Re: R3 and R16
Hi nbrophy, no you don't have to remove them, but they do cause 500mv of dc offset at speaker terminals (on my boards). This is regardless of whether you change the input caps or not.
I think removal of these resistors ( R3 & R16 ) and caps C3 & C24 is more important than changing the 0.8uf input caps ( C13 & C21 )..The SI T-Amp had 0.33uf input caps, less than half the value. Please try the amp before changing the input caps, it may have enough bass for your speakers as stock..
PS, all the mods described here assume that the boards have not been changed and have the same value parts as the boards I am using..
nbrophy said:
Hi nbrophy, no you don't have to remove them, but they do cause 500mv of dc offset at speaker terminals (on my boards). This is regardless of whether you change the input caps or not.
I think removal of these resistors ( R3 & R16 ) and caps C3 & C24 is more important than changing the 0.8uf input caps ( C13 & C21 )..The SI T-Amp had 0.33uf input caps, less than half the value. Please try the amp before changing the input caps, it may have enough bass for your speakers as stock..
PS, all the mods described here assume that the boards have not been changed and have the same value parts as the boards I am using..
Hello audio1st,
Having thus far removed only C3 & C24 (to address the relative 'dullness' I perceived, as per your suggestion), I find there is ample bass (with the speakers that I use), but still find the overall sound considerably softer in the higher frequencies, when compared to a stock S.I.T-Amp.
Would the removal of the resistors R3 & R16 change the sound, and if so, what kind of change can be expected?
Are there any other obvious candidates (for removal or modification) that may be softening the higher-end output?
Thanks for your help.
Robert_S
Having thus far removed only C3 & C24 (to address the relative 'dullness' I perceived, as per your suggestion), I find there is ample bass (with the speakers that I use), but still find the overall sound considerably softer in the higher frequencies, when compared to a stock S.I.T-Amp.
Would the removal of the resistors R3 & R16 change the sound, and if so, what kind of change can be expected?
Are there any other obvious candidates (for removal or modification) that may be softening the higher-end output?
Thanks for your help.
Robert_S
Hello Robert_S,
Reading back over the posts I see you have tried both 4 & 8ohm speakers with your amp with the same results. With these amps they usually boost or roll off the high frequencies depending on speaker resistance, this is due to the output filter.
As yours is rolled off with different speakers you could try removal of R3 & R16 . If you can just lift one end of each so you can test and replace if you want. This part of the cct is not on the SI amp, so if removed it will more closely resemble the SI.
Please check that the two resistors are the same value as on my board (223, 22k).
Let me know how you get on...
Reading back over the posts I see you have tried both 4 & 8ohm speakers with your amp with the same results. With these amps they usually boost or roll off the high frequencies depending on speaker resistance, this is due to the output filter.
As yours is rolled off with different speakers you could try removal of R3 & R16 . If you can just lift one end of each so you can test and replace if you want. This part of the cct is not on the SI amp, so if removed it will more closely resemble the SI.
Please check that the two resistors are the same value as on my board (223, 22k).
Let me know how you get on...
Just want to say thanks to all who contributed the "good stuff" to make this little guy sound great.
Received mine 12/24 so no fun until today. So far I have;
Shorted C-13,C-21
Removed C-3, C-24
Removed R-3, R-16 (this reduced the offset from 350/368 mv to 5/6.9 respectively!!
Mine has the smaller inductors.
Installed a 100K pot and two 3.3mfd Sonicaps in the front end.
No work on Caps for the rails as yet.
I am currently listening on a pair of Zaph's Hi-Vi B3S's and a CD player and I must tell you the sound is impressive! And when I consider the cost for amp and speakers it REALLY is impressive.
Again thanks to all who provided guidance for this project--great work guys!!!!!
Received mine 12/24 so no fun until today. So far I have;
Shorted C-13,C-21
Removed C-3, C-24
Removed R-3, R-16 (this reduced the offset from 350/368 mv to 5/6.9 respectively!!
Mine has the smaller inductors.
Installed a 100K pot and two 3.3mfd Sonicaps in the front end.
No work on Caps for the rails as yet.
I am currently listening on a pair of Zaph's Hi-Vi B3S's and a CD player and I must tell you the sound is impressive! And when I consider the cost for amp and speakers it REALLY is impressive.
Again thanks to all who provided guidance for this project--great work guys!!!!!
audio1st said:
On my board, the correct location is the other side, nearer to the outputs.
I have also removed the resistors suggested, DC offset came down from about 600mv to 30mv per channel.
I also removed the rogue 100K resistor that was across the inputs of the channel I was having problems with and it appears to have solved the problem of 4.5VDC ocassionally appearing on that channel's output.
This is my first real foray into DIY, so excuse this comment if it is obvious, but I'm finding that different power supplies I'm testing greatly affect the quality of the sound. If you don't like what you are hearing, try a different one. So far best sound is from a 12V acid battery as others have found.
I thought I would have a crack at one of these, having been through most of the Class D amps over the last 18 months or so !
I got one of the 4 channel amps first and just got it working to see what it was like. Mmmm..... losts of hiss and only 3 channels working, but one to work on in the months to come.
So far as the 2024 board is concerned, is there a definitive list of mods that I should carry out ?
(I am being lazy and avoiding reading the whole thread !)
I got one of the 4 channel amps first and just got it working to see what it was like. Mmmm..... losts of hiss and only 3 channels working, but one to work on in the months to come.
So far as the 2024 board is concerned, is there a definitive list of mods that I should carry out ?
(I am being lazy and avoiding reading the whole thread !)
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