Hafler 120 modifications

There is not much you can or should do to this amp's basic circuit topology. This same circuit is used in the SE-120, Pro1500 and Hafler 9180 amp. These later versions have both channels on one planar board but if you study their schematics you can see how identical they all are.

The Hafler 9180 amp is a good one to study as you can see where in the circuit improved (polypropylene) film capacitors are used and locations where 1% metal film resistors are used.

I am using two of these amps in addition to a DH-120 and can testify that, for example, the 9180's sound is more refined and detailed, especially in the upper mids and highs. Swap parts to make your amp more like the 9180 and the quality of your sound will improve.

Another mod consideration is to simplify input signal wiring. Get rid of the level controls, the stereo/mono switch and wiring, and for sure the ambiance speaker output circuit. You will be surprised how much "grunge" is removed by simplifying input and output signal wiring.

I built a custom version using DH-120 circuit cards and made an amp that sounds almost like the DH-220. I used a power trans with about 3 times the amount of current drive, 4 times the amount of PS capacitance, and a separate diode bridge for each channel -- plus the simplified wiring mentioned above. It made a great sounding little amp much improved over the stock DH-120 and with great sound stage and imaging. But, of course it required a larger chassis and heat sinks. Its picture is attached.

So, tell us why you want to mod your amp? What do you hope to gain from mods?

Dick
 

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Hafler Mods

Thank you for the reply and I will look over the circuits . I have 2 of these units . One I bought new in kit form and changed the wiring and input caps also bypassed the caps with poly p caps . It always sounded pretty good with good depth and image . I wanted a small nimble amp to knock around . I also own 2 hafler 200's and a 220 .They have musical concepts boards in them, I also have a modified 101 which I have had for years and just purchased a 110 preamp that was modified by musical concepts and also another stock 101 and 110 . I have quite a collection .Once these units get warmed up for a while they are fantastic . Thanks again. I am going deaf but the volume control still works and I still get chills when I listen to the Rose on my ariston turntable . If cd's would sound that good I would have sold my turntables and my record collection .I have about 300+ albums and three turntables . I love them .
 
I meant Hafler 9130

In my previous post I mentioned the Hafler 9180 amplifier. I should have written 9130. The Hafler 9130 and SE120 are almost identical, same electronics, slightly different packaging.Their sound is slightly more "refined" than that of the DH-120, mostly a result of some superior passive parts in some of the circuit.
 
DH-120 with 4 MOSFETs?

Is it possible to add another pair of MOSFETs to the DH-120 circuit? Does the present PCB circuit have enough drive to handle an extra pair of output MOSFETs?

Of course more MOSFETs would require a larger heatsink and MOSFETs used in parallel must be matched (±10%) on Vgs.

I have an extra Hafler DH-200 chassis and heat sinks and wondered if a DH-120 could be transferred and beefed up?
 
What Does P2 Do?

On the DH-120 PCB are two variable resistors, small pots. One sets BIAS current, the other is labeled "Balance."

What is "balance?" The manual says is should only be adjusted with the use of a 'scope. What would be the result if this balance control had been changed from factory setting?

If I don't have a scope how can I ascertain if a used DH-120 is still working OK as pertains to "balance?"
 
BUMP

Is it possible to use 2 pairs of MOSFETs per channel with, of course, larger heatsinks?

Also, what does P2 adjust and how can I know, without a 'scope, if my used DH-120 is adjusted properly?

Thanks for responses. This is a nice little amp with a tried and true circuit.

Dick
 
Good guess but its place in the circuit probably has nothing to do with DC offset. I would guess that it has to do with the shape of the output waveform, both positive and negative going, and is adjusted for minimum distortion.

To bad we can't get a real expert to chime in here.
 
the mosfet used probabilly are the famous hitahi 2sk135 2sj50 with 100W max dissipation, It's possible using the magnatec mosfet buz901D and buz906D , they have 250W of max power dissipation at 25C° , in pratics these component have two 2sk135 or 2sj50 inside the same pakage, so you can doubling the mosfet without heatsink problems.
But the buz current polarization must be 200-240 mA for each.
 
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I have a broken Hafler 9130 and the output devices are 2SK1056/2SJ160.

Apparently someone accidentally poured a coke on the amp, and he gave it to me to see why it keeps blowing fuses (he says the two issues are unrelated - I beg to differ). A couple resistors seem fried and one of the outputs devices show a burn mark over the pins. Haven't really done anything more since I an crazy busy at work.

Anyway, I told my friend that it would not be worth fixing (replacement of all four output devices and resistors would run about $40, and still may be other unfound issues with it), as these amps working are on ebay for less than $100

I just finished a ESP P-101 that is heavily biased into Class A with the 2SK1058/2SJ162 that really impressed me. When I got the Hafler, I noticed the same family of output transistors and got kinda excited.

I have offered my friend $40 for the broken amp, and may fix it, reuse the chassis for a real nice Gainclone, or drop a UCD400AD pair in it with a new tranny.

Anyone know what the 9130 Tranny secondary voltage and VA is? Too lazy to get it opened and check myself...my guess is dual 28VAC and 250VA?
 
As I pointed out in post #2 there are several Hafler amps that share the same circuit topology and the newer ones all have a similar planar board. Go to Hafler.com (tech archives) and get the manual for the SE-120 or Pro-1200. I believe they have the schematics. The newer versions (not the DH-120) have an international transformer so you can get ±55VDC or ±27.5VDC depending on how the dual primaries are wired.

I, too, have the transformer, chassis and MOSFETs for a broken Pro-1200 I have been saving for a gainclone. The 27.5VDC would be OK for a lower powered version but 55VDC would, of course, be too much.
 
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I have the operation/service manual with schematics for the 9130, but does not say the Voltage. Can be wired for 100V/120V/220V/240V.

Do you know the amps? My guess is around 2.

BTW - the 55VAC is way too much for a GC...29VAC (giving 40VDC Rails) is the absolute max, so the 27.5VAC would be a higher power GC - around 128Watts/channel into 4 ohm and 76Watts/channel into 8 ohm.

The 9130 also has the BIAS and BALANCE Pots - it was my assumption that he BALANCE is DC Offset.

My guess is the GC probably sounds better than the Hafler 9130 anyway?
 
"My guess is the GC probably sounds better than the Hafler 9130 anyway?"

Nope. Most SS amps sound the same, unless they were specifically designed to be not linear, or were done that way out of lack of design knowledge. That said, the LM38XX IC's have protection circuits that are not very graceful so when the amp is driven to clipping it doesn't sound very pleasant. Well designed discrete SS amps, like these Haflers, clip more gracefully and it is less noticeable.

So, aslong as you don't drive the chips to clipping, they'll sound good.
 
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hat said, the LM38XX IC's have protection circuits that are not very graceful so when the amp is driven to clipping it doesn't sound very pleasant. Well designed discrete SS amps, like these Haflers, clip more gracefully and it is less noticeable.

I have always heard that of Tubes, but not SS. As far as what (little?) I know, tubes clip gracefully, and SS amps, just by their design, cannot. I also agree that the LM series chipamps clip badly.

Please don't get me wrong - I have never heard the 9130 I have, or any of the other Haflers - I hope to soon so I can finally form my own opinion. I know Haflers have a strong following, just as many other amp manufacturers. I have always wanted D-220 to tinker with.

I have heard and built many gainclones, Tripaths, UCD, etc. They all have their own "signature", so saying most ss amps sound similar (pre clipping) maybe a bit of an overstatement. I trust that Class A, A/B, H, D are all in the realm of SS? Correct me if not....

I like Gain Clones for their inherent simplicity and low cost vs sound quality. My current preferred amp is not a GC, but a tweaked to the hilt SS Elliott P-101, and can be considered a close cousin of the 9130 in design, so I am not bashing the Haflers or Discreet design by any stretch.

I am also finishing a Krell Clone and Aleph 60, and will round out my SS "experience".
 
Sorry, i should have been more specific. Class A and Class AB amps will sound the same given that the design was not destined to be un-linear, and the amps are not driven to clipping. This is my viewpoint and everybody has their own opinion.

Tubes are known for "soft-clipping". SS discrete designs, depending on the protection circuits employed can clip softer or, like the chip amps, harder. SS amps will probably never clip as soft as tubes, but thats the price you pay for having a linear device. I don't think tubes even "clip", but they "compress". Anyone want to correct me there?

Of course, the only good protection from clipping is building/buying a bigger amp.

Happy Holidays everybody
 
john65b,

BTW - the 55VAC is way too much for a GC...29VAC (giving 40VDC Rails) is the absolute max, so the 27.5VAC would be a higher power GC - around 128Watts/channel into 4 ohm and 76Watts/channel into 8 ohm.

In a previous post of mine I gave the voltages as 55VDC (DC) and 27.5 VDC (DC). The rails of the 9130 run at ±55 VDC.

These little amps have 2 pots per channel. One is to set the bias, the other is to adjust balance. It is not to adjust for DC offset. The DH-120 manual states:

The Balance control, which is P2, . . . should not be adjusted without a distortion analyzer, and even then, only with factory advice, since other factors affect distortion as well.

I just wanted to clarify the info about these points.
 
I don't know the amp rating of the transformer. It drives a 65 watts per channel amplifier so take a guess.

The international transformer allows for wiring for different primary voltages. The data I present are for 120 VAC or wired for 220 but run at 120 vac.

Your Hafler 9130 should make it all clear.
 
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Since class AB, 65W/Channel and +/-55VDC rails, usually twice output wattage is tranny rating - so 260 Watts.

Arriving at somewhere around 3 amps@40VAC secondaries for the transformer.

Just wondering if anyone knew what its rating was for sure.

Sorry for the questions.