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Started by 5thumbs, November 10, 2009, 02:52:23 PM
Quote from: Brymus on November 16, 2009, 12:58:56 AM...I think 1k5 cathode resistors would be an improvement like your OPA hifi opamps(which I want to try now after your glowing endorsment)...
QuoteYou can also stack (solder Pin 1 on Opamp A to Pin 1 of Opamp B, Pin 2 to Pin2 2, etc) two lo-fi op amps to get better response.
Quote6) Remove and jumper the following: C3, C7, R5, R6, R14.
Quote from: J M Fahey on November 15, 2009, 08:09:15 AMThanks for the schematic and comments.I'm always learning, everyday, everywhere.I liked the simple voltage doubler idea very much, and if used carefully, they can power some 12AX* to get something useful.Here, the real distortion comes from the diodes.It's a pity, they could have done more, but I guess the Marketing dept. pressures were greater than the Sound dept ones. Oh well.Most of my "bread and butter" 100W SS amps use around +/- 40 volts, so I'll get those "free" 80V and experiment some tube preamps.Personal opinion: those +9V "tube pres" are toys, but 80V *start* to look reasonable. Up to now, the only tubes I could get "serious" results from with +42 to +35V are 12AU7.This trick opens aup the field.
Quote from: Brymus on November 14, 2009, 06:34:16 PMWhat kind of sound do the 4X4148s to ground give after the first triode?I just tried something similiar with red LEDs and found 2 sounded great but 4 only added a little dirt not very noticable.How does the low plate voltage affect the clipping the make?My triodes are closer to 250V- 300V plate voltage 80v seems low.Also why are they biased with 2k2 instead of 1k5 or 820r?Is it because of the low plate voltage?And finally have you tried added a bypass cap to either triode?Seems like the first one could have a 4.7uf on a switch for a nice warm boost or even a .2 - .68 for some top boost .Thanxs for sharing the schematic and pics,Its nice learning about new stuff.
Quote from: J M Fahey on November 16, 2009, 05:55:50 PMQuoteYou can also stack (solder Pin 1 on Opamp A to Pin 1 of Opamp B, Pin 2 to Pin2 2, etc) two lo-fi op amps to get better response.A *very* curious idea, ¿who/where was that suggested?I'd love to hear the technical explanation.Thanks.
Quote from: J M Fahey on November 16, 2009, 06:28:44 PMQuote6) Remove and jumper the following: C3, C7, R5, R6, R14.Jumpering : C3, C7, R5, R6 will effectively remove needed DC isolation, considering that pins 1,2 and 3 of IC1A normally "live" at around +12V.
Quote from: J M Fahey on November 16, 2009, 06:28:44 PMThe B1Meg suggested as new VR1 will scratch heavily most of its travel, thumping loudly (and killing all sound) on either extreme, whether shorting Pin 1 to ground or placing around -11VDC (relative to Pin 3) on Pin 2, effectively hard switching the output to practically +24V.
Quote from: phatt on November 17, 2009, 08:53:40 AMForgot,, Re Bridge for clipping?? I breadboarded a few a lot of those clippers and the extra diode did little for me but heck try it out and make your own judgement. Marshall used this idea in JCM 900's I think. The only way they could get more crunch from the amps as triodes alone can't do that trick.
Quote1) Replace VR1 (A10KΩ) with B1MΩ pot + 33KΩ (fixed) in series.
QuoteRemove and jumper ...C3
QuoteRemove and jumper ...C7
Quote from: 5thumbs on November 17, 2009, 11:37:13 AMQuote from: phatt on November 17, 2009, 08:53:40 AMForgot,, Re Bridge for clipping?? I breadboarded a few a lot of those clippers and the extra diode did little for me but heck try it out and make your own judgement. Marshall used this idea in JCM 900's I think. The only way they could get more crunch from the amps as triodes alone can't do that trick.The diode polarities on your diagram do not match mine. On the two "left side" diodes, they need to "point" inwards towards each other (and the + side of the "middle" diode). On the two "right side" diodes, they need to point outwards away from each other (and the - side of the "middle" diode.)The diode arrangement in your diagram will block flow from the signal-side through the bridge rectifier to Vref/GND (except once reverse-breakdown voltage is met in the diodes, but I doubt you'd ever hit that voltage in this scenario. )EDIT: If you "rotate" the 4 bridged diodes 90-degrees to the left (and reposition the middle diode accordingly, but flip its polarity), your bridge rectifier clipper would work as expected.