Making a chipamp to take on my SET monoblocks

[beau2317]

After some insight gained from another thread I thought I would start a new thread to get input for a new amp. The idea is to build a pair of monoblocks that will:

-- drive my Magnepan 3.6s - 4 ohm fairly resistive load
-- give my parallel 211 hot-rodded SET tube amps a run for their money

My initial thoughts are to

-- have regulated power supply based on 5A chip regulators 30-0-30
-- use parallel chips (which ones??)

My first chipamp, a standard, by the book Audiosector kit, does not come close to the tube amps. Hopefully the second attempt will.

Right, input please....

[Nordic]

Maybe add a valve buffer to gain some of tat tube sound?
I'm busy makeing one like that... I hope

[beau2317]

I have a nice sounding tube preamp to drive it; second iteration of an Aikido using 6H30 (so called russian super tube) and ECC99, with tube regulated power supply.

That should provide a clean input (strongly recommend the Aikido btw, I have built at least 10 preamps over the years, SS and tube, and the Aikido is so far the best)

[Shoog]

The question is , Is this a realist goal ?

Chip amps and valve amps have there own strengths and weaknesses. Having built a number of chip amps and then a SET, nothing in my chipamps have come close to the enjoyable relaxed sound of the SET.
If you try to force a chip amp to sound like a SET - are you going to lose the best of the chip amp - without ever achieving the midrange of the tubes. I think that a top notch valve buffer might help, but it would have to be a lot better than a simple low voltage ECC88 cathode follower which is common practice.

I really think the fundamental issue is can you drag a valve like midrange out of a devise which fundamentally doesn't have it ?? My answer would be to build the best best chip amp possable (which will be excellent), but don't expect to stop hankering for your 211 SETS - as it aint going to happen.

Shoog

[tiltedhalo]

Won't happen, and I am a chip-amp fanatic, but they are two different worlds. A chip amp based on the overture series is fantastic, but will not compare to the sound of tubes, they are two totally different types of sound. A well put together chip will have tight controlled bass, clear mids, and detailed highs, but be rather harsh for most tube lovers and adding a tube buffer will help, but I agree with shoog it will have to be more then a simple cathode follwer useing cheap tubes

[beau2317]

I think you are right that it won't happen. But this is for fun and for knowledge; for instance it will be interesting to see how different (if at all) it sounds from the basic g/c I have already built. The current difference between my basic g/c and SET is not small or subtle.

As I mentioned it will have a tube buffer (of sorts) in the form of my tube preamp, which is not a simple cathode follower made with cheap tubes (see previous post a few above this one).

I find that my SET has tight controlled bass, clear mids, and detailed highs. It has nothing of the characteristics that SS fans often say make up the "tube sound" (I would call that the "old tube" sound). Modern well designed and well exectuted tube amps don't seem to have that sound in my experience.

Anyone have any suggestions of what chip to use; Will the LM3876s that I have on hand be OK?

[mateo88]

I would say use an lm3886. I've never used an lm3876, but I have used lm3875 and the 3886 is better, especially in the bass, IMO.

Follow CarlosFM's schematic, or at least keep the feedback resistor low (that is important). Change the capacitor values on the rails as you see fit; just find a combination that you like. Also you may want to lower the voltage to something like 24-0-24, or maybe even 18v rails. I like the way lower voltage sounds, and it keeps the chips much cooler.

[tiltedhalo]

IMHO I would use lm3875's, they do not have the mute circuit, they are the easiest to lay out well and have better overall sonic charecter, PS the mute works by taking drive away from the LTP this effects the bias current and can cause very small variations in drive, I perfer simple and the 75 is more simple then the 86.
I tried this one already used a non inverted design 27db gain jensen input transformer two bridged 3875's with tied NFB's into a custom wound output trans, came close, still use it in the bed room system.

[pinkmouse]

I'm going to post against current fashion, and say if you use the LM3875, go inverting. To me, the non-inverting circuit has always sounded inferior for that chip.

[Shoog]

If you go inverting you need to apply an onboard buffer to make the whole thing universally consistant, and to shorten the effective feedback loop. This also allows you to apply a little bit of low pass filtering which will take the bright edge off things. There are a number of good buffers to concider, the bipolar and jfet buffers on DECIBEL DUNGEON would be top of my list.
Avoid the T-feedback mod as this will give you detail at the expense of warmth.

Shoog