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OK, I volunteered via a PM with another member to get some info from Tom (the amp designer) on the gain resistors/pot situation. Here is his response:First, the amps are AC coupled (EDIT BY RAINDANCE - So you can try them with your Little Dot Mk III if you want). The gain is in the first stage of the amp. I was very careful in selecting the pots that come with the amps. They feature high quality conductive elements and are pretty much dead quiet. Of course, you can use stepped attenuators for possibly a little better performance, but most could never be able to hear the difference. These do not come with the kits because as I’m sure you already know, you can spend allot more money on quality stepped attenuators than the cost of the amp kit. Fixed resistors are another and possibly the best choice as long as you know the correct gain to set the amp at to get the most out of your preamp or other input device. Without taking this into account and just changing to a fixed resistor, it is possible that you won’t achieve the optimum sound quality from your equipment if your preamp is not matched correctly to the amp and adjusted to find the maximum and optimum sweet spot of the preamps volume control. Distortion from the preamp can be a problem on many units if the volume control is turned up too high, and you also might not be getting the best from your preamp if the volume is turned too low… they are all different. To put it simpler… The gain controls are used to match the amplifier’s gain to the gain of the other amplifiers in the system as in active or passive preamps, DAC, iPod or mp3 players, etc. The gain controls allow you to match the amplifier to the input device. Not all input devices have the same maximum preamp output voltage. Some preamps are capable of producing 15 volts RMS out while others are only capable of 1.5 Volts RMS out. Most preamps or other input device will reach its maximum output level (clipping) well before the volume control reaches the upper end of its range, usually at a point of 75-90% of its maximum range. For those who wish to change the pots for fixed resistors, here are resistor values to produce required gain. Gain is listed in dB: To change gain potentiometer to a fixed resistor, you would connect a fixed resistor between the yellow and black wires on the gain controls (of course, remove the gain pots). Leave the red wire disconnected. Use high quality 1% resistors: 560 Ohm = 31 dB 1K = 30 dB 2.2K = 27 dB 5.2K = 23 dB 6.2K = 18 dB 7.5K = 16 dB I hope this is of some help. Please feel free to post this on the forums if it will help others. On my personal systems here, I use the same pots that come with the kits.
Hi, First of all, I don't know which model you have. From what I understand the units come with approximately 32DB of gain. Now, that's ok if you have a buffer, or passive Pre-amp which has no gain. if you have the CD units, before you buy, you should ask tom to make it approximately 27DB of gain, which is about standard in the industry for amplifiers. Now if you have a SDS unit, it has a buffer built in, as well as providing a volume pot for each channel. At max the gain is 32DB. Rather than dial it down and guess if you have the gain set correctly, you can just sub these pots out for resistors of specific values. It appears that certain brands of resistors do make a difference in sound. If you are using a pre-amplifier, then you want to have at least the lower 27DB of gain, which means you need a 2.2 K-ohm resistor. This DB gain factor is from 0 at input to 27DB at output. I'll let the more technically minded give you a further explanation. So to answer your question, as a summary, if you are using a buffer, then leave the gain at max 32DB. if you are using an active pre-amplifier, SolidState or Tube, then you need to lower the gain to at least the standard 27DB. Hope this helps.Now, some have lowered the gain anyway even though they had a buffer, and the sound improved.Ray Bronk
