Dick, I'm just gonna get basic... I figure that starting slow is probably best for me... These the ones with the screws... I figure I can worry about soldering after I learn a bit more theory...
Yup. Those big things that look like hand grenades with wires... This morning I replaced the Sangamos in my (already favorite) 200 with some new blue thangs, and the amp _does_ sound somewhat more alive. It already sounded good, and this seems to add a little to the low mids/lows...
Yup. Those big things that look like hand grenades with wires... This morning I replaced the Sangamos in my (already favorite) 200 with some new blue thangs, and the amp _does_ sound somewhat more alive. It already sounded good, and this seems to add a little to the low mids/lows...
Big caps replace
On my side I have picked the Cornell Dubilier computer grade type series DCMC.... You have to be prepared that they are quite expensive.
In one amp, I have installed 4 x 14000 uF ( 2 x 14000 using 2 separate diodes bridge pack per channel).
In the other amp, 2 x 30000 uF.
You have to check for cap value, voltage of 75V nominal, size (2 inches diameter to fit into the dh-200 cap holders), low post terminal depending on height of cap (so it can fit into the amp with the cover closed).
Bogie said:
On my side I have picked the Cornell Dubilier computer grade type series DCMC.... You have to be prepared that they are quite expensive.
In one amp, I have installed 4 x 14000 uF ( 2 x 14000 using 2 separate diodes bridge pack per channel).
In the other amp, 2 x 30000 uF.
You have to check for cap value, voltage of 75V nominal, size (2 inches diameter to fit into the dh-200 cap holders), low post terminal depending on height of cap (so it can fit into the amp with the cover closed).
Big caps replace
I am not sure of the question but anyway:
Make sure that the cap height is lower than the height of the dh-200 chassis while the dh-200 chassis cover is installed. In my case, only as an optional precaution, I have added isolation tape on the dh-200 cover interior at the location of the caps screws to prevent any contact for any reason between the caps contacts screws and the metal cover.
Bogie said:
I am not sure of the question but anyway:
Make sure that the cap height is lower than the height of the dh-200 chassis while the dh-200 chassis cover is installed. In my case, only as an optional precaution, I have added isolation tape on the dh-200 cover interior at the location of the caps screws to prevent any contact for any reason between the caps contacts screws and the metal cover.
DH-200 New card Tests
Here are some news:
I have done some progress on the NO sym card for the DH-200/220 but I am not happy with the bench test results. I may continue later. By the way the Hafler SE-120 uses a NO sym card to drive lateral power mosfets too.
I decided to complete the already advanced SYM circuit that included my previously discussed mods. In additon there are some other mods that I could not do on the stock DH-200 card. A pcb is populated and bench tested with a +/- 28 Vdc power supply. Here are some results:
*THD at 1K Hz <= 0.02% (could be less but my home made meter is not that accurate) at Vac = Vdc -10V in 8 ohms (see scope screenshot)
* Rise time = 2 us (see scope screenshots at 10KHz Square wave)
* 8 ohms + 1 uF at 4 Vac (see scope screenshots at 10KHz Square wave)
* 8 ohms + 2.2 uF at 4 Vac (see scope screenshots at 10KHz Square wave)
Not installed in DH-200 yet so I have not listened to it.
I will post the scope screenshots on the next posts.
Here are some news:
I have done some progress on the NO sym card for the DH-200/220 but I am not happy with the bench test results. I may continue later. By the way the Hafler SE-120 uses a NO sym card to drive lateral power mosfets too.
I decided to complete the already advanced SYM circuit that included my previously discussed mods. In additon there are some other mods that I could not do on the stock DH-200 card. A pcb is populated and bench tested with a +/- 28 Vdc power supply. Here are some results:
*THD at 1K Hz <= 0.02% (could be less but my home made meter is not that accurate) at Vac = Vdc -10V in 8 ohms (see scope screenshot)
* Rise time = 2 us (see scope screenshots at 10KHz Square wave)
* 8 ohms + 1 uF at 4 Vac (see scope screenshots at 10KHz Square wave)
* 8 ohms + 2.2 uF at 4 Vac (see scope screenshots at 10KHz Square wave)
Not installed in DH-200 yet so I have not listened to it.
I will post the scope screenshots on the next posts.
DH-200 New card Tests
Picture of populated board under test:
It was not easy to fit all the components on a pcb of this size that fits in the DH-200/220.
I made 2 small mistakes on the pcb layout which I have easily corrected by drilling a hole to cut an extra trace and used a to-92 leg to connect to an adjacent point (missing trace).
Picture of populated board under test:
It was not easy to fit all the components on a pcb of this size that fits in the DH-200/220.
I made 2 small mistakes on the pcb layout which I have easily corrected by drilling a hole to cut an extra trace and used a to-92 leg to connect to an adjacent point (missing trace).
Attachments
DH-200 New card Tests
Thanks for the nice comment. I put a lot of work into that circuit.
I am awaiting comments also from DickWest and Still4given who had already indicated interest in a pcb with those mods.
The circuit is the same topology as the stock DH-200/220/500.
The pcb is in fact "configurable": it can be the same circuit as the stock DH-200 pc-6 board depending on the components not mounted and replaced with jumpers. Or, it can include some or all the mods. The circuit shown includes all mods:
- input diff stage CFP cascode
- current sources with increased tail current
- Enhanced darlington VAS CFP cascode stage
- CFP front-end driver for output mosfets with increased current and speed-up cap
- Symetrical CFP VBE Bias stage
- Low overall negative feedback (< 40 db)
- Lot of local feedback for each stage
- Mosfets source resistors
- Regulated front-end voltage supply on the pcb
- Voltage reference for all cascode voltages
- diodes for VAS stage overload as in DH-220/500 pc-19 board
- No output choke but only RC network
- matched NPN and associated PNP based on HFE within about 10%
- separated ground points to return to a single star point
The circuit could also be mounted to correspond to my actual 2 DH-200 mod amps.
So far, I got only one board done. Unfortunately, I got more tests to do including audio test as well of course.
I did not really think about selling boards. This first board cost me about 150$ in parts (pcb alone was 92$!).
CaliforniaBob said:
Thanks for the nice comment. I put a lot of work into that circuit.
I am awaiting comments also from DickWest and Still4given who had already indicated interest in a pcb with those mods.
The circuit is the same topology as the stock DH-200/220/500.
The pcb is in fact "configurable": it can be the same circuit as the stock DH-200 pc-6 board depending on the components not mounted and replaced with jumpers. Or, it can include some or all the mods. The circuit shown includes all mods:
- input diff stage CFP cascode
- current sources with increased tail current
- Enhanced darlington VAS CFP cascode stage
- CFP front-end driver for output mosfets with increased current and speed-up cap
- Symetrical CFP VBE Bias stage
- Low overall negative feedback (< 40 db)
- Lot of local feedback for each stage
- Mosfets source resistors
- Regulated front-end voltage supply on the pcb
- Voltage reference for all cascode voltages
- diodes for VAS stage overload as in DH-220/500 pc-19 board
- No output choke but only RC network
- matched NPN and associated PNP based on HFE within about 10%
- separated ground points to return to a single star point
The circuit could also be mounted to correspond to my actual 2 DH-200 mod amps.
So far, I got only one board done. Unfortunately, I got more tests to do including audio test as well of course.
I did not really think about selling boards. This first board cost me about 150$ in parts (pcb alone was 92$!).
I always have an interest in mods to Hafler amps and like to look at schematics and evaluate different circuits. You obviously have spent a great deal of time and effort to develop your present modified boards. However, the costs you mentioned and the time it would take to source and stuff parts does make me hesitant to jump into another project. I hope you don't feel your efforts are not appreciated.
Personally, I have spent considerable time in the last 3 months evaluating several Hafler amps to determine which has the sound most preferred by me. As a reference point I use the Musical Concepts PA-3B circuits as installed in an old Hafler chassis. I have concluded I don't like a symmetrical circuit and instead prefer those that begin with a LTP, such as the MC cards and the DH-120, SE-120, Hafler 9130 and Pro 1200. This is just where I'm "at" for now.
Also, I spent the last 2 weeks listening carefully to a Hafler XL-280 amp with a symmetrical circuit and JFET inputs. It had a very clean and clear sound, great bass and highs, but somehow was tiring to listen to. It was just not as "musical" as the other circuits mentioned above. I wonder why?
If your circuit gets built by others and has favorable reports my interest will increase but for now I can't guarantee I would persue it.
One thing that could be of interest to me and perhaps others would be a schematic and parts layout for the voltage regulators for the circuit cards I see you have built into to your version. These little regulators, as "wings" to present cards, could be attached to and bolted underneath the present card and sufficient space should be available for them in a stock amp. Any thoughts on this?
Personally, I have spent considerable time in the last 3 months evaluating several Hafler amps to determine which has the sound most preferred by me. As a reference point I use the Musical Concepts PA-3B circuits as installed in an old Hafler chassis. I have concluded I don't like a symmetrical circuit and instead prefer those that begin with a LTP, such as the MC cards and the DH-120, SE-120, Hafler 9130 and Pro 1200. This is just where I'm "at" for now.
Also, I spent the last 2 weeks listening carefully to a Hafler XL-280 amp with a symmetrical circuit and JFET inputs. It had a very clean and clear sound, great bass and highs, but somehow was tiring to listen to. It was just not as "musical" as the other circuits mentioned above. I wonder why?
If your circuit gets built by others and has favorable reports my interest will increase but for now I can't guarantee I would persue it.
One thing that could be of interest to me and perhaps others would be a schematic and parts layout for the voltage regulators for the circuit cards I see you have built into to your version. These little regulators, as "wings" to present cards, could be attached to and bolted underneath the present card and sufficient space should be available for them in a stock amp. Any thoughts on this?
DH-200 New card Tests
Thanks for your comments Dick
I understand that you have a "crunch" for the Musical Concept board.
I think that you have a good approach too by comparing different circuits with same output transistors. I learned a lot doing that too...more than comparing too different amps.
Regarding the difference between Symetrical and non-symetrical circuit I do not believe that one is better than the other. The LEACH amp which is so much appreciated is a SYMETRICAL circuit. In fact I used several of Leach circuit idea in my new amp circuit. A non-sym circuit can sound bad and a sym circuit too or they can both sound good also. It really depends on the implementation details of the circuit. Also, I am sure that you will agree that a lot of appreciation in sound is sometimes more a matter of "taste" than true real performance of the circuit. For example some peoples do not like to hear the "defects" of certain recordings and prefer a more "rounded" sound to not hear the defects.
The LTP is also used in a symetrical circuit, it is just that there is two (one LTP per polarity) in the input stage.
Do not pay attention to the price because it is only the first board. With higher qty the price could be cheaper if required.
My first aim is that this is a personal project to improve the sound of my system and share my findings. If some peoples are curious enough to try it and want to share their opinion on the sound...As I have indicated in previous posts the peoples has positively commented my actual mods without knowing that my DH-200 amps had mods.
For the regulator circuit, I have previously indicated to send me e-mail since it is a pain to have the information segmented in different parts so it can be posted. I received several requests so far which I have responded. I have attached a picture of the regulator boards in one of my DH-200 amp. The board is attached with "glued" low profile posts on each side of the transformer. The electrolytic caps are quite high and may be hard to locate the board between the stock circuit and the heatsink.
Thanks for your comments Dick
I understand that you have a "crunch" for the Musical Concept board.
I think that you have a good approach too by comparing different circuits with same output transistors. I learned a lot doing that too...more than comparing too different amps.
Regarding the difference between Symetrical and non-symetrical circuit I do not believe that one is better than the other. The LEACH amp which is so much appreciated is a SYMETRICAL circuit. In fact I used several of Leach circuit idea in my new amp circuit. A non-sym circuit can sound bad and a sym circuit too or they can both sound good also. It really depends on the implementation details of the circuit. Also, I am sure that you will agree that a lot of appreciation in sound is sometimes more a matter of "taste" than true real performance of the circuit. For example some peoples do not like to hear the "defects" of certain recordings and prefer a more "rounded" sound to not hear the defects.
The LTP is also used in a symetrical circuit, it is just that there is two (one LTP per polarity) in the input stage.
Do not pay attention to the price because it is only the first board. With higher qty the price could be cheaper if required.
My first aim is that this is a personal project to improve the sound of my system and share my findings. If some peoples are curious enough to try it and want to share their opinion on the sound...As I have indicated in previous posts the peoples has positively commented my actual mods without knowing that my DH-200 amps had mods.
For the regulator circuit, I have previously indicated to send me e-mail since it is a pain to have the information segmented in different parts so it can be posted. I received several requests so far which I have responded. I have attached a picture of the regulator boards in one of my DH-200 amp. The board is attached with "glued" low profile posts on each side of the transformer. The electrolytic caps are quite high and may be hard to locate the board between the stock circuit and the heatsink.
Attachments
Is this thread still active? If so I would be glad to post experiences with making a pair of monoblocks out of a DH-220 using the PC-19C circuit cards. Also, several PS cap changes were evaluated for sound. Some wiring was changed to be similar to that used in the MC mods, such as bypassed speaker fuse loop, floating RCA inputs jacks and enhanced star grounding. All in all a good sound pair of monoblocks that now sound quite different and better than the stock stereo DH-220 amp. Heck, I'll even include some pictures. Just let me know of your interest.
Thanks........
Thanks........
