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Hello, i'm having an issue with my Sunn Beta Preamp build:
https://tagboardeffects.blogspot.it/2016/03/sunn-beta-preamp.html the output volume is very low and the level (volume) pot works backwards. If i remove the TL071, the volume issue is solved but the level pot is not working. I've tested the circuit with an audio probe, if i take the signal after the 12k resistor that leaves that OUT 2 of the 4558 on the top right corner, the volume level is good and the level pot works as it should. The diodes are 1n456A: https://www.musikding.de/1N456A_1 On this schematic they are 1n458A: http://viva-analog.com/wp-content/uploads/2016/08/SUNN-Beta-Lead-pre-amp-schematic.jpg I'm powering it using Mark's bipolar converter: http://tagboardeffects.blogspot.fr/2014/01/bipolar-voltage-converter.html and then connecting it to the Rusty Voltage Converter: https://tagboardeffects.blogspot.it/2014/03/tronographic-rusty-box.html V+ 13.70 V V- 13.66 V Here are the voltages: First 4558 1) -0.297 V 2) 0 V 3) 0 V 4) -13.63 V 5) 0 V 6) 0 V 7) -12 mV 8) 13.68 V Second 4558 1) 0.242 V 2) 0.242 V 3) 0.242 V 4) -13.15 V 5) 0 V 6) 0 V 7) -16 mV 8) 13.46 V Third 4558 1) 0.14 V 2) 0.14 V 3) 0.14 V 4) -13.17 V 5) -12.88 V 6) 7.83 V 7) 13.45 V 8) 12.63 V TL071 1) -13.20 V 2) 8.27 V 3) 0 V 4) -13.20 V 5) -13.20 V 6) - 11.90 V 7) 13.46 V 8) -0.17 V 4069UBE 1) 0 V 2) 7.69 V 3) 0 V 4) 7.56 V 5) 3.87 V 6) 3.97 V 7) 0 V 8) 3.85 V 9) 3.83 V 10) 3.89 V 11) 3.88 V 12) 3.85 V 13) 3.90 V 14) 7.70 V ![]() ![]() ![]() Thanks! |
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Hello,
just replying to my post for an update: i finally found the mistake, as usual a stupid one that i managed to make twice! (I built two preamps to be combined as in the original Sunn Beta) The link that connects the cathode of D1 with the pin 8 of the 3rd 4558 (the one on top) was actually connected to the 33k resistor, a row above. Now the volume pot works fine, it's very loud and it's not fizzy as before. I've tested it connecting the preamp to an old stereo amp (Technics SU-8022) into my 1x12 loaded with a Celestion Heritage g12h 75 hz Here are the working voltages: V+ : 16.10 V V- : -14.94 V First 4558 1) -0.328 V 2) 0.6 mV 3) 1.4 mV 4) -14.94 V 5) 1.7 mV 6) 1.7 mV 7) -0.143 V 8) 16.17 V Second 4558 1) 1.1 mV 2) 1.6 mV 3) 2.2 mV 4) -14.9 V 5) -2.3 mV 6) -3.2 mV 7) -16 mV 8) 16.19 V Third 4558 1) 0.145 V 2) 0.145 V 3) 0.145 V 4) -13.17 V 5) 0.140 V 6) 0.143 V 7) 0.139 V 8) 16.20 V TL071 1) -14.90 V 2) 0.7 mV 3) 0.9 mV 4) -15.10 V 5) -14.93 V 6) -2.51 V 7) 16.18 V 8) fluctuates between 5-9 V 4069UBE 1) 1.5 mV 2) 8.75 V 3) 1.5 mV 4) 8.75 V 5) 4.14 V 6) 3.82 V 7) 1.8 mV 8) 4.12 V 9) 4.12 V 10) 4.12 V 11) 4.19 V 12) 4.18 V 13) 4.16 V 14) 8.76 V |
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