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Challenger Reverb Problem [message #27115]

Sat, 01 December 2018 17:16

ARKustom
Messages: 37
Registered: January 2014
Location: United States

Member

I just got one of these and can't get the reverb to work. When I bought it the reverb only made a loud hum when the knob was turned up, so I got the guy to come off the price. When I opened it up to clean and inspect connections, one of the reverb springs was loose. The ferrite beads were loose in the reverb pan, so I bought a replacement pan. I got it today and connected it, still no reverb. It will crash, so the output works, The background hum increases when the reverb knob is turned up (not like the loud hum before), but there is still no reverb effect. Any ideas? It seems like none of the signal is getting diverted through the reverb tank.

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Re: Challenger Reverb Problem [message #27116 is a reply to message #27115]

Sun, 02 December 2018 06:22

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

If you have or can get your hands on a voltmeter set it fior D.C. Volts and see what you read when you hook it up across the RCA jack that goes to the input side of the pan.
You should read near zero, if you do not then the two section IC chip ( I1A and I 1B ) is bad on the I1A side of it.
Please report back on this test.

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Re: Challenger Reverb Problem [message #27118 is a reply to message #27116]

Sun, 02 December 2018 14:54

ARKustom
Messages: 37
Registered: January 2014
Location: United States

Member

I got a reading of 9.8v.

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Re: Challenger Reverb Problem [message #27120 is a reply to message #27115]

Sun, 02 December 2018 22:25

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Seems like the chip is bad.

You also need to be certain that the input jack of the replacement tank has its ground connection isolated from the metal case, as the input coil is part of the feedback loop of the op amp.

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Re: Challenger Reverb Problem [message #27121 is a reply to message #27120]

Tue, 04 December 2018 18:17

ARKustom
Messages: 37
Registered: January 2014
Location: United States

Member

The tank has insulated input and grounded output. I suppose I'm going to need to find a suitable replacement chip.

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Re: Challenger Reverb Problem [message #27122 is a reply to message #27115]

Tue, 04 December 2018 21:16

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

The chip is a 5558 dual op amp. You can use almost any modern 8 pin dual as a replacement.

1458, TL072, 4560, etc.

Have you tested the two 12 volt power supplies?

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Re: Challenger Reverb Problem [message #27123 is a reply to message #27122]

Fri, 07 December 2018 12:18

ARKustom
Messages: 37
Registered: January 2014
Location: United States

Member

Cool, thank you for the replacement info.

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Re: Challenger Reverb Problem [message #27124 is a reply to message #27122]

Fri, 07 December 2018 12:19

ARKustom
Messages: 37
Registered: January 2014
Location: United States

Member

I haven't tested the power supplies.

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Re: Challenger Reverb Problem [message #27125 is a reply to message #27124]

Fri, 07 December 2018 12:56

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

I'm not saying that this is your problem, but if one of the two low voltage supplies is low, it can cause strange things to happen to on the outputs of op amps.

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Re: Challenger Reverb Problem [message #27204 is a reply to message #27125]

Sat, 23 February 2019 16:04

ARKustom
Messages: 37
Registered: January 2014
Location: United States

Member

Well, I finally got around to opening this amp up. The chip that it came with is already a LM1458. I had also ordered some LM1458's, but there's a problem. The ones that I ordered are tiny compared to the stock chip. I did make sure to get non surface mount, though. What's a good source for the full sized LM1458's?

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Re: Challenger Reverb Problem [message #27205 is a reply to message #27115]

Sat, 23 February 2019 21:31

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

I'm not sure that I understand what you got instead of the standard 8 pin DIP style case. The correct type would be an LM1448-N, or whatever 5558, TL072, etc. N should be a standard 8 pin DIP.

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Re: Challenger Reverb Problem [message #27227 is a reply to message #27205]

Wed, 03 April 2019 23:26

ARKustom
Messages: 37
Registered: January 2014
Location: United States

Member

I think they just sent the wrong thing. I ordered a couple of National Semiconductor LM1458N's from eBay and popped one in this afternoon. The reverb works great now.

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Re: Challenger Reverb Problem [message #27228 is a reply to message #27115]

Thu, 04 April 2019 06:14

stevem
Messages: 4773
Registered: June 2004
Location: NY

Senior Member

great to hear, congrats!

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