DIY PCB Board OTL Tube Headphone Amp Aikido White Cathode Follower 6SN7 6BX7

$30.0 Buy It Now or Best Offer
free,30-Day Returns

Seller Store hvforless
(1235) 100.0%,

Location: Boulder, Colorado
Ships to: US,
Item: 144817850848

Restocking Fee:No
Return shipping will be paid by:Buyer
All returns accepted:Returns Accepted
Item must be returned within:30 Days
Refund will be given as:Money Back
Compatible Brand:Universal
Unbranded:Unbranded
Type:Board

This auction is for ONE bare PCB. I started this auction by selling extra boards from a personal project. The reception was great so I had more made and made a few improvements. The original goal of this project was to have a compact octal tube OTL headphone amplifier that would drive low impedance headphones (down to 32 Ohm). I chose an Aikido input with a White Cathode Follower output (input/output stage design credit to John Broskie of TubeCad). Sounds easy enough to pull off but the power supply requirements were a bit tricky. I wanted to use a single standard power transformer with high voltage and filament supply. I also wanted an external choke. All those needs forced a custom PCB. The tricky thing was the power supply design with DC heaters in mind. To drive low impedance headphones with the White Cathode Follower circuit requires the use of 6BX7 or 6BL7 output tubes. Those pull 1.5A each. With 6SN7 input tubes the entire heater draw adds up to 4.2A of DC current. That’s not trivial. After a few tries I made some great boards that work perfectly. It sounds clean, loud, and amazing. This will drive any pair of headphones you may own.Heater Circuit:Regulated 6.3VDC from 6.3VAC winding with the use of schottky diodes and super low dropout regulator. Trimpot adjustment to dial in the final voltage.Huge capacitance for ultra-low ripple. 45,000uF capacitance.Full 4.2 amps of DC heater current. High current components and heat management designed in. Heat sink on LDO and heat sinks on all rectifying diodes. Remember you need 1.8X the DC current from your transformer. A safer rule of thumb is 2.0X the DC current. The transformer I use puts out 8A @ 6.3VAC. High Voltage Circuit:Regulated output using Maida circuit.Huge capacitance for ultra-low ripple. 256uF capacitance.Tube rectified power. I like the look of the extra tube and I like the slow start. Use a 5AR4/GZ34. Want to use a cool looking 5U4G instead, you just need more B+ headroom due to the additional voltage drop. In the US, the Hammond 372JX does the trick.Designed for external choke filter (C-L-C).Ridiculously quiet power.Additional Features:¼ B+ reference circuit built in. Elevates the heater ground to ¼ of the B+ voltage. Provides for hum free power and max heater/cathode difference isn’t exceeded.House ground isolation circuit built in. House ground attach to the board for a hum free experience.Chassis ground tied through one of the mounting holesDesigned for use with high end audio grade components (Wima MPK series, Nichicon KX and KW series, etc).500uF coupling capacitance on output. I’m using a 470uF electrolytic with a 30uF film capacitor in parallel. Response well below 20Hz. Small and compact. All this circuitry is smartly arranged on a 6.50” x 7.75” board.Super thick PCB (2mm) with 2 ounce traces!!!Schematic shown above.I purchased a B18-HB case from Ebay a while ago for this project. I most recently purchased a 1907e chassis from aliexpress that had the same dimensions. 194*70*311mm are the external dimensions. This is the case I sized the PCB for. Don’t skimp on the airflow if you go custom. CAD is shown to make cutouts simple. If you choose the Hammond 372JX transformer instead of the 272JX, note that it’s 0.50″ longer and a few holes have to move.Uses (2) 6SN7 input tubes and (2) output tubes being either 6BX7 or 6BL7.4 jumpers are provided to switch between the (2) 6BX7 and 6BL7 output tubes. The White Cathode Follower is a little different than most output stages. It’s optimized for a given output impedance with a given tube. The two output tubes that work in this application are similar, but have different operating points as a result. Instead of a compromise I fixed two output points into the design. Move the 4 jumpers and swap tubes. Simple.Everything you need to build this is spoon fed. Use this board, the BOM below, and find an appropriate case that has a volume pot and the jacks. As described above, I’ve designed this with jumpers so you can switch between precise operating points for 6BL7 tubes and 6BX7 tubes for headphone in the 32 Ohm range. It’s a simple task to use those jumpers to switch between 32 Ohm and 300 Ohm for one of those output tubes instead. Many users love the 6BL7 tubes and uses this amp with 32 Ohm and 300 Ohm headphones. The BOM below defaults to a 32 Ohm setup with tube swapping. Make substitutions from this chart if you want the impedance and operating point options from the jumpers. What if you’re headphones aren’t 32 or 300 Ohms? The formula and chart below will help you dial in the value for R17. No need to be super exact, just get close. For example, I have a pair of AKG K702 headphones that have an impedance of 45 ohms. I use the 32 Ohm setting and it works fine, because it’s literally a matter of a few ohms difference on R17. Output Tube 6BL7 6BL7 6BX7 6BX7 Output Impedance 32Ohm 300Ohm 32Ohm 300Ohm Idle Current 21ma 21ma 32ma 21ma rp (approx) 2000 2000 1200 1450 mu (approx) 15 15 10 10 R11 (sets idle current) 270 270 290 470 R17 (output impedance) 140 170 127 205 Formula: R17= (rp + 2 x Output_Impedance) / mu A BOM from Mouser is below. I used all high end components (Wima and Nichicon Audio caps, etc). Full schematic and board layout are above. Please know your skill level and knowledge of electronics before considering this PCB. If Mouser is out of something try DigiKey. You should be comfortable specifying substitutions, although I do my best to take care of that below. For example, if a capacitor is out of stock try a slightly higher voltage or capacitance of the same lead spacing and series. Or try another high quality capacitor with the same specs. Also, there’s some wiggle room with resistor values of the same wattage. However, I do my best to keep the Mouser BOM up to date and also list alternatives below.*** The Microchip LDO that’s vital to this circuit is out at Mouser (and everywhere else I’ve looked) and has a long lead time. I have some available that can be purchased with this PCB.Quick way to load the BOM below is to do a web search for “Mouser Project & Cart Sharing”. Follow the first link and then enter this project ID: b3769f5416 Part Value Mouser Alternative Additional Needed Other C20 56uF 647-LKX2W560MESY25 C21 100uF 647-LKX2W101MESY40 C24 100uF 647-LKX2W101MESY40 C34 10kuF – 15kuF 647-UKW1A153MHD 647-UFW1A153MHD C31 10kuF – 15kuF 647-UKW1C103MHD 647-UFW1C103MHD C32 10kuF – 15kuF 647-UKW1C103MHD 647-UFW1C103MHD C3.1L 1kuF 647-UFG1C102MHM C3.1R 1kuF 647-UFG1C102MHM C1.1L 470uF 871-B43647B5477M057 C1.1R 470uF 871-B43647B5477M057 C1L 30uF 400V Parts Express C1R 30uF 400V Parts Express C27 .01uF 505-MKP20.01/100/5 C28 .01uF 505-MKP20.01/100/5 C29 .01uF 505-MKP20.01/100/5 C30 .01uF 505-MKP20.01/100/5 C33 .1uF 505-MKP20.1/100/5 505-MKP20.1/100/10 C35 .1uF 505-MKP20.1/100/5 505-MKP20.1/100/10 C26 .1uF 505-MKP4F031003C00JF C60 .1uF 505-MKP4F031003C00JF C22 .1uF 505-MKP4-0.1/630/5 C23 .1uF 505-MKP4-0.1/630/5 C25 .1uF 505-MKP4-0.1/630/5 C3.2L .22uF 505-MKP2D032201K00JO C3.2R .22uF 505-MKP2D032201K00JO C6L .22uF 505-MKP4J032204J00KF C6R .22uF 505-MKP4J032204J00KF C5 4.7uF 400V 505-MKP44.7/400/10 Parts Express D1 1N4007 621-1N4007 D3 1N4007 621-1N4007 D4 1N4007 621-1N4007 D2 1N5341 833-1N5341B-TP D5 625-SBLF10L25-E3 625-SBLF10L25-E3 D6 625-SBLF10L25-E3 625-SBLF10L25-E3 D7 625-SBLF10L25-E3 625-SBLF10L25-E3 D8 625-SBLF10L25-E3 625-SBLF10L25-E3 KK1 SK104-PAD 532-513102B25 532-4880M KK2 SK104-PAD 532-513102B25 532-4880M KK3 SK104-PAD 532-513102B25 532-4880M KK4 SK104-PAD 532-513102B25 532-4880M KK5 SK104-PAD 532-513102B25 532-4880M KK6 SK129-PAD 532-529802B25G 532-4880M JP11L 3X1X2.54 571-3-644456-3 538-15-29-1024 JP11R 3X1X2.54 571-3-644456-3 538-15-29-1024 JP17L 3X1X2.54 571-3-644456-3 538-15-29-1024 JP17R 3X1X2.54 571-3-644456-3 538-15-29-1024 TR1 0-1000 594-64W102 TR2 0-1000 594-64W102 B1 RECTIFIER-GBU4 512-GBU6M 512-GBU8M R10L 300 71-RN60C300F0F R10R 300 71-RN60C300F0F R11L(A) 270 71-RN60D2700F R11L(B) 287-291 71-RN60D-F-287 R11R(A) 270 71-RN60D2700F R11R(B) 287-291 71-RN60D-F-287 R12L 1M 71-RN60D-F-1M R12R 1M 71-RN60D-F-1M R13L 10k 71-RN60D-F-10K R13R 10k 71-RN60D-F-10K R16L 470K 71-RN60D-F-470K R16R 470K 71-RN60D-F-470K R17L(A) 140 71-RN60D-F-140 R17L(B) 127 71-RN60D1270F R17R(A) 140 71-RN60D-F-140 R17R(B) 127 71-RN60D1270F R1L 1M 71-RN60D-F-1M R1R 1M 71-RN60D-F-1M R20 100 660-MOS3CT631R101J R21 100 660-MOS3CT631R101J R22 200k-300k 603-RSF3WSJT-73-270K R23 200k-300k 603-RSF3WSJT-73-270K R24 22K 279-ROX3SJ22K R25 10 660-MOS3C100J 660-MOS3CT631R100J R26 10 660-MOS3C100J 660-MOS3CT631R100J R27 68k 660-MOS3CT631R683J R28 300K 603-RSF100JB-73-300K R29 100K 603-RSF100JT-73-100K 66-CMO11003JLFTR R2L 470 71-RN60D4700F R2R 470 71-RN60D4700F R30 100 603-RSF1WSGT-52-100R R3L 300 71-RN60C300F0F R3R 300 71-RN60C300F0F R4L 470 71-RN60D4700F R4R 470 71-RN60D4700F R5L 1M 71-RN60D-F-1M R5R 1M 71-RN60D-F-1M R60 10 660-MOS3C100J 660-MOS3CT631R100J R6L 1M 71-RN60D-F-1M R6R 1M 71-RN60D-F-1M R7L 1M 71-RN60D-F-1M R7R 1M 71-RN60D-F-1M R9L 300 71-RN60C300F0F R9R 300 71-RN60C300F0F IC1 LM317 511-LM317T IC2 BUT11A 512-BUT11A IC3 MC29502 998-MIC29502WT TRAN 272JX 546-272JX CHOKE 193B 546-193B Parts Express V1(6SN7) OCTAL Parts Express V2 OCTAL Parts Express V3(6SN7) OCTAL Parts Express V4 OCTAL Parts Express V5(5AR4) OCTAL LIABILITY DISCLAIMERA person who constructs or works on electronic equipment may be exposed to hazards, including physical injury, the risk of electric shock or electrocution, and exposure to hazardous substances such as lead, mercury, and other inorganic or organic compounds. These hazards can result in health problems, injury, or death. Only qualified persons who understand and are willing to bear these risks themselves should attempt the construction of electronic equipment. By purchasing this item, the buyer acknowledges these risks.Vacuum tubes operate at high temperatures, may contain toxic substances, and may have exposed parts that carry hazardous voltages. There is a risk of electric shock, electrocution, burns, or fires that is inherent in the construction and use of vacuum tube equipment. By purchasing this item, the buyer acknowledges these risks.IN NO EVENT SHALL THE SELLER BE LIABLE FOR ANY SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY NATURE including, but not limited to, property damage, personal injury, death or legal expenses. Buyer’s recovery from Seller for any claim shall not exceed the purchase price paid by Buyer for the goods, irrespective of the nature of the claim, whether in warrant, contract or otherwise. By purchasing this item, BUYER AGREES TO INDEMNIFY, DEFEND AND HOLD SELLER HARMLESS FROM ANY CLAIMS BROUGHT BY ANY PARTY REGARDING ITEMS SUPPLIED BY SELLER AND INCORPORATED INTO THE BUYER’S PRODUCT. If you do not agree to this disclaimer, DO NOT BUY THIS ITEM.

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