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LD91+ MonoMax with P:USH Power For DIY and assembled units DIYHFS 5/16/2012 Contents 1.0 Introduction and Overview:...2 2.0 Parts list...5 3.0 AC Wiring...6 4.0 Output Transformers Choose Connections according to Speaker...8 5.0 Filament Supply...10 6.0 Capacitors and Power Supply...12 7.0 FCUPS Jumpers Settings:...14 8.0 310A Grid Cable...14 9.0 Resistors, Input and Ground Wiring...15 10.0 Detail Photograph of Finished Chassis Single...17 11.0 Detail Photograph of Finished Chassis Left and Right...18 P. 2
12.0 Startup Instructions...19 12.1 General:...19 12.2 AC voltages:...20 12.3 DC Voltages:...20 12.4 Insert Tubes:...21 12.5 Operational Notes:...22 13.0 Circuit Diagrams:...23 14.0 Amendment...25 [v1.6] P. 3
1.0 Introduction and Overview: diyhifisupply Our universe became a little disordered when we introduced the single chassis LD dual mono. Due to escalating costs the 8 year old LD monoblock was not sustainable as a product on two counts: 1. cost of materials and manufacturing had almost tripled since the original Billie was offered for $700 (including all the upgrades we progressively built into the kit) and 2. shipping overseas by Fedex had doubled from <$200USD originally to >$400USD by 2009 (also due to the extra weight of all the upgrades and enhancements). The single chassis LD dual mono gave us an opportunity to keep a sane selling price and also to forever dump the poison of electrolytics in the power supply and thus offer the one and only all film cap SET amplifier. This is where our universe became disarranged - the single chassis LD sounded better than the monoblocks. I guess not a surprise since the single chassis LD has everything the monoblocks had except minus one power transformer but plus 200uf of film caps. Raise the bar and that's what happens. In the meantime we've developed our own filament supplies and FCUPS (film cap universal power supply) which raises the bar again. We still had in mind to show some respect to the establishment. This is it: LD MonoMax in Projekt monobock chassis with FCUPS and filament supply standard. The added performance of the FCUPS is not subtle and is too good to not have. The discerning eye will notice this is our 91 circuit with Level 3 parts. Considering the powersupply enhancements this one is called the LD Mono Max with P:USH power. So what's this P:USH Power business? Power for Ultimate Signal Headroom! Because the FCUPS with its huge store of inductive energy and virtual battery mode is in a totally different league than banks of caps, resistors and even big chokes in their little puddle of inductance. You are about to hear it:- inductive energy store is totally better than capacitive energy. Like Iron Man beats Chickenman. P. 2
The LD MonoMax is beautifully simple and designed to really display the advantage of a directly heated triode 300B in single-ended class A, no global negative feedback configuration. Using a tube rectifier and P:USH power supply it gives true musicality - especially when connected to horn and single driver full range speakers. The self bias design makes tube rolling into an easy task. Single-ended class A amplifiers are the elite among tube amplifiers. Famous Hi-End manufacturers like Jadis, Cary, Audio Note...etc all offer their top models based on the 300B single-ended amplifier design. The most famous vintage single-ended amplifier is Western Electric s WE 91A, which was used for theatre and public PA application. They began in 1935 using a single 300B (early models were using 300A) with two 6C6 pentodes and an input transformer to accept balanced input. The 300B has very good linearity, coupled with a simple class A single-ended circuit so the harmonic distortion generated at the rated output is relatively small. Usually the total harmonic distortion at maximum output is less than 5% and is mainly second order. Matching with greater than 90dB speakers generates a tapestry of rich musical sound and transparency. This is especially true with vocals and classical music where richness of timbre are paramount to recreating the experience of live music.. Before 1946 WE91 theatre amplifiers made in the US were using the triode as the power tube. Standard frequency response was 80Hz to 10KHz and the output power ranging from 10 to 16W. They were used for driving horn speakers. In the late 60s, the development of single end class A amplifier shifted to Japan and since then their popularity has continued to increase. The tubes used most were mainly the directly heated 300B, 2A3 and 845. Among them the 300B has the best sound. Later proclaimed the tube of the century this realization quickly spread to Europe and then the whole world. The LD MonoMax now offers universal flexibility to build with multiple drivers and output tubes. The single-ended output transformer used by DIY Hifi Supply uses high grade Z11 steel and good design to enable good low frequency response while at the same time providing low high frequency distortion. A special mounting core is used and the whole assembly is vacuum impregnated. WE91: Although in tube-fi less is more, the 91 circuit embodies some justifiable complexity. The famous WE connection from anode to cathode increases dynamic range and lowers the noise floor. 0.2mv is quite possible with DC heaters. The bootstrap cap from cathode to gridleak adds bass kick. The pentode driver gives greater input sensitivity and makes the amp perhaps the easiest to drive 300B. All these circuit concepts were developed, then lost, and recently rediscovered as more individuals mine the archives for gold. The original 91 was bandwidth limited (80 to 10k) due to speaker/output transformer limitations. Our version of the LD+/91 is flat from 20 to 20k due to some circuit tricks credited to Thorsten Loesch and also choosing high quality parts and output transformer materials. The 91 is all about tone; no other circuit captures tone so well. Enjoy. P. 3
This kit can not be returned for a refund. Defective parts will be replaced provided they are returned within 30 days of purchase and confirmed defective - not abused. No further warranty is expressed or implied. This is to protect you so that you are assured of receiving a new kit, not one that has been returned and fiddled with (and who knows what else) by someone else. Specific included parts may change from time to time as improvements are made. Since these 300B monoblocks have minimum parts count, are partially pre-assembled and employ a simple circuit design, they are easy to assemble. If wiring connections are carefully checked for accuracy and good soldering technique is used, there are very few things to go wrong. Soldering: It is assumed you know how to dress a wire and solder, however the vast majority of problems are caused by poor solder joints. A tight mechanical connection between wire and tab will give better heat conduction and thus better solder joints. Solder needs to melt and flow over both wire and tab and then be allowed to cool naturally without movement. Wiring: Double check all connections when doing the wiring and then once again as each section step is completed. WARNING: THE HIGH VOLTAGES PRESENT IN THIS KIT CAN KILL. THE HIGH OPERATING TEMPERATURES CAN BURN. OBSERVE ALL PRECAUTIONS. NEVER CONNECT THIS KIT TO ELECTRICAL POWER UNTIL IT IS FULLY ASSEMBLED AND READY FOR TESTING PRIOR TO OPERATION. YOU ASSUME TOTAL RESPONSIBILITY AND LIABILITY FOR THE USE AND OPERATION OF THIS KIT BOTH FOR YOURSELF AND THOSE AROUND YOU. WAIT 5 MINUTES AFTER SHUTDOWN BEFORE ATTEMPTING TO SERVICE THE KIT TO ALLOW FILTER CAPS TO DISCHARGE Octal sockets pin numbering: count clockwise from the notch starting at 1 to 8 Don t rush. Have fun. The meaning is in the journey. Now you can proceed. Be sure to check the start up instructions at the end of the wiring diagrams Step 1: Unpacking Remove the bottom cover from both chassis, take out the loose kit parts and check against the list: Attention: To make it easier to assemble, the current generation of kit has a higher level of pre-assembly so some of the following hardware has been pre-installed. P. 4
2.0 Parts list diyhifisupply Part list is now printed and packed with the amplifier. P. 5
3.0 AC Wiring Important Note: Remember to twist all AC wires tightly. Do not place AC wires close to or parallel to signal or DC wires as this will couple and create noise. If AC wires are near other wires make sure they cross at right angles. Use a heat sink On and off do switch not overheat connections to IEC AC input connector. IEC socket On off switch Connect to power transformer. See the following page P. 6
Choose the wiring configuration suitable for your voltage P. 7
4.0 Output Transformers Choose Connections according to Speaker P. 8
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5.0 Filament Supply 1 2 3 4 5 8 Pin 6 and pin 7 were added to 9 new module. Need to short pin 6 and pin 7. Other connections remain the same P. 10
Amendment D P. 11
6.0 Capacitors and Power Supply AAmeennddmeennt t AA P. 12
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7.0 FCUPS Jumpers Settings: Make sure the 2 yellow jumpers are set as shown in the previous two diagrams. This is for virtual battery mode. 8.0 310A Grid Cable P. 14
9.0 Resistors, Input and Ground Wiring Amendment C P. 15
Amendment C P. 16
10.0 Detail Photograph of Finished Chassis Single P. 17
11.0 Detail Photograph of Finished Chassis Left and Right P. 18
12.0 Startup Instructions 12.1 General: Do not insert tubes yet! Measure AC voltages by one probe of meter on each AC wire. Measure DC voltages with one probe on measurement point and one probe to chassis. Best is to use probes with clip-on connectors. Do not switch on power until your hands are clear of chassis. Observe all safety precautions around high voltages. Best is to always keep one hand in pocket when taking voltage measurements. WARNING: THE HIGH VOLTAGES PRESENT IN THIS KIT CAN KILL. THE HIGH OPERATING TEMPERATURES CAN BURN. OBSERVE ALL PRECAUTIONS. NEVER CONNECT THIS KIT TO ELECTRICAL POWER UNTIL IT IS FULLY ASSEMBLED AND READY FOR TESTING PRIOR TO OPERATION. YOU ASSUME TOTAL RESPONSIBILITY AND LIABILITY FOR THE USE AND OPERATION OF THIS KIT BOTH FOR YOURSELF AND THOSE AROUND YOU. WAIT 5 MINUTES AFTER SHUTDOWN BEFORE ATTEMPTING TO SERVICE THE KIT TO ALLOW FILTER CAPS TO DISCHARGE P. 19
12.2 AC voltages: Switch on power and measure AC voltage input to: filament supply. It should be 6.8-7V. Less and there will be output noise; more and there will be too much heat. You can trim the AC in voltage by adding/removing 0.47ohm/10w resistors in series with the AC input to the filament supply. Tube filament and high voltage connections. The 310a filament AC supply wires should measure about 9 to 10V AC across pins 1/6 The rectifier should have about 5V AC across pins 2/8 and 400-430V AC across pins 4/6. If all voltages are too high or too low you can select a different primary configuration on power transformer. Switch off power 12.3 DC Voltages: Switch on power Filament supply output side. Adjust blue trim pot to get 5V DC across the +- of the supply. Later when you insert power tube you can come back and fine tune the adjustment. With tubes in place best is around 4.9-5v dc. FCUPS Power Supply Power off. Insert Rectifier tube. Power on. Check that the input voltage is about 450V dc (one probe to ground, other on connector labeled Tube Rectifier Cathode.) At the output side at connector labeled Positive High Voltage output check the same way. There should be about 450v dc (this will change after tubes are inserted and power supply is loaded). P. 20
12.4 Insert Tubes: Power off. Insert 310a and 300B. Connect 310a grid cap. Power on. Check voltages as per following: Measure the AC voltage across 2 and 8 of the rectifier. Should be about 5v AC. Measure the AC voltage across pins 4 and 6 of the rectifier. Should be about 800v AC Measure the AC voltage on the 310A pins 1 and 6. Should be about 10v. Short the input jacks. Attach a ~8r 20watt resistor to speaker output. 310a: Match the 2 larger pins to the 2 larger holes. Failure to do so will destroy a very expensive tube, not covered by warranty. 300b: same as above. It is possible to insert the wrong way so pay attention please. Rectifier: should only insert one way. Here s what we want. 300B anode, pin 2 to ground about 420+v DC. Pins 2 to pin 1 should be about 360v Across the 880 ohm adjustable resistor about 70v (I=V/R so about 80ma current) 310A anode pin 2 to ground about 180v-210v, screen pin 2 about 100-120v all DC. Can be adjusted. See Schematic. Output noise across the speaker binding posts should be about 0.2-0.3mv!. If all OK now you can play music. It ll take about a week for things to settle in. P. 21
12.5 Operational Notes: Notes: 1. 310a tube pins and cap are often tarnished. Cleaning them with fine grit emery paper will make for better stability and cleaner sound. 2. Oscillation: When testing the amplifier, always short the inputs. If there is a problem with oscillation, remove the 150pf polystyrene cap or try a smaller value, 75pf or so. Likely the hf response is enough without the cap. You can also install a 1k ½ to 1w resistor in series with the 310a grid inside the grid cap. Also a 1k resistor in series on the screen tube pin (310a pin 3) connection and the 300B grid tube pin (pin 3 of 300B socket) can help. 3. If the 310a plate voltage is too low, you can change the 1k1 cathode resistor to 1k5. 170 to 200v is ideal on the anode of the 310a. This will change depending on the 310a used since it is a high gain tube and there is more variation of where the votlages settle in. 4. Different rectifiers will give different operating voltages. 274 the lowest, 5AR4/GZ34 the highest (about 40-50v spread. 5U4 and 5Z3p will be in between and are a good choice when 274b is not available. 5. The LD91 is our favourite SET circuit. It serves the 300B well, dispelling the notion that the 300B is soft, fuzzy and can t do bass. The small amount of pfb applied to the screen of the LD91 is a unique feature which brings back the treble >10k. As the transformer runs in you ll notice a bloom and energy seldom achieved from SET. It will take several months to reach full potential; that is the nature of magnetics. Enjoy! DIY Hifi Supply Ltd P. 22
13.0 Circuit Diagrams: To adjust 310a voltages and Typical Voltages: P. 23
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14.0 Amendment (A) 23/5/2011: use film cap for section 6. (B) 23/5/2011: add 2x 22uF/35v caps in the final photo. (C) 23/5/2011: Use two 150k/2w in parallel instead of one 75k/2w for each channel (D) Connection from LED to 1N4007 and resistor P. 25