Shine7.com

GainClone ver 2 - LM3875T with Regulated power supply




After building my first version of Gainclone, while I am impressed by its good mids and highs, I think the sub-bass performance is not good enough. When I listen to music with deep bass, e.g. big drums, the bass sounds deep but not tight. I have a feeling that the GC is not controlling the woofer very well. I measured the voltage supply while listening to music with lots of bass at high volume level, I found that the voltage level of the supply dropped about 10-20%. That could be a casue of the bass problem I have.

 

Therefore I decided to build a second version of GC with a regulated power supply.

In this version the pot is removed from the Amp, I built a seperate passive preamp for my GC.

 

The transformer is changed to one 500VA 2x25V from two 250VA 2x18V. I do this because the regulator will drop about 5V, and I want to try a higher supply voltage. (which turned out to be better)

The voltage regulator used is LT1083, it can provide about 8A of current, which is more than enough as I only use one LM3875 per channel. I have 10000uF per rail before the regulator and 100uF at the output of the regulator. The VR is for setting the output voltage, the range is from 20V to 32V. I am using 30V at this moment. The diode used is MUR860.

LM3875 in a non-inverted configuration, the 2 caps are 100uF Panasonic FC.

The 1U server type copper heatsink on the outside.

Result : The sound improved a lot, especially the bass. The regulated GC has very detail and clean mid and highs as the orginal GC, and the bass is now deep and tight. The better bass could be a result of higher supply voltage or the regulator or both. I believe it is beneficial to provide a steady voltage supply.

 

Power supply and regulator schematic :

 

Gainclone schematic :

UPDATE 10 Sept 2004 : This GC circuit works fine as long as you don't get high frequency interference. I found out after I placed a DAC on top of this GC, some HF noise is present on the speaker output when the DAC is on. My guess is that the noise comes from the DAC's digital circut, and got coupled into the amp. To solve this problem, I added various HF filters :

 

1. Add a RC filter at input RCA socket, valuse used are 680 ohm and 470pF :

 

2. Add a 220pF capacitor between the + and - signal input pin of LM3875.

 

3. Add 0.1uF bypass capacitors in parallel to the 100uF power decoupling capacitors.

 

After adding all these the HF noise is completely gone.

 

 

 

Privacy Policies | Site Map | Contact Us |