Where To Get Bass Amp Repaired

Kustom Groove 1200 bass amp repair

A client dropped this bass amplifier off for repair. It had been at another repair shop. They weren't able to repair it.

roove 1200 bass amp repairing

Upon assessment I establish that the input strain relief was missing.

I wasn't able to discover a suitable size strain relief to fit the rather huge hole so I decided to fit an IEC connector socket. Looks meliorate to me anyhow.

kustom groove 1200 bass amp fix

After:

kustom groove 1200 bass amp fix and repair

I slowly applied power to the unit of measurement with my Varaic and Isolation transformer. Luckily it didn't draw much current. I likewise checked for DC get-go on the speaker output.
All these tests turned out to be good.

I then practical a 440Hz sine wave to the input of the amplifier and while monitoring the output with a telescopic. It soon became credible that the clip limiter excursion wasn't working.
This circuit limits the power amplifier stage output signal to prevent clipping.

kustom groove 1200 bass amp fix and repairing and fix

I confirmed this by applying the aforementioned signal to the fx loop return socket.
Looking at the schematic I could come across that the amplifier stage uses a CA3080 Transconductance amplifier IC. These IC's are obsolete and are hard to become. This must be why the other shop declined the repair.

power ic photo

A bit of research found that there are a couple of Transconductance amplifier IC'due south bachelor. One of these is the LM13700. This is a 14 pin device and has iv single amplifiers in the same package.
I apace drew up a double-sided pcb on Easy PCB to accept the 14 pin device and some PCB header pins to have the 8 pivot DIL space on the board. I used only ane of the amplifiers within the LM13700 and plain the supply pins.

power board amp repair

I also found that all five of the front end panel potentiometers were faulty. I somewhen decided to replace these as the original pot wafers were all cracked.

bad vr in amplifier

bad vr in amplifier repair

I had to cut the shafts slightly shorter as the ones I had were longer. The unit was reassembled and tested. Hither 1 can encounter the max output bespeak into a 4ohm load. (1kHz). This confirms that the limiter is working. Shown: 53,78V RMS. This amounts roughly to 723 Watts.

rms waveform

brymen 869 meter

I cleaned all of the controls, switches and sockets. Closed the unit up and informed the client that his unit was ready for drove.
If someone is interested in the PCB layout, they are welcome to contact me.
Happy repairs.

This article was prepared for you by Riaan Diedericks. He runs his own electronics repair shop in Pretoria, S Africa. He specializes in Pro Audio repairs. Delight give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.

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You tin also check his previous repair article below:

https://jestineyong.com/master-smps-transformer-overheated/

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