*** GainClone for Bi-Amping? ***

[beatrix_choice]

Hello everybody,
I have decided to build 4 monoblocks GC.

Keep in mind that two of them will drive a "88 dB/8 ohms, two speaker, subwoofer" and the other two a couple of "98 dB/8 ohms, Fostex FE206E, satellites".
I will obviously have to use two attenuators/pots on the satellite-driving GC to match their higher sensitivity.

The signal comes from a "two channel output" Rotel RC980BX Preamplifier (output sensitivity 1V/100 ohms).

Before ordering from Brian I have a couple more questions:

1) which is the "right" toroid suited for this monoblock configuration? a 160 VA, 1x24 V would do the job or I need more power?

2) which kind of attenuator/pot should I use in the previously described system, since I have read that using an attenuator/pot could change input impedance and should be carefully matched to GC layout.

Thank you for your interest and time

Best regards

_luca

[Nuuk]

Hi Luca,

Brian's circuits are of the non-inverted variety and will not be affected by the volume control as is the case with the inverted type.

For sound quality use a stepped attenuator for the main amps. This isn't quite so important for the sub.

It is generally recommended to use the 3886 chips for subwoofer use, and to include some extra capacitance in the PSU.

If you are building true monoblocks, you should have a transformer for each of the four amps. But you can get away with a 160VA for the two main amp channels and perhaps a 300VA for the two sub amps.

I suggest twin secondary windings (or around 18-22 volts) and two rectifier bridges for best performance.

[beatrix_choice]

Thank you,

I have some other questions that will help me to understand before building:


Subwoofer GC:

1) you are simply suggesting to switch the LM3875TF for the LM3886TF in the BrianGT kit?
2) or I have to buy the PCB only, and provide the components by myself, accordingly to another project/design?
3) and, if yes, which is the favourite design/project for a subwoofer?

Subwoofer PSU:

1) I should buy one 300VA transformers per channel, provide some extra capacitance
(accordingly to http://www.tnt-audio.com/clinica/ssps1_e.html), right?
2) The transformer I can source has two secondary 25V, 150VA each. I have to connect the secondary in parallel to have 25V, 300VA. Right?
3) I will have one rectifier bridge for each channel (and transformer, of course), right?




Satellite GC:

1) I will add a stepped attenuator, to match the subwoofer emission. Since I already have a couple of 8 position switch, I would eventually build the attenuator by myself. Given the 10 db difference in efficency between the subwoofer and the satellites, would you suggest a resistor ladder to deal with?

Satellite PSU:

1) I would use a transformer wiyh the following specifications:




I beg your pardon for my questions that may seem obvious, but I'm a complete newbie in DIY electronics, and, while I can understand quite everything in theory, I lack some practice in amplifier/PSU buiding...


Best regards

_luca

[Nuuk]

If you are a complete newbie to this DIY hi-fi, I strongly advise you to build the amps for the sattelites first.

Please read all the information on my Gainclone pages at Decibel Dungeon .

When you have successfully built the sattelite amps, you will be in a much better position to build a sub amp for which you may need to build a bridged version.