(written October 2019; overhaul Aug 2021)

(referencing a 1989 Ampeg SS-140C with a fluctuating volume)

Notice: The addition of a fan did not solve my volume problem, though it seemed to reduce the occurrence for a short time. This page explains one thing I tried after reading about a few owners with overheating chorus boards, and other possibilities. In any case, this fan mod should theoretically extend the life of your SS or VH circuits. The first part of this page discusses solving the problem, while the second part delves into the nostalgia and history for those interested in these awesome amplifiers. If you have any wisdom to share to help keep these amps alive, please shoot me an email.

VOLUME LOSS: I had bought a used 1989 SS-140C in 2019, and was 45mins into playing it when the volume began to repeatedly dip and return like a water swell (similar to a modulation pedal that is underpowered). Forum searches had me blaming the cliff jacks (plug a single patch cable into the loop to diagnose/remedy this; clean the jacks) 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. It seemed the open air was apparently enough for the chorus board to radiate excess heat away. However, I had noticed this area of that particular board had a subtle discoloration to it and now the two ceramic resistors there were very hot to the touch - Ampeg did cut holes in this circuit board directly under these large, white resistors to allow heat to radiate off, but maybe it just wasn’t 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 does not appear to be as simple as just leaving the chorus effect off.

* this cooling mod was unsuccessful, but I hope it will help to keep the remaining circuits in good health longer.



COOLING OPTION: 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. 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 chassis’s 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 settled on 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 automatically switches polarity, so assembly will be fool-proof. I opened this adapter using a Dremel to cut a notch along the seams, then inserted and twisted a flat head screwdriver to break the housing open. The circuit board layout of this supply was not as compact as the previous one I had chosen, so things were going to be a little tight when mounting it inside the chassis.

* I originally started with one of those crumby BluCoil 9V 670mA pedal supplies. It will work, but the nine volts didn't spin the fan fast enough for my own liking. 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 ordered the Noctua NF-A6x25 FLX computer fan, which is rated for DC12V at 0.12A (120mA). This very quiet fan will 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 where the power cord exits the chassis because of this fan’s 25mm thickness.

After taking reference pictures of the circuit boards for reassembly, I removed the Ampeg’s 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 didn’t 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 that’s a fairly easy swap if I ever change my mind. Why the upgrade to 16AWG? Mainly because I couldn’t 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 appear 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 amplifier's built-in courtesy outlet wasn’t long enough and I didn't want to extend 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 cord’s cable gland between the common ground hole and the original bridge rectifier hole. I was careful with placement of this gland, as I didn’t 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 hole between the new common ground and the old power cord hole - this would have alleviated all 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 cord’s pass through hole.

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

For the new fan hole, I used a 2.25” Milwaukee Dozer hole saw centered within the rear chassis’s 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 chassis 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 7/32”. 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 “sealed” chassis. So, I’ll 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” 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 built-in courtesy outlet.

For the hidden exhaust ports, I chose to put two 1.75” holes in the bottom of the metal chassis, near the front corners. First, I moved the Caution label (advises what fuse to use) to sit 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 standard 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. The fan was noiseless at 9V, but because the fan spins faster at 12V, I was able to hear it if sitting 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. The fan seemed to have helped, but not completely - I still noticed the volume dip and swell on occasion, but the difference was not as dramatic as it once was.



OTHER REPAIR OPTIONS: The cooling didn't fix the issue, but it was still likely heat-related. Something was on the brink of failure and enough heat build-up would push it there. I dug some other possibilities up after I sold my SS, just in case it ever happens to my beloved VH. Some people have blamed the ICs (Integrated Circuits) in the preamp circuitry and I found a page for trouble-shooting them here. I had eventually discovered that I could eliminate the issue if I bypassed the preamp (just plug the guitar into the effects return), so maybe this was my problem?

One of the more common things I have seen over the years that cause solid state amps to fail is the power amps. For some reason, this is why some claim to avoid them - but from what I can tell, it is repairable. I read a few forum posts that I hadn’t seen before by someone who lived in St Louis and knew a few former-SLM engineers. They told him that the volume swell is commonly caused by the stereo circuitry, where one of the two power amps begins failing. I'm an electronics noob, but I believe the suspect parts ("power amps") would be the two MJ15001 NPN and two MJ15002 PNP transistors soldered to the power amp board. The original ones used by Ampeg are Motorola that were made in Mexico. Here is a video I found showing how to replace them.

(not mine)

Sometimes, like in the above photo, the boards fry (note the four power amp transistors). I have run across a few people that have etched their own replacement boards for these amps! A guy name John Heisz built a VH clone from scratch and posted his efforts on diyAudio here and here. John even shows us how to print our own boards here - John's site, and all of his projects, are incredible!

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 it’s 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 it’s 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 wasn’t 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.
John Heisz discovered a possible misprint on the chorus board schematic. The pic below is the issue, and this is his version of the board. Note that a pro might be able to find the correct circuitry on the SS schematics above.

MANUALS: Here are the original owner’s manuals for the SS-140C and the VH-140C.


FINDING VALHALLA: My first amp and a broken hardshell case were thrown in with a used 1984 Squier Strat purchase when I was sixteen. That guitar was (still is) pretty nice, but that practice amp was a total piece of shit. It was supposedly 5watts of rock and roll sadness. It sounded awful, so was no fun.

Approaching my twenties, I of course assumed more wattage meant better sound ...simple math. There was this Ampeg VH-140C with the standard Ampeg-Eminence speakers listed in the newspaper classifieds. I can’t for sure remember how much I paid for it, because sometimes I believe it was $550. But I'm thinking there’s no way I saved that much! Maybe it was $350? It was in perfect condition and remained that way for as long as I, and my buddy, owned it. I wouldn't I realize how fantastic this particular amp was until decades later ...I naively thought all name brand amps sounded this 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 ‘59 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. At least I felt I was nailing the tone of 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 never really a metal guy 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 Ampeg nostalgia. I learned of the SS-140C* in September 2019 and this broadened my Craigslist search, immediately stumbling onto a decent 1989 SS-140C with original footswitch that I drove 75mins to and haggled down from $280 to $220. Back home, I placed an Ibanez TS7 and an MXR M108 in the effects loop, then dimed the gain. Instantly, I had the tight tone I always wanted. My mistake twenty years ago was not buying an equalizer to fine-tune the signal for maximum crunch. A seagull EQ pattern on my M108 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 and responsive chug of a solid state amplifier is what my ears crave. And the stereo sound? God Mode! I became smitten and my beloved 1992 Peavey Ultra 120 wasn’t being played much anymore. By late 2019, I had also acquired a near-mint 1997 VH-140C head for $400. Shortly after that, I took up playing bass, sold the SS and Ultra, but kept the VH.

* 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. 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 found a 1997 VH-140C head locally for $400 in October 2019 (comparison below).

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. 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, my SS-140C combo seems to do the opposite and loses a bit of volume when the chorus in engaged. Even odder, running the SS through the stereo 412 cab, the volume difference is almost negligible when the chorus is engaged. What the? Who knows?! 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).

The VH sounds slightly tighter and 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. This may be why my SS produces nicer, more natural sounding harmonics. It could just be my particular amps, but the reverb on my SS has more hiss than my VH, which gets more noticeable as it is dialed up - it is tolerable at my preferred 6, though. Could I have lived without the VH? Certainly, but this is nostalgia for me and I do like it's tightness and stereo chorus better. Do I want to sell my SS, now? No way, it's still fun to mess with and, at times, I prefer the tone of the SS's Channel A. I think the SS is 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 channel. I have found both to be exceptionally pedal friendly.

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-capable 412 (or add a mono 212) and an EQ pedal. For something uniquely spectacular, I ran an effects chain with this setup that included a DigiTech Drop (set to Oct+Dry) between the guitar and input, then my DigitTech Polara (set to Spring), and MXR M234 Analog Chorus in the loop - all this doubling beefed the texture up even more to sound like a giant, angry, beautiful robot.

ALTERNATIVES TO THE VH-140C: For me, it is the simultaneous wet and dry signals that push the incredible tone to the next level, so I prefer something that has the stereo chorus. That would make the SS-70C and SS-140C the next best thing, with just a little less brutal of a preamp. Forgoing the additional circuitry of stereo awesomeness, the VH-150, the SS-70, or the SS-150 might be more reliable options. Frankly, without the stereo option engaged, I find the tone to be one-dimensional and uninspiring.

There are quite a few Crate heads and combos that possess a preamp that many claim sound very similar to the Ampeg VH-140C. Identifying reliable information is difficult, but the Crate GX-130C is the one that most often pops up as being the closest equivalent. It is said to be muddier (also described as “less focused”) than the Ampeg, but it does have the dual power amps with onboard chorus. The G130C XL and G40C XL seem to be very similar, also with stereo outputs and chorus. Following that, the VTX200S appears to be the latest dual-amp offering that might get you the stereo and chorus VH sound. The Crate XLP Preamp is supposedly the GX-130C preamp circuit in rackmount form, but you’d need a stereo power amplifier (or two power amps) to get the jaw-dropping wet/dry stereo effect.

Other Crate amplifiers that have been mentioned to contain preamps similar to the VH series, but are not stereo-capable, are the GTX3500 Tidalwave and VTX350. Those two models have DSP chorus circuits, but lack stereo, so there is no benefit to the onboard chorus circuit. There are two more amps that are rumored to have a VH-esque preamp, but do not have stereo or chorus, and they are the GT3500 Shockwave and the G1500. As mentioned, more reliability is a supposed benefit of a stereo-deficient alternative.

Note that a Crate model that ends with an “H” is a head version.

If stereo isn’t a priority (even though it should be to witness the true greatness), the best option might be running a VH-clone pedal into a power amp. There is the PLX FX Spirytus, SNK VHD, Master Effects Misanthrope, Berserker Dead Ringer, thiSHEAvyearth Flesh Rot (tweaked a bit), and GUPtech VeJ1, which all replicate the Variable Harmonic distortion circuit of the VH-140C's Channel A and can be used as preamps. These are popular and highly-rated alternatives for those not able to find, afford, or have room for an actual VH. I bought the PLX FX Spirytus pedal to try and I got a very accurate VH sound - albeit, it didn’t deliver me to Valhalla since the pedal lacks the simultaneous wet and dry signals of the real deal. Running the Spirytus between my guitar and my VH, I could not tell the difference between a dry Channel A on the head and the engaged pedal.

SPEAKERS: One thread that I saw claimed an SLM rep from the 1990's stated that any Crate or Ampeg combo/cabinet that didn't have Celestions in it from the factory, had speakers outsourced through Eminence. 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 (again, manufactured by Eminence). Remember that the "C" stood for chorus and not Celestion.

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 brittle 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.

CrankyGypsy (established 2001)