Congrats on your success with new caps.
Lateral Hitachi MOSFETs are rugged devices and if kept properly fused and used with at least a modicum of caution, they rarely fail.
BIAS can be checked with a DC ammeter that can handle up to 500 ma of current. At this juncture you really should be using a Variac to slowly ramp up the voltage to your amp to make checks on things such as bias and DC offset at the outputs. But, first, your new caps should be "formed."
Remove the line fuses from both channels and install load resistors (3000 ohms 10 watts) across the caps. Ramp up the voltage to the caps slowly, say over a period of an hour, while monitoring their voltages. You should bring the voltage up to your caps to 10% over, to around 70 VDC. After an hour or so of forming you can remove power and observe if both caps bleed off their votage at approx the same rate.
Then, while still using the variac, you can check the bias. replace just the line fuse to the negative PS rail, for one channel only. Attach your multimeter to replace the missing positive line rail fuse. Observe that the meter's leads are properly polarized. Oh, make sure the screws are removed that hold this channel's heat sink to the chassis. You want to fold out the heat sink to gain easy access to the adjustment potentiometers.
I forgot, are you working with a P-230? If you are not working with a DH-200 then your circuit card will have two potentionmeters on it. P1 adjusts DC offset and P2 adjusts bias.
Begin to apply voltage and note DC amp reading across the location for the positive rail fuse. As you ramp up voltage you should see the bias reading increase. I believe the manual specifies around 280 ma bias. Many users routinely bias their amps to a higher level, such as 350 ma, as the higher level of bias is supposed to improve the sound. If you boost bias make sure the amp is properly ventilated as higher bias = higher idling current = more heat. Your final bias reading should be made with this channel fully warmed up, after 20 minutes or so.
You should also check this channel for DC offset. Place a 8 or 10 ohm resistor across its output terminals. I use a 10 watt sand cast variety. Place your meter's leads on either end of this resistor and measure for DC voltage. You should get a reading of 50 mv DC or less. You can adjust P1 to null out DC offset to almost zero. Note that changes in circuit temperature will change this reading but you should be able to get a less than 10 mv reading.
Remove all line fuses and do the same things with the other channel.
Most of all of this is explained in the DH-200 series of manuals (DH-200, DH-220) and in the P-225 and P-230 manuals. Good luck.............
Lateral Hitachi MOSFETs are rugged devices and if kept properly fused and used with at least a modicum of caution, they rarely fail.
BIAS can be checked with a DC ammeter that can handle up to 500 ma of current. At this juncture you really should be using a Variac to slowly ramp up the voltage to your amp to make checks on things such as bias and DC offset at the outputs. But, first, your new caps should be "formed."
Remove the line fuses from both channels and install load resistors (3000 ohms 10 watts) across the caps. Ramp up the voltage to the caps slowly, say over a period of an hour, while monitoring their voltages. You should bring the voltage up to your caps to 10% over, to around 70 VDC. After an hour or so of forming you can remove power and observe if both caps bleed off their votage at approx the same rate.
Then, while still using the variac, you can check the bias. replace just the line fuse to the negative PS rail, for one channel only. Attach your multimeter to replace the missing positive line rail fuse. Observe that the meter's leads are properly polarized. Oh, make sure the screws are removed that hold this channel's heat sink to the chassis. You want to fold out the heat sink to gain easy access to the adjustment potentiometers.
I forgot, are you working with a P-230? If you are not working with a DH-200 then your circuit card will have two potentionmeters on it. P1 adjusts DC offset and P2 adjusts bias.
Begin to apply voltage and note DC amp reading across the location for the positive rail fuse. As you ramp up voltage you should see the bias reading increase. I believe the manual specifies around 280 ma bias. Many users routinely bias their amps to a higher level, such as 350 ma, as the higher level of bias is supposed to improve the sound. If you boost bias make sure the amp is properly ventilated as higher bias = higher idling current = more heat. Your final bias reading should be made with this channel fully warmed up, after 20 minutes or so.
You should also check this channel for DC offset. Place a 8 or 10 ohm resistor across its output terminals. I use a 10 watt sand cast variety. Place your meter's leads on either end of this resistor and measure for DC voltage. You should get a reading of 50 mv DC or less. You can adjust P1 to null out DC offset to almost zero. Note that changes in circuit temperature will change this reading but you should be able to get a less than 10 mv reading.
Remove all line fuses and do the same things with the other channel.
Most of all of this is explained in the DH-200 series of manuals (DH-200, DH-220) and in the P-225 and P-230 manuals. Good luck.............
Hi Dick,
Thanks for the informative post. You suggest a Variac. Looks like something I will get some use of. Can you make some suggestions as to which type to buy for my needs? I looked at some on ebay, but there are many different types and sizes. I don't want to buy more than I need. This is just a hobby for me.
I hope I didn't hurt the new caps. All I did was install them turn the amp on. Didn't think about "forming" the new caps. I guess that's why techs get the big bucks.
I can get by without the amps right now so I will let them sit until I can do the things you've suggested. Thanks for all the help.
Blessings, Terry
Thanks for the informative post. You suggest a Variac. Looks like something I will get some use of. Can you make some suggestions as to which type to buy for my needs? I looked at some on ebay, but there are many different types and sizes. I don't want to buy more than I need. This is just a hobby for me.
I hope I didn't hurt the new caps. All I did was install them turn the amp on. Didn't think about "forming" the new caps. I guess that's why techs get the big bucks.
I can get by without the amps right now so I will let them sit until I can do the things you've suggested. Thanks for all the help.
Blessings, Terry
A Variac (autotransformer) is just a Variac. I got a used rotary model that originally was mounted through a hole in a panel on a test bench. They should last forever, given typical use patterns.
Three things to look for:
1. A panel meter showing the AC output would be a nice touch, though not required as long as it has a dial.
2. A wiring diagram to make sure it is connected properly for your local voltage source. Some can be reconfigured to work with 100 VAC sources, etc.
3. Get a Variac with the proper volt/amp rating. You want a variac husky enough to run an amp such as a Hafler p-230. I think a 7.5 amp rating is sufficient but a 10 amp would be even better. Don't get one of those little 2 or 3 amp varieties advertised.
I mounted my rotary model in an old AT computer power supply case.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=73153&item=3844605142&rd=1
This is one that looks like it would work for you. Maybe something similar is available cheaper. As I recall I paid $45 for mine.
Here is another one:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=23787&item=3844627332&rd=1
Hope this helps................
Three things to look for:
1. A panel meter showing the AC output would be a nice touch, though not required as long as it has a dial.
2. A wiring diagram to make sure it is connected properly for your local voltage source. Some can be reconfigured to work with 100 VAC sources, etc.
3. Get a Variac with the proper volt/amp rating. You want a variac husky enough to run an amp such as a Hafler p-230. I think a 7.5 amp rating is sufficient but a 10 amp would be even better. Don't get one of those little 2 or 3 amp varieties advertised.
I mounted my rotary model in an old AT computer power supply case.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=73153&item=3844605142&rd=1
This is one that looks like it would work for you. Maybe something similar is available cheaper. As I recall I paid $45 for mine.
Here is another one:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=23787&item=3844627332&rd=1
Hope this helps................
Hi still4given,
A 2A variac will allow you to get most amps up. The larger 10A models cost much more unless you are lucky. An ammeter is extremely useful. You can measure bias by putting a 1 ohm resistor across a blown fuse body and measure away. Normally, there are source resistors you can measure across.
I have a 2A unit permanently on my bench with all meters (V&A). My heavier units are on a shelf until I need them. This normally means a big tube amp.
Measure the DC offset *without* a load. Do not use a resistor or speaker. You do not want to draw current if you have an offset. If you want to stick a resistor in, use a 1/4 to 1/2 W unit that will open quickly. A witness resistor if you will.
Your bias current should still be in the ball park as long as the controls were not disturbed. You can fine tune that later. This will take a few hours, so be patient and let the amp stabilize between readings.
Dick,
The difference between the transistor types is the threshold voltage as far as testing goes. The lateral fets may begin to turn on around 2V, the vertical units over around 3V. Either way, the information on Nelsons site holds and is true. BTW, I am familiar with both types. Nelson Pass also makes reference to these differences.
Dynamically, The IR units in N channel have a very non-linear gate charge vs Vgs characteristic. This is somewhat different than the lateral fet. It will not matter in testing and matching. If testing the fets dynamically, you should be using a low impedance drive circuit. The same is true in circuit.
-Chris
A 2A variac will allow you to get most amps up. The larger 10A models cost much more unless you are lucky. An ammeter is extremely useful. You can measure bias by putting a 1 ohm resistor across a blown fuse body and measure away. Normally, there are source resistors you can measure across.
I have a 2A unit permanently on my bench with all meters (V&A). My heavier units are on a shelf until I need them. This normally means a big tube amp.
Measure the DC offset *without* a load. Do not use a resistor or speaker. You do not want to draw current if you have an offset. If you want to stick a resistor in, use a 1/4 to 1/2 W unit that will open quickly. A witness resistor if you will.
Your bias current should still be in the ball park as long as the controls were not disturbed. You can fine tune that later. This will take a few hours, so be patient and let the amp stabilize between readings.
Dick,
The difference between the transistor types is the threshold voltage as far as testing goes. The lateral fets may begin to turn on around 2V, the vertical units over around 3V. Either way, the information on Nelsons site holds and is true. BTW, I am familiar with both types. Nelson Pass also makes reference to these differences.
Dynamically, The IR units in N channel have a very non-linear gate charge vs Vgs characteristic. This is somewhat different than the lateral fet. It will not matter in testing and matching. If testing the fets dynamically, you should be using a low impedance drive circuit. The same is true in circuit.
-Chris
OK, well I bought this multimeter from Radio Shack. Will this do all the tests we've talked about here?
I guess the next thing would be to get a variac and a scope. I will keep my eyes open for a good deal on those.
The manual I have for the P225-230 doesn't have the section about checking the bias. I'm missings pages 5-12. I wonder why Hafler leaves those out of the download.
I bridged my two P230's last night and ran one for each channel. One of them is a little louder than the other. I replaced the transformer in that louder one with a new TT-XL280E. It is the multi voltage version. I think it puts out a little more voltage than the stock unit. Not a lot, maybe 4 or 5 volts. Could this account for the louder output? I have a second TT-XL280E. I bought two when I was told that the tranny was bad in the one I had checked. It was after finding out that the caps were bad that I didn't bother changing out the second one.
Will it hurt anything having the extra voltage?
Thanks, Terry
I guess the next thing would be to get a variac and a scope. I will keep my eyes open for a good deal on those.
The manual I have for the P225-230 doesn't have the section about checking the bias. I'm missings pages 5-12. I wonder why Hafler leaves those out of the download.
I bridged my two P230's last night and ran one for each channel. One of them is a little louder than the other. I replaced the transformer in that louder one with a new TT-XL280E. It is the multi voltage version. I think it puts out a little more voltage than the stock unit. Not a lot, maybe 4 or 5 volts. Could this account for the louder output? I have a second TT-XL280E. I bought two when I was told that the tranny was bad in the one I had checked. It was after finding out that the caps were bad that I didn't bother changing out the second one.
Will it hurt anything having the extra voltage?
Thanks, Terry
Hi Terry,
That meter should do fine. Be careful that the least significant digit in the accuracy spec is +/- 4 digits. The last digit on your reading is basically useless. Just keep this fact in mind and you will be okay. Neat looking meter though.
The loudness difference is a gain difference. Run a 1KHz tone into the amp., both channels, and measure the output voltage. Try loaded and unloaded (not too loud). If you measure a difference, look at the feedback network resistors. If there are any electrolytic caps to ground in the feedback or input stage, just replace them with new. A higher voltage should not change the gain by any great amount, if at all.
The only thing you should check is to make sure the rectified voltage does not exceed the voltage rating on your filter caps, or any others from the supply to ground.
-Chris
That meter should do fine. Be careful that the least significant digit in the accuracy spec is +/- 4 digits. The last digit on your reading is basically useless. Just keep this fact in mind and you will be okay. Neat looking meter though.
The loudness difference is a gain difference. Run a 1KHz tone into the amp., both channels, and measure the output voltage. Try loaded and unloaded (not too loud). If you measure a difference, look at the feedback network resistors. If there are any electrolytic caps to ground in the feedback or input stage, just replace them with new. A higher voltage should not change the gain by any great amount, if at all.
The only thing you should check is to make sure the rectified voltage does not exceed the voltage rating on your filter caps, or any others from the supply to ground.
-Chris
Terry,
Anatech gives good advice, even if it might be technically a little over your head. Do you have a signal generator and a scope and know how to use them? Many of us do not.
I would caution against transformer swapping. The XL-280 transformer has two sets of secondary windings. One will provide ~75DVC after rectification. The other set of windings provide the same as the P-230 transformer (~65VDC). The booster windings with the higher voltage are not high amperage ratings. This 2nd set of windings is only intended to run the low level circuit card which only uses around 500 mA of current.
Don't fuss too much about slight differences in output level of two different amps. These amps have input level controls which can help balance the perceived loudness level of each channel.
The low level circuit card in the P-225/P-230 is the same as that in the DH-220. Download the DH-220 manual and you will find the info desired about bias level setting, etc. The P series manuals are skimpy and I believe Hafler assumes these amps will be used by Professionals who do not need all of the extra info.
Anatech gives good advice, even if it might be technically a little over your head. Do you have a signal generator and a scope and know how to use them? Many of us do not.
I would caution against transformer swapping. The XL-280 transformer has two sets of secondary windings. One will provide ~75DVC after rectification. The other set of windings provide the same as the P-230 transformer (~65VDC). The booster windings with the higher voltage are not high amperage ratings. This 2nd set of windings is only intended to run the low level circuit card which only uses around 500 mA of current.
Don't fuss too much about slight differences in output level of two different amps. These amps have input level controls which can help balance the perceived loudness level of each channel.
The low level circuit card in the P-225/P-230 is the same as that in the DH-220. Download the DH-220 manual and you will find the info desired about bias level setting, etc. The P series manuals are skimpy and I believe Hafler assumes these amps will be used by Professionals who do not need all of the extra info.
Dick West said:
Hi Dick,
No, I don't have a scope and sure don't know how to use one.......yet I do have signal generator software that I think I could use for that. I'm not sure about that.
Thanks for the warning about the atransformer. When I bought them, they came with a copy of the page from the Hafler mnual showing how to wire them. I'm pretty sure I've got it right since it plays and sounds fine. I could at this point put the old one back in if I ned to since it was the caps that were the problem.
Most of what you guys are telling me is over my head right now but I am progressing just the same. It's mostly the terminology that makes my head spin. I really need to get a good electronic for dummies book so I can learn what all the terms mean.
As far as the manual goes. i have the original manual for the DH-200. It came with the DH-200 that I bought. I searched through it but don't see any instructions for setting the bias. I look more closely, perhaps i missed something.
Thanks so much for your help.
Blessings, Terry
Terry,
Download the manual for the DH-220. Its circuit card is very different from the one in the older DH-200. Your DH-200 manual is of little use for a P-230. At the bottom of the DH220 manual, page 10, you will see the section heading "Adjustments for Bias and DC offset."
Also, you can study the manuals for the bridging kit for the DH-220. Do not confuse it with the bridging kit for the DH-200.
Tell us more about how you installed a XL-280 transformer in the P-230. Did you install a 2nd small bridge rectifier to supply voltage to the low level circuit cards?
In the XL280 the main secondary (65VDC) goes only to the MOSFETs. The booster winding secondary (~75VDC after rectification) goes ONLY to the rails of the low level circuit card.
Download the manual for the DH-220. Its circuit card is very different from the one in the older DH-200. Your DH-200 manual is of little use for a P-230. At the bottom of the DH220 manual, page 10, you will see the section heading "Adjustments for Bias and DC offset."
Also, you can study the manuals for the bridging kit for the DH-220. Do not confuse it with the bridging kit for the DH-200.
Tell us more about how you installed a XL-280 transformer in the P-230. Did you install a 2nd small bridge rectifier to supply voltage to the low level circuit cards?
In the XL280 the main secondary (65VDC) goes only to the MOSFETs. The booster winding secondary (~75VDC after rectification) goes ONLY to the rails of the low level circuit card.
Dick West said:
Thanks Dick,
I'll DL that manual.
As far as the XL-280 transformer. I hooked it up based on the drawing in the P230 manual for overseas wiring. I didn't hook up the secondary wiring at all.
The drawing showed it landing on a terminal strip but didn't show anything else hooking up to it so I just left them off. I thought that the secondary winding must be for a different model since the P230 had no such wires. If this is not right, please tell me.
Thanks again, Terry
You were smart (and lucky) to leave the 2nd set of secondary windings un-connected. The main secondary winding provides ~65VDC after rectification, which is the same voltage provided by the P-230 transformer as well as that of the transformers in the P-225, DH-220, DH-200 amplifiers. In other words, installing the XL-280 transformer provided you with no sonic benefit.
DL the XL-280 manual and you can see how the booster winding is connected to operate the circuit cards at a voltage ~ 5VDC higher than that which goes to the output section (MOSFETs). About 5VDC are required to turn on the gates of the MOSFETs so a low level circuit card that runs at ~5VDC higher than the MOSFETs can help the amp eke out a few more watts of power with about the same amount of power consumed and heat produced. But this is only for the XL-280 amp with circuit card parts values sized for the higher voltage.
The MOSFETs you have are only safe to use with +/- 65VDC rail voltages. Running them on 75 or 80 VDC will probably blow them up rather quickly. If you must have a higher output from an amp get a DH-500.
The parts on the P-230 (and DH-220) circuit cards are almost all identical to the cards in the DH-500 which runs at +/-90VDC. The values of several small resistors are varied in the DH-220 and DH-500 amps to set the proper operating voltages for transistors.
You need to DL the schematics and parts lists for these various amps and study them thoroughly. Then, you will begin to understand a little more about how to work with them and why there are similarities and differences in their parts values.
Dick
DL the XL-280 manual and you can see how the booster winding is connected to operate the circuit cards at a voltage ~ 5VDC higher than that which goes to the output section (MOSFETs). About 5VDC are required to turn on the gates of the MOSFETs so a low level circuit card that runs at ~5VDC higher than the MOSFETs can help the amp eke out a few more watts of power with about the same amount of power consumed and heat produced. But this is only for the XL-280 amp with circuit card parts values sized for the higher voltage.
The MOSFETs you have are only safe to use with +/- 65VDC rail voltages. Running them on 75 or 80 VDC will probably blow them up rather quickly. If you must have a higher output from an amp get a DH-500.
The parts on the P-230 (and DH-220) circuit cards are almost all identical to the cards in the DH-500 which runs at +/-90VDC. The values of several small resistors are varied in the DH-220 and DH-500 amps to set the proper operating voltages for transistors.
You need to DL the schematics and parts lists for these various amps and study them thoroughly. Then, you will begin to understand a little more about how to work with them and why there are similarities and differences in their parts values.
Dick
Hi Dick,
Thanks so much for taking so much time with me on this. I am really beginning to get a grasp on some of this. The DH-200 manual is very clear on how to adjust the bias. I will do that in the next couple of days as time allows. I will do as you say and DL the other manuals so I can check the differences.
My hunger for knowledge on this stuff is really getting strong. I'm going to have to find a good study on this so I can start understanding all the terms.
Hopefully I'm not too old a dog to learn this stuff.
Blessings, Terry
Thanks so much for taking so much time with me on this. I am really beginning to get a grasp on some of this. The DH-200 manual is very clear on how to adjust the bias. I will do that in the next couple of days as time allows. I will do as you say and DL the other manuals so I can check the differences.
My hunger for knowledge on this stuff is really getting strong. I'm going to have to find a good study on this so I can start understanding all the terms.
Hopefully I'm not too old a dog to learn this stuff.
Blessings, Terry
I have used nothing but the DH-200/220/P-225 series Hafler amps for over 20 years. Their manuals are clear, their internal layouts are clear, and parts do remain available for fixing them. As long as their sound is OK to a person he can do no better than use them. They are cheap and dependable and will tolerate a 4 ohm load all day long.
D/L and study thoroughly the DH-220 manual. Learn to read the schematic for the circuit card. Note that the manual includes a table of voltage values expected for various circuit points (referenced to circuit ground). I have repaired two of these amps using nothing but a VOM and a comparison of these voltage readings between the good and bad channels to help determine which transistors needed to be replaced.
The driver and pre-driver transistors are those that most frequently fail, all things being equal. The 4 transistors in the initial dual differential input circuit sometimes drift out of spec and cause DC offset, sometimes even more DC offset than the P1 nulling potentiometer can correct. These 4 transistors should be matched NPN/PNP and PNP/PNP, NPN/NPN for hFe. Hafler matched them within 10%. Matched sets are no longer available and to get matched pairs one might have to purchase 20-30 of each type and make his own matches, using the hFe function which I hope is included on your VOM.
Then, if you want more sonic bliss for a detailed and nuanced stereo system, consider replacing the circuit cards with the PA-3B cards from Musical Concepts. An old Hafler chassis provides a cheap way to do this mod which creates a new and improved sounding amplifier.
Good luck.
D/L and study thoroughly the DH-220 manual. Learn to read the schematic for the circuit card. Note that the manual includes a table of voltage values expected for various circuit points (referenced to circuit ground). I have repaired two of these amps using nothing but a VOM and a comparison of these voltage readings between the good and bad channels to help determine which transistors needed to be replaced.
The driver and pre-driver transistors are those that most frequently fail, all things being equal. The 4 transistors in the initial dual differential input circuit sometimes drift out of spec and cause DC offset, sometimes even more DC offset than the P1 nulling potentiometer can correct. These 4 transistors should be matched NPN/PNP and PNP/PNP, NPN/NPN for hFe. Hafler matched them within 10%. Matched sets are no longer available and to get matched pairs one might have to purchase 20-30 of each type and make his own matches, using the hFe function which I hope is included on your VOM.
Then, if you want more sonic bliss for a detailed and nuanced stereo system, consider replacing the circuit cards with the PA-3B cards from Musical Concepts. An old Hafler chassis provides a cheap way to do this mod which creates a new and improved sounding amplifier.
Good luck.
Hi Dick,
Thanks for the info about the voltages. I saw that chart but didn't understand it until your latest post. Do you remove the circuit boards from the heatsinks to do the readings or can they be done from the component side?
Also, I looked at the mods on the Musical Concepts website. Have you used any of these boards? Also, they specifiy the DH200/220/XL-280, but say nothing abut the P230. Do you know if these will work in the P230?
As far as the sound of these Haflers, I liked them real well until I got my Soundcraftsmen PCR800 working. Now they sound a bit edgy to me by comparison.
I'm wondering something else. The Soundcraftsmen uses basically the same MOSFET's as the DH-200, yet the Soundcraftsmen puts out 200 WPC and the DH-200 only 100 WPC. Each have 8 MOSFETS. The P230 Has 12 MOSFETS and only puts out 115 WPC. Do you know the reason for this?
Thanks, Terry
Thanks for the info about the voltages. I saw that chart but didn't understand it until your latest post. Do you remove the circuit boards from the heatsinks to do the readings or can they be done from the component side?
Also, I looked at the mods on the Musical Concepts website. Have you used any of these boards? Also, they specifiy the DH200/220/XL-280, but say nothing abut the P230. Do you know if these will work in the P230?
As far as the sound of these Haflers, I liked them real well until I got my Soundcraftsmen PCR800 working. Now they sound a bit edgy to me by comparison.
I'm wondering something else. The Soundcraftsmen uses basically the same MOSFET's as the DH-200, yet the Soundcraftsmen puts out 200 WPC and the DH-200 only 100 WPC. Each have 8 MOSFETS. The P230 Has 12 MOSFETS and only puts out 115 WPC. Do you know the reason for this?
Thanks, Terry
I have an MC modified amp with the PA3b circuit cards and it is my favorite amp here to use to listen to fine details on things such as a string quartet or Diana Krall Live in Paris. The MC circuit cards will work with your P-230.
They will work with the XL280 which has 6 MOSFETs per channel. They will work with your P-230 that has 6 MOSFETs per channel. D/L the installation manual from MC and study the drawings.
MOSFETs used in the early 80s were then available in 3 voltage ratings. They look the same (TO-3 can) but they work on different voltages and definitely have different parts numbers. The Soundcraftsman amp does not use the same MOSFETs as your P-230. It uses a higher voltage version and is driven by higher rail voltages, thus it can produce greater power.
Leave everything connected to check circuit card voltages. Just unscrew the heat sink from the chassis and "fold out" the heat sink/circuit card module to allow access to check points. I use VOM leads that have little "J" hooks on their ends and attach and remove them one at a time to check each component and I usually ramp the voltage up and down on each check. I don't want a meter lead to slip and short out valuable items on the circuit card. This testing is tedious but it works.
The P-230 is a "professional" version of the DH-220 and, yes, it does have a little edge to the sound. There are lots of articles about doing mods on these Hafler amps and many of them have to do with sweetening the sound and improving the upper mids and highs. There is a thread here about doing some of this stuff.
At first you were commenting about bridging these amps to get more quantity of power now you are concerned about quality of sound. You have to decide how you want to use this amp, for what purpose, and with which music and speakers.
They will work with the XL280 which has 6 MOSFETs per channel. They will work with your P-230 that has 6 MOSFETs per channel. D/L the installation manual from MC and study the drawings.
MOSFETs used in the early 80s were then available in 3 voltage ratings. They look the same (TO-3 can) but they work on different voltages and definitely have different parts numbers. The Soundcraftsman amp does not use the same MOSFETs as your P-230. It uses a higher voltage version and is driven by higher rail voltages, thus it can produce greater power.
Leave everything connected to check circuit card voltages. Just unscrew the heat sink from the chassis and "fold out" the heat sink/circuit card module to allow access to check points. I use VOM leads that have little "J" hooks on their ends and attach and remove them one at a time to check each component and I usually ramp the voltage up and down on each check. I don't want a meter lead to slip and short out valuable items on the circuit card. This testing is tedious but it works.
The P-230 is a "professional" version of the DH-220 and, yes, it does have a little edge to the sound. There are lots of articles about doing mods on these Hafler amps and many of them have to do with sweetening the sound and improving the upper mids and highs. There is a thread here about doing some of this stuff.
At first you were commenting about bridging these amps to get more quantity of power now you are concerned about quality of sound. You have to decide how you want to use this amp, for what purpose, and with which music and speakers.
The Soundcraftsman amps used the same exact FETs as the Hafler.
The gate to source voltage is what reduced the output on the Hafler.
The XL280 has the high voltage windings for the front end card to deal with this problem. It put out closer to 160W at 8 ohms.
The Soundcraftsman only ran 4V higher on the power supply than a DH200, but it was a regulated voltage.
An amp with a regulated supply has no 'dynamic headroom', an amp with a supply like the XL280 has a couple of dB of headroom on typical program material.
In reality I find an XL280 can play as loud.
The gate to source voltage is what reduced the output on the Hafler.
The XL280 has the high voltage windings for the front end card to deal with this problem. It put out closer to 160W at 8 ohms.
The Soundcraftsman only ran 4V higher on the power supply than a DH200, but it was a regulated voltage.
An amp with a regulated supply has no 'dynamic headroom', an amp with a supply like the XL280 has a couple of dB of headroom on typical program material.
In reality I find an XL280 can play as loud.
Thanks guys,
A little update.
I ran the voltages last night on one of my Haflers. I wish I would have written them down but here's what I noticed. On the Q*'s the higher voltages were pretty much right on but the lower voltage readings were all off just a bit. I'm not sure if that's important. All of the power mosfets read within a tenth of a volt of being right on, so I guess they are probably alright.
I tried to set the bias per instructions by removing the B+ fuse in F2 and connecting the ammeter across the empty fuse holder, I get +/- 64 volts. They say to adjust P2 to 275mA. I'm not sure where I'm supposed to get that reading from. Anyway the amp plays fine so I should probably just leave well enough alone.
djk,
I have not heard an XL-280 yet so I can't comment on that. Last night I bridged my two P230's and ran one per side in my system. I am running them into a few different speaker cabs by way of a 4 way speaker switch, so I can have a few different options and colors for mixing my recordings. Through each of the different pairs of speakers, the Soundcraftsman still "sounded" like it had more headroom than the Haflers. Bridged, the Haflers are supposed to put out 350watts into 8 ohms. I'm not sure if mine are doing that but you still think there would be a noticible advantage for the Haflers, but to my ears the Soundcraftsmen, still had the most headroom.
Here's a look at the speakers I have set up.
Perhaps I'm confused about this. It has always been my thinking that having more power/headroom would result in better sound quality. I assumed that by bridging two amps I would get more headroom, and as a result, better sound quality. Are you saying that these Haflers will sound better run as stereo amps than they will bridged? Do I lose fidelity when I bridge them?
Thanks again, Terry
A little update.
I ran the voltages last night on one of my Haflers. I wish I would have written them down but here's what I noticed. On the Q*'s the higher voltages were pretty much right on but the lower voltage readings were all off just a bit. I'm not sure if that's important. All of the power mosfets read within a tenth of a volt of being right on, so I guess they are probably alright.
I tried to set the bias per instructions by removing the B+ fuse in F2 and connecting the ammeter across the empty fuse holder, I get +/- 64 volts. They say to adjust P2 to 275mA. I'm not sure where I'm supposed to get that reading from. Anyway the amp plays fine so I should probably just leave well enough alone.
djk,
I have not heard an XL-280 yet so I can't comment on that. Last night I bridged my two P230's and ran one per side in my system. I am running them into a few different speaker cabs by way of a 4 way speaker switch, so I can have a few different options and colors for mixing my recordings. Through each of the different pairs of speakers, the Soundcraftsman still "sounded" like it had more headroom than the Haflers. Bridged, the Haflers are supposed to put out 350watts into 8 ohms. I'm not sure if mine are doing that but you still think there would be a noticible advantage for the Haflers, but to my ears the Soundcraftsmen, still had the most headroom.
Here's a look at the speakers I have set up.
An externally hosted image should be here but it was not working when we last tested it.
Perhaps I'm confused about this. It has always been my thinking that having more power/headroom would result in better sound quality. I assumed that by bridging two amps I would get more headroom, and as a result, better sound quality. Are you saying that these Haflers will sound better run as stereo amps than they will bridged? Do I lose fidelity when I bridge them?
Thanks again, Terry
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