Crate BX-15 Amp Repaired
My son owns this Crate BX-15 30W Amplifier and was hoping that I could repair it for him. He said that it works, but the sound is low and it will not get loud. So I brought it home to see what I could do. The Amp is designed for a bass guitar, but my son uses it for his electronic drum set that he uses for practice. I figured that maybe there was something wrong with the volume potentiometer (Pot).
So let’s check it out.
Looking at the Amp from the back we can see that we have to remove the speaker wires from the speaker and pull them up through the hole in the speaker cabinet before we can remove the power supply housing and look at everything.
The previous two photos show the tags on the back of the power supply housing for those that are interested.
Someone has had the speaker out before it was handed to me. We know that because they hooked the wires up to the speaker backwards. You can see the “+” and “-“, markings on the speaker better later in image# 24.
I disconnected the speaker wires and carefully fed them up through the hole in the speaker cabinet so I could remove the power supply housing and begin the repair.
Here is a good photo of the speaker. I do not know if it is the original speaker or one that someone else has put into the Amp. But everything that I have seen indicates that the Amp should have had a custom Crate 8 inch 30W speaker inside it.
I do know that the owner’s manual says that if you plug an external speaker into the external speaker plug on the front of the Amp next to the power switch, the impedance of the external speaker must be 4Ω or greater. The speaker in the cabinet is a 3.2Ω. Hopefully the speaker will perform well in the little Crate Amp.
My Brymen BM869s is reading the resistance of the Peavey speaker at 2.91Ω. Hopefully it will be ok and perform well. Everything else about the speaker seems fine. The magnet is strong and I see nothing wrong with the speaker.
The transformer checked to be fine. It seemed a little weak using my Blue Ring tester, but that isn’t very unusual. The transformer has a built-in thermal fuse that is good. I’m going to operate on the premise that the transformer is good.
The above photo is the last image I took before I removed the transformer and board out of the housing. You can see the two 25V, 2200µF filter capacitors.
Three of the 50K Pot’s checked to be in pretty good shape. I decided to use one of them for the volume.
Here is the original Audio Amplifier Part# TDA2030 that I’ll replace with a newer one that can handle more power. It’s hard to know how much it has been used. It is probably still good but since they are not too expensive, the Amp will be more dependable with a new Audio Amplifier installed.
Here I have the new Hi-Fi Audio Amplifier Part# TDA2030A and the new 50K potentiometers installed onto the board. The new Audio Amplifier will handle 18W where the original was only rated for 14W.
The new 50K Pots are made by or for Fender amplifiers, Part# 0038655000. They are the only ones that I could find that matched the original Pots.
My guess is that whatever was spilled into the amp got onto the 50K volume Pot. You can see the rust and corrosion all over it. It was ruined inside as well. The new Fender Pots have center detentions which is not really suitable for the volume control.
So I used one of the original 50K Pots that looked and checked to be good to replace the volume control Pot with, after cleaning it with some good electronic cleaner.
In the photo above you can see the part number of the original 50K volume control Pot and the rust all over it.
AliExpress was the only place that I could find an original VTL5C7. I bought a couple of them. I’m sure this Amp is not the last one that I repair and they may come in handy in the future.
The two above photos are of the Vactrol Part# VTL5C7. The Vactrol is an Opto-Isolator (Coupler) that has the LED on one side like usual, but the other side has a photocell (LDR). So you can’t check the photocell like a PN junction.
I didn’t realize it had a photocell at first and thought it was bad, but it checked to be ok. I found a replacement Part# NSL-32SR3 from Allied Electronics and ordered it before looking at the datasheet. They weren’t very expensive, but checking the datasheet first would have been the best thing to do.
You can see one of the new Vactrols soldered into the board a couple of photos down. I forgot to take a close-up photo of it. I decided to see how well the new Vactrol will perform in the Amp.
I decided to solder in an 8-pin DIP socket for the Op-Amp to make future replacements a snap. I normally do that for all Op-Amps because I hate to have to remove a board just to replace an Op-Amp. Plus Op-Amps are inexpensive and plentiful so it makes sense to use sockets. I also pay a little more to get better quality sockets.
Here you can see the new Pot’s on the board as well as an original Pot in for the volume control. I’m using Rodico to hold the new Vactrol down so I can flip the board and solder the leads.
The board is nearly finished and ready to be reinstalled into the housing.
Here you can see that I am reinstalling the board back into the housing. You can see the new Vactrol that is installed onto the board.
The board and transformer are installed back into the housing.
Here is a broader view.
Here I’m hooking the speaker up and putting it back into the cabinet. You can see the “+” and “–“, markings where the wires are supposed to be connected.
I took the Amp to my son’s house and he hooked it up to his electronic practice drum set. The Amp sounded great and was loud and clear! This repair worked out great. I hope you guys enjoyed the article.
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Robert Calk is a hobbyist from the USA who loves Electronics, Leatherworking, and Watchmaking.
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Please check out his previous repair article below: