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"Estudiante" Hybrid (7370 + MOSFET)
"Estudiante" Hybrid (7370 + MOSFET)
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Old 7th September 2017, 03:37 PM   #11
anatech is offline anatech  Canada
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"Estudiante" Hybrid (7370 + MOSFET)
Hi,
Yes, you need a DC reference to common ground that doesn't change DC resistance. Using a series capacitor and a high value resistor (100K or so will be fine) to ground should settle that down. Otherwise every tiny change with the resistance will create noise in the tube.

For microphonics, which sounds like your noise problem when physically causing vibrations, a new tube might solve. Or, a new tube could be worse also. Luck of the draw. If you do want a quiet tube, rewire the socket for a 12AU7 and try the Electroharmonix version. I have found these to be very good overall, and they are not prone to excessive microphonics.

-Chris
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Old 12th October 2017, 10:34 PM   #12
xrk971 is online now xrk971  United States
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I got 3 new tubes in the mail. I also have some LM317HV's now. Maybe I can retry this witha CCS now and a tube with less microphonics.
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Old 14th October 2017, 05:21 PM   #13
JPS64 is offline JPS64  Germany
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I've build today 1AD4 hybrid (CCS, LM317, IRF510) breadboard to compare with my PASS HPA driving HD600.

There's a lot of potential for this 30 build (cheap Meanwell 24V wall cube).

JP
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Old 16th October 2017, 11:47 AM   #14
twocents is offline twocents  South Africa
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JP - I don't see a tube? Is this the same amp we are talking about here?
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Old 16th October 2017, 01:51 PM   #15
xrk971 is online now xrk971  United States
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It's that opaque ampule shape in the middle. Two Raytheon compact tubes. Probably used on 1960's jet fighters.

NIB Raytheon USA 1AD4 Vacuum Tube Subminiature | VIVA TUBES | Reverb

@JPS: nice work! You are a person who appreciates PCB connectors, I like that. One question is why your vol pot is in middle of board rather than on the edge - how do you adjust the knob?
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Old 16th October 2017, 03:31 PM   #16
anatech is offline anatech  Canada
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Hi JPS64,
Interesting design. I bet the tubes are a lot more reliable than the connectors on the board! Are you going to use a shaft extension for the volume control?

-Chris
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Old 17th October 2017, 03:29 AM   #17
ammel68 is offline ammel68  United States
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Quote:
Originally Posted by xrk971 View Post
One question is why your vol pot is in middle of board rather than on the edge - how do you adjust the knob?
Don't you guess he uses his fingers to turn the volume pot's shaft?
He doesn't have a knob on the shaft.
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Old 17th October 2017, 03:55 AM   #18
xrk971 is online now xrk971  United States
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Nah...., this is strictly proto for purposes of listening sound check - he put the pot in the middle to keep wires short. Do you see the 3.5mm and power jacks? The exit out the bottom side of the PCB so doesn't make sense for shaft to have knob at 90deg to jacks. JPS makes nice layouts for real boxes so now that the sound check is good, a real PCB will be forthcoming is my guess
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Old 17th October 2017, 07:45 AM   #19
JPS64 is offline JPS64  Germany
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Ive fairy fingers!

But PCB existing, Im never starting breadboard before PCB routing finished.

I need to find time for measurements. Listening not bad with high impedance headphones (HD600, DT880 600R), lets say more bass as Waynes HPA supplied with +/-18VDC?!

Meanwell performed not as expected: linear laboratory supply much better.

CCS LM334 improuving (dont know, 10M45, BJT, JFET or Ales one); adding K-Multiplier? +Ub increases up to +48VDC (COTS wall cube existing)? heatsink changes for better TO220 mounting skills.

Definitively no microphonics and for 30 not bad at all

JP
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Old 17th October 2017, 08:07 AM   #20
ammel68 is offline ammel68  United States
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Originally Posted by xrk971 View Post
Nah...., this is strictly proto for purposes of listening sound check - he put the pot in the middle to keep wires short.
If you already knew the answer, then why ask? Obviously, no one wants long wires(or traces) running from the volume pot to the amplifier.

Should he design a board and post the Gerber files, I'm sure you'll be the FIRST to send the Gerbers to a Chinese board house and get some boards made so you don't have to do any of the work!.

Sweeeet!
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