Hi Chris and others,
"My honest appraisal would be to avoid these "upgrades" like the plague."
You are saying this about Bob Cordell's DH-220C re-design, without any review or evaluation? If so, sorry, I find your comments to be a very near sighted opinion imo. I can only speak for DH-220C, the others I have not evaluated to form an opinion, so I just avoid comment.
The only matched parts for DH-220C are the dual jfets themselves with their inherent matching as part of the device process.
Since the DH-220C is all THT, matching other pairs is easier than discrete smd. If I was to do the design in smt, of course I would use the dual DMMT5551 and 5401 parts in the SOT-26 package.
Once/if you take the time to review the DH-220C design, what other parts in the DH-220C design are you suggesting need to be matched for improved performance?
Further to 'Maybe its helpful to add also the external components to the schematics." I have been in contact with Bob Cordell, he has provided me with additional information as to his DH-220C mods, in so much as a new wiring diagram for the mosfets and additions he did in his re-design. I will ask Bob if he will allow me to share this information with everyone in this forum.
Cheers
Rick
Did you look at the DH-220C schematic I posted, review Bob Cordell's presentation and compare it to the original?
"My honest appraisal would be to avoid these "upgrades" like the plague."
You are saying this about Bob Cordell's DH-220C re-design, without any review or evaluation? If so, sorry, I find your comments to be a very near sighted opinion imo. I can only speak for DH-220C, the others I have not evaluated to form an opinion, so I just avoid comment.
You are commenting on a posted schematic design in which you have not even bothered to look at! I suggest to do your homework first before blindly shooting something down.
The only matched parts for DH-220C are the dual jfets themselves with their inherent matching as part of the device process.
Since the DH-220C is all THT, matching other pairs is easier than discrete smd. If I was to do the design in smt, of course I would use the dual DMMT5551 and 5401 parts in the SOT-26 package.
Once/if you take the time to review the DH-220C design, what other parts in the DH-220C design are you suggesting need to be matched for improved performance?
Further to 'Maybe its helpful to add also the external components to the schematics." I have been in contact with Bob Cordell, he has provided me with additional information as to his DH-220C mods, in so much as a new wiring diagram for the mosfets and additions he did in his re-design. I will ask Bob if he will allow me to share this information with everyone in this forum.
Cheers
Rick
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FYI-
To give proper credit to the designer:
The DH-200 was designed by Erno Borbely, who passed away a few years ago. He was originally hired by David Hafler to work for Dynaco (1969?) and left shortly after Hafler sold the company in 1972. When the David Hafler Company was started in 1978, Borbely came back and designed the original Hafler products. He didn't stay with Hafler very long, as there was some disagreement over compensation. I think the DH-220 is just a slightly tweaked version of Borbely's design.
DH-220C for Erno Borbely
I think Erno Borbely would be proud that we can implement a version of his treasured complementary jfet design in the DH-220 chassis using modern available parts.
I have on file a DC100 drawing that I assume was done by Erno, looks a lot like a DH-220C to me.
Erno are you out there, can I email you with the DH-220C layout for your review
Found this to read
https://www.audioxpress.com/assets/upload/files/The Borbely AnnalsAX012_019.pdf
https://www.americanradiohistory.com/Archive-Amateur-Audio/Audio-Amateur-1984-1.pdf
Enjoy
I think Erno Borbely would be proud that we can implement a version of his treasured complementary jfet design in the DH-220 chassis using modern available parts.
I have on file a DC100 drawing that I assume was done by Erno, looks a lot like a DH-220C to me.
Erno are you out there, can I email you with the DH-220C layout for your review
Found this to read
https://www.audioxpress.com/assets/upload/files/The Borbely AnnalsAX012_019.pdf
https://www.americanradiohistory.com/Archive-Amateur-Audio/Audio-Amateur-1984-1.pdf
Enjoy
Attachments
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Thanks for pointing that out, credit where credit is due!
I'll let Chris defend his comments. However, I took them as a "be cautious" general statement about putting in significant changes to the original circuits. Including a myriad of circuit designs that I don't have schematics for, nor have I seen tests of. Which I agree with.
In my opinion the design by Bob Cordell is at another level, and has obviously been intelligently implemented. Bob has also shown that he has bread boarded his design and taken measurements showing significant improvements. All included in his talk.
Thanks to rsavas for all his work to get a board designed that might allow us to implement Bob's design for further tests and listening.
I'm the one who started this question regarding the multitude of designs available.
My take away thus far is that for now I will stick with the original design with upgraded components. Until such time that I can give Bob's design a try, hopefully with another amp that I am trying to acquire.
gabo
Are you sure Erno passed away?
I know David Hafler did.
mlloyd1
I am happy to be wrong about this.
The Borbelyaudio website became inactive nearly ten years ago and I had assumed far too much.
I used to fix and mod the DH200 back in the late 70's. Back then, a number of them were starting to generate significant DC offsets due to C-B leakage in the input stage. I fixed one by wiring in some other complementary small signal transistors I had (Motorola 2N5210, 2N5087 of Tiger amp fame) as new inputs, with the original transistors as cascode tops, like this:
This was done by just pulling the emitter and base leads of the original devices from the board and inserting the new added devices into the holes and twisting and wiring the arrangement with a few jumpers.
This put the C-B voltage of the (new) input transistors at around 100mV or so, so they didn't leak, even if the original high voltage input transistors leaked moderately. The DC offset dropped to nearly zero. When I started modding the amps later, I added an integrator and inverter circuit using TL074 opamps to form DC servos, making the cascode leakage fix probably un-necessary, but I assumed then (with no way to measure or simulate) that distortion would be better with the cascode. I don't have any Hafler amps anymore -- the last one I had developed a mechanical hum/buzz in its power transformer that was driving me nuts so I gave away the amp, so no way to measure anything now.
Maybe some here can comment whether my quickie-cascode arrangement was an improvement or degradation of the original input arrangement?
Bill, you modified my DH-200 back in the horse and buggy days and it was an improvement. I still have it.
It's in his presentation file which can be found here.
https://www.diyaudio.com/forums/att...mp-2016-a-cordell_burningamp2016_dh220c-1-pdf
And there is a youtube of the full presentation here.
YouTube
gabo
https://www.diyaudio.com/forums/att...mp-2016-a-cordell_burningamp2016_dh220c-1-pdf
And there is a youtube of the full presentation here.
YouTube
gabo
AuroraB,
I am working off the slide set of the presentation material that is publicly available from Bob Cordell. There is a link a few threads back. It includes the complete design, enough for me to do up the design. Bob made up one channel in proto form, see pics. Bob is including the design in more detail in the new book.
Ray,
That is great information, Chris should take note as well cascode IPS for the best amps, hands down
Do want to pay for the extra performance, is it worth it, will you notice?
Cheers
Rick
I am working off the slide set of the presentation material that is publicly available from Bob Cordell. There is a link a few threads back. It includes the complete design, enough for me to do up the design. Bob made up one channel in proto form, see pics. Bob is including the design in more detail in the new book.
Ray,
That is great information, Chris should take note as well
cascode IPS for the best amps, hands down Do want to pay for the extra performance, is it worth it, will you notice?
Cheers
Rick
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yes, he retired a while ago and shut down his audio site.
but most of it is still available via the waybackmachine site.
mlloyd1
but most of it is still available via the waybackmachine site.
mlloyd1
The EB-SA2 is a mind-blowing mega-amplifier, achieving literally twice the sonic power and control of the legendary EB-SA1. It begins with a dual-differential input stage studded with the finest J-FET transistors available – transistors specifically designed for audio applications. This is brilliantly integrated with a MOS-FET pre-driver stage, MOS-FET driver stage and fully balanced Lateral MOS-FET output stage – featuring 24-each closely matched devices per channel.
Price: $34,995
And I think I am going over board with an exotic design
studded jfets, marketing hype.
What do you think, Linear Systems or Interfet jfet devices?
lateral mosfets from who?
Price: $34,995
And I think I am going over board with an exotic design
studded jfets, marketing hype.
What do you think, Linear Systems or Interfet jfet devices?
lateral mosfets from who?
Bi-amping with 2 different models or even brands for that matter should not be an issue.
I put my most powerful amp on the bass drivers, and my best sounding amp on the mid/high drivers.
If your DH200 and DH500 are still vintage & original, you should consider at least recapping them though, as the electrolytics are well past their prime.
Also with the Haflers, many of them were built as kits and it wouldn't hurt to have them checked over by a pro technician.
I have seen some pretty scary builds myself, some I would not even test fire as is for risk of possibly damaging some hard to replace components.
I put my most powerful amp on the bass drivers, and my best sounding amp on the mid/high drivers.
If your DH200 and DH500 are still vintage & original, you should consider at least recapping them though, as the electrolytics are well past their prime.
Also with the Haflers, many of them were built as kits and it wouldn't hurt to have them checked over by a pro technician.
I have seen some pretty scary builds myself, some I would not even test fire as is for risk of possibly damaging some hard to replace components.
Gabo, not sure if you are aware or not, but Qu-aco seller Ed Fantasia has a significant history with Dynaco and Hafler.
From his auction details:
"Being intrigued with audio since 1973 has given much insight on the topic of amplification and proper design practice. My interest in audio continues to be both my hobby and my passion. Employment at both Dynaco as a technician and Hafler Co. as a project engineer was not only enjoyable but allowed me to work and converse with some very accomplished audio engineers."
From his auction details:
"Being intrigued with audio since 1973 has given much insight on the topic of amplification and proper design practice. My interest in audio continues to be both my hobby and my passion. Employment at both Dynaco as a technician and Hafler Co. as a project engineer was not only enjoyable but allowed me to work and converse with some very accomplished audio engineers."
Provided that both amps have the same gain of course. Fortunately, the dh200 and 500 have both about the same gain. More precisely, the only difference in gain comes form the input divider resistors circuit. 2k/22k ohm for dh-200 and 1k8/47k ohms for dh-500. So about 4% more gain for the dh-500 which is relatively small. Added to that is the output impedance of the circuit feeding the amplifiers which will change a bit this value too.
Fab
yup. Further, your EXO should allow adjustment to balance bass to upper frequencies.
yup. I allowed the damping factor to decide - 1000 into 8 ohms for woofers.
yup
yup
see above.
Hi Rick, all,
My comments are always in general unless I refer specifically to a shop, designer or famous hack artist. That last bit was thrown in as humour least someone take offense.
My long experience is that many mods done that change the schematic to any great degree are often done by people who really don't understand how to design something. Typically prickly individuals who don't take to questions too kindly. I'm sure you know the type.
Rick, I did not look at your posted schematic as I'm really under the gun at the moment as far as time is concerned. I only commented that I would like to see you work sometime. That is hardly a negative comment.
Best, Chris
My comments are always in general unless I refer specifically to a shop, designer or famous hack artist. That last bit was thrown in as humour least someone take offense.
My long experience is that many mods done that change the schematic to any great degree are often done by people who really don't understand how to design something. Typically prickly individuals who don't take to questions too kindly. I'm sure you know the type.
Rick, I did not look at your posted schematic as I'm really under the gun at the moment as far as time is concerned. I only commented that I would like to see you work sometime. That is hardly a negative comment.
Best, Chris