JUST LOOKING
Johnson Electronics Labs announces two new products to expand the input selection capability of stereo amplifiers. The AX 101 CD-to-Phono Input Adapter enables amplifiers without a CD or auxiliary input to accept a CD (or any other auxiliary device) through the magnetic phono input. Features include passive circuit design, selector switch for CD or phono operation and RIAA response accuracy to within 1dB.
The AX 100 Auxiliary Selector enhances amplifiers with limited input capability to increase selection of up to five different input sources. It features silver-plated switch contacts, dual tape outputs and tape monitor switch to allow monitoring of either recorder. The AX 101 has a suggested retail price of $29.95; the AX 100, $89.95. For further information, contact JEL, 409 Angus Blvd., Warner Robins, GA 31088.
The Hybrid III Package from Sutherland Engineering provides a means of up grading the Dynaco Mark III amplifier.
The old driver board is replaced with a fiberglass board containing a JFET/ MOSFET cascode gain stage and phase inverters. The Hybrid III design includes 1% metal film resistors and non-inductive film caps. Today's capacitor technology offers higher storage capability in smaller packages with a lower equivalent series resistance than was available when the Mark III was manufactured.
The Hybrid IIT Package is available for $135 plus $5 shipping and handling.
For further information, contact Sutherland Engineering, 619 E. 8th, PO Box 1363, Lawrence, KS 66044, (913) 841-3355.
Mouser Electronics, a nationwide catalog sales firm, has recently become a distributor for the following products:
Amplite connectors, assemblies and shields.
Goldstar oscilloscopes and accessories.
HEXFET power transistors and surface mount diodes and rectifiers, manufactured by International Rectifier.
Anodized-finish aluminum and brass heatsinks from International Electronic Research Corp.
For more information, contact Mouser Electronics, 2363 Hwy. 287 N., PO Box 719, Mansfield, TX 76063, (817) 483-0165, FAX (817) 483-8157.
Analog Devices has introduced a new monolithic quad op amp, the AD713. In addition to settling to 0.01% in just 1-us (10V step) it offers input offset voltage of 0.5uV and bias current of 40pA.
Guaranteed matching characteristics include a maximum offset voltage of 0.8mV, maximum input offset voltage drift less than 25uV/ °C and input bias current of 35pA. A low total harmonic distortion of 0.0003% at 3V makes the AD713 well suited for multi-channel applications. Other features include a minimum unity-gain bandwidth of 3MHz, slew rate of 18V/us, high open-loop gain of 400V/pV and minimum common mode rejection of 84dB.
The top grade AD713 is available for $5.90 (100s) in plastic DIPs, $3.50 for lower grades. For further information, contact: Analog Devices, 804 Woburn St., Wilmington, MA 01887, (617) 935-5565.
Sage Audio Electronics has introduced its new 100-500W SUPERMOS 2, the latest in its SUPER-series power amplifier modules. It has only five connections and uses a dual rail power supply.
The SAGE active Class A circuit maintains Class A operation to the maximum current capacity of the output stage, typically 50A-80A, eliminating crossover distortion.
SUPERMOS 2 has a zero distortion amplification stage based on operating the semiconductors at a constant cur rent level and with a constant V,, eliminating all forms of nonlinearity. It has a slew rate 20 times greater than most audio amplifiers and uses local feedback loops for stability, carefully matched in put/output impedances between stages and symmetrical n-p-n/p-n-p circuitry, eliminating all transient distortion (TID).
For additional information contact Sage Audio Electronics, Construction House, Whitley St., Bingley, W. Yorkshire BD164JH, England. Tel (0274) 568647, Telex 517783, FAX (0274) 551065.
Museatex Audio has announced the MAXIM Preamplifier and Amplifier. The preamplifier successfully incorporates remote control without the loss of sound quality, using proprietary solid-state control circuitry designed by Edmund Meitner. It features eight inputs and two tape outs with the ability to record any in put while listening to any other, two pairs of main outs and an additional processor loop. A phono stage is available as an option. The amplifier, a stereo amp with output capability between the STR-55 and MTR-101 mono blocks, utilizes the Floating Charge Power Supply as found in the Meitner STR/MTR amplifiers. The MAXIM Series is scheduled for release in late 1989.
For more information, contact: Museatex Audio, 3305 Thimens Blvd., St. Laurent, Quebec H4S 1W2, Canada, FAX (514) 333-0382.
The latest in the line of Audio Control Technical papers, Number 106, is available. It is a discussion of the equalizer topology known as constant Q and is written by sound engineer Rick Chinn.
For more information, contact: Audio Control, 22313 70th Ave. W., Mountlake Terrace, WA 98043, (206) 775-8461, FAX (206) 778-3166.
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About this issue
Level controls of quality continue to pose serious problems since US manufacturers seem uninterested in making units of anything other than conductive plastic. So we offer two potentiometer articles this time, which look in opposite directions. Fernando Garcia Viesca explores what is probably the future for most systems, the digital domain (p. 8). In amore classic approach, Joseph O'Connell suggests a three-knob format to accomplish level and balance with switched resistors, eliminating tracking and noise problems (p. 33).
Contributing Editor Erno Borbely gets down to brass tacks (hardware) this time with his elegant and unique multi-output generator that provides every test signal that matters for quantifying audio distortion, starting willon page 13. Who says we don't care about measurements?
If you're driving a Ford lately, John Buschmann has some upgrade info on their generic audio equipment, starting on page 30. Don't miss a revealing discussion in guest editorialist Keith Arm strong's words about digital's effects in the control room.
Others present this time include Contributing Editor Gary Gale on mono CDs and help for readers in his Ask TAA offering (p. 36), an upgraded Borbely power amp and power supply in the Audio Aids section (p. 42) and music reviews by John Sunier, host of the popular weekly national broadcast Audiophile Audition.
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AUDIO AIDS
BORBELY DC 100 AMP UPGRADE
I HAVE LOOKED high and low for a great amplifier at a good price, which I thought impossible until I read Erno Borbely's Servo 100 and DC 100 amp articles. One design drawback in these amps is the power supply section. Mr. Borbely is cut ting this design far short by only suggesting we use as many large caps as we can get our hands on to try to maintain stability. Building a large bank of caps by itself is anything but a stable approach, and to further dilapidate this design he suggests cutting the transformer down 10% to take line regulation into account.
This power supply design is like using poor gasoline in a high performance sports car. With the suggested design we are doomed with the following parameters: Maximum =*56.6V at the rails, which will make maintaining the specified 100W in 8-ohm very difficult. Very poor regulation-10% line regulation and 5% transformer regulation (if over-specified VA). Very poor dynamic impedance will result in a loss of power at the low ends.
Maybe this design was used in the consideration of cost, but actually it will be quite expensive. After all, the caps are not cheap, and neither is over-specifying the toroidal transformer.
I suggest you use a regulated voltage supply. This will give excellent regulation, premium rail voltage can be obtained and maintained, and the resulting flat dynamic impedance response will greatly improve the low end.
PARTS LIST
DC 100
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Resistors R1 1M, mounted on input jack R2, 2A, 5, 25, 29, 34 2.21k R3 110k R4, 24 2210 R6, 26 2000 R7, 27, 40, 42 22.10 R8-11, 18, 19, 2 28.38 R12, 20 R13, 21 R14-17 R28, 36 5110 R30, 35 22K, 1.1W, 5% Resista WK 2 R31 2.2K, 4.5W, 5% Resista WK 8 R32 3320 R37 22k, YaW, 5% Resista WK 4 R38 1k R39 5620 R41 1500 R43 10, 9W* R44 100, 9w** R 100, 1.4W, 5% Resista WK 4 1000 68.10 6810 22.1K All resistors %W, 1% metal film, Resista MK-2 or equivalent, unless otherwise noted.
* 2x20 in parallel, Resista WK 8 **2x200 in parallel, Resista WK 8 Trimpots P1 5k cermet, 10T P2 1k cermet, 107
Capacitors C1 2.2 uF, 160V (PP, P) C2 330pF, 160V (PP, PS) C3, 6-8, ‘, 12 0.14F, 160V (PP) C4,5 1,000pF, 160V (PP, PS) co 100pF, 160V (PP, PS) C10 S6pF, 160V (PP, PS) C13, 14 47uF, 100V Electrolytic PP: Polypropylene P: Polyester PS: Polystyrene Transistors, Diodes Q1, 2,13 2N5551 Q3, 12 2N2920 (or MP 312) Q4,7 LM334z Q5 NPD5566 Q6 AH5020C) Qs, 11 2N3811 (or MP 352) Q9, 10, 17 2N5401 Q14 BF760 (or BF761) Q15 25K216 Q16 MPSAQ6 Q18 BF757 (or BF758) Q19 28J79 D1, 2,13, 16 D3-10 1N4148 ZPD 5.1 or equiv. (5.1V, 0.5W zener) LM336Z-5.0 ZPY 15 or equiv. (15V, 1W zener) L1 14 turns, ID: 16mm 1.5mm wire, self supporting Required: heatsinks for Q14, 15, 18, 19 and L1.
D11, 12 D14, 15
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I chose to use two mono units as Mr. Borbely suggests, but premium results can be maintained if a stereo unit is de signed with a regulated voltage supply.
I believe Mr. Borbely's superb amps, powered with regulated supplies, will out-perform anything on the market costing hundreds of dollars more.
(AUDIO AIDS)
FIGURE 1: A simple but effective way to design a regulated supply.
Figure 1 shows a circuit which implements both P-channel and N-channel FETs. Stereo operation can be optimized since each channel is isolated from the other via the use of series regulators, thus transients from one channel will not affect the other. Even with lower-voltage transformers that do not provide maximum rail voltage, all the qualities of a regulated power supply can be obtained at a cost of just a few more volts.
I have found a very good supplier of toroidal transformers, and at present they are manufacturing a replacement for the Hafler DH-200. This is a42V @ 700VA, and can be bought through Banner/Optronics Corp. (704) 487-7012.
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Circuit Calculations:
These calculations are implemented when a +40V RMS transformer is used.
The following steps should be taken:
1. The voltage thresholds (V1) of Q2 and Q4 need to be discovered, usually about 3.7 Vy, for the N-channel FET (Q2).
2. Now +V = Vj, = Vin = 56.6V - 3.7V = 52.9.
3. If we choose 1mA to pass through RS1, and P1, then P1 should be adjusted to cause + V to drop about 1.5V, this will cause Q2 to turn on and begin regulation.
If Vg is Vin + 1.5V, then Vg = 5.2.
P1 should be adjusted to about Vg/1mA = 5.2/1mA = 5.2k. RS; can now be selected:
+V=529-15=51.4V
Vrs: = +V-Vp =51.4V-5.2V=46.2V
So RS1 =46.2V/1mA =46.2k
4. RBI supplies Q2 with drain current.
For a current of 10mA we use the following equation:
[+Vin = (+V + Vg)]/10mA = [56.6V - (51.4V + 3.7V)]/10mA = 1500
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EDWARD J. AHO
Santa Monica, CA 90405
Erno Borbely comments:
As Mr. Aho points out, I chose the unregulated supply in consideration of cost, but many readers have reported they used regulated supplies with my amplifier design; mostly, I believe, Boak types, but I have received little feedback on the results.
I certainly recommend regulating the supply for the driver circuits (the boards), especially for the DC 100. For the outputs I am using high-current, unregulated supplies, not only because of the cost, but more importantly be cause of the additional heatsinking requirements of the series pass transistors in the regulators.
Without checking the operation of Mr. Aho's regulator, I would recommend using some capacitors at the out puts as well. As for cutting the supply voltage by 10% for line regulation, this is not necessary when using my latest design, the DC 100A driver circuit (see schematic); in my replies in ‘Letters ’ (TAA 2/89, pp. 52), I comment further on this amplifier upgrade.
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Classic Circuits
Grommes G101 Power Amp (1964) Courtesy of Tom Tutay, Ft. Walton Beach, FL 32549
UNLESS OTHERWISE SPECIFIED ALL RESISTORS ARE 1/72 WATT WITH VALUES IN OMMS. ALL CAPACITORS ARE 400 VOLT WiTh VALUES IN MFD.
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