Even with more output transistors, the power supply in this case is still the main determining factor in maximum power output, especially into 8 ohms. However, into 4 ohms or 2 ohms, the influence of the number of output devices does increase somewhat. This is, in simple terms, because with more output transistors in parallel, there will be less voltage drop from the power rails to the output through the transistors as maximum output is approached. In a similar context, more peak current will be available. This can become more important with difficult low-impedance loads.
Distortion in any given situation will tend to be lower with more output pairs as well, since the dominant source of distortion is in the output stage. The less hard it is to work, the less a given pair tends to create distortion. Put another way, for the lateral MOSFETs, more pairs tends to mean more transconductance, even at a given total output current. As current increases, the Rds_on of the MOSFETs begins to come into play in limiting transconductance.
It is also true that doubling the number of output pairs, and correspondingly doubling the total output stage bias current, doubles the amount of output current that can be produced before the output stage leaves the class A range where both polarities of transistors are contributing to output stage transconductance. This actually quadruples the amount of power at the point of (soft) transition out of the class A region.
Finally, more output pairs means better thermal management, keeping junction temperatures lower for a given amount of output power. When MOSFET junctions get hotter, Rds_on increases, further limiting maximum power.
Cheers,
Bob
Did you also replace the 2 main power supply caps? If so, what did you replacement them with?
David
I did not replace the big ecaps on my DH-200 test unit. Probably could use a changing due to age but I did not test them to determine capacitance and if they are out of spec. They are standard computer grade screw base caps available at local distributors. Might have to alter value/voltage to find what is stocked and economically priced. I’d have to look again at what’s available and in stock. If your unit is working now, any mod should allow the unit to still work, changing the big caps can be done before or after.
Rick and Bob,
I’ve devoured this thread and Bob’s 2016 presentation in the last several days. I’ll be picking up a clean DH-220 tomorrow morning in anticipation of applying the 220-C updates. Fantastic timing for an audio project.
I may have missed it, but what is the gain of the DH-220 with the new boards? Is it adjustable?
Would lowering the gain be of any use, or is the ~2 wpc class A the sweet spot for the existing gain?
Thanks!
Marc
I’ve devoured this thread and Bob’s 2016 presentation in the last several days. I’ll be picking up a clean DH-220 tomorrow morning in anticipation of applying the 220-C updates. Fantastic timing for an audio project.
I may have missed it, but what is the gain of the DH-220 with the new boards? Is it adjustable?
Would lowering the gain be of any use, or is the ~2 wpc class A the sweet spot for the existing gain?
Thanks!
Marc
Hi Marc,
Gain is fixed and not variable using 1 & 2W precision resistors, set at 27.6. I do not think lowering the gain is of any use, doing so might mean having to change other components as well. Class “A” region is dependant on OPS bias current and the amount of output pairs as Bob mentions above.
On a side note the above mono-block amp using four pair of output devices was DC coupled, not every application is able to use DC input coupling.
Rick
Gain is fixed and not variable using 1 & 2W precision resistors, set at 27.6. I do not think lowering the gain is of any use, doing so might mean having to change other components as well. Class “A” region is dependant on OPS bias current and the amount of output pairs as Bob mentions above.
On a side note the above mono-block amp using four pair of output devices was DC coupled, not every application is able to use DC input coupling.
Rick
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Hi Bob and Rick. I’m interested in using the DH-220C boards in a Hafler DH500. Are the boards good for the higher +/- 90v DC rail voltages. Rick, you mentioned in post 1763 that you ran the boards at the high voltage and they survived but the output devices ran hot and suggested using oversized heat sinks. Are there any other changes required? Obviously the Ecaps need to be rated for the higher voltage. Do any resistors need to be bumped in wattage? Thanks, Bill.
Just for the record, I do not know of one DH-500 installation using DH-220C(AFE)/P230(OPS) so far, so tread carefully because you are in uncharted territory.
We have thoroughly evaluated the DH-200, DH-220C and P230.
So Bill, you’re our DH-500C beta tester by default
Maybe best to start a new DH-500 thread if you want to show your work or have open discussions on your build.
Good success
Cheers
Rick
We have thoroughly evaluated the DH-200, DH-220C and P230.
So Bill, you’re our DH-500C beta tester by default
Maybe best to start a new DH-500 thread if you want to show your work or have open discussions on your build.
Good success
Cheers
Rick
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Clean Slate
I am excited to get started on this journey. The DH-220 I picked up is in very good shape. It appears to have gone under the iron not too long ago, with some good cap replacements.
I used it for several days in my main system to get a feel for its stock character and it is surely a fine amplifier for being nearly 40 years old.
I received the boards and jfets today for the 220-C upgrade, so the BOM exercise will commence.
Anything in these photos look awry? The T03 mosfets look original. Though someone wrote a "?" on one of the 2SJ49s.
Enjoy the peek under the hood!
I am excited to get started on this journey. The DH-220 I picked up is in very good shape. It appears to have gone under the iron not too long ago, with some good cap replacements.
I used it for several days in my main system to get a feel for its stock character and it is surely a fine amplifier for being nearly 40 years old.
I received the boards and jfets today for the 220-C upgrade, so the BOM exercise will commence.
Anything in these photos look awry? The T03 mosfets look original. Though someone wrote a "?" on one of the 2SJ49s.
Enjoy the peek under the hood!
Attachments
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Everything looks fairly normal and standard. However, the question mark may mean that the person who put it on was either unsure if the device was good or unsure of its matching to the other same-sex device on that heatsink. Hafler matched output MOSFETs into several bins, each bin designated with a stamped number. We normally expect a pair of devices next to each other to have the same bin number. It may also indicate that the bin number was illegible or that he removed all of the devices from the amplifier at one point and perhaps didn't keep track of where they were put in originally.
Cheers,
Bob
Thanks, Bob.
So in theory, if all the 2SK134s are labeled 3, two of the 2SJ49s are 3, and two 2SJ49s are 4, should the 2SJ49s match up per channel or across channels?
In other words, when I remove the devices and reattach them with the new boards, should I move the 2SJ49s around (swap green or swap yellow in the photo)?
So in theory, if all the 2SK134s are labeled 3, two of the 2SJ49s are 3, and two 2SJ49s are 4, should the 2SJ49s match up per channel or across channels?
In other words, when I remove the devices and reattach them with the new boards, should I move the 2SJ49s around (swap green or swap yellow in the photo)?
