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Kotrach

DT25 class A/B mode volume issue

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Hi Guys, I wrote hoping someone can answer my question.

 

I have a DT25 combo that i bought 2nd hand, I had to replace the stock power tubes and put a pair of JJ. I don't remember how it was before because there was a considerable amount since I played on that amp... Well, Class A mode sound louder (huge difference) than Class A/B (and it supposed that A/B are 25 watts and A 10). Anyone as any idea that what could happened? Class A/B mode sounds loud as I remember class A/B mode, but brighter... and class A/B almost a 1/3 lower than A at the same volume...

 

I think that is not right... but I don't remember which mode sounded louder before...

 

Suggestions?

 

 

Sorry if I wrote something wrong, English isn´t my primary language. I'm from Chile.

 

Thanks!

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If you bought it second hand the previous owner may have loaded other than the default power amp configuration in program slots I-IV and those amps may no longer reflect the default programs and be louder than expected.

Suggest you do a DT reset to go back to the factory configuration. See instructions below (from L6 DT Amp MIDI Implementation Guide)

 

DT Amplifier Factory Reset

As mentioned in the above sections, when customizing any settings via MIDI, your changes remain “saved†internally on the DT amplifier. This includes changes made to the preamp and power amp per Voicing switch value, Reverb and more. To return all settings back their factory default state, you’ll need to perform a “Reset†of the DT amp. To perform the Reset, start with the DT amplifier powered “Off,†then simultaneously hold the Voicing toggle switch DOWN and the Pentode/Triode toggle switch UP while powering the amp “On.†Continue to hold these toggle switches in this position until you see the Voicing “I†indicator light up (this takes about 15 seconds). The DT factory default settings are then fully restored and your DT amp is ready to play.

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I think A/B is the lower wattage, class A is a lot louder on mine as well. Definitely take the time to tweak the onboard setup with DTedit, makes the standalone amp use a lot better. Load your favorite amp rigs on the eight channels.

 

Remember, you are defining the configuration for each, including topo I-IV. If you set them all to topo II in DTEdit, when you toggle between channels I-IV using the amp controls, it will all be topo II. So it's worth dialing around the "behind the scenes" options.

 

Some must be controlled using MIDI, others can be tweaked on the fly. You can tweak A to A/B and pentode-triode on the amp itself. You must use MIDI to change boost on or off, and the topology setting for each amp model.

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I think A/B is the lower wattage, class A is a lot louder on mine as well.

 

On both the DT25 and DT50 amps, the class A operational mode is lower wattage than the class AB mode.  Here is an excerpt from the Sweetwater Tech Tip blog (http://www.sweetwater.com/insync/class-vs-class-ab-guitar-amps/) that summarizes the differences between class A and AB amplifiers.

 
 
Class “Aâ€
Advantages:
  • The tube is ready to amplify the signal at all times.
  • The signal is instantaneously amplified because the tube does not have to “wake up" from a less than full operational state.
  • A 30 watt Class “A†amp will sound louder than a 30 watt Class “AB†amp.
  • Because current is maximum at all times, the amp will have a smooth compression.
  • There is not a lot of headroom because of the lower plate voltages used in Class “A†amps.
  • Instantaneous amplification and smooth compression make for an amp that is responsive to the touch: the amp feels good and playing it is a satisfying experience.
  • Combined with EL84’s in push-pull operation, the amp will emphasize high order harmonics and the amp will “singâ€.
Disadvantages:
  • Maximum current at all times means that the tubes are being strained even without playing.
  • Shorter tube life.
  • Lower power rating than a Class “AB†amp with the same tube configuration.
  • Power transformer needs to be upgraded in order to handle the high current demands.
 
Class “ABâ€
Advantages:
  • Longer tube life because the tubes are “idling†with lower Plate Current.
  • Higher power ratings with the same tube configuration.
  • More headroom.
  • Tighter bass response.
  • Less continuous demand on the power transformer.
Disadvantages:
  • Not as “responsive†as a Class “A†amp.

 

 

 

Cheers!

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