Hi Everyone. Just a couple of questions I need help with. I'm in the process of recapping my Hafler DH-101 preamp. I'm also changing out the RCA jacks for better ones. I'm elliminating the tape inputs & outputs as I don't use them. Is it OK to just remove these wires totally at the switch to have less wires in the amp or do I still have to at least leave the grounds connected? Also, would I be better off replacing the wires to the jacks (or all signal carrying wires} with sheilded cable? And if I did use sheilded cables, is it better to use regular 1 conductor plus sheild, or 2 conductor plus shield? If I use 2 conductor plus sheild, would I connect the sheild to the ground wire at one end to act as a drain? Finally, Instead of using the ground bus wire that connects the grounds of all the inputs, would I be better off adding a star ground with each input ground individually wired to the star ground? Sorry for all the questions, but I want to get it right the first time. Thanks, Bob
Hafler DH-101 Mods
- Thread starter bobjan
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I don't follow your question about removing the grounds at the tape switches. On my 101, there are no ground wires going to these switches.
Shielded cable is a controversial subject. A shield can increase capacitance and self inductance, both generally bad things. Some have advocated using simple parallel wiring like antenna leads for audio interconnects. If you don't need shielding, and in this case you are inside a shielded enclosure, then regular wires are OK, except for very low signal levels like phono inputs. On the other hand, I have used shielded cable for interconnects myself, so make your own decision.
In general star grounding is preferred but the Hafler is not star grounded and it may be impractical to do so - I haven't tried to do it myself on the 101 so I don't know how messy it will be but give it a try if you're up to it.
The best upgrade for the 101 is replacing the tantalum coupling caps with film caps (polypropylene for example). Another good upgrade is using bigger AC feedback caps in the phono section (C5) because the stock unit rolls off the low frequencies to reduce rumble, doubling the value will give you better bass. Finally, you can upgrade the power supply. I switched the transformer to an external toroidal unit because I have read reports that there is some noise coupling from the stock transformer. Also probably a good idea to add additional bypass caps to the power rails.
Shielded cable is a controversial subject. A shield can increase capacitance and self inductance, both generally bad things. Some have advocated using simple parallel wiring like antenna leads for audio interconnects. If you don't need shielding, and in this case you are inside a shielded enclosure, then regular wires are OK, except for very low signal levels like phono inputs. On the other hand, I have used shielded cable for interconnects myself, so make your own decision.
In general star grounding is preferred but the Hafler is not star grounded and it may be impractical to do so - I haven't tried to do it myself on the 101 so I don't know how messy it will be but give it a try if you're up to it.
The best upgrade for the 101 is replacing the tantalum coupling caps with film caps (polypropylene for example). Another good upgrade is using bigger AC feedback caps in the phono section (C5) because the stock unit rolls off the low frequencies to reduce rumble, doubling the value will give you better bass. Finally, you can upgrade the power supply. I switched the transformer to an external toroidal unit because I have read reports that there is some noise coupling from the stock transformer. Also probably a good idea to add additional bypass caps to the power rails.
soundmotor
super modified
I already have caps to replace all the lytics including the tantalums. I also have some higher value caps for the power supply, I figured as long I'm inside, I might as well see what else might help. The phenolic board that holds all the RCA connecters on the back has broken and been glued about 4 times so I am replacing it with a piece of aluminum I cut to fit. Since I have to remove all the jacks anyway, I'm replacng them with better ones. Since I don't use the tape inputs or outputs, I was going to leave these out on the new plate. I just wanted to know if it's OK to just ellininate these wires, or if the grounds still needs to be connected to prevent noise. I figured I could make a hole on the bottom near the center of all the inputs to create a star ground and connect all the grounds to that point. Just wasn't sure if this would really be of any benefit. Would I then change the cord to a 3 conductor and connect the star point to the ground wire? In that article you referenced, their is mentioned some articles on DH-101 mods in old issues of The Audio Ametuer. I was wondering if anyone would have copies of these articles they could send me. Thanks, Bob
In that article, they seemed to recommend shielded cable (and even Cat-5 network cable) but you indicate that shielded cables could cause problems. Would it be better to just use higher quality stranded copper wire of the same guage, or is the wire in their good enough? Is their a paticular wire you might recommend for signal path wire? Thanks, Bob
I don't mean that shielded cable would cause problems, what it can do is roll off the high frequencies slightly due to the added impedance. If you don't have golden ears, go ahead and use shielded cabling (as I said before, I often use it myself). Just wanted to mention the possible drawbacks.
Teflon (or similar material) insulated wire is preferable but is more expensive. I'm not sure of the quality of the stock wiring but I doubt is super high quality. If you don't mind the cost, go with high purity copper or silver wiring with high quality dielectric (teflon, etc).
For the unused jacks, it's probably best to leave the ground returns on them for shielding purposes, but it sounds like you are going to remove the jacks so I still don't follow, where would the unused grounds connect if you were to leave them?
On the grounding issue, be aware that there is already a partial star ground on the power PCB where many of the ground returns go. If you are going to add another ground point somewhere else, it's obviously not going to be a single point ground. So you have to decide where to put the single point ground and do the rewiring for the star grounding, as I said, it may be messy.
I see that many say that replacing key resistors with metal film is a good thing to do for the DH-101. Would anyone be able to tell me which ones are key or are the talking about replacing every resistor in both the line and phono stages? Also, is their a particular brand of metal film that are favored (but not super expensive). I was also wondering if anyone might have copies of the Audio Ametuer articles from Feb 1979 & April 1980 on upgrades for the DH-101 that they could email me? The one from 1980 is available online for $5 so I can order it but the 1979 article is no longer available and I would love to be able to get a copy. Thanks, Bob