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The "ChipAmp" Amplifier

NEW- UPDATE 5/2005

UPDATE (May, 2005): All pictures reformatted to the native (largest) size that I have.

UPDATE 4/2005

UPDATE (April, 2005): I've changed the internal circuits of this ChipAmp or so called "GainClone" to use premade circuit boards, these were bought from Chipamp.com. The reason for this is that the bass/ low frequency response of the prior version was not as powerful as I would have liked. It is said that simply adding more capacitance to the power supply improves this, but worsens the high frequency characteristics. The boards I bought from chipamp.com attempt to give the best of both worlds, employing a "snubber" power supply with large capacitors, and impedance matching to hopefully retain the nice high frequency respnse. So I was interested in trying this. Also, the chipamp.com boards use a noninverting amplification scheme, versus the inverting circuit I had used previously, I have heard some people mention that noninverting is better in some respects so wanted to try it. At the bottom of the page you will see the different schematics for the inverting and noninverting designs. In addition, Images will now load in a new window.

Features and Changes Implemented In The 2nd Version

The 1st version inverting configuration was changed to noninverting pursuant to the new boards.
The 2nd version is DC coupled, I removed the input capacitors. DC offset went from 25mV/27mV (L/R) to 21mV/74mV (L/R).
Input level (gain adjustment) potentiometers were removed; I had them set to near maximum gain anyway.
The "mute" switch was spun around, so that "mute" is up and "unmute" is down, down is illuminated and up is not.
Nichicon UPW series low impedance capacitors (now lead free) are used on the amplifier boards.
Input resistors are 1% tolerance and feedback resistors are 0.1%, providing a very close interchannel gain matching.
Nylon washers now are installed underneath the heat sinks to raise them about 1/8" which improves airflow and cooling.
3rd PCB is the main power supply (actually 2 supplies for L/R), using MUR820 diodes and Elna for audio capacitors (4x10,000 uF)
4th and 5th PCBs are the LM3886 modules for the L/R channels. Some capacitors are installed on the bottom so that the brass clamping bar wasn't blocked.

Prior Features retained in the new design

Other Features Retained From 1st Version

2 inputs (one balanced)
Differential input recievers (INA134) for differential sources and to buffer single ended sources
1st PCB for LEDs, all voltages and intensities are controllable via cermet multiturn trimpots
2nd PCB is for the differential input receivers and associated low noise power supply.
RCA buffering involves grounding one of the differential inputs via a toggle switch on back panel.
Low noise power supply consists of 4 MUR820FS soft recovery diodes, adjustable Linear Technologies surface mount ultra low noise regulators (LT1964 and LT1962), 3300 uF per rail of capacitance (2200 Panasonic FC); 100 Uf output capacitance per rail (Panasonic FC) with small value bypass caps. Set to positive and negative 9.5 volts DC via trimpot.
Low noise power supply separately fused
Low noise power supply separately switched on back panel
Miniplug connector added to rear panel to accept battery power when low noise supply is switched off or output DC when switched on
Rear panel switches to select XLR or RCA inputs, and to select AC or battery power for 3rd power supply.
Front panel colors/ illumination similar to BOSOZ Preamplifier
Capacitors and large movable components epoxyed to boards to prevent vibration.

Click on Graphic For Zoom	Click on Graphic For Zoom	Description
Finished Front Panel	Angle View	A number of ultrabright blue LEDs indicate operating status of all 3 power supplies. They are rated to operate in the 3 to 5 volt range, and they are all set to about 2.7 volts, which is below their minimum. For some reason they stay lit, and are quite bright.
Front View	Top View	Yellow illuminated switches are NKK CWSC series rocker (on/off) and NKK M2100 series toggle with illuminated tip. Chassis is an old Kyocera CD player that has been gutted with a new face plate added and new side panels created. Got 2 of these (1 working) for $30 on ebay.
Distal View	Rear Panel	Rear panel connectors & switches (right to left): AC fuse on lower right corner (6A fast) Furutech Gold AC inlet Switch for selecting AC or battery power for input stage Neutrik XLR connectors Switch for selecting RCA or XLR inputs WBT RCA connectors Vampire binding posts DC (battery) miniplug under speaker binding posts Not so good file work on top cover The table is a DIY item as well, the side panels of the amp are made of the same black walnut.
Chassis Ready for Construction	Chassis, Bottom View	Note: Pads are for Transformer mounting/ dampening Holes under heat sink locations for ventilation rear panel holes were drilled and then expanded with a file attempt to have screw heads on underneath of amplifier to prevent scraping of underlying surfaces Chassis bottom reveals the many screws and nuts that hold this thing together, lots of drilling.
Faceplate	Basic Installation	Note- Basic stuff you see on everyone’s GC’s . Amplifier Module, Dual Bridge Rectifier 500 VA transformer. 8 diodes are MUR1520 soft recovery. heat sinking the diodes is not necessary, they don’t even get warm. The front panel was made by Front Panel Express and cost about $35.00. I designed it using their software, emailed the design to them and this showed up a few weeks later.
1st Version	2nd Version	Here you see the two versions. The first has very small capacitors, the second larger capacitors. The first is inverting the second is not. The differences are described above.
Schematic 1st Version	Schematic, 2nd Version	These are the schematics. I would change the 220K ohm resistor in the first schematic to 440K or so to increase the gain if you have a source that cannot provide a significant output. The circuit as is has a tough time going to the maximum volume without a preamp. This circuit worked fine, but I changed it anyway, just to try something new. The 2nd Version has much higher gain, no changes necessary. Its schematic is taken from Chipamp.com.
1st Version Amplifier Bottom View	Clipping into 5 Ohms	You see in the 1st Version that a lot of components are hand-soldered to the bottom of the board, this was to reduce the length of the signal paths. In the 2nd Version some components were placed on the bottom of the board to avoid blocking the screws that hold in the brass bar which presses the chip to the heat sinks. Oscilloscope measurements of the 2nd Version show the clipping response of the left channel with a 1 KHz input signal into 5 ohms, 10 V/Div, both channels driven. As you can see this clips at around 25 volts into 5 ohms (50 volts peak-to-peak). I'd say this is very good performance for a 60 watt chip.
1st Version Amplifier Top View	2nd Version Amplifier Modules	The boards of the 1st and 2nd Version amplifier channels. You see a nylon washer in the 2nd version underneath the heat sink to raise the heat sink and improve convection cooling, as the case is vented underneath and above.
Ultra Low Noise Power Supply and Differential Receiver Board	Ultra Low Noise Power Supply and Differential Receiver Board	Note: MUR820 high speed diodes Panasonic FC 2,200 uF supply capacitors and Nichicon 1,000 uF supply capacitors Didn’t think I had enough LEDs? PS voltage adjustable via trimpots shown currently set for pos. and neg. 9.5 VDC
Bottom View of Differential Receiver and Power Supply Board	Schematics/ Input and Low Noise Power Supply Portion	Ultra Low Noise Regulator/ Diff. Xcvr Board Note: Linear Technologies LT1964 and LT1962 surface mount ultra low noise voltage regulators mounted on bottom of board; this is essentially the data sheet implementation. compare in size to the ear on a dime You see errors on the board, including vias too small for leads (so they are drilled out), my bad. Jumpers “J_” required because I wanted a low cost 1 level board.
LED Board	External DC Input or Output	Note: each front panel LED is adjusted via trimpots shown also included protective diodes and base resistors so even if the wrong polarity voltage is applied or if the trimpots are turned to 0 the LEDs will not blow. the blue LEDs are actually at their lowest setting to reliably deliver light. If the line voltage drops, the L/R LEDs will turn off. Note that I have this board set up to accept both the long cermet trimpots and the short ones (though this pic has no short ones you can see where they would go). These two boards were designed by me using Cadsoft Eagle and made by PCB Express. The other picture is is 3 contact miniplug which feeds into the regulator outputs. With the transformer switched off, a battery power supply can be used to power the differential receivers. With the transformer on, the low noise DC is available for other components.

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