Yes, upon closer examination of the Hafler Iris Schematic it seems that the approach taken was to lightly load the output of the CD4051 through a matched pair of K163L JFETs. After this it then feeds into the line amplifier section.
I wonder if this is one of the limiting areas with regards to the overall THD performance of the design. I'll have to go through the calculations mentioned in the ti tech note and try to find out what the calculated THD would be at this point. It all depends on what the load impedance is on the the match JFETS.
In other words, you might not really improve overall THD by upgrading the line amp section with, say, one of the newer high performance op amps like TI's LME49720. Which was something I was considering.
I wonder if this is one of the limiting areas with regards to the overall THD performance of the design. I'll have to go through the calculations mentioned in the ti tech note and try to find out what the calculated THD would be at this point. It all depends on what the load impedance is on the the match JFETS.
In other words, you might not really improve overall THD by upgrading the line amp section with, say, one of the newer high performance op amps like TI's LME49720. Which was something I was considering.
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Hi D. Hedin,
Bob was talking about the THD of the output stage only in one section of the video.
The 0.00_ numbers quoted are the closed loop THD @ 1 kHz which includes the global negative feedback.
I hope this helps & answers your question.
-Dan
Hey folks. MOSFET sound fan here in Sun Valley, Idaho (well, Hailey, down the road a bit). Popped in here a couple years back when I received my first Hafler, a P225, which was working fine and I grew to really love. I had it at home, and a Music Hall Class A at work, also MOSFET based. The P225 started popping the left speaker fuse (I still am not super good at electronics DIY, and start to tap out after anything more difficult than replacing pickups in a telecaster). So maybe it is something simple. But I also am interested in improving it, or the XL-280 I picked up and have in use now.BC-1 is still in the works, release some time in I hope winter/spring 2022. It is being designed for the 3Ux300mm chassis. There is a protection & PS pcbs, just like in the book. Nothing released until Bob gives it his blessing, just like DH-220CJust wanted to show you we are moving along, slowly, since you asked.
Good luck with DH-220C, I have mine running since the day I fired it up. Glad I fixed the AC switch issue, now I have to change out those old RCA jacks. I will try these Neutrik NYS367-2 & NYS367-9. The cheap ones from Asia just don't cut it for me.
I also have a previously modded DH-110 that was turned into a MC unit with a big outboard power supply. I received that used, and liked the sound well enough, over a lesser 2006 PS Audio preamp I had before, but it started humming. Kinda sounds like a bad ground. And the old two prong power cord connecting to the outboard power supply seems to be pulling loose, or at least the insulation is. So likely I will need to go through that (or more likely have it gone through). Have read about the disputes regarding MC stuff, and to mod or not to mod, and which way to go if one does. Interested in Mr. Cordell’s work and purchased the articles in AudioXPress to learn more also.
So for now, will keep using the XL-280 which seems to be working just fine, and learn, and see about purchasing either the DH-220C which I would guess would work for my P225? (will read and learn). But wanted to stop in and say hi, and throw out there what I am thinking about. For me, learning, and working to restore and/or improve these designs seems better than spending a few grand on something newer. Plus, I like the kinda beat up, ”Millennium Falcon” vibe my Hafler gear portrays.
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If you are talking about the case, I agree, but as I said, it does not bother me as long as it is working properly and well, from a looks perspective. As I also said, gives off a Millennium Falcon vibe that I am fine with. But yeah, the paint on everything Hafler seems fragile, and they seem to pick up nicks and scratches easily.I'm rather astonished about the marks of severe abuse many of the units shown in this thread (not only your's!) show
Best regards!
BUT, if you are talking about something you see inside the case that indicates abuse, please let me know. I am a electronics DIY newb and trying to learn. Thank you!
@rsavas
Also, I am not seeing where a person can purchase the DH-220C set, as I learn, shop and decide what to do.
Second, can one also purchase the output section set for a 3 MOSFET pair unit such as an XL-280?
Third, what is the BC-1? Somewhere I missed that in the thread.
The DH220C PCBs and jfets are available on eBay. Search for the delta9electronics seller. I highly recommend upgrading your P225 to DH220C. It’s such a great amplifier.
Bob Cordell and rsavas are developing the BC1 as a follow up to Mr. Cordell’s latest amplifier design book. The amplifier is not available yet.
Bob Cordell and rsavas are developing the BC1 as a follow up to Mr. Cordell’s latest amplifier design book. The amplifier is not available yet.
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No, don't panic, I was referring to the external looks exclusively
.Best regards!
The less expensive option is the PCB only. The more expensive item also includes the JFETs you will need to complete the project.
You can use any design of transformer you wish, as long as it meets the voltage and current designs of the project. A toroidal transformer would work fine.
The P230 OPS board will allow you to use three output pairs.
You can use any design of transformer you wish, as long as it meets the voltage and current designs of the project. A toroidal transformer would work fine.
The P230 OPS board will allow you to use three output pairs.
Trying to fit a torroid into the space occupied by the original transformer is a challenge. Space is tight, do some measurements, floor planning first is a good idea.
Bc-1 is up and running, a few things to finish off. Bob has to do his build and evaluation before anything gets released.
Bc-1 replaces the dh-200c as my lab amp, powered off after a long 2 year always on evaluation.
I am planning to put the Dh-220c design into the same 3ux300mm dissipante chassis as is used by bc-1, that way you can start from scratch not needing an old Hafler chassis to build this design.
Bc-1 is up and running, a few things to finish off. Bob has to do his build and evaluation before anything gets released.
Bc-1 replaces the dh-200c as my lab amp, powered off after a long 2 year always on evaluation.
I am planning to put the Dh-220c design into the same 3ux300mm dissipante chassis as is used by bc-1, that way you can start from scratch not needing an old Hafler chassis to build this design.
No, of course not, the DH-220C design is not for the UMS heatsink spec, it is designed for the Hafler DH-200, 220, 500, P225,P230 etc heatsink spec's
You are on your own if you use the kit for another application.
I just drilled & tapped the heatsinks for the BC-1 build so I have to solve this same situation of getting HiFi2000 to do that, if it is required.
Either I or the end user has to pay them to input the info for their CNC or I figure out how to do it myself (DFX,DWG). They charge extra for that service to input data, tap and then more if you want it re-anodized. So far I have a hand drawn drill template for BC-1.
Actually it is pretty easy to do, with a drill press, numbered drill bits, McMaster-Carr M3x0.5 drill/tap, DeWalt portable hand drill, 3 in 1 oil
Use the blank pcbs as your templates for the heatsink placement and drilling/tapping. Watch out for interference with the bottom pierced pan if you use it.
It will be written up in the BC-1 build procedure.
It is extra expense for UMS, something that is relatively easy to do. You do not need all those holes and have to pay for ones not needed.
The chassis is expense enough with shipping from Italy. Sure the US customers get free shipping, but for me in Canada and everyone else, we get the FedEx bill. It was just as much $ when I bought it directly. I bought Bob's off DIYAudio since it was free shipping for him
The UMS is for a 4U heatsink. It is another higher power design option. IMO the DH-220C design should go in the 3Ux300mm chassis to be the most economical and meet the needs of most home owners, unless you do not value your hearing
This BC-1 is a monster in itself, using a 500VA transformer. I just can't see the need for a 4U 200W+monster in a home, but to each their own I guess.
But the UMS was intended for a class "A" amp as well!! need it today, it is -16C out their, instead of warming the hands by the fire I put them on heatsinks under bias, have a good one ...
You are on your own if you use the kit for another application.
I just drilled & tapped the heatsinks for the BC-1 build so I have to solve this same situation of getting HiFi2000 to do that, if it is required.
Either I or the end user has to pay them to input the info for their CNC or I figure out how to do it myself (DFX,DWG). They charge extra for that service to input data, tap and then more if you want it re-anodized. So far I have a hand drawn drill template for BC-1.
Actually it is pretty easy to do, with a drill press, numbered drill bits, McMaster-Carr M3x0.5 drill/tap, DeWalt portable hand drill, 3 in 1 oil
Use the blank pcbs as your templates for the heatsink placement and drilling/tapping. Watch out for interference with the bottom pierced pan if you use it.
It will be written up in the BC-1 build procedure.
It is extra expense for UMS, something that is relatively easy to do. You do not need all those holes and have to pay for ones not needed.
The chassis is expense enough with shipping from Italy. Sure the US customers get free shipping, but for me in Canada and everyone else, we get the FedEx bill. It was just as much $ when I bought it directly. I bought Bob's off DIYAudio since it was free shipping for him
The UMS is for a 4U heatsink. It is another higher power design option. IMO the DH-220C design should go in the 3Ux300mm chassis to be the most economical and meet the needs of most home owners, unless you do not value your hearing
This BC-1 is a monster in itself, using a 500VA transformer. I just can't see the need for a 4U 200W+monster in a home, but to each their own I guess.
But the UMS was intended for a class "A" amp as well!! need it today, it is -16C out their, instead of warming the hands by the fire I put them on heatsinks under bias, have a good one ...
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Friends,
I could use some help debugging a 200-C front end module.
I finished the build in October/November and learned a lot along the way and enjoyed two months of sonic joy.
But at the moment I've got heavy DC (15V or more) coming through the output of one channel.
So I've popped the hood, put her in the service position with just the IPS/VAS board, in the TP jumper mode running, sending a sine wave and scope leads hooked to the drivers. The OPS is entirely disconnected and sitting to the side.
Both the V+ and V- side are passing the signal, but the V- is up in the + voltage range. So I'm thinking something is happening on the V- side of the equation. See attached images. On the second picture, I shifted the V+signal vertical position so you could see the V- signal sitting up in the positive voltage domain.
Voltage drops / current through R12/24 are correct, but nothing, I mean stone dead across R44. Which is weird, because I pulled Q17 and it tests properly in my little transistor tester and I am getting a signal to the driver wire to the OPS... just flipped in voltage.
Also, I've got 15mV across the +/- drive outs (terminal block points 4 and 9) and adjusting RV2 is having no effect on that.
I could use some help debugging a 200-C front end module.
I finished the build in October/November and learned a lot along the way and enjoyed two months of sonic joy.
But at the moment I've got heavy DC (15V or more) coming through the output of one channel.
So I've popped the hood, put her in the service position with just the IPS/VAS board, in the TP jumper mode running, sending a sine wave and scope leads hooked to the drivers. The OPS is entirely disconnected and sitting to the side.
Both the V+ and V- side are passing the signal, but the V- is up in the + voltage range. So I'm thinking something is happening on the V- side of the equation. See attached images. On the second picture, I shifted the V+signal vertical position so you could see the V- signal sitting up in the positive voltage domain.
Voltage drops / current through R12/24 are correct, but nothing, I mean stone dead across R44. Which is weird, because I pulled Q17 and it tests properly in my little transistor tester and I am getting a signal to the driver wire to the OPS... just flipped in voltage.
Also, I've got 15mV across the +/- drive outs (terminal block points 4 and 9) and adjusting RV2 is having no effect on that.
Attachments
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