Hi,
I'm working with a DIYHIFISUPPLY Tram WOT preamp. I had some noise when I initially got it, which I mostly alleviated by converting the 5687 heaters to DC, and even more importantly, by getting my F5 monoblocks farther away from the output transformers. I've got some right channel noise issues left, but they seem related to the pot, and I've got a stepped attenuator coming.
Here are my questions. The output transformers have taps for a headphone output. Specs are hard to come by and say only that the OPT is "4:1" and the output impedance is about 400 ohms, though it doesn't specify whether line or headphones. My goal is to lower the gain a bit if I can, because I think it would improve my system noise floor.
1. Are the headphone outputs likely lower impedance and lower gain? I can check this easily enough, but ...
2. If they do give me less gain, is there any other reason to not use them to drive my power amps? Is it likely that the OPTs will perform worse through those taps? I don't have a good way to measure this. (F5 input impedance is high--100kohm).
3. Finally, regardless of which outputs I use, should I load them? The manual schematic is bare bones, and does not show any loading. However, this schematic shows 620r. TRAM w. I just got the Sound Practices CD ROM that should have the original schematic this is based on, (Diego Nardi article), but I've yet to find a way to read it. (It turns out that I parted with my last CD ROM drive quite some time ago). My thinking is to just stick with the schematic, but as I'm already asking questions about the outputs ....
(And no--I didn't follow the linked schematic for the filaments. While it doesn't explicitly say, that is a mod over the original AC. I don't see how it worked. It took me Schottkys and .1ohm in the middle of big caps to get just over 6V).
Thanks for any advice,
Paul
I'm working with a DIYHIFISUPPLY Tram WOT preamp. I had some noise when I initially got it, which I mostly alleviated by converting the 5687 heaters to DC, and even more importantly, by getting my F5 monoblocks farther away from the output transformers. I've got some right channel noise issues left, but they seem related to the pot, and I've got a stepped attenuator coming.
Here are my questions. The output transformers have taps for a headphone output. Specs are hard to come by and say only that the OPT is "4:1" and the output impedance is about 400 ohms, though it doesn't specify whether line or headphones. My goal is to lower the gain a bit if I can, because I think it would improve my system noise floor.
1. Are the headphone outputs likely lower impedance and lower gain? I can check this easily enough, but ...
2. If they do give me less gain, is there any other reason to not use them to drive my power amps? Is it likely that the OPTs will perform worse through those taps? I don't have a good way to measure this. (F5 input impedance is high--100kohm).
3. Finally, regardless of which outputs I use, should I load them? The manual schematic is bare bones, and does not show any loading. However, this schematic shows 620r. TRAM w. I just got the Sound Practices CD ROM that should have the original schematic this is based on, (Diego Nardi article), but I've yet to find a way to read it. (It turns out that I parted with my last CD ROM drive quite some time ago). My thinking is to just stick with the schematic, but as I'm already asking questions about the outputs ....
(And no--I didn't follow the linked schematic for the filaments. While it doesn't explicitly say, that is a mod over the original AC. I don't see how it worked. It took me Schottkys and .1ohm in the middle of big caps to get just over 6V).
Thanks for any advice,
Paul
I have never had any problems with AC heaters and hum in pre amps or amps.
When investigated any hum was always found to be caused by something else.
Clearly you shouldn't be running heater wires near audio signals.
I have had problems with mains transformers near valves causing hum when they were to close to valves.
Inputs should always be short and any input connections wires screened and pot can earthed.
When investigated any hum was always found to be caused by something else.
Clearly you shouldn't be running heater wires near audio signals.
I have had problems with mains transformers near valves causing hum when they were to close to valves.
Inputs should always be short and any input connections wires screened and pot can earthed.
If you search for 5687 preamps, you'll find that I'm approximately the 1,000th person to have had hum problems. You'll find many folk have said they've never had to run DC heaters. Until they built a 5687 preamp.
There is no question that I have other problems, too. These preamps are well known to make some noise, probably as a result of power supply layout issues. Heck, if you check out the link, that guy built a new everything but couldn't kill all the noise. I'm not going to build a new chassis or rework the layout. But I wouldn't mind a quick and dirty solution. Like the lower gain I asked about.
Paul
There is no question that I have other problems, too. These preamps are well known to make some noise, probably as a result of power supply layout issues. Heck, if you check out the link, that guy built a new everything but couldn't kill all the noise. I'm not going to build a new chassis or rework the layout. But I wouldn't mind a quick and dirty solution. Like the lower gain I asked about.
Paul
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