My new hybrid amplifier

[sajti]

I'm over the first test. Not yet listening, just some measurements. Ther will be some major, and minor issues, I have to solve. The DC offset is is liitle higher than I expected, and the adjustment is not possible. So I have to replace the trimmer, to get wider range for the offset compensation.
Another issue is the stability. The amplifier oscillate if I put more than 1uF capacitor across the 8ohm dummy load. There are some ringing on the square wave output with 1uF. So I have to replace the compensation network.
The output is little over 400W/4ohms.

Sajti

 

[sajti]

There was some different version, to listen, and test. What I found, that the KSC/KSA series transistors have not as good sound as the 2SC/2SA types. I have changed the protection little bit.
The solid state buffer finally based on Marantz SM11-S1, but with more output devices, and approx. 150W/8ohm output power.
Some pictures attached.

Sajti

 

[homemodder]

There was some different version, to listen, and test. What I found, that the KSC/KSA series transistors have not as good sound as the 2SC/2SA types. I have changed the protection little bit.
The solid state buffer finally based on Marantz SM11-S1, but with more output devices, and approx. 150W/8ohm output power.
Some pictures attached.

Sajti

Doesnt what you call the buffer have voltage gain ?? I think it does from what I can remember from the marantz. Marantz must have contracted the designer from pioneer as the schematic is identical to the late 80s early 90s high end series pioneers.

In those days the european and american markets didnt regard the design good, now that marantz produces it its highly rated ???

 

[sajti]

Doesnt what you call the buffer have voltage gain ?? I think it does from what I can remember from the marantz. Marantz must have contracted the designer from pioneer as the schematic is identical to the late 80s early 90s high end series pioneers.

In those days the european and american markets didnt regard the design good, now that marantz produces it its highly rated ???

Yes it has the voltage gain of 2. You can check the schematic on the 1st page of this topic. There is some minor changes since the 1st version, but this are not serious.
This Marantz is a new design, I don't think that it's related to the amplifier form the 80s.

Sajti

 

[homemodder]

I have the service manuals, just did a quick peek some time back. New its not, consult pioneer schematics from that era. In fact it was pioneer which developed that voltage gain stage and at the time it was very much talked about.

 

[sajti]

OK I will check it! For me it's no problem, because it's sounds quite good. I use feedback only in the buffer, the tube stage has only local feedback. The gains gives some flexibility to try different tube types in the 1st stage.

Sajti

 

[sajti]

The input stage will be E88CC two half connected parallel, common cathode.
Expected output power 140W/8ohm, 220W/4ohm, 400W/2ohm (simulated). Option is the bridging to drive my 4ohm subs (2xBeyma 18G550 bassreflex).

Sajti

 

[sajti]

I did some listening tests, and the result was quite good. The amplifier sounds fast, with rock solid bass, and it has some sweetness usually associated with the tubes.
I was quite satisfied, but I had an idea, due my CD olayer has balanced output. So I bridged the two amplifier, and made some listening, only in mono. And it was absolutely different! Another amplifier, like the dirty window compared to the clean...
I set up the another channel, due I have 4 panels, and it was amazing. Strong, detailed and sweet, same time!
So I planned another driver stage, which is under construction. It contains E88CC long tailed, with cascoded DN2540 as ccs at the tail.
So it will be truly balanced amplifier input, to output.
Finnally the measured output power:530W/8ohms, 970W/4ohms before clipping.
The only issue I have to solve is a stronger driver, as I use 2SC5171/2SA1930 currently, and I don't sure that they can handle the current.

Sajti

 

[homemodder]

You can use 2sa1837 and complement, although a little slower they have higher SOA. Another option is to use onsemi drivers (mje1503x series) but again speed penalty. Best way is what Pioneer used to do, parralell two 2sc5171/2sa1930 with a current sharing resistor of around 3 ohms.

 

[sajti]

You can use 2sa1837 and complement, although a little slower they have higher SOA. Another option is to use onsemi drivers (mje1503x series) but again speed penalty. Best way is what Pioneer used to do, parralell two 2sc5171/2sa1930 with a current sharing resistor of around 3 ohms.

Thanks the idea! I used 4793/1837, but the 5171/1930 has better sound. Paralell driver can be option! I will check. With 4ohm resistive load the maximum driver current in 190mA (simulated).

Sajti

 

[sajti]

I did some simulation. Replacing the driver (2SC5171) with 2 paralleled, reduce the open loop distortion from 0.5% to 0.37%, and 3 paralleled reduce it to 0.25%. So it looks good solution!

Sajti

 

[pergo]

what about tube ltp in your new project?

 

[sajti]

waiting for the pcb....

Sajti

 

[sajti]

The input pcbs are arrived today. I planned another one which will contains the 3 drivers, due I don't want to destroy the existing pcbs.
I will put some pictures about the heatsink assembly, hopefully on next week.

Sajti

 

[Junm]

can you post your input stage schematics?

 

[sajti]

Input stage attached.

Sajti

 

[sajti]

I have the service manuals, just did a quick peek some time back. New its not, consult pioneer schematics from that era. In fact it was pioneer which developed that voltage gain stage and at the time it was very much talked about.

I found the A-400 from Pioneer. So it has the output stage looks something like the Marantz. But not exactly same as the Pio contains some opamp as preamplifier on the input. The Marantz circuit looks much more promising, with more carefully designed.

Sajti

 

[homemodder]

I found the A-400 from Pioneer. So it has the output stage looks something like the Marantz. But not exactly same as the Pio contains some opamp as preamplifier on the input. The Marantz circuit looks much more promising, with more carefully designed.

Sajti

It boils down to the same design, just because one just has a IC opamp and the other has a discrete one.

When you take it that the pioneer circuit is more than 20 years old I sure would hope that someone copying could at least do one little thing better although I dont see much that is worth the trouble.

Another fact is Pioneeer developed the CFB part back in 1978, long before comlinear patented in around 1985 the use of diamond buffer input stage for CFB opamps. That design already included the so called super linear vas circuit so in all marantz are 30 year behind in savy.

 

[sajti]

It boils down to the same design, just because one just has a IC opamp and the other has a discrete one.

When you take it that the pioneer circuit is more than 20 years old I sure would hope that someone copying could at least do one little thing better although I dont see much that is worth the trouble.

Another fact is Pioneeer developed the CFB part back in 1978, long before comlinear patented in around 1985 the use of diamond buffer input stage for CFB opamps. That design already included the so called super linear vas circuit so in all marantz are 30 year behind in savy.

I don't really want to fighting with You. So my design is based on Pioneer A-400 power stage.

Sajti

 

[sajti]

I have to make some changes, due the original version use 2sc2240/2sa970 in front end. This parts are not manufactured any more, so I have to find some other to replace it.
In the current mirror, and in the input stage I use BC550C/560C (Onsemi), the VAS use 2SC3423/2SA1360 (I feel lucky to order last 300-300pcs from Mouser. In the remaining 4 position (input cascade, and the ccs on the input) I try 2SC2705/2SA1145, KSC1845/KSA992, but unfortunately the original parts give the best sound, so finally I get some of them.

Sajti