Latest posts of: Kri

Quote from: stratohiker on August 30, 2008, 02:57:41 PM

Recently got an OTS in as a chassis. It's sittin' on top of some Shakespeare books on top of an oversized 1 12 cab (open back, HAD style), with a JBL E120 loaded. I'm awaiting the cab for the chassis, etc. Maybe what I'm seeing is by design but, gotta ask.
I'm noticing some, shall we say unconventional things going on with the tone related controls and switches.
1)Overall, I don't see much effect of/by the treble control. I see some in the jazz position. But, nothing in the rock position.
2)The bright switch seems also to have little, to no effect on things in any position unless maybe the presence is wide open.

I guess maybe, if this is all by design, I'm just used to amps with tone controls that drastically affect the sound of the amp in question.

Any input greatly appreciated.

BTW, sure would be nice if one of our more learned brethren would formulate an owners manual for this amp Grin

Owners manual by is-racer April 11:

"Here is a quick guide to the Overtone.

********Front Panel:**********

FET: This input is for an acoustic guitar pickup.
NOR: This input is for an electric guitar

Volume: Sets the amount of gain for the preamp section. Use the "Master" to set overall amp volume. Higher levels of the Volume will distort the 'Overdrive' channel more.

Bright Switch: Adds a treble boost to both channels

Mid Boost: (similar to the bright switch) Functions in both channels; adds some extra kick, especially in the overdrive channel.

Jazz/Rock: The Jazz setting is a quieter, lower gain setting.

Treble/Mid/Bass: These self-explanitory controls function in both channels. They are bypassed with the "PAB" (preamp-boost)

Drive/Ratio: These function only in the "overdrive" channel. The Drive, works in conjuction wth the "Volume" to control the overall gain or distortion. The Ratio is a seperate master volume. To set the Ratio control, go to the clean channel and set the overal clean loudness of the amp with the Master control. Then engage the "overdrive" channel and adjust the Ratio control to get an appropriate loudness of the overdrive channel.

Master: sets the overall loudness of the amp. Raises and lowers the loudness of both channels together.
Presence: Controls the amount of negative feedback. Higher settings reduce negative feedback and give more distortion. Lower settings increase the negative feedback on the power supply and reduce distortion.

********Back Panel ************

Ground Switch: Places a capacitor between one of leads from the mains to the ground. (May not be hooked up)

ON/OFF; Controls power to the amplifier. Make sure the standby is "off" before switching on. If the tubes get fed full plate voltage (over 400v) without being warmed up first, there can be damage to the cathode part of the tube.

Standby; controls the high voltage power to the tubes. Has the effect of silencing the amp. Let the tubes heat up a few moments before disengaging the standby when first powering up.

Fuse: There are two fuses. One on the back panel and another under the chassis. The fuse on the back panel is the 'overall amp current' fuse and should be a slow blow 3A for 120v systems and a slow blow 2A for 220 systems. The other fuse is an extra saftey measure just to protect the transformer and is a lower value (0.5A).

Speaker impedance: 4/8/16 Set this to the amp cabinet or speaker impedance.

Effects Input and output: This is a passive effects loop, There may be gain mismatch between the input of this jack and that of an effects pedal. Try it and see how it works. If you are serious about having an active loop, you can buy or build a Dumbelator which will plug in here and will have its own input/output into which the effects will plug.

PAB and OVERDRIVE switches on back panel: With the foot pedal unplugged, these switches control the preamp boost (which disengages the tone controls for some extra gain) and the Overdrive channel (which adds gain and distortion to the clean channel). So, they would be "ON" when set to "Manual". When the foot pedal switch is plugged in, keep these switches on "Pedal" for correct function with the foot pedal.

**********Inner Potentiometers (trimmers)***************

FET INPUT TRIMMER: located on the board near the FET input. Adjust this to change the gain of your acoustic guitar plugged into the FET input.

OD TRimmer: Located closest to the guitar inputs on the rectangular board. Adjust for the lowest setting that will produce a good overdrive tone.

Phase input trimmer. Located closest to the power tubes. Used to balance the two sides of the phase inverter tube.

Bias Pot and Bias Points: Put a multimeter lead into the red and black jack and set the meter to millivolts. The reading will approximate the milliamp current draw of the tube. Set using the bias pot, set the value to an appropriate level for the tubes installed.

Tube types: The two larger tubes are 6L6. The three smaller tubes are 7025 or 12AX7. "

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