sunn 200s looping each imput

[EdBass]

It would not surprise me, particularly if input 1 it used consistently, keeping its contacts clean, while input 2 sits idle while oxides slowly build up. Otherwise, I have to believe that two identical inputs have significantly different electrical characteristics for some other reason. Possible, but what might those reasons be?

Absolutely. I was just posting a nearly identical response, and got the "while you we're typing" warning.
Carbon resistor drift is the only other thing I can come up with, but I agree that it would be possible; however unlikely to be as obvious as Dylan describes

[loudthud]

A 200S I bought on ebay some years ago had been modified. The 68K resistors were changed to 47K and one of them had a .001uF cap connected across it. Made a barely audible difference.

[EdBass]

A 200S I bought on ebay some years ago had been modified. The 68K resistors were changed to 47K and one of them had a .001uF cap connected across it. Made a barely audible difference.

A "bright" mod?

[loudthud]

A 200S I bought on ebay some years ago had been modified. The 68K resistors were changed to 47K and one of them had a .001uF cap connected across it. Made a barely audible difference.

A "bright" mod?

Yes, a feeble one. I bet you'll remember this amp. It's 120W on a 200S chassis. Not done very well on the inside and there was a small fire. I'm waiting for a rainy day to re-cap it. Got some polypropylene caps for it but I need to make a small circuit board to hold them and the rectifiers, and it needs a Hammond Choke. Was thinking about trying to eliminate all the electrolytics.

[EdBass]

A 200S I bought on ebay some years ago had been modified. The 68K resistors were changed to 47K and one of them had a .001uF cap connected across it. Made a barely audible difference.

A "bright" mod?

Yes, a feeble one. I bet you'll remember this amp. It's 120W on a 200S chassis. Not done very well on the inside and there was a small fire. I'm waiting for a rainy day to re-cap it. Got some polypropylene caps for it but I need to make a small circuit board to hold them and the rectifiers, and it needs a Hammond Choke. Was thinking about trying to eliminate all the electrolytics.

Is that the one that might have been a 2000S prototype? Why am I thinking that was a Spectrum II chassis, or am I thinking about a different amp?
I would love to get a peek at a small chassis 120 watter, have almost pulled the trigger on a couple of Coliseum PA's just to check out the layout up close!

[Happy Face]

Checking in late on this one, but ....   my 200s also has a noticeable difference between the inputs. #2 has less gain and I use it exclusively because of that.

Or, I should say "used" since I am selling it. 

[Isaac]

I wish you people who insist that your inputs are different would open them up and try to find out why they sound different.

[Soundmasterg]

The inputs on a 200S are just like many of the classic Fenders....the # 2 input has 3dB less gain than the #1 input.

If you plug into input # 1 the 1M to ground comes first, with the 68k connected to the grid. If you plug into input # 2, the signal goes through the first 68k resistor to the tube's grid. With nothing plugged into input jack # 1, its 1M resistor is shorted out and its 68k resistor is connected to ground. This is the same as a 136k pot turned down to the 68k point, or halfway off. This loses half the input signal, or a 3dB loss. If you plug in two instruments, one into each jack, then the 1M resistor is back in circuit and both inputs revert to full gain.

If you plug into input # 1, there is a 1M input impedance. If you plug into input # 2, there is a 68k input impedance. The 68k input impedance loads down the output of the pickup more than the 1M impedance does, and the pickup will react to different input impedances differently too since it is a reactive device. So it makes perfect sense to me why the tone would change if you plug into one input or another input. The low gain input has always sounded dull to me in comparison to the high gain input, probably because there are less highs. Its the same kind of thing when matching up a microphone to a preamp...especially with ribbon mics. Many of them are very low gain and they need a boost, but the input impedance of the mic preamp can make or break the sound of the whole system. That is why the better makers put a variable input impedance in their mic preamps.

Greg

[Isaac]

That is not what the schematic I have indicated, nor is it in accordance with my experience. The schematic shows both inputs going through 68K resistors to a common point, where the 1M resistor goes to ground. What you describe might be true for the 2000S, but not, in my experience, of the 200S.

[loudthud]

The amps in question could have been modified, or there could have been a factory change. Below is the 190B schematic. There are some interesting changes including the input jacks.

[Soundmasterg]

That is not what the schematic I have indicated, nor is it in accordance with my experience. The schematic shows both inputs going through 68K resistors to a common point, where the 1M resistor goes to ground. What you describe might be true for the 2000S, but not, in my experience, of the 200S.

you're right Isaac, I should have looked closer at the 200S schematic before I posted..... The way they have the jacks connected there, they are both in parallel to the grid, so each one is the same and should have the same gain unless there is a jack problem with the amp in question. I don't have a 200S anymore so I can't open one up to look at it and compare to the schematic. The 2000S is much the same as that but there are 4 inputs. Two have a cap in parallel with the input resistor for a brighter tone, and two don't for a "normal" tone. The 2000S uses 47k resistors too instead of the 68k in the 200S.

Greg

[Isaac]

And this is why I'd like those who perceive a difference to find out why it exists. Have the amps been modified? Did Sunn change the circuitry and not tell anyone? Are the contacts oxidized? Inquiring minds want to know!

[EdBass]

My money is on oxidation.