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Preamps and Effects / Re: Randall RG80/RG100 Preamp DIY« on: August 18, 2010, 01:05:50 PM »
Here's new version of the preamp, with some new mods , MC34063 DC converter, to get 24V from 9V battery, plus it has voicing control, exact the same as Century C170II/2000,plus it has added gain stage to compensate volume drop caused by diode clippers.
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Schematics and Layouts / Re: Randall T2 schematic! FIXED!« on: June 16, 2010, 01:58:15 PM »
The schematic is correct, overdrive channel is direct copy of Egnater TOL series amps/preamps.What OPamp, if you mean second half of DC servo, it must be, or it will oscillate.
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Amplifier Discussion / Re: Custom ss guitar amp build« on: June 14, 2010, 07:15:32 PM »I found someone locally (a guy named Tom) who will build a ss guitar amp for me and I am psychedWhat kind of amp, how much power, channels...? 34
Amplifier Discussion / Re: Transformer identification resources(Line6 spider III)anyone got info on these?« on: June 08, 2010, 05:06:21 AM »
Does your amp has 2xTDA7294 chips in poweramp section, or is it discrete one?Take the pics of the poweramp section, we can determine +/- volts by the poweramp, and by the number of winding loops as your uncle said.
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Amplifier Discussion / Re: Transformer identification resources(Line6 spider III)anyone got info on these?« on: June 08, 2010, 03:23:04 AM »
Disconnect mains, and secondary wires from the motherboard, and measure DC resistance between black, yellow and red, and second between mains (white and black), and tell us resistances.
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Amplifier Discussion / Re: Transformer identification resources(Line6 spider III)anyone got info on these?« on: June 07, 2010, 08:46:20 AM »
300W
 , they can write 10KW too, but it doesn't mean that is correct. Rough power can be calculated with this method;your transformer is EI76x41, so 76/3(we get core dimension)=25.3mm x 41mm = 107W, then 107W x sqrt2 = 75.66W, but this is only a rough calculation, actually real power is much less in real life. 37
Amplifier Discussion / Re: Line6 Spider III 75W transformer conversion 220V« on: June 07, 2010, 07:43:40 AM »According to the repair shop the amp is fine, only the transformer burned. Not sure how they figured that out, maybe they are just trying to have me buy the transformer only to realize that the whole thing is broken. It would be great if you could help us, cause we got puzzled by a few facts when opening up the amp:1.Motherboard has a switch probably for two kinds of fuses(one for 110V, other for 220V which is smaller). 3. 3 wires are positive voltage, negative, and ground, other two are AC mains. That way most if not all modern poweramps are designed. Your transformer is standard EI76 x 46 which is about 70W of continous power. 38
Amplifier Discussion / Re: Schematic for the Randall T2? Does anyone have it?« on: June 07, 2010, 04:11:51 AM »Thanks but that's not the issueT2 is 4 gain stage preamp,with marshall tone stack taken from the cathode follower, through 1uF/250V cap, and added mid sweep control (25K pot wired in series with slope resistor/33K). 39
Amplifier Discussion / Re: Schematic for the Randall T2? Does anyone have it?« on: June 06, 2010, 06:02:57 AM »
Can you tell me what happens to be a problem, I can help you, I have the schematics but I can't post them.
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Tubes and Hybrids / Re: Peavey Mace Question ?« on: June 02, 2010, 05:09:32 AM »
I agree with Fahey that diodes are not there to clip, they are to prevent noise to come out.
When there is no signal present at the first triode, ordinary noise is from the mains-50Hz.On the first triode is very small 0.000001 volts or so(this is an example), multiplication on the third stage is already enormous(couple thousands of times), so our noise is multiplied too, and it jumped from 0.000001 to 0.15V.The fourth gain stage has mu of 50 times, and PA has the mu of around 30, so 0.15V*1500= 225V of noise(IN REAL LIFE THIS IS IMPOSSIBLE THIS IS JUST AN EXAMPLE!!!).The diodes are preventing that voltage on the third stage, cause their threshold voltage is around 0.6V, until the guitar signal passes (cause he is a lot larger).The 1M pot is letting the signal and the hum (if there is any) to pass unaffected, something like the mix pot.The same goes for the hiss,which comes from parasitic capacitive, high freq. oscillations which comes from uncontrollable gain... 470K resistor after cc cap is there to reduce the gain, and 1nF is forming low pass filter with 1M pot or resistor (JSX/XXX) of 159Hz, so that basically means that freq under 159Hz are unaffected, only the freq's above are(-3dB's). I think this works like this, on the crunch ch. 1nF cap is not shunting, cause that ch. has a lot less gain than the ultra.When the ultra is engaged cap is shunting. 41
Tubes and Hybrids / Re: Hybrid« on: May 21, 2010, 05:13:30 PM »
Here is the new clip:
Hybrid Ultra.mp3 42
Tubes and Hybrids / Re: Is EC83 the same tube as 12ax7?« on: May 21, 2010, 05:12:23 PM »Hi, I've tried to find out using google, but I didn't got any convincing answers there. The thing is that I've just found some old vacuum tubes, EC83 and EC82 (didn't remember the fabricate but it doesn't matter anyway). And if I'm right the EC83 is the same tube as the 12ax7 and the EC82 is the same as 12au7. Or not?You must be wrong, cause there is no tube with that name, there are ECC83(same as 12AX7, but just Europian name for it), ECL83 which is triode/pentode (almost the same as 12AX7 in triode section, and weaker EL84 on the pentode section). Maybe one of the letters fell off? 43
Tubes and Hybrids / Re: Hybrid« on: April 30, 2010, 08:05:37 PM »
Hi guys,
Recently I worked on the amp, and there is no more sizzle,hum,brum or anything...so I made a new clip: Memmara Hi Gain Ultra.mp3 It's stereo, on the left is modern hi gain tone, on the right it's hi gain marshall mid tone. Tell me what you guys think? Can somebody tell me what would be the values for the blackstar amps tonestack with ISF? 44
Preamps and Effects / Re: JFET Emulation of triode limitation« on: March 30, 2010, 04:28:23 PM »
I put working samples.
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Preamps and Effects / JFET Emulation of triode limitation« on: March 29, 2010, 05:19:05 AM »
http://amtelectronics.com/support/articles/why_tube-like_cannot_measure_up_to_tube_inside/
http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=1&eotf=1&u=http%3A%2F%2Fwww.sugardas.lt%2F~igoramps%2Farticle68%2Farticle.htm&sl=ru&tl=en Samples: Real Mesa Rectifier:Pure-1.mp3 AMT R1:Pure-2.mp3 |
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