I have a Hafler DH-101 with a noisy phono stage. The noise is a hiss that is very apparent at high volume and is not related to the cartridge itself. It is noisy with no phono input connected. All the other inputs do not exhibit this noise. Any suggestions regarding what to check?
Thanks!
Guy
Thanks!
Guy
This is probably normal, the high gain required for phono inputs comes with a price, provided that you cannot hear any pre-amplifier noise during normal playback there is no issue. The noise levels of the phono stage should be well below the surface noise level of the record..
That is comforting. I was in the process of hunting down the cause of a hum from my Thorens TD-160 MkII + Grado MF-1 and wanted to figure out what I was hearing on the bare input first.
Hi, phono inputs always have hiss compared to line level inputs, rgds, sreten.
Grado's seem to be more susceptible to hum than other cartridges,
though I've never had the problem with the ones I've used.
Grado's seem to be more susceptible to hum than other cartridges,
though I've never had the problem with the ones I've used.
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I have a DH-110, and the phono inputs are noisy. I quit using them, and built a Pearl, with which I'm more than happy. I feed the Pearl into the Tuner input of the DH-110.
The phono stage shouldn't be "that" noisy, and I wouldn't replace it -- why not try replacing the MC7818/MC7918 voltage regulators with LM317/337 -- and place 100uF cap between the adjust pin and ground. I think you can get almost an order of magnitude reduction in noise with this simple change. I would also replace the RCA female jacks with new ones. Clean switch contacts with isopropyl acohol, the high test version if you can get it.
Thanks for the tips jackinnj. I have replaced the rca sockets with gold plated and I have cleaned them recently. I just cleaned the switches and pots with Deoxit. I am trying to decide what mods to make first out of the following:
Power supply and line stage capacitor upgrade.
Full capacitor upgrade.
Active components upgrade.
Odd. My power supply has Motorola devices. 185 M2159 QQ7948 is on the right hand side.
--
Guy
Power supply and line stage capacitor upgrade.
Full capacitor upgrade.
Active components upgrade.
Odd. My power supply has Motorola devices. 185 M2159 QQ7948 is on the right hand side.
--
Guy
Have we established whether we are talking about a fault to be repaired or a design shortcoming to be upgraded from? A failing resistor can create noise, or a poor solder joint. Solder flux residue which has got damp can create a lot of noise in a high impedance circuit. I would look for simple repairs like that before doing the usual audiophile thing of 'upgrading' all the components.
I have not taken a magnified examination of the solder joints. I have been using the amp for many years now. What started me on this, was trying to locate a hum, which I now know to be either grounding or RF on the TT. As I was troubleshooting I noticed that the phono inputs were noisy as compared to the line level inputs. I will take a close look at the phono stage and I will also look at replacing resistors, as other threads have indicated that replacing resistors with metal film vs. carbon film has a good effect.
A phono input will always be noisier than a line input, whatever you do. I'm not clear whether you have a problem or not.
DF96, I am convinced that I do not have a problem, but now I am on to tweaking the overall sound of the preamp.
jackinnj; I looked at the data sheet for the 137/337 and based on that, and your comments on adding capacitance i have come up with a schematic. if you don't mind, would you take a look? And having said that, how do i attach/upload a PDF?
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I should have put in a variable resistor for tuning the Vout. Can I assume that Iadj is 1.5A at 18V?
I got my DH-101 in '79 as a kit. I never had a second turntable and disliked the switching of low level signals. In '83 I got my first CD player and all the other high level inputs were in use so I removed the phono 1/2 switching and converted phono 2 to another high level input. The phono input works better without the added wiring and I got my needed high level input.
Try a shorted RCA plug into the phono inputs. The noise should be much lower. If not THEN you have a problem.
G²
I agree generally w/Stratus, especially the last part. If you have a lot of noise even w/a shorted input, then start tapping lightly on the transistors w/a pencil eraser to see if you get a variation in the noise level - I had a TO-92 transistor leg disconnect inside the plastic body on a DH-101 which caused noise. I had to do a bit of searching to find the proper replacement, then buy a bunch to get a decently matched pair.
The answer is very simple and obvious - change the noisey carbon film resistors in the preamp to metal films - non- magnetic Dales or PRP would be good choices, but even cheap metal films wil be quieter.
Not going to make that much difference, although something like the Dale RN55's or CMF-55's will be a lot more stable. The RN55's were mil-spec so would have been pretty expensive at the time the DH-101 was sold, i.e. 1976.
Noise is specified as -86dB below 10mV in the manual (A-wtd).
I can't open PDF's at the moment -- it's an issue going around with Adobe and Windows XP. Bypassing the LM317/337 is easy -- but pretty soon you'll be gilding the lilly.
The Hafler RCA connectors need replacing after a while.
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