dear merlin use more Pm ..just to keep the thread mare clean
I would agree with this. Threads like this are regularly used by builders of equipment. They get very long in any case - hundreds or even thousands of posts - and builders reading the threads for the first time want to see a synopsis of essential information, not have to wade through a lot of details applying just to one particular build or off topic information like how to use basic theory like ohms law in constructing circuits. Keep it relevant to the subject and go with the flow of the primary topics raised by the thread. There are plenty of other threads dealing with things like B+ power supplies for instance.
A number of issues can be resolved by going directly to the relevant websites and reading the information provided there from a lot of hard work and diligence by the designers themselves. Outstanding examples:
Rod Coleman: Filament supplies. See Lyrima
Ale Moglia: Circuit designs and plenty more. See Bartola tubes
Thomas Mayer: Tubes, transformers, designs, builds and filament bias. See Vinylsavor
Kevin Carter: Lundahl transformers and circuit designs. See K&K Audio.
For fundamental theory there are excellent books like Morgan Jones' 'Valve Amplifiers' and a lot of good online tutorials. Even experienced builders have gaps in their knowledge and may look up particular issues from time to time. Nobody's perfect.
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Many thanks.
@nico58
Scusa hai ragione. I'm sorry you are right.
I'm sorry you are right Andy, myself looking for information was in trouble to find the information due to a lot of off topic.
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Hi,
I have been using the 4P1L for a few weeks and have to say it is simply superb, better than any other IDHT pre-amp tube I have ever used. The only problem with it is the microphonics.
My version if the pre-amp currently uses a CCS with capacitor coupling and I think I am right in saying that the gain of this configuration is greater than when a Lundahl LL1660 is used (I assume this as the transformer is step-down). This got me thinking. The microphonics is obviously due to feedback directly from the speakers to the 4P1L tube and therefore if I reduced the gain by attenuating the output of the line stage I might be able to reduce/eliminate the microphonic issue.
As a very simple experiment I took the signal from the capacitor through a 47K resistor to the output of the line stage and put a 1K resistor from the output to ground to create a potential divider. When I tested the linestage the microphonics were gone. So conceptually it works. The ratio of the potential divider probably needs optimising in order to minimise the attenuation whilst eliminating/reducing the microphonic issue.
I was looking at the schematic of the TRAM-2 linestage and see that it also offers different levels of attenuation on the output. The value of the resistors are however, really low (560 ohms from signal to ground and choices of resistance ranging from 470 ohms to 3.2K from the capacitor to the signal output).
I appreciate that the calculation of the resistor values is really important in order to get the sound right. However, I am not sufficiently competent to do the calculations!! Can someone please help me or point me in the right direction.
Cheers
Ian
I have been using the 4P1L for a few weeks and have to say it is simply superb, better than any other IDHT pre-amp tube I have ever used. The only problem with it is the microphonics.
My version if the pre-amp currently uses a CCS with capacitor coupling and I think I am right in saying that the gain of this configuration is greater than when a Lundahl LL1660 is used (I assume this as the transformer is step-down). This got me thinking. The microphonics is obviously due to feedback directly from the speakers to the 4P1L tube and therefore if I reduced the gain by attenuating the output of the line stage I might be able to reduce/eliminate the microphonic issue.
As a very simple experiment I took the signal from the capacitor through a 47K resistor to the output of the line stage and put a 1K resistor from the output to ground to create a potential divider. When I tested the linestage the microphonics were gone. So conceptually it works. The ratio of the potential divider probably needs optimising in order to minimise the attenuation whilst eliminating/reducing the microphonic issue.
I was looking at the schematic of the TRAM-2 linestage and see that it also offers different levels of attenuation on the output. The value of the resistors are however, really low (560 ohms from signal to ground and choices of resistance ranging from 470 ohms to 3.2K from the capacitor to the signal output).
I appreciate that the calculation of the resistor values is really important in order to get the sound right. However, I am not sufficiently competent to do the calculations!! Can someone please help me or point me in the right direction.
Cheers
Ian
I've build and heard a variety of line stages with 10Y, 26, 4P1L, 01A and a load of other DHTs. Microphonics, unless you have bad tubes, is primarily a function of the filament construction. Robust filaments with .5A or more going through them tend to be OK. This is the case with 10Y, 26, 2a3, 45 etc. 01A at 250mA is a bit borderline and so is the 4P1L, which just happens to be rather microphonic if you put low level signals into it. I feed my line stage 4P1L (actually the first stage of my amp) with 2v from a DAC and no problems there.
For signals under 2v you need to starve the filaments and make the whole chassis massive and non-resonant. I use 4mm aluminium top plates and wooden sides. Or if you get desperate, use some kind of rubber mounting system. Or if none of this works for you, use a tube with a beefier filament construction, like 26, 10Y, 46 etc. 26 is easy to use in filament bias, 10Y is OK, 46 is a challenge.
You could also experiment with a step-up transformer before your line stage if your setup allows for this.
For signals under 2v you need to starve the filaments and make the whole chassis massive and non-resonant. I use 4mm aluminium top plates and wooden sides. Or if you get desperate, use some kind of rubber mounting system. Or if none of this works for you, use a tube with a beefier filament construction, like 26, 10Y, 46 etc. 26 is easy to use in filament bias, 10Y is OK, 46 is a challenge.
You could also experiment with a step-up transformer before your line stage if your setup allows for this.
Hi Andy,
I have tried all the tricks detailed throughout this whole thread for reducing microphonics, including the silent blocks from Germany etc, etc. I also have no issue with gain from the streamer (however, I don't like passive preamps, in my opinion they have poor dynamics). The fact that I have sufficent gain from the streamer led me to think about using attenuation on the output as the microphonics is due to the speakers resonating the valves and if you drop the gain of the stage with the attenuators, it goes away. I would dearly like to keep the DHT linestage because as I think you may have written previously they do sound quite fantastic (with the exception of the microphonics).
Using the resistors as descibed i my last post it works, though I am not convinced I havent lost some micr dynamics. I would love to try the Lundhal transformers, but thats quite an expensive experiment as I would have to buy them first!
Before I tried the transformers I was hoping someone could advise me on attenuator design as I want to minimise any frequency roll-off and minimise the affect on the dynamics.
Any help is greatfully received.
Cheers and Merry Christmas
Ian
I have tried all the tricks detailed throughout this whole thread for reducing microphonics, including the silent blocks from Germany etc, etc. I also have no issue with gain from the streamer (however, I don't like passive preamps, in my opinion they have poor dynamics). The fact that I have sufficent gain from the streamer led me to think about using attenuation on the output as the microphonics is due to the speakers resonating the valves and if you drop the gain of the stage with the attenuators, it goes away. I would dearly like to keep the DHT linestage because as I think you may have written previously they do sound quite fantastic (with the exception of the microphonics).
Using the resistors as descibed i my last post it works, though I am not convinced I havent lost some micr dynamics. I would love to try the Lundhal transformers, but thats quite an expensive experiment as I would have to buy them first!
Before I tried the transformers I was hoping someone could advise me on attenuator design as I want to minimise any frequency roll-off and minimise the affect on the dynamics.
Any help is greatfully received.
Cheers and Merry Christmas
Ian
Hello Ian
the microphonics how does it behave,,whisling or how ?
i have tried Lundahl trafo ,,ang gyrator,,the new one..but can not go back to trafo,,the gyrator sound best for me
i have have the Tram2 .and in this i use the minus 3db output,,because off noise..
it must be posible to use the same way of resister in the 4P1L,,but the quality off the resistor is importent..
Merry Christmass to all
Bjarne
the microphonics how does it behave,,whisling or how ?
i have tried Lundahl trafo ,,ang gyrator,,the new one..but can not go back to trafo,,the gyrator sound best for me
i have have the Tram2 .and in this i use the minus 3db output,,because off noise..
it must be posible to use the same way of resister in the 4P1L,,but the quality off the resistor is importent..
Merry Christmass to all
Bjarne
Hi Bjarne,
The microphonics can be heard if I stand by the speakers and clap my hands, you then hear I kind of tizz sound from the speakers that decays. Also if I listen to music at reasonable but not excessive volume, then at any abrupt pauses in the music I can hear the same decaying sound. I have to say that the linestage sounds quite stunning which is in some ways surprising given the microphonic issue.
It is interesting that you have the Tram-2 and have used the -3db attenuation to tame the problem. I will have a dig in my spares box and see if I can find the Tram -3db attenuation value resistors. The schematic I have for the Tram-2 indicates 2.4K kiwame from the capacitor to the output and 560 ohm Takman metal film from signal to ground. These values are far lower than what I originally tried (47K and 1K respectively) it might be that with the lower values I can keep all the dynamics. Unfortunately I don't have the knowledge to calculate and pick the exact values for the 4P1L. I will let you know how I get on.
Happy Christmas,
Ian
The microphonics can be heard if I stand by the speakers and clap my hands, you then hear I kind of tizz sound from the speakers that decays. Also if I listen to music at reasonable but not excessive volume, then at any abrupt pauses in the music I can hear the same decaying sound. I have to say that the linestage sounds quite stunning which is in some ways surprising given the microphonic issue.
It is interesting that you have the Tram-2 and have used the -3db attenuation to tame the problem. I will have a dig in my spares box and see if I can find the Tram -3db attenuation value resistors. The schematic I have for the Tram-2 indicates 2.4K kiwame from the capacitor to the output and 560 ohm Takman metal film from signal to ground. These values are far lower than what I originally tried (47K and 1K respectively) it might be that with the lower values I can keep all the dynamics. Unfortunately I don't have the knowledge to calculate and pick the exact values for the 4P1L. I will let you know how I get on.
Happy Christmas,
Ian
Don't forget that Tram2 output resistance (after the coupling capacitors) only 150R.
If you use large resistive divider after this, drive capability will be drastically deteriorate.
I'm not sure that large attenuating on the output is the good solution. The problem to be solved where there arises: isolating, damping.
Neither (in my preamps/amps) #26, nor 01a or 10/801 tubes don't tend to microphonic. I use isolated (2-3mm thick, relatively heavy) sub chassis, teflon tube sockets, rubber grommets for damping.
If you use large resistive divider after this, drive capability will be drastically deteriorate.
I'm not sure that large attenuating on the output is the good solution. The problem to be solved where there arises: isolating, damping.
Neither (in my preamps/amps) #26, nor 01a or 10/801 tubes don't tend to microphonic. I use isolated (2-3mm thick, relatively heavy) sub chassis, teflon tube sockets, rubber grommets for damping.
