While still waiting for parts to arrive for the Ampeg SVT4-Pro, I set that aside and moved a new client's Fender Vibrolux Reverb combo up to the check-out bench. Noisy and intermittent fuse holder are a couple of the symptoms, so removed the upper rear panel to carefully extract the chassis from the cabinet. Famous last words with so many of the Fender Combo amps I receive. I got the chassis two thirds of the way out before it locked up tight. The chassis width and the cabinet inside width are just tight enough for the sides of this folded chassis to grab hold of the inside Tolex flaps of the ..read more

I have had a couple of speaker failures in a bass rig but I don't know if the problem I'm having is an amp problem or a speaker/enclosure problem. I have a regular jam with some friends and for a bass amp I use my Ibanez Promethean 300 watt 1x10 combo. The internal speaker doesn't give enough volume, so I use an external 1x15 speaker box (homemade) that belongs to one of the other guys. In this configuration I am running the external 8 ohm in parallel with the internal speaker (which is a dual coil speaker that will be 8 ohm when using an external speaker). I don't think the amp does 300W RMS ..read more

I own this Crate amp, and at a rehearsal, I was playing normally with it, and suddenly it started stuttering and after a few seconds, went completely silent. Later I took it home and opened to see if I could spot some damage. Saw a lot of oxidization around a specific IC, proceeded to clean that with isopropyl alcohol and a toothbrush. After thorough cleaning I turned it on to test it. The amp appeared silent, except I could hear a very faint hum, I touched the speakers with my ear, and played my guitar, and I could hear the guitar. So, I tested all the amp's controls, and all of them worked ..read more

I am working on an amp for a friend of mine. I already repaired the amp and brought it back to stock. He wants the amp to be cleaner and a bit louder. For example, the amp starts distorting at 5. He wants it to distort at 7. When he has the bass tone cranked the amp starts to flub out. My guess is the only thing to do is to get a more efficient speaker that can handle more wattage. Then change out the bias resistor to make the bias a bit more negative. I also might change out the capacitor on the bass tone to cut some of the lows. What are your thoughts ..read more

while working on my 25yr old car (305k!) I ran across a very comprehensive repair guide for automotive electrical harnesses and connectors that was compiled by the premier Japanese Manufacturer, Toyota. Since similar connectors have become common in musical equipment I thought some might appreciate it here, enjoy the 451 pages of overkill ! https://www.toyota-tech.eu/wire_harness_rm/RM06H0E.pdf ..read more

I don't do much SMD, but occasionally I will. My Weller soldering station stopped getting hot. I tried a new soldering pencil, but it made no difference. Then I found a pretty easy possible fix, replacing a 2.2uf cap that is known to fail. My question is how the original caps are marked. They are small aluminum can caps with a black stripe down about 1/3 third of the top surface. I have read in several tutorials that the stripe marks the negative side, and maybe just as many saying it points to the positive side. Can you gents say with authority which side the black stripe is pointing to ..read more

Hi folks. I've got an early 80s JC-120 that gates the Chorus/Vibrato effect at lower volumes. I've had this problem for years, and finally found an example of someone who had the same issue managing to mod theirs successfully, over at this thread (https://music-electronics-forum.com/...nel-2-behavior) What I'm wondering is, how could I find the equivalent points of D15 and B3 in my version of the amp? Or if it's even possible to do this mod to mine in a similar way. My version is this one - https://music-electronics-forum.com/...etch?id=969647 Any help or advice would be much appreciated, th ..read more

I'm presently servicing an Ampeg SVT4-Pro that has significant distortion in the Vactec-based Limiter in the front end of the Power Amp Circuit. It uses a Vactec VTL-5C7 in the feedback loop around an inverting 6dB gain stage ahead of the op amp that drives the output stage. The LDR portion of the Vactec is switched in using a J176 P-Ch FET. When I turn the limiter off, allowing the amp to clip, it sounds fine, other than you can drive it into clipping. With the limiting stage in circuit (normal operation), it's preventing full output and does appear to be where the distortion is occuring. I ..read more

Gday , i am a hobbiest luthier in Auckland Nz. I had a mooer preamp live blow up on me. I managed to repair it by replacing blown capacitors. It worked fine for a while and then I sold it. The buyer said it arrived not working so I refunded him the purchase thinking it was going to be an easy fix after he described the symptoms. I found another popped cap and replaced it but the unit is still faulty. I believe I've traced the issue to the dc-dc voltage converter wra1209cs-1w. A Google search for this part led me to this forum where this part was used in a Mooer red truck. The issue with the un ..read more

I am working on a 1975 Silverface Fender Princeton Reverb. These amps never had grid leak or grid stopper resistors. Should I add them or "not fix anything that is not broken ..read more