Let's repair a Marshall JMP 1 and discuss the circuit

[@lexicarter3806]

Got my coffee and ready to watch! so glad you're back!! always learn so much, you make the most complicated repairs understandable!

[@theguitaramptech]

Thank you, Lexi. I appreciate that very much/

[@lestelie4410]

Its great to have you back, Chris. I see in your previous comments that you have been extremely busy with your amp repairs. I am not surprised!

[@theguitaramptech]

Thanks Les. Yes, I thought I would get through that backlog of repairs in a few weeks. It ended up being a few months.

[@uptownphotography]

That looked like a tedious job Chris. I give you credit for getting it working again and having the energy to stick with it. I am like you. Tubes all the way. Great seeing your back strong and you're keeping the videos interesting. Be well. Phil NYC Area

[@theguitaramptech]

Thank you, Phil. Its great to hear from you too.

[@k13m13]

I owned one of these, fun little preamp honestly. Awesome to see you work on one and see some more of the inside and some explanation of the schematic.

[@theguitaramptech]

Thanks K13m. I really appreciate your kind words. It wasn't much fun to work on, but I am very happy that the owner was very happy.

[@k13m13]

@@theguitaramptech haha I can imagine that sir. Take care!

[@markusf.3441]

Hello Chris, great video as always. I own two of these amps and for me they are great. Of course, adjusting the sounds is a bit more involved than with analog amps, but I haven't changed anything in the settings for years 😁 Through my MIDI board I have the ability to access all the sounds I need and with the sound I am more than satisfied.

[@theguitaramptech]

That is excellent Markus. I’m sure if I spent more time with it I may have found some sounds that suit my taste. I hope JMP1s stay reliable for you. 🤞

[@pda49184]

That was an 'epic' repair Chris.. Well done for persisting with it and finding a way round the TX issue. I had a JMP-1 back in the 90's and at the time ( guitar sounds and styles being what they were), I thought is was the dogs dangly bits. Five years ago I found a recording of the band I'd forgotten about. I transferred it from cassette to CD and was shocked at how awful my guitar sounded. The rest of the bands instruments and vocals sounded great, so it wasn't the recording. That sort of explains why Marshall didn't make a Mk-2 version (JMP-2) I recon. Happy New Year from Pete (UK).

[@theguitaramptech]

Hi Pete. Yeah, I don't think I'll be rushing to the second hand market to buy a JMP-1. Every time I work on a 2 or 4 hole JMP, or an early JCM800, I remeber why Marshalls became so famous. Its sad to see how the brand and sound have declined since then. But then again, I'm a Boomer and I like my old school sounds.

[@petertimp5416]

You’re back! 👍🙏

[@theguitaramptech]

Hi Peter. I am very embarrassed about about the long absence. I love making these videos, but I am primarily an Amp Tech, and I was overwhelmed with repair work for months! I am finally catching up and hope to get back to making more videos.

[@petertimp5416]

@@theguitaramptech good to hear your absence was work related and not something worse 🦠🤮☠️…………………🙏👍

[@theguitaramptech]

@@petertimp5416 I had a stent put in in January but that didn’t slow me down for long. 😇

[@krauz111]

great to see you back!

[@theguitaramptech]

Thank you, Carlos. I am primarily an Amp Tech, and I was overwhelmed with repair work for months! I am slowly catching up and hoepfullu I can get back to making more videos. Thank you for being patient.

[@edwardhannigan6324]

Chris who..?? Oh, you're back...🤣🤣Nice to see you man, great video and in depth discussion..Thanks for sharing..Ed..uk..😀

[@theguitaramptech]

Great to hear from you Ed. I was inundated with repairs. I am back down to a 2 week turnaround so it gives me time to do more videos… which is fun…plus I get to talk to nice people around the world… like you, Ed.

[@edwardhannigan6324]

@@theguitaramptech Thank you for your kind words, love learning Chris..Keep safe..😀

[@abijag100]

I can vouch for Chris's repairs.......and great coffee !!

[@theguitaramptech]

Thank you, Steve. Time for another coffee?

[@abijag100]

@@theguitaramptech Indeed good sir .

[@mmmatthews9135]

hi Chris love your channel. I'm just down the road in Wollongong. Need a apprentice.

[@theguitaramptech]

Thank you so much, M!

[@rayprevailer8454]

Good grief. No wonder the Voodoo Mod is so expensive. Fantastic video.

[@theguitaramptech]

Thank you SO much, Ray.

[@saren6538]

Hi Chris that was great to watch (new subscriber) can I ask … I have a 1978 Yamaha e1010 Band delay rack and the volume spikes then silent. I have to turn the unit off and back on again … repeat .. any ideas ? Thanks

[@theguitaramptech]

I'm sorry, but I have never even seen one.

[@JohnyLondon]

Pity you aren't near bye - I've got a PSA-1 with a faulty transformer! Ditto impossible to obtain :(

[@theguitaramptech]

Yes, its a problem, Johny. Look for someone who can do a rewind for you.

[@aquilarossa5191]

Iron Maiden use the JMP-1 and their guitar tones were great last time I saw them. I think their tones would be better if they went back to JMP 1959 and 2203 amps though, but I saw the Angus rig rundown and understand why the mighty Maiden opt not to do that. Angus had a truck load of spare amp heads and a full time repair guy on tour with him to constantly fix the ones that blow up. I wish I had not seen that video. Now I get nervous cranking my JMP 1987 clone into a reactive load. I half expect to smell smoke from a fried screen resistor or something. P.S. Are there any fault conditions in a JMP 1987 circuit that can make the V1 tube behave very microphonic? I tried several tubes and they were all failing the chopstick test to varying extents, plus with some of them the amp wanted to squeal and oscillate when cranked. Great tone apart from that, so it's very close to being a very good amp for the kerrang thing (my nephew plays tricky nu-metal stuff but just played AC/DC riffs on the amp and then said "don't ever sell that amp"). BTW. Would it be tricky to add a slave input to the JMP 1987 clone, so I can use just the power amp with other preamps?

[@theguitaramptech]

Angus' tone is sensational, helped by his talent. The tube is the most likely cause, and brand new tubes can be microphonic. Also try "rubbing" your chopstick against the two 100K plate resistors, the two coupling capacitors and the cathode resistors and their bypass caps. Also make sure you clean all the input jacks and their contact "leaf" has a good connection.

[@aquilarossa5191]

@@theguitaramptech Thanks for the info. Cheers.

[@peterschaefer1665]

What voltage are the 12AX7's actually seeing?

[@theguitaramptech]

I can’t remember Peter. Maybe around 180v … but that’s more of a gut feeling than an actual recollection.

[@erkamgulluoglumusic]

Hi there, I'll be grateful if you help. Mine has wave-like vibrating/oscillating noise (like 2-3 waves per second) on OD channels. I replaced the filter caps but the hum is still there. Do you have any idea? Or can I send you mail to explain more details? The transformer has it's own physical vibrating sound but I want to get rid of the OD channel noise first.

[@theguitaramptech]

The JMP-1 is a complicated circuit that cannot be serviced remotely. The main thing that I can suggest is the check all of the power supply voltages for stability. Check the +/- 15v and +/- 5v on IC 5,6,7 and 8. Of course, you have swapped the tube. Thank you for joining us from Turkey, Erkam. My background is Greek but both sides lived in Turkey until 1922. My father’s surname was Tarakzoglu which he changed when he migrated to Australia. I was lucky to go to Turkey pre-Covid and I found my grandmother’s house in Ürgüp!!

[@erkamgulluoglumusic]

@@theguitaramptech Hi Chris. I'll try your suggestiong asap. By the way I've noticed that the main reason of the noise is myself. More I get close to the preamp the noise gets louder. I'm using g major 2 on my rack, before I noticed that, I had to use noise gate of g major 2 on OD2 channel. but when I get away a little (1-2 mt) the noise is decreased dramatically. In fact, if I get away enough, I don't need to use noise gate on g major 2 at all. But above that, I couldn't figure out that in some presets the preamp give a very very high pitched noise. Do you have any suggestion for this issue? As for your Türkiye background, that's wonderful, Ürgüp is a town of the Nevşehir city. Also it is where the famous Cappadocia is.

[@erkamgulluoglumusic]

@@theguitaramptech Hi Chris. I've checked the IC 5,6,7 and 8. IC5's output is 14.94V, IC6's output is -15.22 (because it's L7915CV), IC7's and IC8's output are nearly identical 5.05V.

[@theguitaramptech]

@@erkamgulluoglumusic hi erkam. Coworker in finding you are the noise source 😂 That’s about all I can suggest remotely.

[@erkamgulluoglumusic]

@@theguitaramptechDo you have any suggestion for the high pitched noise on some presets?

[@lestelie4410]

I just noticed that you were using your manual solder sucker when you had a powered one on the shelf. When do you decide which one to use?

[@theguitaramptech]

HaHa! Well spotted, Les. This is EXACTLY the type of situation where I would use my powered benchtop solder sucker. It is much more gentle on solder pads than a manual sucker. Sadly, it expired the week before filming. I have since received my new powered solder sucker. I still like my manual sucker when removing bulk solder from Fender eyelet boards. The manual sucker is much quicker to clean than the powered one. “horses for courses”.

[@dwightbehm2886]

Uncle would say go grab yerself a beeer.

[@theguitaramptech]

I look forward to sharing a beer with Doug one day, Dwight. You should join us!

[@dwightbehm2886]

@@theguitaramptech yes indeed think I will

[@RennerGutierre]

Hey man. When you share content here on YT you must be ready to accept some criticism and learn from them. Deleting them won't make you better. Cheers (you can delete it also)

[@theguitaramptech]

Thanks for your comments Renner. Firstly, I don’t SHARE content, I CREATE it. Sharing takes a few seconds while creating content takes many, many hours for one video. I leave all intelligent comments where people may have a different approach to me. For example, I am a conservator of vintage amps. I test every component with expensive equipment that I know how to use. I will NEVER take a shotgun approach to a vintage amp and replace components because I am too lazy or stupid to know how to test. We owe it to the next generation of players to keep vintage amps as close to their original sound as possible. The comments I will continue to delete are those where the commenter is trying to hijack my hard work and attempt to make themselves look smarter than me by mindless criticism. I have no issue with different methodologies, but trolls will be deleted. If they can do better than me, then I applaud them. Let them spend thousands on equipment and countless hours recording and editing. If they are good, I will subscribe to their channel.

[@dwightbehm2886]

Chris were you always an amp tech? What is your back ground? you play guitar like a pro. And you are very knowledgeable? Dwight from Allenpark, Michigan, Wayne county USA. near Detroit.

[@theguitaramptech]

Thanks mate. I put a long-winded answer to your other question. I very much appreciate your comments, Dwight.