• Music Man 112 RP Sixty Five • Kyle treating us to some wonderful sounds when picking up the new look Music Man - check the post for the grill cloth transformation:) More importantly though, if you're looking for music lessons definitely check out Ostinato Music School !! Kyle is such a smooth player and by all accounts an amazing teacher too!
• Music Man 112 RP Sixty-Five • Did a grill cloth replacement on this old guy a little bit ago! For whatever reason these grill cloths are not standing the test of time… safe to say it's not for lack of staples though 😮💨 Of course had to get in there and do a little health checkup too, especially with the unique transistor controlled tube output section:)
• Roland RE-501 • This beauty came through the shop a little while ago for a service. It lives down in @5thstreetstudios where it had been giving some troubles with intermittent signal distortion. After I got it back to health I had the chance to drop by 5th Street and see it in action, what a treat :) Such a wonderful little place downtown. If you're looking to get into a studio with some incredible vintage gear and an even better engineer, @ryanhuseman will absolutely take care of you there!
________
Considering the intermittency of the signal issues the best bet was to go through and give this thing a good cleaning and calibration, starting with the transport deck. I cleaned and demagnetized the tape heads. Cleaned and lubricated the pinch roller and tape guide bearings, and then checked tape head alignment and tape path. In this case very little adjustment was necessary.
Then on to the audio circuit. I start with cleaning all the pin/header connections used to pass signal between the separate circuit boards. Over the years a bit of corrosion can build on the pins and cause those intermittent signal issues. Then some typical circuit health checks such as testing electrolytic caps, validating power supply voltages, checking op-amp supply voltages.
Then on to calibration and testing. Before calibrating I clean the internal bias/calibration trim pots which are particularly susceptible to picking up dirt and grime. Then went through calibration procedure laid out very nicely in the original service manual. At this point I fired it up and let it run for a few hours, testing every so often for any signal issues, and the intermittent distortion was gone:)
HOWEVER… the Reverb was had a constant fuzzy distortion in the higher frequencies. I went through and made sure the circuit was healthy, but should have recognized that distortion right away. It was due to an impedance mismatch between the reverb driver circuit and the reverb tank. At some point the reverb tank had been replaced in this unit and the wrong tank was installed. I found the correct replacement and the reverb cleaned right up!
• Fender Princeton Reverb '65 Reissue • @marleyhalemusic with her '65 Princeton :) This one was a quick turn around the week before SXSW. Marley and the band had a heeectic stint of shows, so I'm glad I was able to get this little guy back to full health for them in time!
________
Fortunately it was pretty routine as far as the Fender reissue series go. It had original IC filter caps from 2017 one of which particularly flailing. That's a pretty typical life span for these cheaper caps unfortunately. Got those replaced with F&Ts which cleaned up the amp nicely.
Another issue was a damaged input jack. In this case the jack had become cross threaded at some point and no longer secured to the front panel. The two input jacks sit on a separate little PCB and if the nuts securing it to the front panel come loose PCB mounted jacks become susceptible to damage and you quickly get intermittent signal breaks. So I replaced these with panel mounted solder lug jacks and wired them directly to the main PCB.
Then the final major issue was microphonic 6V6s causing a nasty high pitched ringing. It's unfortunate how often this happens with modern tubes, just another case of build quality deteriorating with the times. Anyway, I replaced those with a matched set of burned in JJs and got them biased to 23mA each for around 10W idle plate dissipation.
• Fender Hot Rod DeVille • Strong man Mike from @shiveringdemons !! Gotta give the Fender Hot Rod series some love, I mean, they are everywhere! … and if you do give em some love they can be that workhorse amp you're looking for :) Mike's DeVille was starting to lose power when pushed, to the point that even the pilot light was dimming when you hit a heavy chord. Generally speaking, Fender took a few shortcuts with these amps to keep the price low but with a bit of work we can get make them a lot more reliable. For one, replacing those original filter caps is often a must as it was in this case with one of them already completely failing. Another step is to mount the high current components away from the circuit board as the heat they emit damages the circuit board traces, I'll get into that in the next Hot Rod post:)
• Gallien-Krueger 400RB • Here's @bigfeelingzhaver with their GK bass amp a few weeks back! Ry is an amazing bassist aaand guitarist, I was lucky to see them playing a lil guitar with @redbud.dy for a duo set recently:) Normally you can catch them on bass with the full band though, and I would highly recommend checking them out!
_________
Ry brought this by because of intermittent signal issues. Interestingly, I believe someone had previously tried to fix this issue since the switched return jack for the effects loop had been soldered together - the switches on these jacks gather corrosion over time and can cause such signal issue. However, in this case the problem was that the pin header that the send/return wires connect to had a bad connection to the PCB. After fixing that connection I replaced the return jack with a new switchcraft switched jack per Ry's request so the effects loop could be used again as designed.
Then I just went through and did a basic health check, tested the electrolytic caps, re-biased the power transistors to a lower idle current, cleaned up the internal pin connectors, pots, etc… and it's back to life:)
• Sony MCI JH-110 • In honor of my favoritest new album, "I Still Love San Antone", here is @blondebill reuniting with his MCI JH-110 back in December!! You simply must go listen to this wonderful creation from @garrett_t_capps and @blondebill , it's a whole new flavor of Tex Mex :)
Ok now, I can't believe I haven't shared this one yet. Bill brought this by after it spent a couple years out of commission. It had a few issues that needed attention to get it back healthy and then it was calibration time. Thank you Bill for trusting me with this repair, it was so cool to really dig into how these work and go through the whole calibration process.
________
First order of business was getting power to the motors. The issue was that the 22V power rail was being grounded. As it turned out, during a previous attempted repair one of the 2N3055 power transistors had been removed and when reinstalled the tech had left off the insulating pad which isolates the TO-3 package from the chassis ground. Something so innocuous bringing the whole thing down…
From there I started testing the transport motors and found that the take up motor was not idling properly. The MCI service manual is a beautiful thing as it goes beyond schematics and lays out exactly which parts - specifically op-amps in this case - might be causing specific failures. So after swapping a few op-amps between sockets I was able to find and replace the culprit. Then I started on calibrating the motors as per the same wonderful service manual.
Finally came my favorite part, calibrating the audio electronics: VU meters, input and repro balance and EQ, tape bias, erase head adjustments, etc…. This was a long process that I won't detail here, but if you're interested then a quick read of the MCI-J110B Service Manual might be right up your alley. It was very satisfying to go through the process and listen to this thing come back to life!
Thanks again Bill for trusting me with this beautiful tape machine!
• Yamaha CP-25 • I shared a time-lapse reel of this this a while back but wanted to share some pictures too because I really came to love this thing. The weighted keys are so nice to play and it sounds wonderful. It also uses a clever mix of analog oscillators and digital circuitry to detect key velocity and trigger notes, which was fun to wrap my head around.
When Joey brought this into the shop it powered on but made no sound. Because these units use a mix of analog and digital circuitry they actually have separate power supplies for the two: a +15V and -15V for the analog circuit, and a separate -15V supply for the digital circuit. The failure here was with the voltage regulator for the +15V voltage regulator which had been shorted to ground when it was at some point twisted from it's original position as seen in the photos. After replacing and securing that regulator the analog oscillators had power again and the sound was back!
You can also see the reel I posted a while back for some work I did on the physical keys and contact points to even out the key velocity across the board:)
• Yamaha SPX90 • An absolute classic here, Yamaha started production of these units in 1985 and we all still love em today for that '80s digital magic. I at least had too much fun testing it out :) I got this fixed up a little while ago for @dbsguitarworks . When he picked it up it wasn't powering up at all. Thankfully, the issue was contained to the power supply circuit and the digital side was all healthy. I did however have to rebuild a good portion of the power supply circuit as multiple capacitors, diodes, resistors and transistors were completely dead. Left me curious what failed first. Anyway, once that was rebuilt the unit came right to life:) I made one more preemptive change in replacing the original soldered in battery with a battery holder and a new battery. It's unfortunate that when these batteries finally fail you have to remove the whole circuit board and get out the soldering iron to replace them.
• Yamaha SPX90 • An absolute classic here, Yamaha started production of these units in 1985 and we all still love em today for that '80s digital magic. I at least had too much fun testing it out :) I got this fixed up a little while ago for @dbsguitarworks . When he picked it up it wasn't powering up at all. Thankfully, the issue was contained to the power supply circuit and the digital side was all healthy. I did however have to rebuild a good portion of the power supply circuit as multiple capacitors, diodes, resistors and transistors were completely dead. Left me curious what failed first. Anyway, once that was rebuilt the unit came right to life:) I made one more preemptive change in replacing the original soldered in battery with a battery holder and a new battery. It's unfortunate that when these batteries finally fail you have to remove the whole circuit board and get out the soldering iron to replace them.
• 1960s Fender Showman • Gale with his Showman! Gale brought this by when he could no longer get a clean sound through it even with the volume around three. Details on the repair below, but now that we've got it all fixed up I want to talk about his setup… he's going to be run his Azola upright bass through it into an original Showman cabinet! Ain't that something :)
______
As for the repair, the lack of headroom was due to a couple of factors. First, the preamp section was noisy due to failing cathode bypass capacitors, which were all original - sad to have to pull those out. Particularly the bypass cap in the first preamp stage can cause a lot of noise as any noise generated in this stage gets amplified by each following stage. Replaced these with quality Sprague Atom capacitors.
The other major issue was the flailing IC filter capacitors that had been installed previously, so we got those replaced with some quality F&T caps.
Then looking forward to reliability, the screen grid resistors were drifting well out of spec, 30+% off. I'd love to keep those original, but once they start drifting that far reliability becomes an issue and I think it best to replace them before they completely open.
• 1957 Ampex 601 • Here's an old reel-to-reel I restored a little while back. My main focus was on getting the tube preamp up and running for use as an outboard preamp a recording setup. These work beautifully as mic preamps!
Frankly this unit didn't need too much work: a few filter capacitors were well out of spec so I replaced those, and then slowly brought it up on a variac over the course of a couple hours. At this point I found some leaky coupling caps which I replaced but the tubes all tested fine and the unit sounds wonderful. I'd considered converting the heaters to DC but it's surprisingly quiet as is so no need to mess with that yet.
I also did confirm that the transport works but haven't gone into any testing or calibration with tape yet, that's a future project. I would, at some point, love to get it all functioning and tested as originally designed though!
