Hi Ron,
Imo, your application is outside the scope of this discussion thread, so it should probably end here, as I will not respond with answers nor suggestions to perpetuate it further. We can discuss this in a new and different thread possibly or offline as my time allows.
Supporting this new DH-220C design in other than intended applications, enters into un-chartered territory for which it should be done separately and in many cases you are on your own with limited or no support from me at least. Same goes with DH-500 at this point in time until DH-220C can be evaluated in that application, as my time permits as well.
Rick
Imo, your application is outside the scope of this discussion thread, so it should probably end here, as I will not respond with answers nor suggestions to perpetuate it further. We can discuss this in a new and different thread possibly or offline as my time allows.
Supporting this new DH-220C design in other than intended applications, enters into un-chartered territory for which it should be done separately and in many cases you are on your own with limited or no support from me at least. Same goes with DH-500 at this point in time until DH-220C can be evaluated in that application, as my time permits as well.
Rick
No problem Rick. There is plenty of interest here with the DH-200/DH-220. Sorry to muck up the conversation. I'll keep future posts here on target with the original intent of the thread.
Ron
Great looking end product / loaded boards.
Respectfully, they must sound marginal
or OK, with grossly limited stock supply.
May'be a film bypass over PS caps??
I certainly would not care to 'model circuit'
with standard rectifier and wretched filter
caps...
Sorry to be critical of approach.
I would struggle to trust it.
Respectfully, they must sound marginal
or OK, with grossly limited stock supply.
May'be a film bypass over PS caps??
I certainly would not care to 'model circuit'
with standard rectifier and wretched filter
caps...
Sorry to be critical of approach.
I would struggle to trust it.
So I saw the output boards on Ebay. (DH-220C OPS)
I went to purchase a couple, but the shipping was almost as much as the 2 boards!
But cheaper shipping options became available after I went to "checkout"--I bought 2 sets of boards.
So don't be scared off by the initial shipping cost shown!
Ron
David Hafler DH-200, DH-220, P225 Output Stage pcb (new) | eBay
I went to purchase a couple, but the shipping was almost as much as the 2 boards!
But cheaper shipping options became available after I went to "checkout"--I bought 2 sets of boards.
So don't be scared off by the initial shipping cost shown!
Ron
David Hafler DH-200, DH-220, P225 Output Stage pcb (new) | eBay
I have been doing some snubber optimization measurements on some Hafler amps using the Mark Johnson Quasimodo board. I thought the results would be relevant to this thread. I post them below, and to learn more please see the following thread:
Simple, no-math transformer snubber using Quasimodo test-jig
The measurements below were taken in order to optimize the value of R in a snubber circuit placed on the secondaries of the transformer in these amps as shown below.
Although it is not certain that the transformers for all the same type of amplifier are similar enough for these values apply to every amplifier, the fact that I obtained very similar results across 3 different DH-200's I measured leads me to believe that these values likely good for most of the amps out there. But if anyone has measured different values than this it would be good to know.
Ron
Simple, no-math transformer snubber using Quasimodo test-jig
The measurements below were taken in order to optimize the value of R in a snubber circuit placed on the secondaries of the transformer in these amps as shown below.
Although it is not certain that the transformers for all the same type of amplifier are similar enough for these values apply to every amplifier, the fact that I obtained very similar results across 3 different DH-200's I measured leads me to believe that these values likely good for most of the amps out there. But if anyone has measured different values than this it would be good to know.
- Hafler P-230: Single secondary with CT yielding DC rails +/-65 VDC
Cx = 0.01 uF
Cs = 0.15 uF
Rs = 29 Ω
(Both sides measured the same R, see below)
Note: I'm not positive this is the same type of transformer used in DH-220, but it likely is.
Cs = 0.15 uF
Rs = 29 Ω
(Both sides measured the same R, see below)
Note: I'm not positive this is the same type of transformer used in DH-220, but it likely is.
- Hafler DH-200: Single secondary with CT yielding DC rails +/-60 VDC (I measured 3 different Hafler DH-200 amps, they all yielded similar results)
Cx = 0.01 uF
Cs = 0.15 uF
Rs = 35 Ω
Note1: I consistently obtained a slightly different result for R when I measured the 2nd secondary (against CT) vs. the 1st secondary. The results for each were 40 Ω vs. 28 Ω. So I think 35 Ω is an OK value for either side.
Cs = 0.15 uF
Rs = 35 Ω
Note1: I consistently obtained a slightly different result for R when I measured the 2nd secondary (against CT) vs. the 1st secondary. The results for each were 40 Ω vs. 28 Ω. So I think 35 Ω is an OK value for either side.
- Hafler DH-500: Single secondary with CT yielding DC rails +/-90 VDC
Cx = 0.01 uF
Cs = 0.15 uF
Rs = 65 Ω
Cs = 0.15 uF
Rs = 65 Ω
- Hafler XL-280: Dual secondaries each with 2 leads, (high current and low current) giving DC rails of +/- 65VDC and 75 VDC respectively. (All secondaries measured approximately the same for R.)
Cx = 0.01 uF
Cs = 0.15 uF
Rs = 12 Ω
Regards,Cs = 0.15 uF
Rs = 12 Ω
Ron
Attachments
So I guess maybe this part of the thread should be moved to the Vendor section. I'm sorry if I wrote something out of line.
Thanks! An important feature I incorporated into the output boards is the inclusion of twin Zobel networks in close proximity to the sources and ground with the goal of increasing VHF stability. Twin Zobels also distribute Zobel resistor power dissipation, allowing the use of smaller 3-watt metal oxide film resistors that are naturally virtually non-inductive.
Ditto local bypassing of the rails. The 470 uF electrolytics on the output board also help to resolve the class-AB half-wave-rectified currents local to the output stage, especially at high frequencies, reducing the amount of those currents flowing in the power supply leads back to the main amplifier reservoir capacitors.
The front-end boards should be available quite soon. The design and layout is now essentially frozen, after quite a bit of component value and layout tweaking. Those boards will be made available with through-hole pads for use of TO-71 JFETs on the top of the board (socketed or soldered) and will also include pads on the bottom of the board for SOT-23 surface mount JFETs that are less expensive. A number of prototypes have been built and evaluated by both Rick Savas and myself. BTW, his PCBs are very professional and a pleasure to work with. The Mouser BOM also makes ordering the needed parts quite convenient.
The prototype has been tested with loads as low as 2 ohms, and works fine. Quite high levels of power are available at 2 ohms on a burst basis that does not tax power dissipation over too long a period of time. It has also been tested for stability with direct capacitive loads from 0.001 uF up to 1.0 uF.
Cheers,
Bob
Thanks, Bob. Sounds exactly like what I need. I’ll wait until all the boards are available and place my order then.
I’m a bit of a Hafler fan. I’m also looking forward to a possible expansion to the DH-500 and XL series.
If I am able to give back something useful to this community I am very happy because I have received much help here from people of much higher skill than myself (e.g. Bob Cordell, Rick Savas, etc.).
The optimization procedure is the brain child of Mark Johnson. In his own words,
Instead of measuring the transformer and then calculating the snubber, why not simply connect an adjustable snubber across the secondary, stimulate the resonant circuit to make it ring , and then adjust the snubber until you find a setting where all ringing is perfectly damped?
The adjustment is accomplished using a 20-turn pot instead of a fixed R. The ringing is accomplished using a jig (circuit) designed by Mark which when connected to the transformer secondaries and powered produces ringing which can be observed on an oscilloscope. The pot is turned until the ringing is critically damped, revealing the optimum R for the snubber circuit.
Per the procedure defined in Mark Johnson's white paper (available in the thread referenced in my previous post) the transformer is isolated from the circuit during the testing, the primaries are shorted and the secondary not under test is grounded to CT. The value of Cx is chosen so as to be much larger than the transformer secondary capacitance as well as the rectifier capacitance, rendering their contribution to the "answer" negligible. Or again quoting Mark Johnson,
CRC snubber capacitor Cx is connected in parallel with the tranformer's secondary capacitance CT. (Cx is also in parallel with the capacitance of the rectifier(s)). Therefore the total capacitance of the resonant circuit is the parallel combination (CT + Cx + CRECTIFIER ), and it is this total capacitance which determines the oscillatory behavior...the CRC topology gives the freedom to choose Cx >> CRECTIFIER, thereby making the capacitance of the rectifier a negligible fraction of the total. ...If Cx >> CRECTIFIER , it simply doesn't matter what the actual value of CRECTIFIER happens to be.
I think this answers your concern.
I've attached some data from my own testing. Mark Johnson's white paper also has some excellent examples.
Regards,
Ron
Attachments
Nice work, Ron. This definitely answers my question. Kudos to Mark as well.
Cheers,
Bob
Hi all,
I picked up a DH-220 a few years ago for a good price at a flea market and got a cap kit for it, and, well, with an enforced sabbatical these days, maybe it's time to fire it up. It's stock, looks like maybe factory build, no newer parts or janky solder joints I can see. Pretty clean.
I read through this whole thread and cobbled together a list of minor upgrades/fixes, but at this point I want to restore more than mod. So, thanks for all the amazing thinking and experience here.
BUT, opened up the case and saw that both rail fuses on one channel were blown. I had been planning planning on just turning it on to verify it worked before starting to swap out caps and anything else. Since I've read it's possible that bad filter caps could cause problems, I went ahead and swapped those out for the new, higher value ones, but didn't do anything else. I pulled all the rail caps and checked the voltages, which were all in the high 60-something volt range; seemed OK.
So...did my best to check the big mosfets. Did that little trick where you short out the pins to discharge, then put a probe on the case, touch one pin and you get an open circuit, then hit the other pin to charge it up, then back to the first pin and it shows conductance. All 4 mostfets showed this active behavior--I'm assuming this means they're at least not blown out--correct?
So, wondering what my next move should be. Should I make a light bulb rig and turn it on with that? Just plug it in and see what happens--and check the bias and offset?
Don't want to make matters worse. Any thoughts appreciated.
I picked up a DH-220 a few years ago for a good price at a flea market and got a cap kit for it, and, well, with an enforced sabbatical these days, maybe it's time to fire it up. It's stock, looks like maybe factory build, no newer parts or janky solder joints I can see. Pretty clean.
I read through this whole thread and cobbled together a list of minor upgrades/fixes, but at this point I want to restore more than mod. So, thanks for all the amazing thinking and experience here.
BUT, opened up the case and saw that both rail fuses on one channel were blown. I had been planning planning on just turning it on to verify it worked before starting to swap out caps and anything else. Since I've read it's possible that bad filter caps could cause problems, I went ahead and swapped those out for the new, higher value ones, but didn't do anything else. I pulled all the rail caps and checked the voltages, which were all in the high 60-something volt range; seemed OK.
So...did my best to check the big mosfets. Did that little trick where you short out the pins to discharge, then put a probe on the case, touch one pin and you get an open circuit, then hit the other pin to charge it up, then back to the first pin and it shows conductance. All 4 mostfets showed this active behavior--I'm assuming this means they're at least not blown out--correct?
So, wondering what my next move should be. Should I make a light bulb rig and turn it on with that? Just plug it in and see what happens--and check the bias and offset?
Don't want to make matters worse. Any thoughts appreciated.
I think it would be prudent to build that dim bulb tester(DBT) & use that to power up as a start. You could also replace the rail fuses temporarily with 100 Ohm/5W resistors soldered across the old blown fuses to measure the current being drawn. Then perform the regular tests for DC offset. Once you determine that currents drawn seem normal you can then put it back to normal.
Received my boards--very weighty, feel nice.
Found a couple Mouser parts out of stock. For the first one there are variants of higher voltage rating with same dimension that I think will do fine:
- replaced MKP2D031001F00KI00 with 505-MKP2F03100F00JS
- replace FKP2D022201L00KSSD with FKP2F021501L00HSSD (?)
Thanks,
Ron
Actually I found a Mouser P/N that is very close:
FKP2D022201L00HSSD
Seems identical but with closer tolerance (2.5% vs. 10% for the specified P/N)
Changed the cart for 505-FKP20.022/100/2, since none are on order for FKP2D022201L00KSSD. Good you found it too, nice to have lots of alternatives.
My choices for subs,
505-MKP2.1/100/10
505-FKP20.022/100/2
In the future, it is best to email me at the address I supply in the docs. It so happened I visited this site today, so got an email notification. If you do not go to this site, on a daily basis, they do not send out emails, so it is easy to miss questions like this one.
My choices for subs,
505-MKP2.1/100/10
505-FKP20.022/100/2
In the future, it is best to email me at the address I supply in the docs. It so happened I visited this site today, so got an email notification. If you do not go to this site, on a daily basis, they do not send out emails, so it is easy to miss questions like this one.
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