panasonic Aavid
75 ohm
ARF1177-ND CCM1115-ND SC1134-ND SC1134-ND CKN1019-ND
p 69 p 223 p 74 p 74 p 329
Amphenol Corcom Switchcraft Switchcraft C&K Total:
$ 2.92 $ 0.29 $ 0.29 $ 0.75 $ 0.83 $ 0.83 $ 0.73 $ 0.29 $ 0.75 $ 0.73 $ 0.88 $ 0.88 $ 0.88 $ 0.88 $ 0.07 $ 0.07 $ 0.07 $ 0.07 $ 0.07 $ 0.07 $ 0.07 $ 0.25 $ 0.25 $ 0.25 $ 0.25 $ 0.23 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.06 $ 0.06 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 0.11 $ 3.60 $ 0.29 $ 0.29 $ 1.44 $ 1.96 $ 2.52 $ 2.24 $ 11.65 $ 10.00 $ 10.00 $ 4.16 $ 37.94 $ 1.68 $ 1.68 $ 4.62 $ 546.14
9
Schematic:
R1 R2 Q1 ZD1d ZD1c C17 D1 W1 C4 C29 C30
LB+
C31
C1
C2
ZD1b
R4 C34
RB+
C35 R26
C3
ZD1a
C33 T1 W2 C5 C6 C19 D5 C20 W3 C7 C8 R6 C22
R7 D20
R25
U2
IN
LM317 OUT ADJ
D17 R5 C32
+FIL -FIL L+Va
U3
C9
C10 C21 D9
LM317 OUT IN ADJ
C38
C39
Line
C11
R8
C26
C12
C23
U4
MOV
T1 W1: 260V 50 mA W2: 13.6V 1.5 A W3: 13.6V CT 500 mA T2 W1: 13.6V CT 500 mA
LM317 OUT IN ADJ
R9
D21
C40
C41
R+Va
R10
C28
U5
IN
R11 LM337 OUT ADJ
D22
C42
C43
L-Va
R12
C36
U6
R13 LM337 OUT IN ADJ
D23
C44
C45
R-Va
Note: If only 6.3 volt filament tubes are to be used, W2 can be reduced to 7.5 V
R14
C37
U1
IN
R15 LM317 OUT ADJ
D18
C18
+Vd
T2
W1
C13
C14 C25 D13
R16
C46
C15
C16
C27
U0
IN
R17 LM337 OUT ADJ
D19
C24
-Vd
Analog Ground
R18 C48
Digital Ground
SDS Labs Tube DAC Power Supply
10
FRAME SYNC
LB+
1
14
D+5V C103 C104 D-5V R33
+5V
R28
SDATA 13
U11
Q2
+5V S1 R24 D +5V U9 DGND
LED1
7486
R30
PCM63P
4 GND 5 24 23 22
C102 C54 D +5V DOR A-5V R21 DOL
25 25 1 2 27
C107 C108
+5v 4 28
WCKO
IN (bnc)
MCK 6 7
DGND C51
C49
5
24
6 +5v GND 9 20
4 R22
23
+5v 8 21
7
22
CS8412
NPC5843A
C47
GND
8
21
9 10 19 18 17 16
DGND DGND 1 SB1
20
TR3
10 11
U8
19
11 12 13 14
C53
18
12
17
1
C55 +5V R30 Q3
PCM63P
7404
LED2 A-5V
C152
SDS Labs Tube DAC 3.5b
Switch 1 2 Off On On Off Off Sample Rate 32.0 KHz Switch 3 Off 44.1 KHz On On Off 48.0 KHz On De-Emph OFF Filter 25 Tap Switch 4 Clock 153 Tap Off On Free Sync.
3
2
1
28
26
DGND R29
4
25
NOTE: The input connector should not be connected to the chassis or to ground.
U10
C151
6
5
23
C150
8
7
21
D +5V
9
20
SCK
0.1 mF
11
10
18
14 15
15
12
17
R20
13
16
13
U12
14
U7
3
15
26
3
DGND C106
26
3
26
BCKO
4
25
2
C101
27
2
27
5
24
1 1
C105
28
28
6
23
C100 Iout
8
7
21
DGND
9
20
PWR
11
12
10
16 17
R27
1
2 3
C109
C52 D +5V
15 18 19
V1
OUT
R34
6
22
A +5V A -5V
R31
7 8
R35 R32
RB+
1
16 19 22 24 27
11
D+5V C153 C154 D-5V
2 3
C110 R83 V51
OUT
R84
6
Iout R81 C155 C156 A +5V C157 C158 A -5V R85
7 8
R82
SDS Labs Tube DAC V3.5b board
LED1 LED2
Note: The two caps directly to the left (C46 & C48) are labeled as C40 & C43 on the circuit
POWR BNC IN TR3 c Q2 C103 R20 e R30 C49 b C47 C104 C105 C106
S/N ___________
C109 C39 C107
C48
OUTL
U0 C27 C24 + + D19 R17 R28 U7 R21 R18 C46
+VA
R33 R35 C108
R34
C25
CT
U11
R32
U1 C18 R24 C51 S1 D18 R15 R16 U9 +
+
R22 R27 C100 R30 e c C101 Q3 C156 b U10 C155 R29 C157 C41 C153 C154 C43 C102
-VA
R31
C13 C14
U5
D13 C42 + C53
C36
C159 C52
C55
OUTR
+
The Circuit Board (Component Outlines):
U6
C37
U8
U12
C44 +
C23
D23 R13 R14 C28
-VA C54 C45 C152 C150 SB1 C22 C151 ZD1a-d
CT
+
C21
U4
C40
+
+
U2 + D17 R5 R6
Q1 R25 R26 C32 + C33 C29
C35
C31
D21 C9 C10 U3 D9 + D20 R7 C12 R8 R9 R10 C26
R2 C1 C20 C38 + + C2 + R1 C19 + + D1 + C17 C34 C3 D5 C8 C7 C6 C5 C4 +
R4
C30
C11
+
12
R85 C158 R81
C15 C16 R11 R12
D22
+VA
R83
R84
R82
The Circuit Board (Ground Side):
13
C106 LED2 LED1 PWR C105 C107 C48 + e R30 C49 U0 C24 + U7 D19 R17 R18 CT R21 + C27 + Q2 b -VD +VD R20 C47 c C39 BNC TR3
C109
SDS Labs
Tube DAC V3.5b
OUTL
R33
+VA C104 C103 R28
R34 R35
C108 U11 +
R32
C46 C18 R24 C100 + + c C156 b C155 C157 R29 C41 -VD +VD + C53 C154 C153 C52 C55 C42 U9 U10 C101 R30 Q3 e C102 R27
C25
R31
C43
-VA U1
+
S1 C51 R22
The Circuit Board (Signal Side):
D18 R15 R16 C36
C13 C14
Hollow-State Analog Section C159
+ +VA
+ + U5
D13
OUTR
R83 R85 C158
U12 U8
D22 R11 R12 C37
R84
C15 C16
C54
C45
C152
C30 C34 +
C17 +
D1
C19 +
C7 C3 C4 C5 C6 C8 D5
+
+
14
R81
C150 + C22 + C151 SB1 -VA R26 + C29 ZD1a-d + C33 C32 R25 U2 D17 R5 C1 C2 + R1 R6 C20
+ U6 C44 +
C23
D23 R13 R14
+
R82
CT
Q1
C40
U4 + D21 R9 R10
C28
+
C21 +
C31
C35
R2
R4
C9 C10 C26 + C38 U3 + + D20 R7 R8 D9
+
C11 C12
Connect the analog supplies to the DAC chips
Connect ground planes together here
SDS Labs
Tube DAC V3.5b
+ +
Digital transformer wires go here
+ + + +
+
Hollow-State Analog Section
+ +
Digital center tap
RCA (left): signal ground
+
+
RCA (right): signal ground
+
+ + + + + +
Analog transformer wires go here
Wiring The Circuit Board:
+ + + + + +
B+ transformer wires go here
Filament transformer wires go here
Analog center tap
15
+ + + +
+
+
+
+
Digital Filter Settings:
Switch 1 2 Off On On Off Off Switch 3 Off Switch 4 Clock Off On Free Sync.
Sample Rate 32.0 KHz
Filter 153 Tap 25 Tap
On 44.1 KHz On Off 48.0 KHz On De-Emph OFF
The chart above summarizes the different filter settings. Set DIP switches 1 & 2 for the sampling frequency most commonly used. For CD's it would be 44.1 KHz. This sets the correct coefficients for the de-emphasis filter. If you also listen to DAT tapes (sampled at 48 KHz) don't worry about switching the filter each time, the difference in coefficients is very slight. In fact the error from having the switch set for the other frequency is actually less than the error in many deemphasis filters implemented in the analog domain. Switch 3 is an interesting one. The digital filter has two filter settings. The higher tap setting is a steeper filter, and is the one that yields the best measured performance. The second filter is a much more gentle sloped filter. The two setting have a slightly different sound, pick the one you like. Switch 4 sets the filter in either free running or forced synchronizing mode. There may be a slight difference in jitter specs between modes, but it hasn't been noticeable in listening tests. If in doubt, keep it in Sync mode. Customizing and Making Substitutions: The analog stage as shown uses 6DJ8, 6922 or 7308 tubes. The DAC can be easily changed to accommodate quite a few different tubes. For tubes with twelve volt filaments, change the value of R5 from 499 to 221. This will allow the use of the 12A_7 family of tubes and their variants. The values of resistors R32, R33, R82, & R83 may have to be changed to increase or decrease the bias current depending on the tube chosen. The sound of each tube can be tailored somewhat depending on the bias point chosen. The B+ voltage can also be adjusted by substituting different value zener diodes into the string. For example, using four 75 volt zeners would yield a B+ voltage of 300 volts. If the filament supply chosen uses the 13.6 volt transformer winding (suitable for both 6.3 volt and 12.6 volt filament tubes), and 6.3 volt filament tubes are being used, a 5 ohm (10 watt) resistor can be inserted in series with one of the transformer leads going to the circuit board. This will reduce the power dissipated by the regulator and make it run cooler. If the DAC is only ever going to use 6.3 volt filament tubes, a transformer with a 7.5 volt filament winding can be used. If different analog stage parts would like to be substituted, the following resistors are the ones to change, in order of importance: R35 & R85, R31 & R81, R32 & R82, R33 & R83, R34 & R84. The output capacitors can also be changed. Polypropylene caps work very well. C109 & C110 are the most critical followed by (in order of importance): C31 & C35, C39 & C41 & C43 & C45. Ideally the DAC should be housed in a metal case to shield your other components from the DAC's RFI. But it's not required. The prototype is still being used, and it is open to the world with no problems. If the DAC is enclosed in a metal case, make sure that the input BNC plug is insulated from the case, or the benefit of the input transformer will be lost.
16
Corrections: There is an error in the labeling on the circuit board. There are two C40 and two C43 labels. The numbering on the Component Outlines included here is correct.
17