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April 07, 2020, 02:08:01 AM

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91
Guitar News / Coronavirus hitting the music industry
« Last post by joecool85 on March 11, 2020, 02:05:47 PM »
All performing artists are going to start feeling the hit of Coronavirus, even if they don't get infected.  Most large venue concerts have been cancelled or probably will be soon due to mounting concerns of the virus spreading even farther.  I recommend what others have been saying for a while now on this: wash your hands regularly, stay away from large group gatherings, keep yourself healthy (eating properly, exercise, plenty of sleep, etc) so you can combat it if you do get infected.

https://www.gearnews.com/coronavirus-worries-mount-over-effect-on-live-music-for-2020/
92
Amplifier Discussion / Re: JC 120 speaker question
« Last post by Psc on March 11, 2020, 01:15:03 PM »

Ok, that makes sense.  I have another stereo amp that needs a 4 ohm load.  So I could build one 2-12 speaker cabinet with 4 ohm speakers and turn both amps into heads?  That might simplify things for me.
93
Amplifier Discussion / Re: JC 120 speaker question
« Last post by joecool85 on March 11, 2020, 10:53:32 AM »

Hi all.  Quick question, hopefully someone can show me what I'm missing.  I understand that the speakers used are 8 ohm.  The schematic shows that when you connect an external speaker you should also use 8 ohm, but it shows them connected in parallel, which would make it 4 ohms.  I would have thought 4 ohms was too low.

https://www.ssguitar.com/index.php?action=dlattach;topic=4786.0;attach=8708

Thanks!

I believe it is stable for 4 ohms.  The reason they use 8 ohm speakers internally is so that you can then connect the external speakers without dipping below 4 ohm total.  Also, circuits output more wattage at lower impedance.  So when running external speakers along with the internal, when set up as parallel and the amp sees 4 ohms total, it is a boosted output.  If you had internal and external 4 ohm speakers and hooked in series, it would work, but you would have the amp seeing 8 ohm and have a lower total wattage.
94
Amplifier Discussion / JC 120 speaker question
« Last post by Psc on March 11, 2020, 10:15:50 AM »

Hi all.  Quick question, hopefully someone can show me what I'm missing.  I understand that the speakers used are 8 ohm.  The schematic shows that when you connect an external speaker you should also use 8 ohm, but it shows them connected in parallel, which would make it 4 ohms.  I would have thought 4 ohms was too low.

https://www.ssguitar.com/index.php?action=dlattach;topic=4786.0;attach=8708

Thanks!
95
CMOS circuits can fizz, especially when you lower the Voltage (this increases the gain) and you won't see any ringing on the waveform. Increase the Voltage and the gain goes down and they start clipping softer. Fizz is mostly from too much feedback. Solid state circuits have hundreds of times more feedback of tube circuits. A tube power amp may have 20dB of feedback. A typical opamp has 40 to 60dB or more feedback. Same goes for chip power amps.
96
To me the most obvious difference in the preamps ss vs tube
Is the onset "fizz" of the opamp or generally transistor when it
Starts to clip. At least i figure this is from transistors because all ss
Amps that i have do it.  I have a marshall 3203 which, if it wasnt for
That fizziness would sound rather close to a marshall 2204 or similar.
Maybe its just bad design from the old marshall ss amps.
Maybe jfet dont fizz.

I'm inclined to believe the "fizz" is from "ringing" when the signal gets clipped.  Tubes naturally go from clean signal to squared-off clipping in a very gradual manner that doesn't "ring" like squared-off waves do.  Transistors are clean until they hit the limits, then *BAM*... Gibbs Phenomenon.  This is why people like (ab)using CMOS chips (and JFETs, to a lesser extent) for "tube-like" distortion; they exhibit a gradual onset of clipping as the signal approaches the limits, though not completely analogous.
97
Amplifier Discussion / Re: Peavey CS400
« Last post by Enzo on March 10, 2020, 01:21:16 AM »
R17 is zobel network.  But look on your schematic.  R16 is parallel to the output choke L2.   L2 is heavy wire.  It carries the main current to the speaker.  The only reason for R16 to burn is if that coil is open.  More likely the solder fails at one end, or the coil wire breaks at one end.  In which case unwind a turn and fix it.

R16 is 50 ohms, but in circuit the coil is parallel so it measures "shorted".  If R16 measures 50 ohms, then the coil is open.  Open coil means all the output has to flow through that resistor.
98
Without the output Tx cutting all the fizz I don't see any great advantage.
SS power amps are DC coupled and hence don't cut the fizz generated by over driven stages. :'(
The OTx is part of the magic of Valve amps,, most of the great Valve amps did not use hi spec OTx's and so they smooth out the hi freq crud.
Valve pwr stages also cut very low freq because of caps (AC coupled circuits) and maybe some miller effect.
Most SS pwr stages (Especially ones like you mentioned) are dead flat,,, So unless you have an intricate understanding of how to circumvent all that then my advice is leave the SS pwr stage stock and do all the fancy stuff in a well designed preamp.
Or just research some pedals there are plenty out there 8|
Phil.
99
Amplifier Discussion / Re: Peavey CS400
« Last post by phatt on March 10, 2020, 12:53:58 AM »
First check the DC Voltage at the speaker output?
If not very close to Zero then the circuit is faulty.
Yes could be HF problems.
If the amp is working (No DCV on output) then I'd replace the burnt components and see if they run hot. Better minds here will know more. :tu:
Phil
100
Amplifier Discussion / Peavey CS400
« Last post by gbono on March 09, 2020, 09:27:41 PM »
http://schems.com/bmampscom/peavey/Peavey_CS-400%20(C-Series,%207-79)%20Schematic.pdf

CS400 with damaged (but functional) R16/17 - part of a zobel network? The amp is causing the light bulb limiter to glow brightly but the amp did not blow fuse. Is this an issue with high frequency oscillations on the output?
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