need a schematic
- Thread starter 1big1
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MississippiMetal
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I would imagine it uses the same circuit as the JCA22 head version, which can be found here: http://www.guitarampboard.com/forum/vie ... f=5&t=3840
i talked to the tech who was working on mine and asked him if the schematic for a 20h would be helpful and he said no.. they aren't the same circuit because he'd already looked at it. i know the 2112 combo is based on the astroverb 16.. but i'm not sure if that schematic would be helpful either. i'm still waiting to hear from the folks at jet city. mike? doug? help! 
the guy who's working on mine said the schematic would be helpful because the scope says the problem is somewhere between the input and the phase inverter. it would be more helpful to have the schematic for doing the math rather than just start swapping out parts. that just runs the bench time bill up.
the guy who's working on mine said the schematic would be helpful because the scope says the problem is somewhere between the input and the phase inverter. it would be more helpful to have the schematic for doing the math rather than just start swapping out parts. that just runs the bench time bill up.
MississippiMetal
New member
1big1":1swqw2ln said:i talked to the tech who was working on mine and asked him if the schematic for a 20h would be helpful and he said no.. they aren't the same circuit because he'd already looked at it. i know the 2112 combo is based on the astroverb 16.. but i'm not sure if that schematic would be helpful either. i'm still waiting to hear from the folks at jet city. mike? doug? help!
the guy who's working on mine said the schematic would be helpful because the scope says the problem is somewhere between the input and the phase inverter. it would be more helpful to have the schematic for doing the math rather than just start swapping out parts. that just runs the bench time bill up.
So you track down the Astroverb schematic and use it to navigate the circuit. If you can't do that, id advise you to put the amp back together and take it to ANOTHER tech, as yours is questionable when he needs a scope to tell him the problem is between the input and the PI.
Or you can use this schematic because it can't be a world of difference between the head and combo circuit. These are budget amplifiers. It doesn't make business sense to have separate PCB's drawn up and manufactured.
http://starin.info/Product%20Info/Jet%2 ... ematic.pdf
thank you for the schematics. the guy was just trying to avoid having me drop a bunch of coin on it because they're budget amps. i'll see if i can find an astroverb schematic. thanks. he also said that he was getting an asymmetrical signal on his scope that he's never seen before. that was making things hard to pin down. the schematic would be helpful in sorting that out. 
thank you. 
MississippiMetal
New member
So with the exception of a simple reverb drive and recovery circuit, it's the same amp.
1big1":2mkrxl36 said:my tech guy said he needed the schematic for signal tracing. he's pretty sure it's a signal cap.. but he needs to figure out which one.. rather than change them all. btw.. doug just sent me the schematics.
They have a good support setup, he's busy but has always gotten back to me. You can also email the support group on the support page from the website. Their amps are well built and easy to work on.
their gear pretty much rips. i like it.. budget or not. my tech guy said he needed the schematic for signal tracing. hopefully i can pick it up early next week. doug did say he was sorry my amp failed. i told him it's not that big of a deal. when you're dealing with mass produced parts sometimes marginal parts slip through. it happens. thanks again for your help.
thanks again for your help.
MississippiMetal
New member
1big1":1oyvpp2d said:my tech guy said he needed the schematic for signal tracing. he's pretty sure it's a signal cap.. but he needs to figure out which one.. rather than change them all. btw.. doug just sent me the schematics.
I have a feeling you're going to get that amp back with a dozen parts swapped out and some vague explanation of what was wrong.
my tech said that there's a 1.8k resistor in the voltage circuit of the second triode of v-2. that causes an overvoltage to the second triode and makes the signal asymmetrical. the reverb driver is also tapped into that part of the circuit rather than a separate driver/recovery circuit. he piggybacked another 1.8k to the existing resistor to drop the voltage to a normal operating voltage. he figured the proper value for that resistor should be 1k. he'll check the waveform for symmetry and double check the voltage. if it looks right i can have it back.
Ummmm, maybe I'm way off here but that is supposed to be that way - it that's a shared cathode between the two stages which makes it an effective .9k for each individual stage. So if he added another 1.8k in parallel he made it .45k. Those help set the bias for the that stage, basically the lower the more gain so he added gain for that stage. What problems are you having with your amp anyway?
distortion and lack of response in the tone control section. it sounds distorted and compressed and the tone section lacks sweep. it reminds me of one of the old bakelite knobbed peaveys. you turn the tone controls and they don't do a whole bunch. he knows it's a shared stage. he's looking for the cause of the asymmetry. he said it reminds him a lot of an ac15.
he knows it's a shared stage. he's looking for the cause of the asymmetry. he said it reminds him a lot of an ac15.Does anyone have a schematic for a Johnson JM60 Marquis amplifier? Having trouble; the power amp is fine, but the pre-amp either is not working or not communicating with the power amp. This amp is a hybrid of sorts. It does have a AX7 preamp tube and the rest of the electronics are closer to a computer. Thanks in advance..