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Crate BX-15 Amp Repaired

By on July 2, 2018
tl072cp ic amplifier repair











crate bx15 amplifier repair

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.

crate bx15 amplifier repairing

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.

crate bx15 amplifier fix

how to repair amplifier

The previous two photos show the tags on the back of the power supply housing for those that are interested.

speaker checking

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.

speaker 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.

testing speaker

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.

transformer internal fuse

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.

checking amplifier

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.

2200 filter capacitor

three potentiometer

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.

tda2030 ic

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.

original potentiometer

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.

50k pot

In the photo above you can see the part number of the original 50K volume control Pot and the rust all over it.

amplifier fix and repair

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.


tl072cp ic

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.

troubleshooting amplifier

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.

troubleshooting amplifier ic problem

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.

checking transformer linear

The board and transformer are installed back into the housing.

amplifier circuit board

Here is a broader view.

connector to speaker

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.

Please leave any comments or suggestions that you may have below. Thanks!

robert calk junior

Robert Calk is a hobbyist from the USA who loves Electronics, Leatherworking, and Watchmaking.

Please leave any comments you have below. Thanks.

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Please check out his previous repair article below:




  1. Riaan

    July 2, 2018 at 7:49 pm

    Good work man. I have repaired my fare share of crate amps. Honestly I hate the build quality.
    I Have also used the NSL 32's with great success.

    • Robert Calk Jr.

      July 3, 2018 at 3:52 am

      Thanks Riaan. I agree with you but considering how inexpensive that they are, you can't expect a whole lot. It sounded better than I expected.
      The new Vactrol seems to work fine so far.

  2. Parasuraman

    July 2, 2018 at 8:07 pm

    Excellent! Very meticulous and thorough work. Very informative and detailed article. Thanks for sharing!

    • Robert Calk Jr.

      July 3, 2018 at 3:53 am

      Thanks Parasuraman.

  3. J Denmark

    July 2, 2018 at 8:30 pm

    Smart using rodico to hold that in place so you could solder the other side.

    • Robert Calk Jr.

      July 3, 2018 at 3:59 am

      Thanks J Denmark. Rodico works great, cleans whatever it touches, and doesn't leave any residue.

  4. Mark

    July 2, 2018 at 8:50 pm

    Great job Robert.
    Hopefully you were able to clean up the 'puke' on the board. It made a real mess and looks pretty crusty! Well done on the adapting of parts.

    • Robert Calk Jr.

      July 3, 2018 at 4:03 am

      Thanks Mark. lol
      I'm not sure what it was, maybe soup, but it looked nasty. I cleaned most of it off - it had been in there for quite some time.

  5. albert van bemmelen

    July 2, 2018 at 9:24 pm

    Interesting read and like always nicely detailed with those text balloons Robert. It has become your good article trademark. Those Vactrol VTL5C7 components are new to me. About quality sockets I believe they are called machine IC sockets. The expensive quality sockets have cilindrical (female) inserts that fully enclose any inserted IC pin/leg.

    • Robert Calk Jr.

      July 3, 2018 at 5:00 am

      Thanks Albert,
      I try to write decent articles. I think I learned something about Vactrol's years ago, but forgot about them and just assumed the VTL5C7 was a regular opto-coupler. But it's ok, I have some extra Vactrol's now and the next time I need one I won't have to wait for them to be shipped to me.

      My machine IC sockets are called, "Hi Reliability" sockets. I didn't use one of them for this Crate amp, but the socket I used is supposed to be better than the plain jane ones. They have been doing a good job so far.

      I used them for my Blue ESR and Blue Ring Testers and other devices. They definitely looked better than the sockets that came in the kits. The sockets that came with most kits that I have purchased over the years went straight into the trash.


    July 3, 2018 at 1:37 am

    Hi Robert,

    an interesting article however, I personally avoid IC sockets as, regardless of their quality, they introduce un-reliability. A properly soldered component will always be more reliable and particularly where it could be exposed to vibration as in a speaker cabinet.

    • Robert Calk Jr.

      July 3, 2018 at 9:13 am

      Thanks Anthony. You make a valid point. I like to test things, so we will find out how well the socket performs. So far I haven't had any problems with my IC sockets.

  7. Humberto

    July 3, 2018 at 4:19 am

    Great job Robert. You dedicated too much time in this mending and the result was 100% satisfactory. Congratulations.

  8. Robert Calk Jr.

    July 3, 2018 at 9:22 am

    Thanks Humberto. It just seems like a lot of time. The Amp got put aside a few times for other things.

  9. Yogesh Panchal

    July 3, 2018 at 2:27 pm

    Good Detailed article & investigation work!
    Thanks for Sharing.

    • Robert Calk Jr.

      July 3, 2018 at 7:46 pm

      Thanks Yogesh. The Amp should perform great for many more years.

  10. Julian Valls

    July 4, 2018 at 3:08 am

    i have enjoyed and learn a lot with this repair. I didn´t know this Vactrol.
    Big shout from Spain 🙂

    • Robert Calk Jr.

      July 4, 2018 at 2:52 pm

      Thanks Julian. I'm glad that you enjoyed it. Thanks for commenting!

  11. Tyrone

    July 5, 2018 at 8:42 pm

    Very good repair Robert I enjoy your articles and superb pictures.

    • Robert Calk Jr.

      July 5, 2018 at 9:45 pm

      Thanks Tyrone. I appreciate you taking the time to comment!

  12. Gary Gemmell

    July 6, 2018 at 9:03 am

    Very informative and well detailed article with great photos.

    • Robert Calk Jr.

      July 6, 2018 at 11:37 pm

      Thanks Gary. I'm glad that you enjoyed it.

  13. Ulises Aguilar

    July 6, 2018 at 9:42 am

    Mr Calk grate job Sir

    • Robert Calk Jr.

      July 6, 2018 at 11:38 pm

      Thanks Ulises. I appreciate you taking the time to comment.

  14. Andrea Del Corso

    July 8, 2018 at 12:44 am

    Very good article...complimenti!

    • Robert Calk Jr.

      July 9, 2018 at 10:10 pm

      Thanks, Andrea. I am glad that you enjoyed it.

  15. Tito

    July 26, 2018 at 10:47 pm

    Robert, i just found out that I have finished reading. The repair story is too interesting. I have learnt about vactrol, something I was ignorant of.

    • Robert Calk Jr.

      July 28, 2018 at 3:13 am

      Thanks Tito. I'm glad that you enjoyed my article. I had read about Vactrol's before, but that was the first time that I remember seeing one.

  16. Jeff

    November 30, 2018 at 12:42 pm

    Hello Robert.

    How did you get to the speaker? The back of my BFX15 does not appear to be removable and there are no visible screws.



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