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Everything posted by federicopol
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Repair and restoration of my STAX SRA-12S
federicopol replied to Quad's topic in Headphone Amplification
Hello everyone, sorry for the necroposting: my sra 12s is misbehaving so time to grab the soldering iron. the plan was to get it repaired but... in the end i decided to do it myself. PLAN: Strip and Rebuild the AMPLI board completely Recap, and new diodes/resistances for the psu, recalculate the voltage divider for the normal bias from 200v to 230v Redo the pro bias circuit i added some years ago. Maybe strip and rebuild the IS amplifier stage (that i never turn on, so not useful per se but will do just because) I have a couple of questions: i remember seeing a service manual for this amp somewhere here but i can't find it anymore, someone has it? I see the toshiba to3 transistor is difficult to obtain nowadays, is this one suitable? https://www.mgelectronic.rs/tranzistor-2sc-1167# Do somone has a reliable sorce for 2SK30-O and 2SK30-GR? (or can point me to a substitute?) Thank you very much -
Thank you very much. That way i will need one trafo only at expense of some more small parts. Will study, will copy, then probably ask again if doing it correctly. Thank you very much again
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Hello everyone, here asking for some help wuth a build i am planning: I'd like to build a amplifier that has: pro bias and normal bias. Sounds reasonably good, Proven circuit. Simple to make and not to much expensive because i want to build up skills and confidence before a more serious build. So i choose the tubecad curcuit (stealing the schematics plus PS that @chinsettawong posted on his thread on the other forum) the only problem is that i also need normal bias. I plan to put a voltage divider on the BIAS PS and take 230v from that. Is my curcuit modification ok? Did i commit basic newbie errors that will kill me and burn my house? Or is the voltage divider a stupid idea per se? i plan to use an hammomd rrafo for valve amplifiers for HV and Heater and two small trafos with one wired backwards for the bias. Thank you very much
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Hello, while i wait for some parts for restoring my sra12s i made some new earpads for my sigmas. I also made the internal dampening. Following the advice of Spritzer i used the most dense material i could find. By pure luck the material and quantities i used seems to be ok. The soundstage seems here, definitely the best of the headphones i own. The bass is present and clear so i am pretty happy of the final result. I decided to substitute the earpads because i don't feel comfortable using earpads that have been used by someone else for 30 years... I decided to not use a spare pair of lambda earpads because of the different shape of the lower back part. I made them in leather following the procedure Stax (or their supplier) probably used. I used an embroidery machine to sew the ear oval on the reverse side of fabrics, then i reversed the fabrics. With the fabrics now on the right side i added some low heigh memory foam cutted a couple of mm smaller than the finished earpad. Now i used the embroidery machine to close the earpads. Cutted the excess leather and here they are. They are a bit bigger than the original ones and are less stuffed, nothing dramatical but i will remade them the next time i have time to use the embroidery machine. The same method can be used to make them with a sewing machine for the oval and an overlock machine using 3 threads and a short lenght stitch.
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Thank you very much, i'll remove them and try with something dense. By the way in my sra12s i have a +640V rail on the PS that feeds the amplifer board. Using that 640v point and a 2 resistors voltage divider to create the pro bias voltage is the normal way to do that? Ir therebis a better way? Thank you very much and sorry for the newbie requests...
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Hello, i am new here and since the Mafia reside here... i'm gonna ask for a help to the Padrino or some of his associates.... I recently bought a sra-12s that needs some love (a recap, a pot cleaning and an adding of a pro bias out), i got a discount on the original asking price and i got gifted a pair of stax sigma Normal bias ("because i don't know what to do with them if i sell the amplifier"). The Sigma are really ok, the drivers are ok, they simply need a cleaning AND a new damping because the original glass wool dampening have been removed. My question is: What can i use for remake the dampening? (I llan to use quilt batting, is that ok?) What shape the dampening should have? (Should i cover all the planes except the driver one, am i right?) And there seems to be a pair of resistor attached to the cable connecting the driver, are they normal? Thank you very much.