diyhifisupply press

Author: simon

  • Chapter 3 – Hardware

    Chapter 3 – Hardware

    Follow the wiring diagrams at the end of this manual for connections which are best made in the order found in the following sequences of wiring diagrams

     

    Preparation:

     

    Carefully remove 0.5cm of insulation from all the transformer wires. Do not pull on the wire where it comes out from the body of the transformer at any time as it may cause an internal break.

     

    Notice that all transformer are labelled with a number, symbol or letter. These are your references for making connections.

     

    Read through the entire manual as some connections have more than one wire atached. This can quickly be determined by comparing the wiring diagrams.
    Remove the selector and attenuator switches by loosening the nut on the front of each.

     

    Adjust the 23 position selector switch as follows (if not already done, there should be 23 positions but it may come from the factory set for 21 positions):

     

     

    Remove the switches at the back the same way.

     

    Make the connections as shown on the following wiring diagrams, installing piping as shown. Solder. Don’t overheat RCA jacks. This can be avoided by inserting an RCA plug into the jack being soldered. Ground connections to RCA can be made by using the thicker part of your soldering iron at the notch. These tabless ground connections are a little more difficult to make but are far superior to the separate ground tab types.

     

    Wiring of front panel switches:

     

    It is important to note that the selector switch has 2 pairs of wafers. The inside (transformer side) wafer is for the left channel and has 24 tabs, next wafer has 2 tabs.

     

    Then there is a metal plate and two more wafers for the right channel. The diagram shows the connections for these tabs, first, right channel then left channel as if the wafers have been separated.

     

    Proceed to make and solder these connections. It is easier to make the connections with the switch removed from the chassis but allow enough length of connecting wires to reinstall.

     

    When finished, reinstall the cover with 4 screws. Attach the knobs to the shaft.

     

    It takes about 2 weeks to run in the Django before the sound reaches full potential.

     

    Troubleshooting:

     

    A TVC is a simple device so trouble shooting usually involves finding the cold solder joint or misconnected wire. A good way to start is connect an ohmmeter across the RCA output and the adjacent ground tab. Operate the attenuator. Resistance should increase in even steps and never decrease as the attenuator is turned from lowest to highest position. Otherwise. A wire is misconnected. Check selector operation by connecting to each one of the RCA inputs and its ground. Choose that position on the selector. There should be continuity. Resistance depends on the setting of the gain switch.

     

  • Chapter 2 – Installation Notes – Specification and Parts

    Chapter 2 – Installation Notes – Specification and Parts

     

    Parts List for Django
    • 1 pr SQ supermalloy TVC
    • 4 XLR jacks
    • 10 RCA jacks
    • 6 position Seiden selector switch
    • 23 position Seiden attenuator switch
    • 12 tab Miyama 2 way toggle switch x 2
    • 6 tab Miyama 2 way toggle switch x 2
    • two way toggle switch for ground
    • 7m Hookup wire
    • 2M silver solder
    Chassis complete with mounting hardware, knobs and selector extension rod

     

    Recommended Solder

     

    It is recommended that included silver solder be used.

     

    Solder Technique

     

    Solder means to apply the iron tip to the point that needs to be soldered to heat it and at the same time apply the solder. The iron and solder come together at the same time when soldering any joint or tinning a wire and the solder should start to flow evenly around the joint. Allow the solder to cool naturally and do not blow on it. The finished joint should appear shiny and not dull.

     

    Many problems are due to poor solder technique. Clean the iron tip regularly on a wet sponge between each soldering step.

     

    Connections

     

    Attach means to dress a wire by stripping off enough insulation and then attaching it to the designated point or component. The connection is NOT to be soldered at this time. It is a good idea to tin all wires before attaching them. Always wrap the wire around the connection point to make a good mechanical connection.
    Connect means to dress a wire by stripping off enough insulation and soldering it to the connection point or first tinning the wire. When connecting a wire to a valve base pin it is recommended that enough insulation be removed so the wire can be wrapped around the pin to form a good mechanical joint before soldering. When attaching wires to any of the PCB’s or switches you should strip off a small amount of insulation and then apply solder to the exposed wire to tin it before fixing it to the PCB.

     

    Teflon coated high purity copper Single Strand Magnet Wire

     

    This wire comes with an enamel coating so the part of the wire, which will form part of a joint, must have its enamel removed before fixing and soldering. This can be done by boiling off the enamel in a solder pot or by holding the tip of a hot soldering iron with a little solder on the end against the wire until you see the enamel start to boil away. Clean the iron tip on a wet sponge afterwards and then tin the newly exposed wire. You can also use a fine sand paper to remove the enamel. This wire is ideal for signal ground connections.

     

    Tips for Successful Kit Building

     

    Study the drawings carefully: they look simple but there is much detail that is important. Do not conclude there is a mistake in the drawings; the problem is usually a mistake in seeing.
    Follow the sequence of instructions: These instructions were designed to make assembly as simple as possible and minimize interference between assembly steps.
    Identify parts: Be sure of the identity/value of each part before you install it.
    Follow the schematic: It is a good idea to have the schematic diagram of the unit nearby and to compare the instructions with the schematic.
    After installation, check the instructions again: Once a part is installed, double-check the installation against the printed instructions.
    Check off each assembly step when completed: Use a pencil to place a check mark next to each connection when it is completed.

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  • Chapter 1 – Introduction

    Chapter 1 – Introduction

    TVC was unheard of only a few short years ago but are actually a very early form of volume control. With the advent of much cheaper carbon wiper pots, TVC were pushed aside and forgotten.
    But a TVC is superior:
    1. No signal loss. Resistor attenuators throw away signal by converting electricity to heat. It could be analogous to controlling the speed of an automobile using the brake while the gas peddle is pushed to the floor. The TVC simply trades voltage for current by stepping up/down, much like a gearbox trades gear ratio against torque. Result is full dynamics even when playing at low listening levels and greater dynamics/transparency across the range.
    2. Passive operation so no power conditioning issues. No self noise.
    Back panel functions: 2 positions for grounding- hard, float. Choose the one that gives lowest system hum
    The net result is a very dynamic, involving linestage which can drive most any load that sounds tonally correct.

     

    Requirements
    The kit builder needs to have basic soldering skills and be able to read and understand the wiring diagrams presented. Refer to the text and diagrams at each step throughout the manual and ensure you double check all wiring at each stage. It is also advantageous to refer to the circuit diagrams at the back of the manual throughout the build.

     

    Warrantee
    The kit cannot be returned for a refund. Defective parts will be replaced provided they are returned within 30 days of purchase and are confirmed defective and not misused. No further Warrantee is expressed or implied. This is to protect you the buyer to be assured of receiving a brand new kit and not one that has been returned by someone else which may have been misused.

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  • Bias Voltage

    Bias voltage

    A negative bias voltage is needed to prevent runaway current in a vacuum tube. The negative voltage can be applied to the cathode or to the grid.

     

    1. Cathode bias: When applied to the cathode, it becomes self biasing, and the Anode voltage needs to be increased by the amount of voltage drop across the cathode resistor. So cathode bias circuits generally require a higher anode voltage to achieve the same power output.

     

    2. Grid bias: when applied to the grid, a lower anode voltage can be used to achieve the same power. However Grid bias is not self adjusting and is referred to as “fixed bias”. In the case of grid bias an adjustment pot or some other means of controlling the grid voltage is needed because if the negative voltage on the grid is lost there will be runaway current through the tube. In the case of push pull amplifiers, we want the same anode current flowing through each tube on the “push” and the “pull” sides of the output transformer. As tubes warm up and age they tend to conduct at a different rate. This causes the DC current to flow through the output transformer which in turn, produces a greater or lesser amount of saturation. Bass frequencies are the first to go. So while we may manually adjust the Anode current to be In perfect balance, a short time later there may be some imbalance and the amplifier is then not performing at itsoptimum level and sonics are degraded.

     

  • ABS Supply Principle

    ABS Supply Principle 

    ● The reference voltage is developed across an exchangeable resistor which can also be an external adjustable resistor
    ● The control loop adjusts the bias such that current through the sampling resistor (10R) produces the same voltage as the reference voltage, but it does so extremely slowly, to reject the dynamic variations introduced by the music.
    ● During startup the Active Bias System is set to apply the maximum bias and is locked into this stage for around 15 Seconds. During this time the “Error” Leds are lit up (they may briefly flicker on/off as the control loops stabilises).
    ● The the Active Bias System starts ramping up the Bias voltage slowly, reaching full bias within around 45 Seconds.
    ● If any one Valve connected to the Active Bias System cannot be biased to achive nominal current, but continues to have increased current, the “Error” LED will re-light and the “Error” output will be pulled low (open collector) to allow external protection circuitry to protect the Amplifier from the defective tube.

  • Discussions

    Discussion:

    Requirements: 

     

    To use the ABS Module, the amplifier must have the following:

     

    1. At least one 6.3V….15V AC winding that has either one side grounded or is floating (not connected to ground at all – can be tested using a multimeter). If one side of the AC filament winding is grounded then this grounded side must be connected to pin 4 of the ABS. Centertapped windings will not work unless the center tap is disconnected.

     

    2. A Bias supply voltage that is sufficient to bias any tube you may wish to use (eg. many EL34 Amplifiers have insufficient bias voltage under load to reliably bias all KT88 and 6550 Valves (you need at least 70V to reliably bias these with 430V HT).

     

    3. A “current sampling resistor” in the cathode of each individually biased tube of 10 Ohm (or 1 Ohm in case of high current applications). If multiple tubes are paralleled one ABS PCB is needed per each pair of individually adjusted valves.

     

    Example 1:

     

    The ATM-3 Amp from Air Tight has six tubes per monoblock, all individually biased, so three ABS PCB’s are needed per monoblock and each tube gets it’s own 10R resistor. The each ABS PCB should handle one pair of Push-Pull

     

    Tubes (that is the “left & right” or “upper & lower” pair in the schematic). All ABS PCB’s can share the same AC supply windings and bias voltage, as long as the same terminals are wired in parallel.

     

    Example 2:

     

    The Convergent Audio Technologies (CAT) Stereo Amplifier uses a complex bias system that combines all four paralleled KT88 in total. As a result despite having 16 Output Tubes only two ABS PCB’s can/need to be used. Each “side” of the push-pull block runs at around 150mA (nominal) total bias, but has a common compound cathode resistor of 1 Ohm, with a further 1 Ohm cathode resistor common to both halves.

     

    This means at nominal current each blocks common cathode will be at around 450mV. So on each ABS PCB the reference resistor R14 needs to be set to the value for 45mA with a 10 R “current sampling resistor”, despite the complex cathode metering scheme.

     

    In cases like the CAT Amplifier it is best to actually measure in place, with an optimally biased amplifier, the voltages that will be used to monitor the current in the tubes and to select the reference resistor R14 from the table (see below) based on reference voltage.

     

    reference resistor R14/Voltage:

     

    The ABS PCB contains a resistor intended for replacement by the customer to set the desired current through the valves. We fit as standard a “reference” Resistor (this is the small leaded resistor R14 in the front of the PCB as shown in above diagram) a 3k3 resistor.

     

    This resistor produces a settled current of 38mA with a 10 ohm resistor between cathode and ground (“current sampling resistor”).

     

    Below is a table listing the resistor R14 values for a given current and reference voltage value using the nearest E48 and E24 series resistor.

     

    Instead of the resistor R14 a suitable value potentiometer can also be wired in, if the value is too high a suitable resistor may be wired in parallel to limit the amount of current adjustable.

     

    Example:

     

    Maximum desired current: 60mA

     

    Theoretical reference resistor R14: 5K62

     

    Potentiometer: 10K

     

    Place a 13K resistor in parallel with the Potentiometer, giving a maximum combined resistance of 5K65 so at maximum turned up current only 60mA will be allowed.

  • Circuit and Wiring connections

    Circuit and wiring connections as follows:

  • ABS Module Features

    ABS Module Features

    • Eliminates need for constant re-adjustment of Bias to compensate for mains variations and valve aging
    • Regulation of cathode current of tubes from around 1mA to 250mA with10R cathode resistor current match between halves depends on cathode resistor tolerance ± 1% due to circuit (typical mismatch << 0.1mA). Perfect current balance produces better bass
    • Current regulation is not influenced by music signal
    • Current set by standard 1/4W leaded resistor (exchangeable)
    • Current can be adjusted from 0mA to 90mA per tube if a 10K Pot is connected instead of the resistor
    • reduces noise on bias supply by at least 40db (100 times) so even the most basic bias supplies sound good.
    • Lower noise improves resolution and imaging
    • Turn on Delay of 45 Seconds
    • Slow ramp up of current over a further 45 Second
    • Fault Indication via LED’s (Red) on PCB; they can be re-mounted on the Amplifier chassis
    • Fault Indication via TTL compatible open collector output (can be used for additional protection circuitry or for our upcoming electronic choke PSU PCB)
    • multiple mounting holes for easy mounting
    • Can be fitted to any existing fixed bias equipped Amplifier without changing the original circuit and with absolutely minimal modifications, except bias potentiometers (and possibly cathode resistor changes)
    • Small size due to use of existing supplies already present in your amplifier
    • No high voltage connections are required to be made

    Electrical Parameters

    • Maximum Tube current up to 250mA with 10R Cathode resistors
    • Output voltage up to -150V (depending upon the original bias supply in the amplifier)
    • Outputs can sink at least 2mA current or much more
    • Requires a single, ground referenced 6.3V to 12.6V AC supply (ie power tube filament supply draws 60-100ma) for the actual module and the original negative bias supply of the Amplifier

    Mounting And Installation

    • Designed for easy installation: one module can control two power tubes.
    • The only connecting voltage is needed are the existing DC 70 — 130 V bias voltage,a 6.3 — 12V AC connection (taken from the filament supply of the power tube {note: must not be a center tapped winding unless the winding is disconnected and if one side of AC winding is grounded then THAT side must connect to pin 4 of the ABS module} current draw 60ma/100ma—6.3v/12.6v)), and then a single connection to the grid and cathode of each tube to be controlled.
    • Designed to fit right into the current Ella chassis with no special mounting hardware or fixtures needed.

  • Active Bias Control

    Active Bias Control

    The ideal solution to fixed bias stability is to use an electronic circuit to actively sense current flow through the tube.

     

    Benefits: tube life is extended, saturation of the output transformer is avoided, amplifier always operates optimally, better bass performance, more dynamics, danger of runaway tube current when amplifier is unattended is minimized. Also since most bias voltage supply filter networks tend to be very simple single diode or half wave, there is usually a great deal of ripple in the most sensitive signal path in the amplifier – the grid! And active bias system is also an opportunity to design a bias supply with extremely low levels of ripple. This imbues a sense of stillness and low-level detail not obtainable with standard bias voltage supplies.

     

    Challenges: since the music signal its self effects a change in current through the tube, how can we devise a tube current sensor that responds only to changes in standing current but not respond to dynamic changes in current due to the musical signal on the grid? Also, since the circuit used to control the bias voltage will need to have some solid state devices, how can we make sure that we isolate the sound of solid state from our lovely tube’s sound?

     

    Through creative engineering and careful design this has been achieved with the DIYHFS Active Bias Supply (ABS module)

     

  • Other applications of the Universal Tube Output Stage

    4 – Other applications of the Universal Tube Output Stage

     

    Due to its design the Universal Tube Output Stage can be used in a number of additional Roles.

     

    Each module can be configured as Single Ended or Balanced Circuit with the following levels of Gain and input Impedances (assuming source with output impedances that are small compared to the input impedance):

     

    Gain Input Impedance
    ~ 30dB ~ 47 kOhm
    		 ~ 47 kOhm
    ~ 12 dB ~ 200 kOhm
    ~ 6 dB ~ 400 kOhm
    In addition other gain levels can be set by using the “30dB Gain” configuration and inserting a resistor in series with the signal. Some of them, in steps of 6db are listed below

     

    Gain Series Resistor
    30dB 1 kOhm
    		 1 kOhm
    ~ 24 dB 33 kOhm
    ~ 18 dB 91 kOhm
    ~ 12 dB 220 kOhm
    ~ 6 dB 40 kOhm

     

    Due to the extremely wide number of possibilities in configuring these Modules we are showing only a small number of the most common options.

     

    4.1 – Settings and Input wiring for use as SE Linestage 6db Gain

     

    This type of Application requires the following jumper settings:

     

     

    The input connections should follow the Scheme shown underneath:

     

     

    4.2 – Settings and Input wiring for use as SE Linestage 12db Gain

     

    This type of Application requires the following jumper settings:

     

     

    The input connections should follow the Scheme shown underneath

     

     

    4.3 – Settings and Input wiring for use as Balanced Linestage 6db Gain

     

    This type of Application requires the following jumper settings:

     

     

    The input connections should follow the Scheme shown underneath:

     

     

    4.4 – Settings and Input wiring for use as Balanced Linestage 12db Gain

     

    This type of Application requires the following jumper settings:

     

     

    The input connections should follow the Scheme shown underneath:

     

     

    4.5 – Settings and Input wiring for use as simple single ended stereo RIAA equalisation preamplifier

     

    One possible application is to use two Universal Tube Output Stages together with a minimal number of external components to form the RIAA Equalisation network as Phonostage.

     

    One Module will be used for each channel, so Tubes used should be identical in manufacturing and preferably matched.

     

    This application will produce a Moving magnet and High Output Moving compatible Phonostage with 47kOhm input impedance, 36 – 38db Gain (depends on the exact tube type and manufacturer used).

     

    When using narrow tolerance or selected parts (tolerance 0.5% or better for capacitors and 0.1% for resistors) for the RIAA as equalisation the RIAA EQ will be better than +/-0.1dB from 100Hz to 20KHz with an 0.5dB rolloff at 20Hz and a -3db point below 10Hz.

     

    If 1% tolerance resistors and 5% tolerance capacitors are used the RIAA EQ will be better than +/- 0.2dB with no more than 0.6db rolloff at 20Hz. For example: +/-0.2db RIAA requires 2.5% Tolerance capacitors. With 5% Tolerance around +/-0.3db are guaranteed. With 10% Tolerance capacitors around +/-0.5db. With 1% tolerance Capacitors it is better than +/-0.15db

     

    This type of Application requires the following jumper settings:

     

     

    The input connections and other connections should follow the Scheme shown underneath.

     

    The Resistors and Capacitors form the RIAA Equalisation. In principle other applications (such as tape head amplifier) could use the same principle diagram but with the Equalisation Network values adjusted to suit.

    4.6 – Alternate 12db Gain Stage in Shunt mode

    Attached an alternative way to do a 12dB Gain linestage with the UTS, using the attenuator in shunt mode.

    This allows you to tune the sound with the two series resistors. Some believe shunt mode is better.

     

    The UTS configuration is that in 3.01, but Vcom is not connected.

     

    4.7 – Pro-Audio Project

     

    On the “Pro-Audio” side of things, what is needed in today’s world is a good 2-Channel Microphone Preamp for recording into a digtal workstation and a downmix line level input mixer (say 8:2) and a 6-Way Cello Palette style tone control.

     

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    The Cello Palette style gig could also work for HiFi as a full preamplifier:

     

     

    Tone control can be done fully passive.

     

    This needs two UTS and (optional) line input (10K:10K Mu Metal Core + 20dBu) & output transformers (10K:600 Mu-Metal Core, +20dBu output) for balanced operation, plus tons of switches/pots.

     

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    A Microphone Preamp (balanced in & out) would need a Mic input transformer (1:5 or 1:10 with > 1K primary), two UTS and Output Transformer (10K:600) plus various small parts.

     

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    The 8:2 line mixer (balanced in & out) would need 8 pcs 10K:10K line transformers and two UTS plus two output Transformers and again tons of pots & switches.

     

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    Past the above the same transformers and UTS could also be used in Compressors and also for example a Pultec Equaliser copy…