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Attenuator experiments
There were some attenuator discussions here some time ago.
I built a test attenuator using relays. I use 8 relays, so I get a range of 48dB. The attenuation from 0 to -31dB is in 1dB steps, and after that the steps are -33, -34, -36, -39, -42, -48dB and off - 39 steps from full on to off. I just used E12 resistors, so the actual steps are not that accurate... My conclusion so far is that 39 steps are enough, but I think 12 steps are too little and 24 steps is less than I would like also. But as the amp I use (2 6SN7 gain stages into a 2A3) is much too sensitive, so I find that I actually need more steps in the low end. I guess I should just add a 20dB attenuation on the input of the attenuator - or change the input stage on the amp to lower the gain... Or perhaps a 7-relay attenuator with a switchable 20- or 30dB pre-attenuator would be a good idea? I have read many places that make before break switches are essential, and that break before make switches cause clicks and other noise. The relay switch I use is both I guess, as the relays don't have the exact same switch time. But I get no noises at all - I can adjust the volume setting with no problems and without muting. Are the clicks only a problem on direct coupled SS amps? If anybody's interested the schematic can be seen he http://stiftsbogtrykkeriet.dk/~mcs/8bitatt.gif And the mono prototype can be seen here (behind the big, grey monster): http://stiftsbogtrykkeriet.dk/~mcs/00000005.jpg Best regards, Mikkel C. Simonsen |