Dear Members
I have the T2 amp. I was wondering if anyone has suggestions on how to improve its sound quality even further with 4ohm speakers.
So far i had changed the input caps with better quality & had a slight improvement with the mid frequencies.
I want some suggestions about the output filter. Also i measured the dc offset with a 4ohm load. It is -10mv (it is reversed). I don't know which technique hifimediy used to adjust it but i guess i must adjust close to zero & maybe this is the reason that i don't have a crystal clear sound with high frequencies.
Any replies would very appreciated.
I have the T2 amp. I was wondering if anyone has suggestions on how to improve its sound quality even further with 4ohm speakers.
So far i had changed the input caps with better quality & had a slight improvement with the mid frequencies.
I want some suggestions about the output filter. Also i measured the dc offset with a 4ohm load. It is -10mv (it is reversed). I don't know which technique hifimediy used to adjust it but i guess i must adjust close to zero & maybe this is the reason that i don't have a crystal clear sound with high frequencies.
Any replies would very appreciated.
info
Speakers are amphion helium 520 floor standings, made in Finland ( Helium 520 | Amphion ). Tweeter is titanium dome from seas but it is specifically made for these speakers & they don't give its characteristics because of a secret patent they have. Also i have a pair of alesis monitor one mkii that i use with this amp. I've seen your posts. Do we have to know tweeter specifications to make the proper filter or do we just measure the whole speaker unit ?
Speakers are amphion helium 520 floor standings, made in Finland ( Helium 520 | Amphion ). Tweeter is titanium dome from seas but it is specifically made for these speakers & they don't give its characteristics because of a secret patent they have. Also i have a pair of alesis monitor one mkii that i use with this amp. I've seen your posts. Do we have to know tweeter specifications to make the proper filter or do we just measure the whole speaker unit ?
Unfortunately you need to know the resistance and inductance of the high frequency driver for the filter to be exact.
What you can do now is to unsolder one lead of the resistor in the zobel, which will disable the entire zobel. If the zobel is causing a significant rolloff of high frequencies you should get a boost. If you do, you can then connect a test zobel across the speaker outputs. I would start with the value capacitance that is currently used and try progressively higher values of the resistance. As you increase the value of the resistor (one half ohm is a good increment) over the current value the highs will increase (think of it as though you are approaching infinite resistance which is what you did when you unsoldered the resistor lead). I find that as you get closer to the sound you like the highs get sweeter, and as the highs get stronger than what you like they become more aggressive and harsh. The capacitance determines the corner freq of the zobel.
This method won't be perfect but the sound will be a lot better.
I am getting a Hifimediy T2 in myself (soon I hope). We can exchange info.
By the way your speakers look awesome. I bet they will play loud and clean. I wish I could hear them. 🙂
What you can do now is to unsolder one lead of the resistor in the zobel, which will disable the entire zobel. If the zobel is causing a significant rolloff of high frequencies you should get a boost. If you do, you can then connect a test zobel across the speaker outputs. I would start with the value capacitance that is currently used and try progressively higher values of the resistance. As you increase the value of the resistor (one half ohm is a good increment) over the current value the highs will increase (think of it as though you are approaching infinite resistance which is what you did when you unsoldered the resistor lead). I find that as you get closer to the sound you like the highs get sweeter, and as the highs get stronger than what you like they become more aggressive and harsh. The capacitance determines the corner freq of the zobel.
This method won't be perfect but the sound will be a lot better.
I am getting a Hifimediy T2 in myself (soon I hope). We can exchange info.
By the way your speakers look awesome. I bet they will play loud and clean. I wish I could hear them. 🙂
Considering the price point of you speakers I'll bet they use a Seas 27 series. And, considering the crossover point they are using the motor from something like the Seas Prestige 27TBFC/G (H1212), and I bet their changes don't effect the reisitance or inductance much.
So, I would try a zobel close to C=0.89uF and R=7.5ohms and increase the resistance from there.
If the output filter of the T2 was actually designed for 4 ohms, and the tweeter is actually 6 ohms, there should be a small peak in the highs from this. If you can send me the values of the output filter, I could tell you what resistance the filter was designed for.
So, I would try a zobel close to C=0.89uF and R=7.5ohms and increase the resistance from there.
If the output filter of the T2 was actually designed for 4 ohms, and the tweeter is actually 6 ohms, there should be a small peak in the highs from this. If you can send me the values of the output filter, I could tell you what resistance the filter was designed for.
many thanks.
I really appreciate your info here. I was thinking, before doing what you suggest, to disconnect the leads from the tweeters & measure resistance/inductance with a multimeter. Then use your -Class-D Output Filter - A Case Study - thread & find the values for the capacitor + resistor.
Since you'll get the T2 amp we will have a common device to work on.
I have a Sure 2*100 2050 board also modified. On this one the zobel consists of a 10ohm resistor & 0.47uf capacitor on the outputs. This amp achieved an amazing sound with upper frequencies but is outperformed by the killer bass & mids of the T2. I knew that class-d has to be auditioned with different speakers to get the final result for the listener.
Anyway, about amphion if you ever find them anywhere you will be amazed. I was lucky to buy them in a discount offer . These made me not to look for any other speakers.
I really appreciate your info here. I was thinking, before doing what you suggest, to disconnect the leads from the tweeters & measure resistance/inductance with a multimeter. Then use your -Class-D Output Filter - A Case Study - thread & find the values for the capacitor + resistor.
Since you'll get the T2 amp we will have a common device to work on.
I have a Sure 2*100 2050 board also modified. On this one the zobel consists of a 10ohm resistor & 0.47uf capacitor on the outputs. This amp achieved an amazing sound with upper frequencies but is outperformed by the killer bass & mids of the T2. I knew that class-d has to be auditioned with different speakers to get the final result for the listener.
Anyway, about amphion if you ever find them anywhere you will be amazed. I was lucky to buy them in a discount offer . These made me not to look for any other speakers.
I had another thought. We may be able to keep the T2 board inductor and let the cutoff freq change by changing the capacitor to match our speakers. The inductor looks pretty good. I have sent an email to Hifimediy to see if he will give us the value of the inductor.
I did a rough approx in Excel and it looks like the freq won't change enough to be a problem. And I am confident that getting the Output filter to match our speakers will make a much greater difference than changing the cutoff frequency, as long as the frequency stays significantly above 20,000Hz.
To get the capacitor value to match your speakers, first solve:
f=1000*(0.2251*Rs)/Lf
fThis gives the new cutoff frequency using the actual value of the on board inductor. Remember to change the value of the inductor from uH to mH.
Then solve for C:
Cse=1000000*(0.1125/(Rs*f))
And since the T2 output is BTL:
Cbtl=Cse/2
Then, all we need to do is unsolder one lead from each of the capacitors on the output filters to disable it, or if we are confident enough, just remove them. And disable the zobel, then we can test the new filter and zobel with an external temp setup so we can try different values and types of capacitors. Don't worry about the stray capacitance and inductance of the test leads. Just keep the leads fairly straight.
I did a rough approx in Excel and it looks like the freq won't change enough to be a problem. And I am confident that getting the Output filter to match our speakers will make a much greater difference than changing the cutoff frequency, as long as the frequency stays significantly above 20,000Hz.
To get the capacitor value to match your speakers, first solve:
f=1000*(0.2251*Rs)/Lf
fThis gives the new cutoff frequency using the actual value of the on board inductor. Remember to change the value of the inductor from uH to mH.
Then solve for C:
Cse=1000000*(0.1125/(Rs*f))
And since the T2 output is BTL:
Cbtl=Cse/2
Then, all we need to do is unsolder one lead from each of the capacitors on the output filters to disable it, or if we are confident enough, just remove them. And disable the zobel, then we can test the new filter and zobel with an external temp setup so we can try different values and types of capacitors. Don't worry about the stray capacitance and inductance of the test leads. Just keep the leads fairly straight.
By the way, if the manuf of your speaker included a zobel on the tweeter (most don't), or a series inductor to shape the response of the tweeter (most don't do that either), the effective inductance will change. The same goes for resistance if they chose to change that in the crossover also.
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