Hi,
You can try. It may be literally pickup through the Air. DHT's tend to be finicky and poorly shielded... Some types are very quiet, others are very noisy, also the rectifier often comes into play as it radiates a health field.
Which tubes do you use?
Ciao T
You can try. It may be literally pickup through the Air. DHT's tend to be finicky and poorly shielded... Some types are very quiet, others are very noisy, also the rectifier often comes into play as it radiates a health field.
Which tubes do you use?
Ciao T
Hello Thorsten, you are exactly right on noise pickup from the rectifier. I switched from a Sovtek 5U4GB (straight side- newer version) to an older model Sovtek 5U4GB (globe type) bulb and the noise was reduced (I'm using a Russian 6AS7 - a Sovtek 6AS7 was noiser for some reason). I use Valve Art 2A3s primarily due to low noise and essentially no microphonics, although I have tried Shanguang 2A3C (very microphonic) and Sovtek 2A3 as well. Although, it is still not quiet enough for me to switch from the -12 to the -3db output, I'm getting closer. If you have additional recommendations (beyond adding the heater resistors), I would be eager to try them.
Thank you and best regards, Jeff
Thank you and best regards, Jeff
Hi,
Try finding the right matching rectifier. With current production Valve Art 2A3C (the Single Plate ones) and Valve Art 274B Rectifier we have very low noise, around -90dBA re 1V from the +6dB Output.
Also confirm all operating conditions are pukka and all connections on the heater supplies are tight.
Ciao T
Try finding the right matching rectifier. With current production Valve Art 2A3C (the Single Plate ones) and Valve Art 274B Rectifier we have very low noise, around -90dBA re 1V from the +6dB Output.
Also confirm all operating conditions are pukka and all connections on the heater supplies are tight.
Ciao T
Hi,
You do not need to re-check the voltages when changing rectifiers, but it is advisable with different signal tubes and the 6AS7.
Ciao T
You do not need to re-check the voltages when changing rectifiers, but it is advisable with different signal tubes and the 6AS7.
Ciao T
Hi, I just bought a Tram preamp second hand. Very impressed by it so far. However I find I need to alter the db output. At present +6db is too much and the others are too little. So I figure +2 - 3db should do the trick. Do I simply need to add another resistor in series on the +6db output to reduce gain ?. Also what value should I use ?. I thinking another 470r but I'm only guessing.
Cheers Peter.
Cheers Peter.
Hi,
You would need to change the resistors in the level divider in the output. Are you sure that the gain on -3dB is insufficient? Even with the volume control all the way up you do not get enough loudness?
Ciao T
You would need to change the resistors in the level divider in the output. Are you sure that the gain on -3dB is insufficient? Even with the volume control all the way up you do not get enough loudness?
Ciao T
Hi Thorsten,
No even with the volume all the way up some of my cd's were just a tad over moderate volume. I think most of the problem lies in the mismatch between my power amp, Yamamoto 45 amp ( 2 watts ) and my speakers ( 93 db). With my previous preamp, a passive ( volume pot in a box ), I could get sufficient levels to keep me happy but with the Tram I find -3db not enough and +6db way too much. I think +2db or thereabouts would probably be ideal.
At the moment I have the standard configuration of a 470r resistor going to the +6db and a 2.4k going to the -3db split by the input wire from the obligatos. What changes would I have to make to get the db output down to +2 ?.
You've probably guessed I'm a bit technically challenged so you might have to go easy on the explanation. Thanks.
Peter.
Hi,
Just to be clear, "all the way up" means the indicator led at the end of the "Arc" is lit, not the one at the top of the arc (sorry, but some people misunderstand this part).
Do you have noise issues at +6dB? If not, just turn the volume a little lower perhaps and use +6dB?
Ciao T
Just to be clear, "all the way up" means the indicator led at the end of the "Arc" is lit, not the one at the top of the arc (sorry, but some people misunderstand this part).
Do you have noise issues at +6dB? If not, just turn the volume a little lower perhaps and use +6dB?
Ciao T
Hi,
No I guess the noise is not too egregious. It's mainly tube hiss which you can't really hear unless you're a couple of feet away. Considering I use old RCA globe 45's in both the preamp and the power amp it's pretty remarkable really.
I suppose what I'm trying to do is finesse the gain down thereby reducing noise at the speaker level and giving me more usable volume further up the scale if that makes sense. Most cd's I play I don't push the volume much past 12-1 o'clock whereas it was my impression that around 3 o'clock was the optimum. Anyway I'll just keep fiddling with various resistor values, which I did last night ( replaced the the 470r with an 820r ), until I reach an acceptable compromise. Cheers.
No I guess the noise is not too egregious. It's mainly tube hiss which you can't really hear unless you're a couple of feet away. Considering I use old RCA globe 45's in both the preamp and the power amp it's pretty remarkable really.
I suppose what I'm trying to do is finesse the gain down thereby reducing noise at the speaker level and giving me more usable volume further up the scale if that makes sense. Most cd's I play I don't push the volume much past 12-1 o'clock whereas it was my impression that around 3 o'clock was the optimum. Anyway I'll just keep fiddling with various resistor values, which I did last night ( replaced the the 470r with an 820r ), until I reach an acceptable compromise. Cheers.
Hi,
I can see your point.
Raising the shunt resistances (to ground from -12dB and from -3dB to -12dB) will increase the level. If the total is raised by around 50% you get around 3dB more level.
Ciao T
I can see your point.
Raising the shunt resistances (to ground from -12dB and from -3dB to -12dB) will increase the level. If the total is raised by around 50% you get around 3dB more level.
Ciao T
Thorsten, I implemented your recommendations to install the dropping resistors (total 0.16Ohm) from the power supply and rebiased with the VA 274B and Shanguang 2A3C tube combination.
Now, there is a very slight buzz noticable only a foot or two away from my Zu Druids (>97db efficient). Probably picking up some minor EM. Also noticed that my dimmer switch was throwing noise into the system also, so that is gone. Have some Herbies dampers arriving and have the unit on a set of StillPoints.
Thorsten, I appreciate all the help and hopefully your recommendation can also be used by others. Thanks, Jeff
Now, there is a very slight buzz noticable only a foot or two away from my Zu Druids (>97db efficient). Probably picking up some minor EM. Also noticed that my dimmer switch was throwing noise into the system also, so that is gone. Have some Herbies dampers arriving and have the unit on a set of StillPoints.
Thorsten, I appreciate all the help and hopefully your recommendation can also be used by others. Thanks, Jeff
Hi,
Good to know you got things sorted.
No worries, glad I could help.
Ciao T
Good to know you got things sorted.
No worries, glad I could help.
Ciao T
One of the Trams that I assembled developed a fault in the bias supply boards. See the pic. One channel supply is showing red diode next to its 2SA940 transistor. Bias voltage on that side is 16V only. This happened after only 6 months of normal operation.
What went wrong here? Is it possible to get a replacement from Simon?
What went wrong here? Is it possible to get a replacement from Simon?
Attachments
Hi,
Are you sure it's the Bias Module? These very rarely cause any trouble.
Just return the faulty module for replacements. Hard to say what specifically went, any possibility, something was shorted? It may still work afterwards for a while but something may have taken a knock...
Ciao T
Are you sure it's the Bias Module? These very rarely cause any trouble.
Just return the faulty module for replacements. Hard to say what specifically went, any possibility, something was shorted? It may still work afterwards for a while but something may have taken a knock...
Ciao T
Hi,
The Red Led is the "cannot control current even though I tried" indication. It basically tells you "Tube dead". If the tubes are under warranty you may be able to get a replacement from DIY.
Ciao T
The Red Led is the "cannot control current even though I tried" indication. It basically tells you "Tube dead". If the tubes are under warranty you may be able to get a replacement from DIY.
Ciao T
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