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AMPEG SS-140C VOLUME LOSS MOD

(referencing a 1989 Ampeg SS-140C that was losing volume due to an overheating chorus board)

PREFACE: My first amp and a broken hardshell case were thrown in with a used 1984 Squier Strat purchase. That guitar was (still is) pretty nice, but that practice amp was a total piece of shit. It was 5w of rock and roll sadness. It sounded awful, so was no fun - this only adding to my distaste to practice because my lessons included how to read sheet music (huge fail their) and not playing anything cool. I didnít even know of power chords until a few years later!

I was saving money for a new amp and had no clue what was good. Approaching my twenties, I of course assumed more wattage meant better sound ...simple math. There was an Ampeg VH-140C with the standard Ampeg-Eminence speakers listed in the newspaper classifieds and I drove 40mins to pick it up from some dirt rocker just a couple years older than me. I canít for sure remember how much money I paid for it, because sometimes I believe it was $550, but I'm thinking thereís no way I saved that much! Maybe it was $350 ...that makes more sense, I guess? It was in absolute mint condition and remained that way for as long as I, and my buddy who I sold it to, owned it. I had no idea what an Ampeg was in 1994 because it wasnít the ubiquitous Marshall, nor would I realize how fantastic this particular amp was until decades later ...I naively thought all name brand amps sounded really good.

Unbeknownst to me, the Ampeg VH-140C became a quintessential brutal tone machine for death metal guitarists. During my ownership, I never got the tight, concussive crunch I wanted. I was kind of disappointed not finding the full-bodied chug (ala Metallica) from Channel A and made a few misguided effects purchases (Boss DS-1, Rocktron Gainiac, Zoom 505) that barely got me any closer to where I desired. However, the cleans (Channel B) were pristine and beautiful with nothing but an instrument cable and a Ď59 humbucker between the strings and the amp. Channel B was absolutely noiseless without sounding sterile and you could switch on the built-in high-quality reverb and chorus for something I remember as ethereal and angelic. Auditory shimmering. At least I was nailing my favorite Metallica intros as a kid. I moved out of PA at the end of 2000 and sold the Ampeg to my only guitar friend, Chad. He kept it for a while, but he was always what I considered ďa Fender guyĒ who eventually got into building his own tube amps ...so he let it go.

I got back into guitar (again) and began wanting another VH-140C after looking them up and finding how revered they became for their monster gain and effects pedal-friendliness. I knew the cleans were amazing, but I was reading how brutal everyone said the thing could be. I started collecting vintage USA-made amplifiers in December 2018 and set my sights on that nostalgic Ampeg. When I finally committed to the idea, a seemingly mint (and only a mere $185) VH-140C combo slipped through my fingers while I was on vacation. I learned of the SS-140C* in September 2019 and this broadened my Craigslist search, immediately stumbling onto a 1989 SS-140C that I drove 75mins to and haggled down from $280 to $220 (included an original footswitch). Back home, I x-cabled a Boss NS-2, an Ibanez TS7, and an MXR M108 through the effects loop, then dimed the gain. Instantly, I had the tight tone I always wanted ...and in the low input, no less. My mistakes twenty years ago were never buying an equalizer to fine-tune the signal or a gate to tame the gain noise when it was cranked. Holy crap! A seagull EQ pattern on my M108, in the loop, punched my signal up to the crisp, beefy palm-mutes that I once thought were impossible with this amp. The SS-140C also took the boost from the TS7 beautifully, making feather-light hammer-ons ring through as if they had been picked. Yes, tube amps are awesome, but the tight response of a solid state amplifier is just my style. I became smitten and my beloved 1992 Peavey Ultra 120 isnít being played much anymore.

* In March 1986, SLM (St Louis Music, who had been producing Crate amps since 1978) acquired the Ampeg rights and inventory after its previous owners had filed bankruptcy. By 1987, SLM was producing the new line of Ampegs, including the SS models for guitar. These were the predecessors to the VH series (Variable Harmonics) and they were very similar, with some years looking indistinguishable to the casual observer. The SS and VH amplifiers share power amps, but the VH received a slightly more brutal preamp than the SS, along with the patented Variable Harmonics circuits to mimic vacuum tube characteristics. The Crate GX-130C is also said to be essentially the same as the VH-140C. These guitar amplifiers have so many usable features packed into them that they are easily the most versatile vintage USA-made solid state 2-channel amps you can score. I picked up a 1997 VH-140C head locally for $400 in October 2019 - now Iíd love to get my hands on one of the all-tube Ampeg VL heads engineered by Lee Jackson ...or Crate Stealth, which this VH owner also had and offered to sell me, but one was enough that day. The VL/Stealth do not sound like a VH and they do require mods to update them for reliability/longevity, though.

THE VOLUME LOSS: I was playing the hell out of my SS-140C that first day for about 45mins when the volume began to repeatedly dip and return like a swell. Forum searches had me blaming the cliff jacks (plug a patch cable into each of the loops to diagnose/remedy this) or requiring a touch-up on all the solder joints. Ugh! Then I came across two actual SS-140C owners mentioning overheating chorus boards. This appears to be something Ampeg may have corrected in the VH series. A few days later, I pulled the electronics chassis out to do a quick exam of the circuit boards and then played it again with no problems - I built longer speaker cables out of an old guitar cable that I cut in half and added female spade connectors to. The open air was apparently enough for the chorus board to radiate excess heat away. However, I had noticed an area of that particular board had an extremely subtle discoloration to it and now the two ceramic resistors there were very hot to the touch - Ampeg cut holes in this circuit board directly under these large, white resistors to allow additional heat to radiate off, but it just isnít enough. There are also two heatsinks on the underside of the chorus board here, though they are very small. Take note that these particular resistors produce substantial heat regardless of the chorus being engaged or disengaged, so it is not as simple as just keeping the chorus effect off.

So, thereís the problem! And hereís my solutionÖ

Sealed up, there is simply nowhere for the resistor heat to go in these amps. When opened, you will notice that the giant heat sink on the back of the chassis has nothing to do with the chorus board mounted at the front. I read of one owner successfully shimming the chassis down a little and drilling holes in the top of the cabinet for improved passive cooling - I was not going to ghettofy my new baby. The easy fix is to plug a small desktop fan into the courtesy outlet on the back of the amp to cool the chassisís exterior a little and then hope for the best. But frankly, that sort of solution is really not going to get the job done properly and is for people too inept to change a car tire. I like my vintage amps to look original even if modified, so I wanted to install an internal power source operated by the power switch along with a discreetly placed computer fan. My problem is I have near-zero understanding of electricity, as the concepts are way over my head. I began a brain-hurting attempt to learn how to build a small circuit board that I could wire to the available terminals on the power distribution board inside the amp (next to the On switch) and step the 110V down to 12V for a computer fan. I spent a few hours researching, calculating current, and gathering the parts on Amazon only to eventually realize that I had some cheapo power supplies that I got with used effects pedals, but tossed in a box because they made too much noise. I grabbed the tiniest one (BluCoil) and checked the specs printed on it - this just might work! These power supplies are far more advanced than anything I could come up with and are cheaper than buying the few parts that I needed to build a very simple one.

Polite Request: before going any further and performing this mod yourself, please consider your skill level. I am fairly meticulous and spent a few hours a day, over a couple days, carefully planning and doing this modification cleanly. These are vintage amps that cannot be replaced - to me, American-made amps are special since ďMade in the USAĒ doesnít appear on cool stuff like this very often nowadays. I spend a small amount of my hobby time collecting and refurbishing old American amps just to keep them going for a future generation. So, if thereís a chance you could totally botch this, or if it could turn out looking like crap, please just take it to an amp tech or a trusted friend that is a craft-type hobbyist. Advise them of this idea and pay to have it done right, if you have to. Also, if your USA-made stuff ever fails, donít scrap it. Instead, try to find someone who wants to fix it and then sell it to them cheap ...or give it to them for free. You know, make it worth their effort to keep this Americana alive. Thanks.

HOW TO IMPROVE COOLING: I made sure the amplifier was unplugged, marked the reverb RCA cables to their respective jacks (the one closer to the transformer is the signal return) and disconnected them from the chassisís underside, removed the entire chassis out of the cabinet (see below), and remained careful not to poke around where it was not needed because capacitors can store electricity. I took the BluCoil 9V 670mA power supply and used a Dremel to cut a notch along the seams, inserted a flat head screwdriver, then twisted the screwdriver to break the housing open. I easily removed the outlet prongs and cut the cord to leave enough wire to work with later. The Noctua NF-A6x25 FLX computer fan is rated for DC12V at 0.12A (120mA). This very quiet fan will run on the BluCoil 9V* supply (albeit, spin slower) and only draw the small amperage that it requires. Converting to the DC current will also reduce any unwanted cycle hum from the new circuit. A 60mm fan fits perfectly on the back of the chassis (80mm might fit snugly, but it would certainly encroach on the serial number), however I moved the power cord because of this fanís 25mm thickness.

* My build with the BluCoil 9V supply didn't spin the fan as fast as I had hoped. Granted, it was moving a fair amount of air, but I was looking for something with a little more oomph. I decided to order a 12V supply to ensure I was taking full advantage of my design. The 12V supply definitely increases the RPM - I can hear the fan running at 12V, which wasn't the case at 9V. Also, I ran across a similar modification done to a homemade amp that instead used a 9V battery, but the math says that might last 3-5 hours before needing a battery change. I would certainly not waste any of your time with that solution.

I opted to order a very generic 12V power supply, referred to as "the adapter" from now on, to maximize the fan's airflow. This adapter is rated to step 100-240V AC down to 12V AC/DC (whichever the item it is powering needs). It can deliver a maximum of 1A, not that that is needed. It will also automatically switch polarity (like the BluCoil), so assembly will be just as fool-proof. I opened this adapter in the same manor, cutting along the seam, and prying it open. The circuit board layout of this supply was not as compact as the previous one, so things are going to be a little tight when mounting it inside the chassis.

After taking reference pictures of the circuit boards for reassembly, I removed the Ampegís power cord by disconnecting it from the power supply board and the common ground screw. The plastic strain relief grommet requires a special tool that I didnít have, so I used pliers to squeeze it together and pull it all out the bottom. Since my power cord was showing excessive wear, I chose to replace it. The factory installed an 18AWG cord that is about 9-feet long, but I decided to order a 10-foot 16AWG cord along with an assortment of cable gland grommets. I almost regret not getting the 15-foot cord for added convenience, but thatís a fairly easy swap if I ever change my mind. Why the upgrade to 16AWG? Mainly because I couldnít find an 18AWG cord over 6-feet that appeared to be the same quality as the one I bought. Thinking in my normal overkill fashion, the thicker copper wire more than guarantees delivery of all the power this amplifier could need.*

* the SS-140C manual specifies that it draws a max of 6A (18AWG can carry 10A; 16AWG can carry 13A) and the transformer wires are 18AWG. I later noted that the wires to the courtesy jack are larger than 18AWG, so a 16AWG power cord seems like a fairly practical upgrade to me. Plus, a good rule of thumb is to choose electrical supplies rated to handle twice the need (6A vs 10A vs 13A).

I originally intended to move the common ground to the other side of the bridge rectifier (the square item with four red wires coming off it), but the ground wire from the courtesy outlet wasnít long enough and I opted not to extend/replace it. So, I decided the best way to make everything fit was to first move the bridge rectifier closer towards the chorus board. When remounting the bridge rectifier, apply some fresh CPU paste to improve heat transfer to the chassis surface. I used a Rotabroach to make a new hole for the power cordís cable gland between the common ground hole and the original bridge rectifier hole. I was careful with placement of this gland, as I didnít want it too far towards the front (where it may rub on the speaker) or too close to the transformer. To do over, I might have moved the common ground closer to the new bridge rectifier position and then placed the new power cord pass through between the new common ground and the old power cord pass through - this would have alleviated any concerns of the power cord ever rubbing on the speaker. I hot glued a piece of Maxmoral Fan Mesh Dust Filter material onto the chassis floor to cover the original power cordís pass through hole.


These pics show the before and after layouts. Note how the power cord was interfering with this fan.

For the new fan hole, I used a 2.25Ē Milwaukee Dozer hole saw centered within the rear chassisís Caution and Warning information. I did my best to vacuum out any debris after every cut or drilled hole. Using a half-round file and some sandpaper, I smoothed out the fan hole and removed the burrs. Then I added some light-colored tape to the corners and lined up the fan so I could transfer the mounting hole locations to the tape. I double-checked this alignment with the metal fan guard, and drilled the four holes out to 7/32Ē. I had originally planned to sandwich a piece of Maxmoral Mesh between the chassis and fan guard to help keep dust out (and hide the white print), but decided it would hinder the flow of air from this fan too much. Unfortunately, this will now allow dust into a previously ďsealedĒ chassis. So, Iíll plan to remove the chassis and clean the boards at least once a year, just like my desktop computer - I use a soft brush to kick up the dust and then a shop vac to get rid of it.

To mount the fan's power supply inside the chassis, I made a bracket from some spare plastic pickguard material and 1/16” x 1/2” angle aluminum. Taking the half of the adapter housing that has tiny risers to prevent the solder points from touching plastic, I cut the outlet prong section off then used my belt sander to level the housing down to about half the original thickness. To make the housing shorter, I also cut the ends off that extended beyond the edge of the circuit board. I cut a rectangular piece of pickguard about 6cm x 7cm and drilled a hole in it to make a mounting surface. Placing the housing against this pickguard surface and clamping it, I applied hot glue within the drilled hole and the prong hole to join it to the adapter housing. I re-secured the circuit board to the housing/bracket using two small screws through the board's mounting holes.

To get the 110V from the Ampeg’s power supply board to the salvaged adapter board, I soldered 15cm of 18-guage wire (scavenged from the amp’s original power cord) to the adapter's posts, then added a 0.25” female spade connector to the opposite ends of these wires. The "posts" on my supply were a little odd to utilize, but I managed to solder the wire within the clasps and then reinforce each with large shrink tubing. It doesn’t matter which wire is positive or negative because the adapter’s outlet prongs were the same dimensions - I confirmed that the unit changes polarity on its own. The Noctua fan included a two-wire 4:3-pin adapter that I cut and hardwired to the output wires of the adapter's circuit board - now I can do a quick disconnect of the fan, if ever needed. The adapter’s new spade connectors will get plugged into the two available tabs along the bottom of the amplifier’s power supply board once it is mounted.

I secured the supply and bracket to the angle aluminum with a rivet, then mounted this entire assembly to the bottom of the amplifier chassis with two rivets, tightly situating it between the Ampeg’s power supply board and courtesy outlet.

For the hidden exhaust ports, I chose to put two 1.75Ē holes in the bottom of the metal chassis, near the front corners. First, I moved the Caution label advising what fuse to use between the polarity switch and courtesy plug with 3M Super 77 Spray Adhesive. I removed the chorus board* to center the one exhaust directly below the resistor on the underside (being mindful of the transformer, again). I took some Stainless Steel Woven Wire Mesh and cut squares a little larger than these holes with tin snips, then hot glued the mesh to the chassis floor. I chose the wire mesh here because it is hidden from view and allows much more airflow than the mesh dust filter. Before reassembling, I took this opportunity to clean all the cliff jacks with DeoxIT D5 and insert a cable plug several times. I also cleaned the reverb RCA jacks on the underside - during my volume diagnosis, I was also suddenly not getting any reverb from my pan because of a dirty connection.

* take a pic of the entire board and then carefully remove the four ribbon-style connectors from the chorus board only. Pull the three chorus knobs straight off, unscrew the retaining nuts on these three pots, then remove the two Phillips-head screws holding the board down. Tilt the rear of the board up, then slide it back, up, and out.

RESULTS: I tested it to make sure everything was still functioning with the chassis outside of the cabinet before placing the chassis back in. Though the fan is absolutely noiseless (as promised), I was a bit disappointed how much airflow the fan was producing with the 9V supply. Slower was foreseen, but I was hoping for a little more CFM (cubic feet per minute) than what I got. Though the airflow becomes concentrated onto the problematic resistors and the small heat sinks once mounted back in the cabinet, I desired more air flowing through the chassis. There was enough positive pressure being produced from the 60mm fan at 9V that I could faintly feel the air current at both of the exhausts, so I knew it was evacuating some of the excess heat being generated. Still, within a few days, I had upgraded to the 12V supply and have been much more at ease with it in this configuration. Because the fan spins faster at 12V, I am now able to hear it, but only at the back of the amp. The 12V supply I bought has a red LED that I left mounted to the board, which lights up the fan.
Done.

 


HOW TO REMOVE THE CHASSIS: Make sure everything is unplugged from the rear of the amplifier and unplug the two reverb RCA cables from the underside of the chassis (mark one jack and itís corresponding cable with a Sharpie to facilitate reassembly). Still at the rear, remove the upper cross-bracket that essentially adds rigidity to the combo cabinet. Supporting the underside of the chassis with one hand, unscrew the four silver Phillips-head machine screws located at either side of the top of the cabinet - the chassis will slowly lower itís weight onto your hand. Tilt the rear of the chassis down so the front lip of the control panel clears the top edge of the speaker cover frame, remove the speaker cover, then slide the chassis out the back. I used a couple old effects pedal boxes to level and support the chassis so it wasnít resting on the transformer and the heat sink while working on it. The speaker cover is velcroed on, so you simply pull it off - I removed both speakers and cleaned the dust off the back of the cones with a soft brush. Reassembly is the exact reverse and a flashlight will make lining up the top-mount screws much easier.

SCHEMATICS: Here are the original schematics for the SS-140C and the VH-140C.

MANUALS: Here are the ownerís manuals for the SS-140C and the VH-140C.

SS vs VH: Running them both through the stock speakers of the SS-140C combo, I seem to prefer the VH-140C. The VH gets super-brutal easier with lots of headroom left over - I set the gain around 6 on the VH, whereas I simply dime the SS. However, this difference does make for the SS to be a little more manageable and forgiving. The pots on the SS feel like they have a larger, smoother sweep, while the level and gain knobs on Channel A of the VH can seem less like dials and more like on-off switches at times. This is especially noticeable when my VH head is connected in stereo to my Carvin 412 cabinet: if the chorus is engaged while running higher gain levels on either channel, the volume increases dramatically. This occurs even though my Carvin 412 produces an 8ohm load per side (verified with a meter), just like the SS-140C combo. Oddly, this doesn't happen on my SS combo or when the VH head is connected to the SS's speakers ...nor do I recall this with my VH combo. Even odder, running the SS through the stereo 412 cab, the volume difference is almost negligible when the chorus is engaged. So with a VH, you'll want to snag the AFP-3 footswitch to prevent accidentally bumping the volume up a fraction of a hair when switching channels in the bedroom (seriously, it will make Channel A ring your ears for a while).

Overall, the VH sounds slightly tighter, seems to produce harmonics a little easier, and also has a much more dynamic reverb and chorus. And by that, I'd swear these go to at least 11 when compared to the SS's effects and add a far more complex texture (likely assisted by the patented Variable Harmonic distortion). It could just be the particular amp, but the reverb on my SS has more hiss than my VH, which gets more annoying as you dial it up - it is tolerable at my preferred 6, though. Could I have lived without the VH? Certainly, but this is nostalgia for me. Do I want to sell my SS, now? No way, though I'm not sure how much I will be playing it. I think the SS is still a stellar and wallet-friendlier option for someone who isn't totally obsessed with the legendary VH mega-brootz. The SS seems slightly more genre-versatile due to the knob forgiveness and overall smoothness, nearly achieves the VH's apocalyptic-level crunch (especially with an EQ), and possesses that same beautiful clean tone ...it just needs a cooling fan.

STEREO RULES THEM ALL: As if the tone wasn't awesome enough for me, stereo with the chorus engaged is where these amplifiers really blew my mind all over my face. I generally consider myself a purist: I prefer 2D movies over 3D movies and I like my vintage stuff to look original. So, I almost naturally considered stereo to be somewhat of a gimmick. My old VH-140C combo and my current SS-140C combo (both 8ohms; both open-back) sound pretty good in stereo with the chorus. However, plugging my VH-140C head into my stereo-ready Carvin 412 closed-back slant-cab loaded with English-made Celestion G12S-50 speakers (running 8ohm per side in stereo) sent my ears into confused uber-bliss ...and the cab isn't even baffled to separate the dry and wet signals. I say "confused" because I cannot understand what wizardry could make it exponentially better than it already was. Maybe it's the closed-back cab, but in this configuration, the EQ wasn't even needed to get a really good tone out of it. I cannot put the sound into words - it is just incredible. If you have the combo, do yourself a favor and get a quality stereo 412 and an EQ pedal. For something uniquely spectacular, I will also run an effects chain with this setup that includes a DigiTech Drop (set to Oct+Dry) between the gutiar and input, then my DigitTech Polara (set to Spring) and MXR M234 Analog Chours in the loop - this beefs the texture up even more and the Drop makes it sound like a giant, angry, beautiful robot.

ALTERNATIVES TO THE VH-140C: Aside from the earlier SS models, there are quite a few solid state amplifiers that are debated to possess a preamp that is very similar to the Ampeg VH-140C. Identifying reliable information is difficult, but the Crate GX-130C is the one that pops up as being the closest equivalent. The Crate G1500, Crate Tidalwave GTX3500, and the Crate XLP Preamp are also normally mentioned as having "the same preamp" as the VH. Some other possibilities include the Crate Shockwave GT3500H, Crate VTX350H, and Crate VTX200S. The G130XCL is said to be quite different to the amps already mentioned. For pedals, there is the SNK VHD and the PLX FX Spirytus, which replicate the Variable Harmonic distortion circuit of the VH-140C's Channel A. These pedals can also be used as preamps. I use the Spirytus in my bass rig. After discussing it with Paul of PLX FX, I opted to substitute the linear volume pot with a logarithmic/audio pot (Alpha A100k right angle PCB mount) so I could achieve unity with my G-K 800RB's dry signal. Prior to this, the pedal's volume was also more like an on-off switch that I had to be very delicate with to tame it down to a bedroom level.

SPEAKERS: One thread that I saw claimed an SLM rep from the 90's stated that any Crate or Ampeg combo/cabinet that didn't have Celestions in it from the factory, had speakers outsourced through Eminence. I theorize that later years had both Ampeg and Eminence printed on them, while earlier years only displayed the Ampeg name. Early Crate models may have just had "Custom L" printed on the Eminence-made speaker. The speakers in my SS-140C combo have "Ampeg Custom Speaker - SLM Electronics" printed on the label. Per the manual, the combo listed as model VH-140C came with G12K-85 Celestions, whereas the VH-140CA model came with the standard Ampeg Customs (Eminence).

REVERB NOTES: I had several issues with the reverb. During one of my tests, the reverb was not functioning and I believe the RCA connections were dirty - some DeoxIT D5 fixed that problem. While diagnosing that, I removed the cardboard from the bottom of the reverb tank, but replaced it with Darice foam sheeting (similar to neoprene). Strangely, this caused the reverb tank to produce an unstoppable feedback. So I removed the foam and instead cut six pieces of neoprene (about 10mm x 40mm), attached them to the bottom of the tank as shock-absorbing feet, then placed it back inside the amp's reverb pouch.

CrankyGypsy (established 2001)