Opinions on Dynahi vs. Headcode from a design point of view?

[philodox]

I was just wondering what people thought of these two designs. Obviously there are very few [probably none] that have heard both a Dynahi and a Headcode, but I thought I would start this thread to get some healthy speculation going.

The Larocco Headcode ST [one power supply] seems to be coming in at the same price point as the Veda Audio Dynahi SA, so comparisons between these will probably crop up once the ST goes into production.

I read over the information on the BiCode design and it certainly sounds impressive. I also understand a little behind the Dynahi design and am equally impressed. My knowledge is not great enough to develop any sort of prediction based on the design methodologies and specs though and I was hoping that there might be some experienced DIY'ers on here that could offer an opinion.

Thanks,

Jay

 

[Glassman]

Headcode design is definitely more advanced, more complex.. Dynahi is, on the other hand, pretty minimalistic design with everything taken to the extreme in terms of voltages and biases..

 

[bg4533]

Is there a schematic for the Headcode publically available?

 

[chillysalsa]

Probably not, but if you do a goole search you can find pictures, and a pdf with descriptions of the topology and design philosophy. Though, that still leaves a lot up to the imagination!

 

[Banfi T.]

The shematic of the Larocco desing is not a mistery if you study Borbély Ernő's and Nelson Pass's white papers. What they cal acu biasing (or something like that) can be found on the Pass site for example with detailed explanations and diagramms (however the site is down now so I can't insert the link). A very similar full cascoded symmetrical design can be seen here. Only this is designed with JFETs, not BJTs and the output's cascode bias is at a reference point and does not float with the output as described in the Pass whitepaper.

I would say very good and honest job.

The Dynahi is not that complex as a circuit but I don't see the problem there

The DC servo is also clever and intuitive.

The common point between the two is that both of them is a symmetrical desing (they use both NPN and PNP devices) and both are practically small power amps.

I did built similar amplifiers a while ago but I found balanced single ended designes even better in terms of sound quality.

 

[SnoopyRocks]

dynahi schematic
The dynahi is a push-pull (both input and output) design that's very similar to the dynalo. The main differences are more power (both increased voltage and current), promting the choice of different transistors, and cascodes on the second gain stage as well as both input pairs. Not all that different from cmfb circuits used on fully differential amplifiers, the servo loop is a clever way to implement offset reduction even if only over a limited range and with the response time snail. It's an interesting use of LEDs.

headcode summary
headcode pics
Hmmm...haven't seen the headcode headcode before. It apears to be a very nice amplifier. Larocco audio sure is laying it on thick in their preoder summary though. It's not as much a technical description as it is marketing banter. They make it seem like they reinvented the cascode. Using a cascode is nothing new and has been common practice for well over a decade. From their description, I presume that audio missed the boat.

It seems like the output stage is class AB, which is not surprising considering the claim of 3A rms of available output current. Quote:

Beyond Class A is the Accu~track biasing of the output stage employed in the HeadCode. This technique provides for optimum bias of the output transistors and elimination of crossover distortion under dynamically changing output conditions.

 

[Banfi T.]

"They make it seem like they reinvented the cascode. "

I felt the same.

 

[amb]

Snoopyrocks, the dynahi schematic you linked to is an old version. Kevin has since deleted the cascodes on the second stage. So, aside from the additional cascodes in the first stage, the topology of the dynahi is identical to the dynalo. The difference is the higher supply voltage, operating points of the circuit (thus differing resistor values), and different choice of transistors.

 

[SnoopyRocks]

Quote:

Originally Posted by Banfi T. "They make it seem like they reinvented the cascode. " I felt the same.

I get the impression that they're of the opinion that they (re)invented a lot more that just the cascode in designing this amplifier. If it's one tenth as good as they make their circuit design out to be, it would be one amazing amplifier.

 

[kevin gilmore]

AMB is fairly accurate in his description.

The dynahi is pure class A and runs on higher power supply voltages.
It is significantly faster in terms of slew rate than other amps out there.
It did start out with lots more parts, but in the fine Zenith tradition many
of the parts were removed because they served no useful purpose.
Keeping the delay time as short as possible is far more important than
red, white and blue led's. (and green too). And a single output stage
is far more linear than a triple darlington.

If you want the ultimate in complication look at some of peranders
ultra high component count amplifiers.

Phil should post the schematics so that we could have a healthy discussion
of circuit differences. Many people already have the schematics anyway

 

[Banfi T.]

"Keeping the delay time as short as possible is far more important than
red, white and blue led's. (and green too). "

However they are good for current source reference (the LEDs).

I am glad that you joined this topic Mr. Gilmore.

 

[Glassman]

despite using only one color of LEDs in his amps, Kevin sure loves them just as much as Phil, it's more about esthetics

Kevin knows what is he doing, that's for sure.. it's a different school of thinking though.. also Kevin's designs are free to use for all of us, that's another major point here

 

[00940]

Speaking of cascodes... During the summer, I'm gonna try that, playing with some different output stages. The diamond buffer with cfp output still has some appeal on me.

http://peufeu.free.fr/audio/memory/m...-complete.html

 

[SnoopyRocks]

Quote:

Originally Posted by amb Snoopyrocks, the dynahi schematic you linked to is an old version. Kevin has since deleted the cascodes on the second stage. So, aside from the additional cascodes in the first stage, the topology of the dynahi is identical to the dynalo. The difference is the higher supply voltage, operating points of the circuit (thus differing resistor values), and different choice of transistors.

Quote:

Originally Posted by kevin gilmore AMB is fairly accurate in his description.

Quote:

Originally Posted by kevin gilmore Keeping the delay time as short as possible is far more important than red, white and blue led's. (and green too).

Oh. I wasn't aware of that. Then I presume that the miller capacitance was only an issue for the input pairs. The dominant pole comes from the first stage then? How much faster is the dynahi than the dynalo?

Quote:

Originally Posted by kevin gilmore It is significantly faster in terms of slew rate than other amps out there.

What's an estimate of the slew rate and at what load?

 

[Banfi T.]

The Pass website is back, so here is the link for the white paper on cascodes. It includes the floating cascode output stage as well.