The 3e-audio boards have an input buffer comparable to the one of the 700.
If you want to drive it single ended, just ground one side. The used OP-amp is made to be driven both ways.
If you want to experiment with the "sound" of vale stages, maybe just put it in a pre-amp. Be very careful, as additional power supplies are not easy to integrate into a chain. They might give more problems than profit.
Personally, I know some really nice valve stages, for example my maybe best sounding CD player (AMC CD6b) has a valved output stage. I do not think this is the only reason for it´s fine, powerful and detailed sound.
Any HIFI installation has some kind of unique "sound". Many people think they could improve the sound by adding something (like a tube stage) if they are not satisfied with the music reproduction.
IMO a better way is to remove the components that do not sound good. Anything that is not there can not degrade sound quality.
So please don´t expect to much of a valve stage, they are no cure for anything, just my give a light touch to the sound. With power amp´s you should have a perfect one, before you tune the sound in any direction.
If you want to drive it single ended, just ground one side. The used OP-amp is made to be driven both ways.
If you want to experiment with the "sound" of vale stages, maybe just put it in a pre-amp. Be very careful, as additional power supplies are not easy to integrate into a chain. They might give more problems than profit.
Personally, I know some really nice valve stages, for example my maybe best sounding CD player (AMC CD6b) has a valved output stage. I do not think this is the only reason for it´s fine, powerful and detailed sound.
Any HIFI installation has some kind of unique "sound". Many people think they could improve the sound by adding something (like a tube stage) if they are not satisfied with the music reproduction.
IMO a better way is to remove the components that do not sound good. Anything that is not there can not degrade sound quality.
So please don´t expect to much of a valve stage, they are no cure for anything, just my give a light touch to the sound. With power amp´s you should have a perfect one, before you tune the sound in any direction.
Agreed, I’m going to order two of the 700as1 modules and see how they sound as is in SE mode with the integrated buffer driven straight from my preamp.
I will probably probably still build a tube CF stage just to try it.
As for the Lundahl transformer you mentioned in your last post, I read the data sheets and the link you posted, other than that I didn’t find much else about them. That said, it sounds like it would provide unity gain if needed along with some other benefits, but I’m not exactly sure.
Looking at the chart I see several different ways to wire this. Some change the turns ratio and some are 1:1. I’m assuming I want 1:1 but what does changing the turns ratio do for the input signal? I assume it doubles it or cuts it in half depending is it’s wired 2:1 or 1:2.
It also looks like you can have balanced output which the Icepower module excepts while feeding the transformer with either a balanced or SE signal. Can you in fact feed it an SE signal on the primary with balanced connections on the secondary?
Thanks a lot for your help!
I will probably probably still build a tube CF stage just to try it.
As for the Lundahl transformer you mentioned in your last post, I read the data sheets and the link you posted, other than that I didn’t find much else about them. That said, it sounds like it would provide unity gain if needed along with some other benefits, but I’m not exactly sure.
Looking at the chart I see several different ways to wire this. Some change the turns ratio and some are 1:1. I’m assuming I want 1:1 but what does changing the turns ratio do for the input signal? I assume it doubles it or cuts it in half depending is it’s wired 2:1 or 1:2.
It also looks like you can have balanced output which the Icepower module excepts while feeding the transformer with either a balanced or SE signal. Can you in fact feed it an SE signal on the primary with balanced connections on the secondary?
Thanks a lot for your help!
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Yes you are right, the transformer gets connected to the balanced input of the (ICE) amp. Then you can wire it up single ended or balanced. Usually you put an RCA and an XLR connector on the back of the amp. With a simple switch you enable the cinch input, by grounding the balanced cold (-) side.
High quality transformers like the Lundahl´s do not degrade the sound and, opposite to the valve stage, do not add hear able distortion. That makes them expensive. They are simple in use, need no power supply and sound as neutral as the best active buffer stages. For HIFI the only downside is the high price. If you calculate the normal profit gain with HIFI gear, adding a pair will make an commercial pre- or power amp at least 1000$ more expensive, while an active buffer is not even 2$ in parts.
One main advantage is that you can isolate the amp from any other gear. This way you do not have any ground voltages flowing, that might induce hum. The amp is driven "over the air" in the transformer, without ground wire.
Next point, you can generate a balanced signal from a single ended, which in some cases is the most important part.
As the transformers are inductive, they limit the frequency range, this is a good thing, as unwanted high frequency dirt will enter the amp suppressed.
Another advantage may be their impedance. Because of the relative low (typical 3k ohm, constant in audio band) resistance, the amp has to deliver quite some current, which results in suppression of noise. Compared to a, maybe, 20k ohm input. No decent pre-amp should have any problems to drive loads as low as 600 ohms.
Jeff Rowland Design has used these transformers on the older ICE modules and these amps are considered world class. Quite nice, but expensive.
Very well made transformers are used in lots of studio gear, as a reliable problem solver.
Chances, most of your recordings have passed some of them, are high. Just like NE5532 OP-amps, that probably 95% of any well recorded music has passed.
I would see the transformer as the objective brother of the valve buffer, which is a more special gadget. The valve is not really needed today. We play around with for for the fun of it´s very individual, antique construction and it´s optics. Both are principles that have been around for a century or longer.
I think your decision to use the 700 "as is" first is a good idea.
Please notice that you could use a 300A1 "hanger" amp with the 700AS1.
Maybe leave room in your build for such an addition and a second set of connectors. The 300A1 Is very small (2”x4”).
An option is, if you have speakers that allow it, to use it for bi-amping. Some speakers (and amps) profit from driving the main load (bass) with a separate amp. While the questionable bi-wiring is often mentioned in the same context, real bi-amping can give improved sound quality. Both amps get the same signal (so no active x-over), but see very different loads over the frequency range. The mid-high amp still amplifies the low frequency voltage, but without the current to move the bass. This may help the amp to drive the mid-high section more easy, cleaner. I write “may” because the results may vary from hardly noticeable to huge improvement. It all depends on your set-up, speakers and complexity of x-over components.
Think of one amp like you would be riding a bike up a steep hill, while trying to hand write a letter. Some artists may be able to do it, some only if there is no hill or in a hand writing hard to read...
Another nice option is to run the bass with a DSP and match it to the room, while the mid-high gets the “clean”, unmodified signal. This will have a huge impact in most rooms, as you can defend resonances.
Yesterday I measured/ matched the bass sections of a bi-amped speaker system in a large, irregular room with a DSP in the bass amp. The result, compared to the previous sound, was a “boom” free reproduction, with very unique, unexpected correction curves for each individual side.
So many options...
High quality transformers like the Lundahl´s do not degrade the sound and, opposite to the valve stage, do not add hear able distortion. That makes them expensive. They are simple in use, need no power supply and sound as neutral as the best active buffer stages. For HIFI the only downside is the high price. If you calculate the normal profit gain with HIFI gear, adding a pair will make an commercial pre- or power amp at least 1000$ more expensive, while an active buffer is not even 2$ in parts.
One main advantage is that you can isolate the amp from any other gear. This way you do not have any ground voltages flowing, that might induce hum. The amp is driven "over the air" in the transformer, without ground wire.
Next point, you can generate a balanced signal from a single ended, which in some cases is the most important part.
As the transformers are inductive, they limit the frequency range, this is a good thing, as unwanted high frequency dirt will enter the amp suppressed.
Another advantage may be their impedance. Because of the relative low (typical 3k ohm, constant in audio band) resistance, the amp has to deliver quite some current, which results in suppression of noise. Compared to a, maybe, 20k ohm input. No decent pre-amp should have any problems to drive loads as low as 600 ohms.
Jeff Rowland Design has used these transformers on the older ICE modules and these amps are considered world class. Quite nice, but expensive.
Very well made transformers are used in lots of studio gear, as a reliable problem solver.
Chances, most of your recordings have passed some of them, are high. Just like NE5532 OP-amps, that probably 95% of any well recorded music has passed.
I would see the transformer as the objective brother of the valve buffer, which is a more special gadget. The valve is not really needed today. We play around with for for the fun of it´s very individual, antique construction and it´s optics. Both are principles that have been around for a century or longer.
I think your decision to use the 700 "as is" first is a good idea.
Please notice that you could use a 300A1 "hanger" amp with the 700AS1.
Maybe leave room in your build for such an addition and a second set of connectors. The 300A1 Is very small (2”x4”).
An option is, if you have speakers that allow it, to use it for bi-amping. Some speakers (and amps) profit from driving the main load (bass) with a separate amp. While the questionable bi-wiring is often mentioned in the same context, real bi-amping can give improved sound quality. Both amps get the same signal (so no active x-over), but see very different loads over the frequency range. The mid-high amp still amplifies the low frequency voltage, but without the current to move the bass. This may help the amp to drive the mid-high section more easy, cleaner. I write “may” because the results may vary from hardly noticeable to huge improvement. It all depends on your set-up, speakers and complexity of x-over components.
Think of one amp like you would be riding a bike up a steep hill, while trying to hand write a letter. Some artists may be able to do it, some only if there is no hill or in a hand writing hard to read...
Another nice option is to run the bass with a DSP and match it to the room, while the mid-high gets the “clean”, unmodified signal. This will have a huge impact in most rooms, as you can defend resonances.
Yesterday I measured/ matched the bass sections of a bi-amped speaker system in a large, irregular room with a DSP in the bass amp. The result, compared to the previous sound, was a “boom” free reproduction, with very unique, unexpected correction curves for each individual side.
So many options...
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Thank you!
I really like the idea of this transformer. As for the turns ratio options, I’m assuming you could step the signal up or down depending if it is wired 2:1 or 1:2.
Would I wire it 1:1 to be powered by most preamplifiers? I also noticed a low impedance input wiring method, what would that way be used for?
I really like the idea of this transformer. As for the turns ratio options, I’m assuming you could step the signal up or down depending if it is wired 2:1 or 1:2.
Would I wire it 1:1 to be powered by most preamplifiers? I also noticed a low impedance input wiring method, what would that way be used for?
As easy as a transformer basically works, for a perfect match you need to know both sides, pre- and power-amp.
A valve pre would prefer a high impedance input of the transformer, a transistor or OP-amp based should work with 560 Ohm.
There are transistor pre-amps around, that can easily drive a head phone or small loudspeaker with their output stages. It depends on the stuff you physically have.
The LL 1545a should work well for you, with any average pre amp. This is high end HIFI, you can not exactly predict sound. You have to build, measure and listen. Often these transformers are only for isolating the amp from other gear, the output is then buffered at the amp side, again, before it enters the amp. Quite complicated for a part you might not even need.
A valve pre would prefer a high impedance input of the transformer, a transistor or OP-amp based should work with 560 Ohm.
There are transistor pre-amps around, that can easily drive a head phone or small loudspeaker with their output stages. It depends on the stuff you physically have.
The LL 1545a should work well for you, with any average pre amp. This is high end HIFI, you can not exactly predict sound. You have to build, measure and listen. Often these transformers are only for isolating the amp from other gear, the output is then buffered at the amp side, again, before it enters the amp. Quite complicated for a part you might not even need.
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Attached is the preamplifier circuit I use.
So with a 2:1 turns ratio, would the transformer effectively double the 47k impedance of the IcePower 700 as seen by any sort of preamp increasing the input impedance of the amplifier?
I’m also trying to have this amp work with both SS and tube preamps rather than tailored to a single type.
Thanks
So with a 2:1 turns ratio, would the transformer effectively double the 47k impedance of the IcePower 700 as seen by any sort of preamp increasing the input impedance of the amplifier?
I’m also trying to have this amp work with both SS and tube preamps rather than tailored to a single type.
Thanks
The reason for a buffer is that the output of the source does not see the other side.
A well build tube stage should be able to drive the 600 Ohm transformer, just like any transistor stage.
See, a transformer has a DC resistance, but this is not important, as it effectively blocks DC. So, important is what a signal from 20-20.000 Hz will see.
The question is always, what do you want, what do you expect. From the tube, from the transformer. The transformer solves problems, the tube produces them, technically speaking. A lot of the speak about tubes is sales talk. Produced by those that sell them and repeated by those that bought them. If you have spend a lot of money, your expensive tube must sound great, even if the CD player, connected directly to the amp, sounds better. So a tube thing is always a very subjective part of your HIFI gear. The power supply for a tube circuit is very critical and can induce buzz and hum. That makes tube stuff expensive. Your circuits do not show this most important part.
Please do not expect too much and don´t mix to many stuff right from the start, just do one thing at a time.
Building a good amp, having excellent speakers and a perfect signal source should be first. Anything else comes second. You may not need a transformer at all. If anything is dead silent, no hum, no hiss, you should be done with the amp.
I do know nothing about your skills, tools, experience and funds. Some will need a few minutes to solve a ground loop problem, some will throw the whole project in the bin because of such a "simple" complication. The more parts you add, the more problems will appear. Even just putting a ICE module in a box and fitting some connectors and wires is no piece of cake. My advice: Start with the minimum and save room for options. This will save you a lot of frustration.
Do you already have some kind of pre-amp?
A well build tube stage should be able to drive the 600 Ohm transformer, just like any transistor stage.
See, a transformer has a DC resistance, but this is not important, as it effectively blocks DC. So, important is what a signal from 20-20.000 Hz will see.
The question is always, what do you want, what do you expect. From the tube, from the transformer. The transformer solves problems, the tube produces them, technically speaking. A lot of the speak about tubes is sales talk. Produced by those that sell them and repeated by those that bought them. If you have spend a lot of money, your expensive tube must sound great, even if the CD player, connected directly to the amp, sounds better. So a tube thing is always a very subjective part of your HIFI gear. The power supply for a tube circuit is very critical and can induce buzz and hum. That makes tube stuff expensive. Your circuits do not show this most important part.
Please do not expect too much and don´t mix to many stuff right from the start, just do one thing at a time.
Building a good amp, having excellent speakers and a perfect signal source should be first. Anything else comes second. You may not need a transformer at all. If anything is dead silent, no hum, no hiss, you should be done with the amp.
I do know nothing about your skills, tools, experience and funds. Some will need a few minutes to solve a ground loop problem, some will throw the whole project in the bin because of such a "simple" complication. The more parts you add, the more problems will appear. Even just putting a ICE module in a box and fitting some connectors and wires is no piece of cake. My advice: Start with the minimum and save room for options. This will save you a lot of frustration.
Do you already have some kind of pre-amp?
Hi,
My preamp was in the last post but I’ve attached it again along with the power supply. I have used it for two years now and is dead silent and sounds great.
I use it to power a pair of tube monoblocks I've built with good results. I will also drive this ice power amp with the same preamp.
I will try the ice power modules alone first. The Lundahl 1545 transformers are relatively in expensive, I may buy those still for comparison.
Thanks
My preamp was in the last post but I’ve attached it again along with the power supply. I have used it for two years now and is dead silent and sounds great.
I use it to power a pair of tube monoblocks I've built with good results. I will also drive this ice power amp with the same preamp.
I will try the ice power modules alone first. The Lundahl 1545 transformers are relatively in expensive, I may buy those still for comparison.
Thanks
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OK, I did not know you had this one. Your pre should be happy with 50K ohm impedance. So it should be able to drive the 700AS1 input buffer single ended.
(The ICE manual seems to be a little bit confusing with the integrated buffer) 20 volt are way to much for the amp, so some resistor might be needed to get a good response of the volume pot.
As an alternative, I would think about something like the LL 1630, which will transform the high output voltage of 20V down to something the 700 can handle.
Your pre-amp seems to be the worst case I thought of. It is optimized for a valve amp as far as I understand. Maybe ask the manufacturer of your kit what would be best to drive a "normal" power amp with it.
(The ICE manual seems to be a little bit confusing with the integrated buffer) 20 volt are way to much for the amp, so some resistor might be needed to get a good response of the volume pot.
As an alternative, I would think about something like the LL 1630, which will transform the high output voltage of 20V down to something the 700 can handle.
Your pre-amp seems to be the worst case I thought of. It is optimized for a valve amp as far as I understand. Maybe ask the manufacturer of your kit what would be best to drive a "normal" power amp with it.
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I looked up the 1630 and it looks like since it’s an audio output transformer, I assume I would install that in my preamp rather than the ice power amplifier? I can’t find a whole lot of other information on it either other than the datasheet to learn more about it. I haven’t seen these before.
Also, how Are you calculating the 20V output from the preamp? Also note, there are 1k resistors in series at each of the outputs of the preamp. I could always increase the resistors on the output driving this amp.
I really like the idea of the Lundahl 1545 you mentioned for the ice power amp for the ground & DC isolation benefits and the SE to balanced conversion . What do you think about powering the ice modules with the 1545 transformers leaving the preamp as is, or with just changing the preamp resistors if need be?
Thanks
Also, how Are you calculating the 20V output from the preamp? Also note, there are 1k resistors in series at each of the outputs of the preamp. I could always increase the resistors on the output driving this amp.
I really like the idea of the Lundahl 1545 you mentioned for the ice power amp for the ground & DC isolation benefits and the SE to balanced conversion . What do you think about powering the ice modules with the 1545 transformers leaving the preamp as is, or with just changing the preamp resistors if need be?
Thanks
As far as I can see, there are some unknown variables in this game.
The manuals of the different ICE amps seem to have some incorrect values. The schematic does not match the values in the text and other manuals, from basically identical circuits, are different. As they only serve the OEM market, this does not really matter. So choosing the right Lundahl is not that simple. I´m not sure which one is the best.
So first I would try to get the 700 modules, then examine the actual input stage. This module is a fantastic amp, that is for sure. So no risk to buy it if you feel you can build it.
I lean to building the ICE amps just as supposed, with an XLR input and add transformers to the pre amp. Maybe switchable, so you can use them both ways.
I can give you hints what should work best, but I try to be careful with exact plans and parts, as I would order parts and build only after thorough examination and some tests. Even then calculated parts may not do as thought and will be changed for others. I do not want to waste your money.
I have been DIYS building amps for about 45 years now, so I have a pretty good idea what will work and what will fail. I do not give advice to buy expensive parts from a few thousand miles distance.
My way would be driving the transformers with different test signals from your pre amp, while it´s output has a resistor as load. If this works well, matching to the 700 would be next.
The 20 volt figure for your pre is from here: OddWatt
There is not much technical information on the oddwatt site.
The manuals of the different ICE amps seem to have some incorrect values. The schematic does not match the values in the text and other manuals, from basically identical circuits, are different. As they only serve the OEM market, this does not really matter. So choosing the right Lundahl is not that simple. I´m not sure which one is the best.
So first I would try to get the 700 modules, then examine the actual input stage. This module is a fantastic amp, that is for sure. So no risk to buy it if you feel you can build it.
I lean to building the ICE amps just as supposed, with an XLR input and add transformers to the pre amp. Maybe switchable, so you can use them both ways.
I can give you hints what should work best, but I try to be careful with exact plans and parts, as I would order parts and build only after thorough examination and some tests. Even then calculated parts may not do as thought and will be changed for others. I do not want to waste your money.
I have been DIYS building amps for about 45 years now, so I have a pretty good idea what will work and what will fail. I do not give advice to buy expensive parts from a few thousand miles distance.
My way would be driving the transformers with different test signals from your pre amp, while it´s output has a resistor as load. If this works well, matching to the 700 would be next.
The 20 volt figure for your pre is from here: OddWatt
There is not much technical information on the oddwatt site.
Thanks for all your help Turbo, learning a lot so far here.
I’m going to order two 700as1 modules today, and we’ll see what we have when they come in.
I built my Forewatt preamplifier with three outputs, so I don’t see why I couldn’t add transformers to just one of the outputs to drop the 20v to make a sort of low voltage out for SS amps and leave the other two outputs alone without any switching.
I have no doubt that these IcePower modules are great so I don’t mind just buying them. And if I really had to, and probably will anyways down the road, build a matching SS preamp for it.
Thanks
I’m going to order two 700as1 modules today, and we’ll see what we have when they come in.
I built my Forewatt preamplifier with three outputs, so I don’t see why I couldn’t add transformers to just one of the outputs to drop the 20v to make a sort of low voltage out for SS amps and leave the other two outputs alone without any switching.
I have no doubt that these IcePower modules are great so I don’t mind just buying them. And if I really had to, and probably will anyways down the road, build a matching SS preamp for it.
Thanks
If there is enough room in your pre, a Lundahl could be fitted inside. They are screened and quite insensitive to noise.
If you decide to buy one (or a pair), maybe first fit a wire with an RCA plug at the input and an XLR for the output to the ICE amp. If you think it works well, then decide where to place the transformer. Shorter wires never sound worse.
The problem of your valve pre is it´s high voltage and low current. The ICE needs maybe 1-2 volt for full RMS power.
If you change the voltage 2:1 or 4:1 with a transformer, you get lower volts with more mA, so you can drive a lower input impedance. So, to say it un-electronically, the voltage gets lower, but stronger. Just connected as is, the volume might be hard to control in a linear way.
This would make your pre more universal, for any amp with more usual input demands, not only the ICE modules. In the new version they should be easy to drive.
This is all theoretical. From the distance and with limited insight in the circuits, no one can not exactly predict the electronic or sonic results.
The resulting sound has to be judged by you. I personally like to make A/B tests. Another way is to listen really relaxed and change gear in between. If you know your tracks well and you have good components, you sometimes may notice single, tiny events in your music that has changed.
If you decide to buy one (or a pair), maybe first fit a wire with an RCA plug at the input and an XLR for the output to the ICE amp. If you think it works well, then decide where to place the transformer. Shorter wires never sound worse.
The problem of your valve pre is it´s high voltage and low current. The ICE needs maybe 1-2 volt for full RMS power.
If you change the voltage 2:1 or 4:1 with a transformer, you get lower volts with more mA, so you can drive a lower input impedance. So, to say it un-electronically, the voltage gets lower, but stronger. Just connected as is, the volume might be hard to control in a linear way.
This would make your pre more universal, for any amp with more usual input demands, not only the ICE modules. In the new version they should be easy to drive.
This is all theoretical. From the distance and with limited insight in the circuits, no one can not exactly predict the electronic or sonic results.
The resulting sound has to be judged by you. I personally like to make A/B tests. Another way is to listen really relaxed and change gear in between. If you know your tracks well and you have good components, you sometimes may notice single, tiny events in your music that has changed.
Thanks a lot,
Can I measure the actual voltage at my preamps output?
I’m assuming it’s not as simple as measuring with a meter at the preamps output.
But I do have a Fluke 289 which as an AC peak mode and I do have a Fuke 123 oscilloscope as well.
How would you measure the voltage out of the preamp?
Also, would connecting “as is” harm the Icepower module if it is over the 12V, if I were to just try it?
Thanks
Can I measure the actual voltage at my preamps output?
I’m assuming it’s not as simple as measuring with a meter at the preamps output.
But I do have a Fluke 289 which as an AC peak mode and I do have a Fuke 123 oscilloscope as well.
How would you measure the voltage out of the preamp?
Also, would connecting “as is” harm the Icepower module if it is over the 12V, if I were to just try it?
Thanks
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If you do not have a function generator, burn your self a CD for your player. There are quite some ISO´s for test CD´s in the net. If you put the player in repeat mode, you have a generator.
Usually 1000 Hz are used for such measurements.
Then take a 50k ohm resistor and connect it from one channels input to ground. Place the probe of the oscilloscope over the resistor. Now you can see the output of your pre amp, turn it up until the sinus starts to become deformed or flat at top of the oscillation. This is the clipping point.
You could also try 20, 100, 10.000 and 20.000 Hz.
Now you can experiment and build an input stage for the ICE amp.
I´m sure your pre has an output capacitor, so if you turn it up slowly, it should not harm the ICE input.
Later, if you have the actual ICE amp set up, connect the pre and put an 8 Ohm load resistor at the output. The oscilloscope will show you what happens, too.
For basic needs, connecting for example 10 resistors of 5-8 watt/ 80 ohm in parallel or what ever combination you like to get near 8 ohm (=what load resistors are cheap at surplus or locally). If you epoxy the resistors to a piece of aluminum, you can use it until they get hot, maybe 100 watt for a very short time. If you feel you have to measure higher load for prolonged periods of time, put such a construction in a (plastic) bucket of water, you can run much higher power into it them than air cooled.
With I=U/R and 1.41xUxI you calculate the output power.
There is no use in a pre amp that drives the amp to full output at the lowest setting of the volume pot. Beside from providing balanced drive, a well matched transformer gives a much better results than resistors that just "burn" the output voltage if it is too high.
Usually 1000 Hz are used for such measurements.
Then take a 50k ohm resistor and connect it from one channels input to ground. Place the probe of the oscilloscope over the resistor. Now you can see the output of your pre amp, turn it up until the sinus starts to become deformed or flat at top of the oscillation. This is the clipping point.
You could also try 20, 100, 10.000 and 20.000 Hz.
Now you can experiment and build an input stage for the ICE amp.
I´m sure your pre has an output capacitor, so if you turn it up slowly, it should not harm the ICE input.
Later, if you have the actual ICE amp set up, connect the pre and put an 8 Ohm load resistor at the output. The oscilloscope will show you what happens, too.
For basic needs, connecting for example 10 resistors of 5-8 watt/ 80 ohm in parallel or what ever combination you like to get near 8 ohm (=what load resistors are cheap at surplus or locally). If you epoxy the resistors to a piece of aluminum, you can use it until they get hot, maybe 100 watt for a very short time. If you feel you have to measure higher load for prolonged periods of time, put such a construction in a (plastic) bucket of water, you can run much higher power into it them than air cooled.
With I=U/R and 1.41xUxI you calculate the output power.
There is no use in a pre amp that drives the amp to full output at the lowest setting of the volume pot. Beside from providing balanced drive, a well matched transformer gives a much better results than resistors that just "burn" the output voltage if it is too high.
I’m assuming you meant it to connect the resistor to one of the channels “outputs” to ground, correct? It do you really test at the input? Just want to be sure.
Then I would basically connect the oscilloscope across the resistor I believe. i.e. connect the ground probe to the grounded side of the resistor and the positive probe to the positive side.
Thank you
Sorry, yes, from one channel of the pre amp output 50k to ground. This is the resistance into which your pre drives best, as the Oddwatt homepage said.
You might later connect 8k ohm as a second resistor to see how it drives lower impedance. Compare the voltages at 20, 1000 and 20.000 Hz with the results from the 50k measurement. You could even use a 50k pot and find the best resistor. This way I would go to get the missing information.
You could as well use some program like ARTA, REW or the like, if you have a good sound card. You only need a few parts, worth a few Cent to make a protection for the interface. Basically a resistor and 5 volt Zener diode.
You first connect a loop back wire to the computer in and out, which produces a correction for the program. Then, with some simple adjustments, you calibrate the sound card. You have an oscilloscope, that makes it easy.
Then you generate signals, put them into the pre amp and at the same time record what comes out of the pre. More convenient than using a CD player and oscilloscope, just the hurdle to use a new program. You get all kinds of curves from these programs, can measure THD etc.
That is a more professional way to find a well suited input stage for pre + power amp.
You might later connect 8k ohm as a second resistor to see how it drives lower impedance. Compare the voltages at 20, 1000 and 20.000 Hz with the results from the 50k measurement. You could even use a 50k pot and find the best resistor. This way I would go to get the missing information.
You could as well use some program like ARTA, REW or the like, if you have a good sound card. You only need a few parts, worth a few Cent to make a protection for the interface. Basically a resistor and 5 volt Zener diode.
You first connect a loop back wire to the computer in and out, which produces a correction for the program. Then, with some simple adjustments, you calibrate the sound card. You have an oscilloscope, that makes it easy.
Then you generate signals, put them into the pre amp and at the same time record what comes out of the pre. More convenient than using a CD player and oscilloscope, just the hurdle to use a new program. You get all kinds of curves from these programs, can measure THD etc.
That is a more professional way to find a well suited input stage for pre + power amp.
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I don't have any experience building class D but Pete Millett's Nutube hybrid amp is something I'm considering ( NuClassD 50W Nutube hybrid amp )
I made a headphone amp he designed, using the Nutube and it's pretty cool. Definitely rich in the kind of subtle harmonic distortion that people like in conventional tube amps. The "tube" (yes it heats electrons in a vacuum) is weird: it's a little flat rectangular box. It is very microphonic so if you bump it, it rings for a few seconds (in headphones it does, when using it as a preamp, I don't notice that). Despite that, I'm excited enough about it's character that I want a power amp that sounds like that.
I made a headphone amp he designed, using the Nutube and it's pretty cool. Definitely rich in the kind of subtle harmonic distortion that people like in conventional tube amps. The "tube" (yes it heats electrons in a vacuum) is weird: it's a little flat rectangular box. It is very microphonic so if you bump it, it rings for a few seconds (in headphones it does, when using it as a preamp, I don't notice that). Despite that, I'm excited enough about it's character that I want a power amp that sounds like that.
That amp looks very cool. Nelson Pass has a nice amp kit out that uses that Nutube as well. Kits are sold out I think.
For mine, I did end up ordering two Icepower 700as1’s today to make a dual mono amplifier. Not sure exactly when I’ll get them because they ship from somewhere in Asia but hopefully soon.
For mine, I did end up ordering two Icepower 700as1’s today to make a dual mono amplifier. Not sure exactly when I’ll get them because they ship from somewhere in Asia but hopefully soon.