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Re: Schematic Accuracy [message #20189 is a reply to message #20097]

Wed, 19 February 2014 13:20

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Resistors R180/R181 and R190/R191 are dropping resistors used to reduce the 40 volts down to a level that will make it easier for the pass transistors to regulate the 8 volts needed by the preamp circuits.

Rather than use a larger wattage resistor they opted to use two smaller resistors in parallel. The value really shouldn't be that critical as the regulator circuitry ultimately controls the final output voltage.

The added circuitry around Q131 is a non-inverting buffer that amplifies the straight signal before it is mixed in with the reverb signal at the reverb depth control. The depth control is actually more like a balance control: CCW straight signal only, CW reverb signal only. This is why when the reverb tank is bad and the reverb signal is not present, the depth control acts like a volume control.

It may be that originally there was not enough straight signal to mix with the reverb signal and keep the overall volume up to spec.

As for the earlier resistor replacement, it's not just the 1% resistors that can change things. Is it possible that you put a wrong value in there? Or swapped the position of two resistor values?

If it was working before the resistor swap, then there is reason to believe that the problem was created by the change. Go back and check what you can, and see if there is anything that seems wrong.

Did you replace a lot of transistors as well? If you did, there may have been a change in the gain of a stage or something that has caused the new problem.

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[Message index]

		Schematic Accuracy By: bluezebra on Mon, 10 February 2014 01:29
		Re: Schematic Accuracy By: stevem on Mon, 10 February 2014 06:30
		Re: Schematic Accuracy By: bluezebra on Mon, 10 February 2014 10:19
		Re: Schematic Accuracy By: bluezebra on Mon, 10 February 2014 10:26
		Re: Schematic Accuracy By: chicagobill on Mon, 10 February 2014 12:40
		Re: Schematic Accuracy By: bluezebra on Mon, 10 February 2014 13:00
		Re: Schematic Accuracy By: stevem on Mon, 10 February 2014 13:17
		Re: Schematic Accuracy By: bluezebra on Mon, 10 February 2014 13:41
		Re: Schematic Accuracy By: chicagobill on Mon, 10 February 2014 16:24
		Re: Schematic Accuracy By: bluezebra on Mon, 10 February 2014 17:10
		Re: Schematic Accuracy By: bluezebra on Mon, 10 February 2014 17:33
		Re: Schematic Accuracy By: chicagobill on Tue, 11 February 2014 12:22
		Re: Schematic Accuracy By: bluezebra on Tue, 11 February 2014 13:25
		Re: Schematic Accuracy By: stevem on Wed, 12 February 2014 09:26
		Re: Schematic Accuracy By: bluezebra on Wed, 12 February 2014 12:55
		Re: Schematic Accuracy By: stevem on Wed, 12 February 2014 17:08
		Re: Schematic Accuracy By: bluezebra on Wed, 12 February 2014 17:20
		Re: Schematic Accuracy By: bluezebra on Wed, 12 February 2014 21:22
		Re: Schematic Accuracy By: chicagobill on Thu, 13 February 2014 10:43
		Re: Schematic Accuracy By: bluezebra on Thu, 13 February 2014 13:57
		Re: Schematic Accuracy By: chicagobill on Thu, 13 February 2014 14:40
		Re: Schematic Accuracy By: bluezebra on Thu, 13 February 2014 15:20
		Re: Schematic Accuracy By: bluezebra on Thu, 13 February 2014 15:25
		Re: Schematic Accuracy By: chicagobill on Thu, 13 February 2014 16:14
		Re: Schematic Accuracy By: bluezebra on Thu, 13 February 2014 17:39
		Re: Schematic Accuracy By: bluezebra on Thu, 13 February 2014 19:36
		Re: Schematic Accuracy By: bluezebra on Thu, 13 February 2014 22:03
		Re: Schematic Accuracy By: bluezebra on Thu, 13 February 2014 22:40
		Re: Schematic Accuracy By: chicagobill on Fri, 14 February 2014 13:04
		Re: Schematic Accuracy By: bluezebra on Fri, 14 February 2014 22:38
		Re: Schematic Accuracy By: stevem on Sat, 15 February 2014 07:43
		Re: Schematic Accuracy By: bluezebra on Sat, 15 February 2014 10:28
		Re: Schematic Accuracy By: bluezebra on Sat, 15 February 2014 12:11
		Re: Schematic Accuracy By: stevem on Mon, 17 February 2014 06:33
		Re: Schematic Accuracy By: bluezebra on Mon, 17 February 2014 11:07
		Re: Schematic Accuracy By: bluezebra on Mon, 17 February 2014 11:33
		Re: Schematic Accuracy By: chicagobill on Mon, 17 February 2014 13:25
		Re: Schematic Accuracy By: bluezebra on Mon, 17 February 2014 14:20
		Re: Schematic Accuracy By: chicagobill on Mon, 17 February 2014 14:54
		Re: Schematic Accuracy By: bluezebra on Mon, 17 February 2014 16:56
		Re: Schematic Accuracy By: bluezebra on Mon, 17 February 2014 17:14
		Re: Schematic Accuracy By: bluezebra on Mon, 17 February 2014 17:36
		Re: Schematic Accuracy By: chicagobill on Tue, 18 February 2014 12:24
		Re: Schematic Accuracy By: bluezebra on Tue, 18 February 2014 13:31
		Re: Schematic Accuracy By: bluezebra on Tue, 18 February 2014 13:37
		Re: Schematic Accuracy By: chicagobill on Tue, 18 February 2014 13:58
		Re: Schematic Accuracy By: bluezebra on Tue, 18 February 2014 18:25
		Re: Schematic Accuracy By: bluezebra on Tue, 18 February 2014 20:53
		Re: Schematic Accuracy By: chicagobill on Tue, 18 February 2014 21:38
		Re: Schematic Accuracy By: bluezebra on Tue, 18 February 2014 23:15
		Re: Schematic Accuracy By: bluezebra on Tue, 18 February 2014 23:17
		Re: Schematic Accuracy By: chicagobill on Wed, 19 February 2014 01:44
		Re: Schematic Accuracy By: bluezebra on Wed, 19 February 2014 10:32
		Re: Schematic Accuracy By: chicagobill on Wed, 19 February 2014 11:13
		Re: Schematic Accuracy By: bluezebra on Wed, 19 February 2014 12:21
		Re: Schematic Accuracy By: chicagobill on Wed, 19 February 2014 13:20
		Re: Schematic Accuracy By: bluezebra on Wed, 19 February 2014 14:02
		Re: Schematic Accuracy By: bluezebra on Wed, 19 February 2014 14:05
		Re: Schematic Accuracy By: chicagobill on Wed, 19 February 2014 17:06
		Re: Schematic Accuracy By: bluezebra on Wed, 19 February 2014 23:21
		Re: Schematic Accuracy By: stevem on Thu, 20 February 2014 06:49
		Re: Schematic Accuracy By: bluezebra on Thu, 20 February 2014 12:03

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