Hi Fab
I read your manual couple of times but I think I overlooked one step that I need to solder the Cz and Rz only after doing the steps listed under 8.13/8.14 and not before that.
The step 8.14 is to:
Adjust P1 for about 0,3Vdc between TP6 and V-.
Adjust P2 for about 0,3Vdc between TP5 and V+.
But now that I have already installed Rz and Cz can I do this step 8.14 or do you want me to remove them and do this step and solder back?
Thanks
Hi manniraj
There is no problem to install in advance Cz and RZ parts in the build sequence. It is only imperative to install the minimum set of parts as indicated in the steps. Thus leave Rz and Cz.
Fab
There is no problem to install in advance Cz and RZ parts in the build sequence. It is only imperative to install the minimum set of parts as indicated in the steps. Thus leave Rz and Cz.
Fab
8 pairs come from a hardly used hybrid amplifier (see this link https://s3.amazonaws.com/hifi.nl/Music-Emotion/ME2-05-Syntaxis.pdf).
8 pairs were bought new from Shaan (PeeCeeBee).
I don't see a brand name on the parts but trust they are genuine.
Would be willing to sell as there are already too many projects unfinished 😉
I ordered ecw type S... Out of curiosity.. Any advantages over non S.for fssa? . Matched vgs right? Or I'm just wasting 15 dollars?
Hi AnthonyA
For the FSSA amp there is no real gain to buy the S version since FSSA output is common drain where transistors difference should not make a noticeable difference in this topology. The FSSA manual does not mention the S version.
Fab
Hi manniraj
Looking forward to having feedback on your first assembled channel.🙂
With 95dB and 6 ohms minimum impedance the USSA5 will have a real easy job to do 😛
By the way it seems to be fine a speaker 😛
I have Troels SBA-10 with 87dB and nominal 4 ohms and my USSA5.1 can play loud enough for optimum pleasure with no problem 😉
Fab
Looking forward to having feedback on your first assembled channel.🙂
With 95dB and 6 ohms minimum impedance the USSA5 will have a real easy job to do 😛
By the way it seems to be fine a speaker 😛
I have Troels SBA-10 with 87dB and nominal 4 ohms and my USSA5.1 can play loud enough for optimum pleasure with no problem 😉
Fab
Last edited:
Thanks Fab, I am almost done with the first amp board with the bias set at 50mV without any fluctuations and offset being 0.08mV 🙂. After my M2x this is the second amp where I could get the offset below 1mV 😀
I think your instructions are spot on and agree that I did not read fully initially but I have now read it multiple times.
The following are the readings per section "Output Mosfet VGS Determination" 8.17.1
Measure voltage between TP6 and V- (VGSN = 986mV)
Measure voltage between TP5 and V+ (VGSP = 1546mV)
8.18.1 Positive side:
IM3pre = VGSP / 147 Ohm = 10.517
o RM3 = VGSP / 23mA = 67.217
o RV1 = RV1A /RV1B = RM3 - 47 = 20.217
o RV1A = 20.217 (this is a positive value, hence I am not going to change the R13)
8.18.2 Negative side:
IM4pre = VGSN / 94 Ohm = 10.489
o RM3 = VGSN / 23mA = 42.869
o RV2 = RV2A /RV2B = RM4 - 47 = -4.130
o RV1A = -4.130 (this is a negative value, hence I have to reduce the R14 resistor value)
I have put in R13/14 as 47R 1/4w resistor, so as per my above calculations how much should I reduce like remove the R14 resistor value of 47R and put in a 33R?
Thanks
I think your instructions are spot on and agree that I did not read fully initially but I have now read it multiple times.
The following are the readings per section "Output Mosfet VGS Determination" 8.17.1
Measure voltage between TP6 and V- (VGSN = 986mV)
Measure voltage between TP5 and V+ (VGSP = 1546mV)
8.18.1 Positive side:
IM3pre = VGSP / 147 Ohm = 10.517
o RM3 = VGSP / 23mA = 67.217
o RV1 = RV1A /RV1B = RM3 - 47 = 20.217
o RV1A = 20.217 (this is a positive value, hence I am not going to change the R13)
8.18.2 Negative side:
IM4pre = VGSN / 94 Ohm = 10.489
o RM3 = VGSN / 23mA = 42.869
o RV2 = RV2A /RV2B = RM4 - 47 = -4.130
o RV1A = -4.130 (this is a negative value, hence I have to reduce the R14 resistor value)
I have put in R13/14 as 47R 1/4w resistor, so as per my above calculations how much should I reduce like remove the R14 resistor value of 47R and put in a 33R?
Thanks
Last edited:
Thanks Do, hopefully by next weekend I should get them to sing in my makeshift cabinet chassis with dual mono PSU and transformers. If this sounds good I may shift it to my M2x cabinet or actually get a mono bloc cabinets 😉 So far the best I have heard is the M2X with the Ishikawa on my audio nirvana super+ 8" drivers speakers. I have to see how the USSA-5 stands against my M2x or the Sony VFET2.
Will wait for Fab's reply on the changing of R14 resistor value.
Hi manniraj
You are doing fine with your calculations !🙂
“... 8.18.1 Positive side:
IM3pre = VGSP / 147 Ohm = 10.517
o RM3 = VGSP / 23mA = 67.217
o RV1 = RV1A /RV1B = RM3 - 47 = 20.217
o RV1A = 20.217 (this is a positive value, hence I am not going to change the R13) : if RV1B is not installed
8.18.2 Negative side:
IM4pre = VGSN / 94 Ohm = 10.489
o RM3 = VGSN / 23mA = 42.869
o RV2 = RV2A /RV2B = RM4 - 47 = -4.130
o RV2A = -4.130 (this is a negative value, hence I have to reduce the R14 resistor value): if RV2B is not installed
I have put in R13/14 as 47R 1/4w resistor, so as per my above calculations how much should I reduce like remove the R14 resistor value of 47R and put in a 33R?...”
———————————————————————-
For R14, it means that even with a jumper for RV2, the R13 should be 47-4= 43 ohms. So you can simply replace the 47 ohms by 43 ohms.
But, if you intend to have more than 1A as final bias (ex: 1.3A or so) you can leave R13 as 47 ohms and put a jumper for RV2 and then recalculate the target current as 0.986v /47 = 21ma (at 1A bias thus 50mv). Then you apply 21ma to target current on positive side thus 1,546/0.021= 74 ohms. 74-47= 27 ohms for RV1.
The goal is to have about equal current on positive and negative sides. When you will bias at final output bias current the driver current should go at least about 23ma or more which is fine.
Fab
You are doing fine with your calculations !🙂
“... 8.18.1 Positive side:
IM3pre = VGSP / 147 Ohm = 10.517
o RM3 = VGSP / 23mA = 67.217
o RV1 = RV1A /RV1B = RM3 - 47 = 20.217
o RV1A = 20.217 (this is a positive value, hence I am not going to change the R13) : if RV1B is not installed
8.18.2 Negative side:
IM4pre = VGSN / 94 Ohm = 10.489
o RM3 = VGSN / 23mA = 42.869
o RV2 = RV2A /RV2B = RM4 - 47 = -4.130
o RV2A = -4.130 (this is a negative value, hence I have to reduce the R14 resistor value): if RV2B is not installed
I have put in R13/14 as 47R 1/4w resistor, so as per my above calculations how much should I reduce like remove the R14 resistor value of 47R and put in a 33R?...”
———————————————————————-
For R14, it means that even with a jumper for RV2, the R13 should be 47-4= 43 ohms. So you can simply replace the 47 ohms by 43 ohms.
But, if you intend to have more than 1A as final bias (ex: 1.3A or so) you can leave R13 as 47 ohms and put a jumper for RV2 and then recalculate the target current as 0.986v /47 = 21ma (at 1A bias thus 50mv). Then you apply 21ma to target current on positive side thus 1,546/0.021= 74 ohms. 74-47= 27 ohms for RV1.
The goal is to have about equal current on positive and negative sides. When you will bias at final output bias current the driver current should go at least about 23ma or more which is fine.
Fab
Last edited:
Thanks Fab for the information.
Coming to your reply I am a bit confused with your explanation. So let me put my understanding and please correct me 🙂
if RV1B is not installed Yes this is not installed
if RV2B is not installed Yes this is not installed
So based on the manual instructions I need not change R13 (47R resistor) as the calculated RV1A = 20.217 is positive. And I need to change R14 (47R resistor) as the calculated RV2A = -4.130 is negative. But looking at your below explanation I am bit confused to what exactly needs to be changed:
For R14, it means that even with a jumper for RV2, the R13 should be 47-4= 43 ohms. So you can simply replace the 47 ohms by 43 ohms.
But, if you intend to have more than 1A as final bias (ex: 1.3A or so) you can leave R13 as 47 ohms and put a jumper for RV2 and then recalculate the target current as 0.986v /47 = 21ma (at 1A bias thus 50mv). Then you apply 21ma to target current on positive side thus 1,546/0.021= 74 ohms. 74-47= 27 ohms for RV1.
You are suggesting to change R13 to 43R or the R14? By the way I have a heat sink sized 300x150/83 so should be good enough for 1.3A bias current I think but I may change this to a regular sized 300x150x65. May be this will not be sufficient for 1.3A current. So I will stick with 1A bias for now as the default.
So if you can tell me what exact value I have to change it either R13 or R14 or both. Also your manual says after changing R14 (when negative calculated RV2) redo the process again. So you meant to redo the section 8.18.1.
Thanks
Coming to your reply I am a bit confused with your explanation. So let me put my understanding and please correct me 🙂
if RV1B is not installed Yes this is not installed
if RV2B is not installed Yes this is not installed
So based on the manual instructions I need not change R13 (47R resistor) as the calculated RV1A = 20.217 is positive. And I need to change R14 (47R resistor) as the calculated RV2A = -4.130 is negative. But looking at your below explanation I am bit confused to what exactly needs to be changed:
For R14, it means that even with a jumper for RV2, the R13 should be 47-4= 43 ohms. So you can simply replace the 47 ohms by 43 ohms.
But, if you intend to have more than 1A as final bias (ex: 1.3A or so) you can leave R13 as 47 ohms and put a jumper for RV2 and then recalculate the target current as 0.986v /47 = 21ma (at 1A bias thus 50mv). Then you apply 21ma to target current on positive side thus 1,546/0.021= 74 ohms. 74-47= 27 ohms for RV1.
You are suggesting to change R13 to 43R or the R14? By the way I have a heat sink sized 300x150/83 so should be good enough for 1.3A bias current I think but I may change this to a regular sized 300x150x65. May be this will not be sufficient for 1.3A current. So I will stick with 1A bias for now as the default.
So if you can tell me what exact value I have to change it either R13 or R14 or both. Also your manual says after changing R14 (when negative calculated RV2) redo the process again. So you meant to redo the section 8.18.1.
Thanks
Last edited:
Hi Manniraj
R13 was a typo since it was meant R14.
So you had 2 choices:
1) Change R14 from 47 to 43 or
2) let R14 to 47 and change target current as explained.
Now if you intend to have 1.3A final bias then you can simply go to option #2.
Fab
R13 was a typo since it was meant R14.
So you had 2 choices:
1) Change R14 from 47 to 43 or
2) let R14 to 47 and change target current as explained.
Now if you intend to have 1.3A final bias then you can simply go to option #2.
Fab
Thanks Fab, looking at seriously I think I will go with 1.3A bias option. So will go with your 2nd suggestion of leaving R14 at 47R and change the target current. I will put in a jumper on RV2B and recalibrate the step 8.17.1 with setting the bias at 65mV.
I hope so 🙂
By the way how critical are these RV1A/RV2A/RV1B/RV2B in terms of using any generic resistors or should I use some known branded ones like Vishay Dale etc., as the resultant calculated values I may need to order them via Mouser US or element14 and usually they are pretty expensive in shipping to India.
Thanks
Hi Manniraj
The calculated resistor values done at 1A stay the same for higher current.
For RV2 it is 0 ohms (piece of wire) and RV1 is 27 ohms. RV1 can be done using RV1A in parallel with RV1B thus many possible combinations for values. You do not need exact value of 27 ohms.
Same quality resistor as the other ones.
Fab
The calculated resistor values done at 1A stay the same for higher current.
For RV2 it is 0 ohms (piece of wire) and RV1 is 27 ohms. RV1 can be done using RV1A in parallel with RV1B thus many possible combinations for values. You do not need exact value of 27 ohms.
Same quality resistor as the other ones.
Fab
Last edited: