Updated:  December 2, 2010


The purpose of this web page is to provide a convenient collection of web resources for people who are interested in learning about and building headphone amplifiers based on the various Kevin Gilmore schematics that are in circulation on various internet forums. For a newcomer, it can be very time consuming and confusing to understand all of the variations and historical timelines.  It is also challenging to get all the information needed to go about acquiring the latest schematic, bill of materials, bare PCB sources, and assembly guides.  It is important to understand that I am not the original designer of these circuits. Rather I am acting as a well informed curator of the data, documents, important thread links, and sometimes the DIY know-how.  Enjoy the site.


January 26, 2009  Toshiba 2SK109BL and 2SK389BL - My Stock is SOLD OUT! - These parts have been increasing difficult to find from local suppliers in the US.  Recent sources were and  It is widely known that Toshiba has not manufactured these parts for a couple of years, but they have remained quite popular among audio enthusiasts.

Available Now! - 2SJ74BL and 2SK170BL hand matched as pin compatible replacements for the SK109BL and 2SK389BL in the Gilmore designs.
See JFET Replacement Guide for pinout information and installation help.

Available at AMB Audio Shop

Dynalo = (2001-present) - Dynalo is the present day name of the original amplifier that is well documented on the site. The project area on this site is widely regarded as the original mecca of DIY headphone projects on the internet. The project file is a must-read if you are interested in building the amp:  "A Pure Class A Dynamic Headphone Amplifier" by Kevin Gilmore.

The project file talks about the great performance of the amp when using low impedance headphones from Grado, so people think it's only suited for low impedance headphones. Wrong. It drives nearly every dynamic headphone 32-600 ohms quite well.  It remains the least expensive and easiest to build so I guess it is the "low end" of the product family. Hundreds, if not thousands, have been built in the DIY community.  They are also commercially available under the product names Gilmore Lite and GS-1.

The DYNALO Rev C PCB Project:

I got interested in the Gilmore dynamic amp project a couple of years after the initial introduction to the DIY community. So, I was late to the party. Like a lot of folks, I used the project files to make a hand etched version. Many people have built this hand etched board, and a few versions of other fabrication house artwork were available on the various forums, but all of them have faded away.

I decided that there was not a decent PCB for this design that was readily available for purchase as a bare board on the web. Lots of other amp designs were out there, but I like the simplicity and symmetry of the pure class-A dynalo design. With the help of another audio enthusiast, we got the schematic recaptured in Expedition and proceeded to layout a two layer board with more attention to details on the power planes and capacitor arrangements. Basically, we were intentionally re-inventing the wheel and having fun.

DIY Forum Links:
Headwize DIY Workshop Dynalo Rev C - Build Discussion - The most active and best supported thread on the Dynalo Rev C Project.

DIY Build Documents:
Dynalo Rev C - Schematic - Two single amplifiers on one PCB, that can be operated in balanced mode if desired.
Dynalo Rev C - BOM (Excel) , Dynalo Rev C - BOM (pdf)- Bill of Material, Part Numbers, pricing.  C27,C28 to be spec'ed.
Dynalo - Detailed Construction (dgardner 5-7-2005).doc (2.59MB) - a work in progress
Dynalo - Detailed Construction (PARS Edits).doc (2.57MB) - a work in progress
Dynalo - Detailed Construction (STACKOFHAY Edits).doc (2.61MB) - a work in progress
Datasheets - go here to find component datasheets for the amplifier.

Dynalo Printed Circuit Board Sales:
Available at AMB Audio Shop
Dynalo Rev C (stereo) - Topside View
Dynalo Rev C (stereo) - Bottomside View

My Dynalo Builds -  Image Gallery:
Populated Board (jpg) - a populated and tested rev c board.
Board in a Hammond 1455N1601 Enclosure - an example of the simplest application of the board. shown with rev b board.

Outdated but Useful Documents:
After studying the circuit for a while and digging into how balanced designs are made, I wanted to capture a more informative set of schematics that showed how various modes are connected and cabled.  No PCB layout was done for this Cadence schematic. Caution: The reference designators have nothing to do with the Rev C board listed above.

Dynalo Page 1 - Shows the main circuit design, much like the original listed above.
Dynalo Page 2 - Shows the amp's negative feedback, DC offset correcting servo, and connectors
Dynalo Page 3 - Shows single-ended operation connectivity
Dynalo Page 4 - Shows balanced / bridged operation connectivity

Dynamid = (2001-present) - Dynamid is present day name for a balanced Dynalo.  The original Gilmore dynamic amp has a balanced bridge option which added an inverted output stage to each channel. That amp has two input stages and four output stages. The balanced bridge amp only needs an unbalanced source. Two outputs are connected to the left side of the headphone and the other two are connected to the right side. It has twice the voltage swing, twice the slew rate, and four times the total power. A fully balanced amp will have four input stages and four output stages as four separate channels. That is how the balanced dynahi is built and how some of the balanced dynalo amps are built. But it requires a balanced source to drive all four channels.

Prior to the Dynahi release, many people considered this to be "the reference amp". After the dynahi release, the proper place in the pecking order the balanced bridged amp must be "the middle", and therefore people started calling it the Dynamid.  This is an unfortunately misleading name. Dozens, if not hundreds have been built in the DIY community.  They used to be commercially available under the product name Gilmore Reference Amp.

Dynahi = (2003-present) - Dynahi burst onto the scene around Thanksgiving 2003 as an un-named Kevin Gilmore amp. It was designed to deliver much higher power output.  Since Kevin boasted it as being great for the "high volume nuts", and good for the especially inefficient K-1000's, everyone assumed it was for high impedance phones and called it the Dynahi. Or perhaps the high power level helped the name along. Or, perhaps the high performance level helped the name along.  That name is fitting and has stuck.

DIY Build Documents:
Amplifier - Schematic - one captured version of the schematic
Amplifier - Bill of Materials (pdf), Amplifier - Bill of Materials (excel) - second group buy
Power Supply - Schematic - first pass design

Power Supply - Bill of Materials (pdf)Power Supply - Bill of Materials (excel)- first pass design
Datasheets - a complete collection of transistor datasheets and other components.

DIY Artwork Databases: - amplifier artwork release version 5 - amplifier artwork release version 6 - amplifier artwork release version 7 - power supply artwork release, small caps - power supply artwork release, large caps

Dynahi AMPLIFIER & POWER SUPPLY Printed Circuit Board Sales:
Available at AMB Audio Shop
Dynahi AMP (mono), Rev 7, Topside View
Dynahi AMP (mono), Rev 7,  Bottomside View
Dynahi PSU, Large Caps, Topside View
Dynahi PSU, Large Caps, Bottomside View

Dynamite (a.k.a. Dynamight) = (2003 to present) - Oh, and don't forget, if you are insane, you can create a balanced Dynahi, which is affectionately know as the dynamite. Without dumbing the gain down, it melts things. I built one. It's cool.  It has twice the voltage swing, twice the slew rate, and four times the total power. A fully balanced amp will have four input stages and four output stages as four separate channels.  It requires a balanced source to drive all four channels.

My Dynamite Build - Image Gallery:
Here is my first pass prototype of a balanced dynahi.
A, B, C, D, E, F, G, H, I, J

Email: dan -at-