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billbeau 29th October 2008 02:09 AM

Im looking into possibly building a set of monobloc chipamps. I will be using a tube pre that has approx 22db of gain. The speakers are a pair of Klipsch RB-81 bookshelfs that have a sensitivity of 97db and are 8 ohms. I am also using a powered sub a Klipsch RSW-10d but that is run off the pre.

What would you suggest for a chip that would sound the best to drive these speakers? What voltage?

Schematic and BOM?

pacificblue 29th October 2008 09:26 AM

Something like this?

billbeau 29th October 2008 12:48 PM

Nope. That is a tube hybrid integrated of sorts. It already has a preamp or buffer that is using tubes. I already have the tube preamp. Just looking of r a good sounding power amp or mono bloc design to build.

There are soooo many designs out there. Just looking for what most people think is the best as well as the best power supply design.

AndrewT 29th October 2008 01:19 PM

most amp systems use near 0dB to +12dB gain in the preamp, then 23 to 30dB gain in the power amp, followed by speakers of 84dB/2.8V/m to 90dB/2.8V/m.
Your system has 22dB of gain @ the pre, >=20dB gain in the power and 97dB/2.8V/m.
This equates to an extra 7dB to 32db of gain from the input of the pre to the speaker output compared to the norm.

This will demand that the input attenuator will always be at low to very low settings. Many resistive track attenuators do not operate well at low levels. The optical attenuators cannot work at very low levels.

I suggest you use a special switched attenuator adjusted to give fine resolution at very high attenuation levels or to abandon the idea of combining all these high gain stages in one system.
+42dB of gain driving 97dB speakers is exceptional!!! So exceptional that a conventional power amp is not required. By that I mean a power buffer after the preamp would give +22dB of gain into your 97dB speaker and still match the gain of +6dB pre into +23dB power into 90dB speakers.

Does anyone else agree that a power buffer may be the solution?

billbeau 29th October 2008 01:52 PM

Ya know what. I am sooooo mistaken! The gain the tube pre was way to high around 20 or so untill I changed the 1st and 2nd stage tubes ftom 12AX7 to 12AU7. the AX has a MU of 100 vs. the AU with a MU of if I remember correctly 17 this decreased the gain to under 12db or at 12db. I am also using a 250K stepped attenuator for the control. here is a schematic of the pre. It has three outputs 2 for the mono blocs and 1 for the sub.

Nuuk 29th October 2008 04:49 PM

Use something like the OPA549 with a gain under 10.

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