If you have an amplifier you want souped-up, DAR has you covered. With a solid understanding of how amplifier circuits are designed and function, as well as how to modify the circuit to achieve a desired result, DAR can take your stock amplifier and make it a tone monster. From a simple tube voicing, speaker swap, or tone component upgrade, to a full on circuit modification, like adding an effects loop or master volume. Want to get more radical, like class A/AB switchable power section or cascading gain modifications? No problem. From simple to extreme, we do it all.

Adjustable Bias Modification

BiasModThis modification converts a fixed bias amplifier into an adjustable fixed bias. An adjustable fixed bias allows the power tube bias to be dialed in for optimal performance. You would think that every amplifier would have an adjustable fixed bias — many do — but oftentimes this is not the case. Many manufactures have opted for a fixed bias (usually this fixed bias runs the tubes cold) as a safety to prevent the tubes from redplating during the manufacturing process, allowing them a fast plug and play, one-size-fits-all approach.

The other reason for a factory fixed bias is so manufacturers can sell you replacement tubes that have been tested to match the amplifier at a premium cost.

Changing your amplifier’s fixed bias to an adjustable bias gives you the ability to adjust the current draw for optimal tone and life of the power tubes, with the added benefit of not being forced to use a specific brand of tubes. New tubes will still need to be matched as well, even if using the same type of tubes (changing of tube type is another modification).

In many cases, DAR can modify the fixed bias with minimal or no permanent modifications to the amplifier at all, meaning it’s 100% reversible. So if you have a vintage collectors item, you can get the most out of it while you play it, and when you are ready to sell it the amp it can be put back to bone stock if desired and not affect the value of the amplifier. All parts used are top quality, usually military specification components.

Tone Capacitor Upgrade

tone caps

Most production amplifiers, effects pedals, and commercial guitars are made with a specific price point and the components are bought in bulk and just dropped into place. The tone capacitor modification involves replacing the critical stock tone caps with hand picked components for maximizing your amplifier’s desired tone and response. From changing component material type to component value, DAR can dial in the exact tone you’re looking for.

Noise Floor Improvement (AKA Studio Treatment)

Replacing the electrolytic capacitors with low-noise audio grade components, replacing plate resistors with metal film, and converting the power cord to a 3-prong earth ground connection are all modifications that can dramatically improve your noise floor.

Power Cord Replacement

Grounded Power CordMost vintage 60’s and 70’s amplifiers came with a 2-prong power cord and ground switch which toggled between hot and neutral to a capacitor, commonly known as the “death cap”, grounding to the chassis. This type of connection floats the earth ground and typically results in a much higher noise floor. Another disadvantage is that without an earth ground, you share the ground of the amplifier through your strings, which means you can get shocked. That’s never fun. Because of the potential of conducting electricity into your person, the UL Safety Standards requires all amplifier design manufacturing to now have a chassis connection to earth ground. This modification not only lowers your noise floor, but it can also save your life! The power cord replacement modification involves removing the old 2-prong power cord, removing the “death cap”, and then unwiring the ground switching switch before installing a new, modern 3-prong grounded power cable.

Solid State to Tube Rectification and Vice Versa

IMG_6992Tube rectification is known for “sag” — the way the amplifier responds to the way it charges voltages, resulting in the tone and responsiveness of the playing to be slower. Solid state rectification is fast to charge, so the notes are much faster to show up. Both methods are desired by players for achieving different tones. The limitations for this modification are space and transformer capabilities, and often it requires drilling holes for additional sockets and transformers. Please contact us to discuss this modification in more detail.

For an example, the amplifier in the picture started life as a phono PA. A cascading dual channel guitar preamp was fabricated, the power section was rebuilt to allow for speaker cabinet integration, the rectifier circuit was tailored to guitar voicing, and the entire circuit was restored. Almost every 60+ year old component was replaced, except for the transformers, as well as the addition of an earth grounded power cord.

Power Tube Type Change

This modification is limited by the voltages and amperage draw requirements of the tubes. If you exceed the limitations of the power transformer, you risk damage to the amplifier that can result in costly repairs. If you are interested in changing the type of power tubes your amp is using, DAR will work with you to find a solution that is tailor-made for your amp and application.