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need help with onboard preamp

brstma

brstma

my dog is an awesome dog
Supporting Member
Nov 20, 2008
1,139
1,073
Florida
soundcloud.com
#1
I just picked up a used Bart HR 5.4 AP / 918 preamp here on talk bass. I am replacing a Bart MK1 active preamp, pickups are MK1

After studying the wiring diagram I found several wires had been wired incorrectly previously. The previous owner had it installed and removed by someone else and doesn't know why the wiring might be different.

So, I proceeded to rewire it as the wiring diagram shows since I know nothing about modding electronics.

Now I get sound in passive mode only, but EQ controls do not have any effect on the sound. Blend and vol work as it should. It has bass, mid, mid select switch, and treble controls

I get no sound when in active mode.

I've checked the wiring several times and I'm sure it's done as the diagram shows. Now I'm assuming that the preamp was damaged from being wired incorrectly before. I paid $130 for it, it's $200 new, so I don't want to spend more money to get a tech to check it and tell me it's no good.

Can anyone advise how I can test the preamp module?
 
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#2
As a test, wire it exactly like the link below shows (temporarily bypassing the active/passive bypass switch (which is connected to a pot). The yellow should come directly off the Blend control pot to the preamp module. Wire the green output wire directly to the volume pot. You can do this by removing these wires from the push/pull bypass switch and twisting them together. Also, insure the red battery + wire goes directly to the preamp module and the black wire to the output jack (I like to use the ring for battery - and the preamp ground on the sleeve connection on the output jack) .
Insert the guitar cable plug and if it still doesn't work then make sure your guitar plug is making contact with the tip, ring, and sleeve. It turns on the preamp by shorting the ring terminal to the sleeve completing the connection from the battery - to the preamp ground (black wire to module.
Invalid Link Removed

If it works then either you have a bad passive/active bypass switch or it is miswired. If it does not work then your module has problems.
 
#3
brstma said:
Now I get sound in passive mode only, but EQ controls do not have any effect on the sound. Blend and vol work as it should.
Click to expand...

First off, this is the way that it is supposed to work. Passive mode means the preamp is not in the circuit, so the EQ won't do anything.

As for active mode, are you sure that the preamp is receiving power from the battery? Check the current draw with the bass plugged in, and ensure that the preamp is getting power.
 
#4
Thanks, I'll try these suggestions and report back

line6man said:
First off, this is the way that it is supposed to work. Passive mode means the preamp is not in the circuit, so the EQ won't do anything.
Click to expand...

Thanks, I was unsure about that. I hoped the EQ would still function in passive mode just as it would on a completely passive setup. Makes sens that it doesn't since it's on a powered board. I guess these pickups are more responsible for the tone I dislike than the preamp is. Very bright and no bottom end when in passive mode, it was the same with the stock preamp at flat settings
 
#7
brstma said:
Thanks, I'll try these suggestions and report back



Thanks, I was unsure about that. I hoped the EQ would still function in passive mode just as it would on a completely passive setup. Makes sens that it doesn't since it's on a powered board. I guess these pickups are more responsible for the tone I dislike than the preamp is. Very bright and no bottom end when in passive mode, it was the same with the stock preamp at flat settings
Click to expand...

Yeah a completely passive setup wouldn't have an EQ at all, usually just a tone control.
 
#10
I bypassed the active / passive switch and there is still no sound so I guess the preamp is shot. If I hit the strings really hard there is about a half a second of a distorted crackle type sound and then it cuts out. I also tested the jack and it is working as it should
 
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#11
brstma said:
If I hit the strings really hard there is about a half a second of a distorted crackle type sound and then it cuts out
Click to expand...

Sounds like a bad connection- could be the wires that connect to the battery terminals: the wires inside the cap that connects to the battery sometimes disconnect/break from the connector.
If that's the case, it'll work in passive, but only make noise in active when the wires touch the connectors. Wiggle the pigtail while plucking and in active mode. Could be the ground side is loose since you have power to the preamp.
 
#12
I checked everything down the line with a multimeter. All connections are soldered well, no splicing and taping. Battery power is solid into the preamp leads. I already went through every wire wiggling them one at a time too.
 
#13
In case anyone is interested in the way it was wired when I got it:

The brown wire that should be connecting the mid pot to the mid switch was disconnected from the mid switch. The green wire that should be connecting the volume pot to the jack was connecting the volume pot to the mid switch where the brown wire should be. The yellow wire that connects the volume pot to the blend knob was connected to the wrong pin on the volume pot, the other yellow wire was disconnected
 
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#14
brstma said:
In case anyone is interested in the way it was wired when I got it:

The brown wire that should be connecting the mid pot to the mid switch was disconnected from the mid switch. The green wire that should be connecting the volume pot to the jack was connecting the volume pot to the mid switch where the brown wire should be. The yellow wire that connects the volume pot to the blend knob was connected to the wrong pin on the volume pot, the other yellow wire was disconnected
Click to expand...
Let us know how it works out. That is weird
 
#15
LoveThatBass said:
Let us know how it works out. That is weird
Click to expand...

Thankfully, the seller has agreed to a return and refund. He didn't do the wiring and didn't know, and I did mention the wiring issues I saw in a message before attempting to install it correctly. I'm not sure how it was working being wired like it was but I'm not an expert on electronics. I just know 100% I have it wired the way the diagrams show and it works in passive mode but not in active mode.

Now I have the old preamp back in and it's working fine, I'm just not thrilled about the sound. I'm not sure I dislike it so much I'd bother changing it again though...could be the pickups too
 

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