What does the +6db input on my amp do to boost the signal? (Schematic attached)

[Dave Locher]

Can someone look at this schematic and explain to me in straightforward terms what the hi input does to the signal to boost it?
*
Changing the speakers in my cabinet altered my sound more than I expected and I have been messing with how I use my 1978 Randall RG100ES (solid state) in a way I haven't experimented since I bought it around 1988. I have discovered that the high input, labeled "+6db" on the amp, not only boosts the gain but also adds some treble. I also figured out that something is switching because the boost kicks in when I plug any cable into the hi input even when my guitar is plugged into the lo ("+0db") input. I like knowing how everything I own works and might possibly try to get the boost without the added bite but mainly I just want to understand what is happening in there.


Double bonus if someone can spot what happens when you pull out the push/pull treble pot! (Adds clipping diodes?)

 

[Adieu]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Thats not a readable resolution schematic

And what it does, if it actually is a +dB input, is run it through/engage an additional opamp chip vs. When only the normal inout is used

 

[Artie]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

That's interesting, because the "Lo" input is typically 0db, (as you have), and the "Hi" input would -6db. In other words, something like a PAF would go into the Lo input, and a high output pup, or actives, might go into the Hi input. But I guess there's no convention here.

And 6db is either a doubling or halfing of the voltage depending on whether or not it's plus or minus db.

 

[Dave Locher]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Sorry about the resolution - I have a really hard time attaching images with my phone. I just Googled "rg100es schematic." It is easy to find because it was part of the two-page owners manual.
The high input definitely says "Hi +6db" and the other is marked "Lo 0db".
Do I understand you correctly that an op amp is doubling the input voltage before it gets to the preamp? Sort of like a full-spectrum boost with no eq control?

 

[Adieu]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Sorry about the resolution - I have a really hard time attaching images with my phone. I just Googled "rg100es schematic." It is easy to find because it was part of the two-page owners manual.
The high input definitely says "Hi +6db" and the other is marked "Lo 0db".
Do I understand you correctly that an op amp is doubling the input voltage before it gets to the preamp? Sort of like a full-spectrum boost with no eq control?

There's simply no other way to increase signal strength in an SS amp

 

[Dave Locher]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Here is a link to a high-resolution pdf:
https://el34world.com/charts/Schematics/files/randall/Randall_Schematics.htm

 

[Dave Locher]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

There's simply no other way to increase signal strength in an SS amp

So would running an eq or od pedal into the Lo input with roughly 6db boost give me the exact same result but with control over the eq of the boosted frequencies?

 

[Adieu]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

So would running an eq or od pedal into the Lo input with roughly 6db boost give me the exact same result but with control over the eq of the boosted frequencies?

Well, yeah.

Different opamp chips have different flavors and EQ changes everything again though

 

[Dave Locher]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Thank you for the info!

 

[Artie]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Ok. Thanks for that link to the larger schematic. This is totally conventional. Labeling may not be. Refer to this segment of the schematic:



And bare with me. (Bear with me?) It's late, and I'm on my eleventy-seventh glass 'o wine. (J/K)

If you plug into "Hi 1", your 1/4" plug pushes the "tip" connector away from that ground connection. So you have a 68k resistor in series with your guitar signal. Since resistors "resist" current, and not voltage, there's virtually no affect given the 1meg input impedance. It's like that 68k resistor isn't even there.

Now, suppose you plug into the "Lo 2" input. Your signal is going through two 68k resistors which go to ground. The signal to the amp is tapped off from the middle of that voltage divider. Ergo, you've cut the input voltage to the amp in half. That's a -6db attenuation.

So, if you have "normal" low output pups, like PAF's, plug into "Hi 1". High output pups or actives, go into "Lo 2". But there's no rules here. Try either with both.

Make sense?

Artie

Edit: And just to be somewhat technically accurate, when you plug into "Hi 1", you do have a voltage divider with 68k on the top of the divider and 1M on the bottom. The attenuation is like a gnats arse.

 

[Dave Locher]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

So the low input is actually cutting the signal by 6db and the hi input is not? As opposed to the high input truly boosting it?

 

[VinceT]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

So the low input is actually cutting the signal by 6db and the hi input is not? As opposed to the high input truly boosting it?

Yup


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[Dave Locher]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Yup


Sent from my iPad using Tapatalk

So Randall has been lying to me for most of my adult life?!? Bastards!

 

[Demanic]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

So Randall has been lying to me for most of my adult life?!? Bastards!

As long as it still sounds good, and you know how to use it, does it really matter that much?

Sent from my Alcatel_5044C using Tapatalk

 

[Artie]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

So the low input is actually cutting the signal by 6db and the hi input is not? As opposed to the high input truly boosting it?

So Randall has been lying to me for most of my adult life?!? Bastards!

Well . . . you can't really say that. Suppose you design the amp with "X" amount of gain. It sounds sweet when clean. Then, you boost the gain x2 and insert a "normal" input that cuts the gain by 2. The normal input gives you the clean that you wanted, and the "Hi" input gives you a true boost. Albeit with sneaky marketing. They didn't lie to you. They just configured their circuit differently.

 

[Dave Locher]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

As long as it still sounds good, and you know how to use it, does it really matter that much?

Sent from my Alcatel_5044C using Tapatalk

No, man, I was joking. It rocks.

 

[Dave Locher]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Bonus round: how about the pull switch on the treble control? It drastically cuts volume on the red channel and increases gain. Clipping diodes??

 

[dystrust]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Bonus round: how about the pull switch on the treble control? It drastically cuts volume on the red channel and increases gain. Clipping diodes??

Yes. Toward the lower right portion of the red channel schematic are D5 and D6 which are normally floating, while pulling the 'sustain' switch on the treble knob connects the ground.

 

[Jacew]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

Well . . . you can't really say that. Suppose you design the amp with "X" amount of gain. It sounds sweet when clean. Then, you boost the gain x2 and insert a "normal" input that cuts the gain by 2. The normal input gives you the clean that you wanted, and the "Hi" input gives you a true boost. Albeit with sneaky marketing. They didn't lie to you. They just configured their circuit differently.

Really that is lying. If they spesifically say +6db boost. It doesn't do that. It's -6db cut on normal.

It doesn't matter if it practically works just as well. That's false marketing.

 

[devastone]

Re: What does the +6db input on my amp do to boost the signal? (Schematic attached)

It's very similar to the way the high and low inputs on old Marshalls works, same values, but slightly different config.