All of the resistors are Audio Note or Shinkoh tantalum. Capacitors have been replaced with Black Gates, V-Caps, Mundorfs, and Elna Cerafines. This one has had some extensive upgrade work. Given that I preferred the relatively lowly DAC 1.1x to anything I had heard before, I was very interested to hear what the full Audio Note dac package could do, and managed to find a heavily modified AN Kits DAC 4.1x, which includes two of the key AN DAC elements - valve rectified and regulated power supply, and transformer coupled output. But the AN DAC 1.1x sounded different, and more ‘right’ than anything I had heard before - mainly in the way it portrays how instruments and voices energise the air around them, sounding to me more realistically lively and dynamic. My long term favourites were the Audio Synthesis DAX (Ultra Analog version) and the Audio Synthesis DAX Discrete. Since the SRPP is biased to about 8.5v, I would suggest an input signal of not more than 8.5/14.5 ≈ 0.586 Vpeak or ≈0.415 Vrms.Until I tried an Audio Note DAC 1.1x, about six months ago, my experience had been that differences between DACs were to do with relatively subtle - if important - nuances of flavour and presentation. So depending on your input voltage and your volume setting, you could be overdriving the SRPP. The other thing to look for is overdrive. This may or may not be your problem, but it is an error on the schematic. To get this lift, based on schematic values, R2 needs to be about 109kΩ, not 87kΩ. This is right at the limit for both the upper and lower triodes. With the voltages in this circuit, you want that heater lift to be about 108v. The cracking you're hearing could be heater-to-cathode breakdown in the SRPP. With the upper cathode at ≈208v this puts the differential at 208-85=123v. It should be around 85 volts according to the schematic, However, according to the Tung-Sol and Raytheon data sheets, the maximum heater to cathode differential is +/- 100v. So inspect all the joints to make sure they all look ok.Īfter that, in this design, look at the heater lift for the 5687. If there are crackling noises in an amp, the first thing I look for is cold solder joints. The louder the music the louder are the cracking noises.Are the cracking noises in one or both channels? Otherwise only one of the two triodes will be heating up.Ī picture of the circuit boards, both top and bottom, would be helpful as well.įirst thing there are cracking noise in the speakers when the music is playing especially around the bass. For this to work properly pins 4 and 5 should be shorted together and the 6.3v winding connected to pins 4/5 and pin 8. The heater is marked as pin 4 and pin 8 on the tube, but the note on the transformer winding say 4 and 5 on the 6.3v winding. There is also something on the schematic that is unclear. But a common problem with some circuit boards is that the tube socket gets soldered to the wrong side of the board. Now I'm going to suggest you check something and I don't want you to take offense. If it's happening on both channels there is a more systemic problem. You were not clear as to whether this was happening in one or both channels. The second clue is that your grid voltage on the upper triode (pin 2) is essentially the same as the plate (pin 1) and I assume the cathode voltage (pin 3) as well. The only way this can be is if there is no current through R17. What this means is that there is no current flowing in the SRPP stage.
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