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Manual for Professional Series amps

Front panel features

Power: Turns the amp on or off.

Standby: A secondary “power” switch. First the power switch is turned on, the tubes are allowed to warm up for a minute, then the Standby switch is turned to the “play” position (up). This ensures tube elements reach proper operating temperature before use. When turning the amplifier off, turning off the Standby switch first and waiting 30 seconds before turning the Power switch off ensures no noise from the relay supply discharging and changing channels/masters as the power is removed.

Damping: This control changes the overall amount of output damping. Less damping (clockwise) gives a more aggressive/deeper sound while more damping (counterclockwise) gives a softer/mellower sound. This helps tailor the response the amp achieves with different speaker cabinets, or to compensate for different acoustic environments.

Depth: Extra bass response generated by the output section of the amplifier instead of in the preamp. Allows for an extra dimension of bass response tailoring and is especially useful to help attain a “big sound” at lower to moderate volumes. Balancing this control with the Damping, Presence, and preamp’s EQ can allow for more tight/focused sounds or more warm/rich sounds; for instance, turning the channel’s Bass control down and turning the Depth up provides a more rich overall sound without getting very percussive in the low frequencies.

Presence: Extra treble response generated by the output section (poweramp) of the amplifier instead of in the preamp section. Its range starts in the range of a channel’s “High” control and extends beyond to allow for a sharper overall sound and more treble clarity. This control, along with the “Depth” control, helps shape the overall sound and response of the amplifier to a specific cabinet and acoustic environment. The first 2/3 of the range is gradual, making its setting easy without the amp suddenly becoming bright sounding. The last 1/3 of its range is more drastic a change, for those who want a lot of brightness from the amp.

The above three poweramp controls should be used cooperatively to achieve good balance. For instance if the bass response is too pronounced but you still want the amp to sound warm, turn the Depth up and the Damping down, then turn the presence up to add some extra sharpness if desired (and to the extent you want).

Master Volume: Overall volume controls for the amplifier (footswitchable on Professional Series dual channel and triple channel amps). These also act as the effects loop return volume level.

Channel switch (Professional Series dual channel amps): Changes channels when the footswitch isn’t connected. Set to Channel 2 (or the clean channel) when using the footswitch. Professional Series triple channel amps have channel switches on the back of the amp near the footswitch jack itself.

Channel Volume: Volume controls for each channel. These also act as the effects loop send level control.

Channel Low, Mid, High controls: EQ with a very wide range of friendly, useful operation.

Gain: Preamp gain controls for both channels.

Crunch switches: These switches change the voicing and feel of the channel’s gain structure, adding more saturation/crunch.

For the Vega channel, the Crunch switch adds some more punch in a particular way, which is well suited to vintage-sounding lower output pickups which otherwise might sound weak (this crunch switch functionality is unique to the Vega design, since people seeking the Vega’s sounds are more likely to use more vintage-based pickup designs than they are to use very strong high output pickups); you shouldn’t have to use very powerful pickups to get the Vega to respond strongly when you use its Crunch switch. Note: the Crunch switch won’t add more saturation for the Vega channel, and the effect it has (adding more punch) might not be noticeable unless you’re using more vintage sounding pickups. It’s a subtle thing.

Edge switches: The Edge switch of an overdrive channel adds more aggression, changing the sweep of the gain control for a more percussive/aggressive sound/feel and a somewhat more focused attack (similar to using a “clean boost” pedal with the amp, but more natural sounding/feeling). For the clean channel the Edge switch generally functions as a “bright” switch. The Edge switches have less effect when the gain is turned up high, so if you want a somewhat warmer response with more saturation (but less aggressive attack), turn the Edge switch off and turn the gain up a bit. For a tighter sound, try the Edge switch on but the Gain turned down below 12 o’clock (and turn on the Crunch switch to compensate if you want).

Back panel features

Footswitch: The amp’s footswitch plugs into this jack. A switch on the front allows for manual selection of channels when a footswitch isn’t connected. Set the switch to “Channel 2″ (or the clean channel) when the footswitch is connected to allow the footswitch to function.

For Professional Series triple channel amps, there are two channel switches by this jack instead of on the front panel. The switch on the left changes between the two overdrive channels (up is for Channel 1, down is for Channel 2), and the switch on the right changes from the clean channel to the overdrive channels (up is for overdrive, down is for clean). Put both switches in the “up” positions (Channel 1, overdrive) for the footswitch to function. (Note: a few of the first Professional Series triple channel amps from 2011/2012 don’t have manual channel switches like this, and require the footswitch to be connected to change channels. Without the footswitch connected, the amp would default to Channel 1 and Master 2.)

Effects: Loop for effects (after the channel Volumes, and before the Master volume). Works well with pedal or rack effects.

Slave out: Provides signal to “slave” another poweramp, or for use in direct recording (when you use a speaker simulator). The signal is taken from the output of the amplifier, and stepped down to a reasonable (line) level. The setting of the Master Volume will determine the signal level as well as the level of the control at this jack. For more info see the notes about the amp’s usage. This feature is not present on Professional Series single channel amps.

Speaker Outputs: Five jacks allow for parallel connection of two separate cabinets (at either 8 or 16 ohms each), or a single load of 4, 8 or 16 ohms. Not intended for using loads of different impedances. Choose one overall impedance and connect one or two cabinets for a proper match, as the markings beneath the jacks indicate.

Bias test points and bias adjust: Using a regular volt meter and small screwdriver, the amp can be biased for replacement output tubes quickly and easily without opening the amplifier. There is a small access hole for the easy-to-adjust 15-turn bias potentiometer and three pin jacks for testing the bias setting during adjustment.

PS Response (wide/normal): Subtly changes the response of the amplifier in terms of its power supply to provide a more “normal” (focused) or a more “wide” (broad) responsiveness. This feature is not present on Professional Series single channel amps (it’s hard-wired internally to the “wide” setting only).

PS Response (modern/vintage): This feature gives the amp’s output some “sag” normally characteristic of using a tube rectifier in a design, but without requiring a tube rectifier. “Modern” has a more forward/punchy sound/feel, while “Vintage” has a warmer more relaxed sound/feel with less “forward” sounding midrange. This feature is not present on Professional Series single channel amps (it’s hard-wired internally to the “modern” setting only).

Fuses: To protect the amp in case of internal component failure (usually a failure of an output tube).
Fuse ratings (100W version, North American models): 3A slow acting (mains), 750mA (3/4A) fast acting (HT). All fuses are rated for 250V.

Power inlet: For a standard detachable IEC type power cable.


Notes about the amp’s usage

All Peters amplifiers use 12AX7 / ECC83 preamp tubes. You can also try a 12AT7 in the phase splitter socket instead (the socket right next to the output tubes); a few Peters amp owners like using a 12AT7 for the phase splitter for a somewhat “tougher” sound/response.

The amps are biased for the output tubes included with it, so biasing after receiving the amplifier isn’t necessary. However, you’ll want to get familiar with the biasing instructions for when you eventually need to bias the amplifier:

Biasing your Peters amplifier

It’s really easy to do, and only takes a couple minutes. Biasing is necessary when replacing output tubes (which typically wear down or fail within a few years of use). Even when you replace output tubes with ones of the same brand/type, you should at least check the bias (since chances are it’ll need to be biased).

As for an initial recommended setting, try this:

-the Master volumes at their minimum setting,
-the channel Volumes around 10 to 11 o’clock,
-Crunch/Edge switches off,
-Depth at its minimum setting,
-Presence at its minimum setting,
-“Modern” and “Wide” Power Supply Response (on the back of the amp)
-all other controls at 12 o’clock

Adjust from there. This setting is a good starting point for dialing in the sound for most people since it’s relatively even/flat and not too aggressive for the “middle ground” of what each channel is supposed to do. As you adjust each control it will become apparent what it does. Finding specific sounds you prefer the most will probably take a while but you should get very good results quickly if you start with this recommended setting. There’s also more information on some control settings below.

The PS Response switches make the most subtle changes in the sound; the controls on the front are the most important ones.

Be careful using both of the overdrive channel’s Crunch and Edge switches in the “on” position with loud volume because feedback will be harder to avoid. It’s doubtful you’d want to set a higher-gain overdrive channel’s Gain that high with a Master also set high, but it’s worth warning about in advance. The Crunch and Edge switches make an overdrive channel noticeably more aggressive when they’re turned on, so start with the Gain set low and only use as much as you need (especially when turning the amp up really loud).

Use the channel Volume controls to set your effect send levels since they’re just before the effects loop’s send. When using pedals in the effects loop, a setting of channel Volume up to the 12 o’clock is good for an overdrive channel, with the clean channel’s Volume control possibly being set higher (depending on the gain settings of the clean channel). If using rack effects devices, you may want to set the channel Volume higher, but the internal settings of the rack effect (input/output sensitivity/levels) might allow for adjustment to a lower level, so consider this first since it will keep setting the volume levels simpler for all devices (especially if you think you may use pedals and rack effects in the loop at the same time). Somewhat lower settings of the channel Volume (9 to 10 o’clock for instance) for the overdrive channel can help keep the sound more even and focused, which some people really like. The two overall Master controls are after the effects loop, so they are considered the effects return levels as well as the overall volume controls of the amp; start with the overall Master controls turned down all the way, then gradually increase their settings to the volume level required of the amplifier.

Remember that the Master volume controls are meant to control the overall volume of the amplifier. With some other amps it might make more sense to use the channel volume controls to control the overall level, but not with Peters Professional Series amps. Find the channel Volume settings you prefer, then use the Master volume controls to change the volume. Things will be easy that way and the sound will be more consistent at different volume levels.

For the Damping and Depth settings, it’s a good idea to start with the recommended settings above. You might be tempted to turn them up higher at first, but their ranges were designed to provide flexibility with various guitars/speakers/etc. and generally speaking it’s not necessary to use these controls with very high settings (especially at very high volumes). The Depth control “fills out” the low end to make it more “broad” but not really more “deep”; increase the Damping to get a deeper bass response, and increase the Depth to get a more “filled-out” bass response. Getting “the right kind of bass response” for your tastes can be a matter of using the Damping, Low (in the channel itself), and possibly also adjusting the channel Volume settings higher or lower. Sometimes turning the Damping down is a good way of starting to get a “thicker” sound despite it having less bass than a higher setting (since it makes the sound more “rich” in a way); adjust the Depth and Low control to compensate for that aspect of the Damping control’s setting. Keep an open mind before deciding which setting of a particular control you prefer “overall” since you might be revisiting it later and using it in a different way.

A higher setting of the channel Volume for an overdrive channel will make the sound more punchy/full, which you may not want (too much can make the sound less “tight”), so start at around 10 to 11 o’clock (for an overdrive channel), and you can expect your maximum desired setting to be around 12 o’clock. The channel Volume settings between 12 o’clock and maximum are more useful for: cleaner sounds (of a clean channel), and/or helping get a correct level for some “line level” rack devices which want to see a stronger signal level.

Keep in mind if you want the sound “fatter” you don’t have to rely on channel Volume control settings; the Damping and Depth controls work well for that.

Depending on how you want to use the clean channel (for cleaner or dirtier sounds), you’ll have to adjust its channel Volume with respect to the overdrive channel’s Volume control. Setting the channel Volume controls to about 10 to 11 o’clock is still a good starting point. If you dial in a very clean sound on the clean channel (using really low settings of its gain control), you may end up with its channel volume set to around 3 o’clock. This is basically acting as though it were a “non-master volume” clean amp, best for the cleanest sounds the channel can produce. Here’s how to do it: turn the clean channel’s Gain control down, turn the channel Volume up high (around 2 o’clock), and use the Gain control of the clean channel to increase the volume level of the channel. This makes the channel function like most dedicated “clean amps” that have no overdrive to speak of, keeping its headroom very clean. You can also set the clean channel’s Gain higher for more drive/crunch, and set its channel Volume lower such as you do with an overdrive channel (to balance out its volume with an overdrive channel).

If you prefer using your bridge pickup for overdrive and the neck pickup for clean, you’ll probably prefer using the clean channel set like a “non-master volume amp” with its Edge (bright) switch on. That will help compensate for the extra fatness of a neck pickup and provide more chime.

Conversely, if you tend to keep the guitar on the bridge pickup all the time, you’ll probably prefer the Edge switch of the clean channel turned off.

When using the clean channel as a “non master volume amp”, the Crunch switch will increase the mids and provide a stronger overall punch while keeping the channel sounding relatively clean; this is a setting you might like for a more “driven bluesy” sort of clean sound. And don’t forget to try the clean channel as a normal master volume amp: set the channel Volume set lower (10 to 11 o’clock), and set the Gain high for more overdrive. It can achieve excellent classic/blues crunch, and when using overdrive pedals it sounds excellent for rock.

A note about using overdrive pedals with the amp: remember that the Edge switches are meant to give a “boosted” sort of sound already. When using overdrive pedals in front of the amp, it will probably seem excessive in some upper mid frequencies if the Edge switches are left on. I recommend turning them off when boosting the amp with overdrive pedals. Either that, or the pedal’s tone control may have to be turned down a lot to compensate.


About the “slave out” and direct recording, with a few general warnings/notes first:

*Be sure to keep your speaker cabinet connected to the Peters amp as usual when using the slave out or when direct recording. If you want to record silently, use the effects send so you can turn the master all the way down (but still get signal from the preamp to record). Always leave a speaker load connected to the amplifier.

*Don’t connect the slave out to the effect return, directly or indirectly, since this will result in extreme feedback and damage to the amplifier. The slave out signal is not meant to return to the Peters amp.

*Regular instrument cable (with 1/4″ mono ends) is recommended for use with the slave out.

The slave out’s signal is taken from the speaker output and stepped down to line level. Because of this it contains the entire sound of the amplifier itself in all its settings (including poweramp controls and power supply option settings). This can be used to drive another poweramp (for “cloning” the sound of the amp to a separate poweramp and speaker cabinet), or for direct recording (if you add a speaker simulation after the recording).

That being said, the effects loop’s “send” jack works well for direct recording too, sounding nearly as good (as long as a speaker simulation is added, of course). The sonic response of the poweramp can be emulated with various compressors in software. Recording the amp via the effects send allows you to keep the signal to the recording strong, while turning the amp’s volume all the way down (from the speaker cabinet) by turning the master volume control down all the way (silent recording).

To slave another poweramp, just connect the slave output to another poweramp’s line-level (or preamp) input. (The poweramp will of course have to be connected to a guitar speaker cabinet, just as the Peters amp will have to remain connected to a guitar speaker cabinet.) Adjust the slave out’s level control to help achieve a balance of volume between the Peters amp and the slaved poweramp since their output levels may not match. As you increase the Peters amp’s volume, the level at its slave out will increase as well. The control knob for the slave out is a way of ensuring you always have separate control over the signal level going to the “slaved” poweramp, so the “slaved” poweramp won’t receive too much signal. Since the entire sound of the Peters amp is at the slave out, slaving even a very transparent poweramp should provide excellent sound.

When slaving a second poweramp, you can also add line-level effects between the slave out and the “slaved” poweramp’s input since the slave out is at line level.

For direct recording to a computer using the slave out or effects send, if you plan to use a speaker simulator (impulse response, etc.) in your computer, it works very well. If you decide to record this way and want some tips, let me know and I’ll be glad to help.