I posted a few pics in the Picture thread. I really like this amp, very smooth sounding.
Genreg,
Would you share a drawing or a picture of how you implemented the Semisouth. I could see that mod on a future front end board.
Next up is an F-5. Probably will do this after the holiday season is over. Then on to a set of speakers.
Chad
Genreg,
Would you share a drawing or a picture of how you implemented the Semisouth. I could see that mod on a future front end board.
Next up is an F-5. Probably will do this after the holiday season is over. Then on to a set of speakers.
Chad
the Semisouth in the front end was a mismatch I suppose, Nelson Pass takes double SJ109 to drive the following SemiS in J2, so the Semisouth R100 replacing IRF610 is not so good.But placing the SemiS R100 in the signalpath of the outputstage does not seem to be a mismatch, there are many other examples here in the forum with other amps.
But a little expensive for an experiment, maybe you take for a try only two pairs per channel..... but difficult to compare then, less damping, less power might give other results.
It's alive!
There's some hum in the psu and the fuse blows sometimes because it's to small, but it works and plays! It was really like plug(&measure)&play!
Only one quick question: Voltage drop over the resistor, where the sense of the negative bias-board is applied, is a bit lower than that over the others, right? V at the sense-resistor was arround 0,62V and all others 0,68V (all measured before fine-tuning the output stage).
Pics tomorrow...
Amazed nightrush
There's some hum in the psu and the fuse blows sometimes because it's to small, but it works and plays! It was really like plug(&measure)&play!
Only one quick question: Voltage drop over the resistor, where the sense of the negative bias-board is applied, is a bit lower than that over the others, right? V at the sense-resistor was arround 0,62V and all others 0,68V (all measured before fine-tuning the output stage).
Pics tomorrow...
Amazed nightrush
So, here are some quick shots.
Amp is working with a 10A fuse I found here at the moment, but I will get some smaller ones, 2.2A or so, don't worry.
The (complete) box is getting relatively hot, don't know the exact temperature, but its above 49°C (I've got to get some cheap meter for measuring, or maybe i can borrow one from chemics teacher).
If it's really to hot, although I don't think so, I will add some holes in the bottom and top and front and maybe add some small fans.
Best Regards, nightrush
Amp is working with a 10A fuse I found here at the moment, but I will get some smaller ones, 2.2A or so, don't worry.
The (complete) box is getting relatively hot, don't know the exact temperature, but its above 49°C (I've got to get some cheap meter for measuring, or maybe i can borrow one from chemics teacher).
If it's really to hot, although I don't think so, I will add some holes in the bottom and top and front and maybe add some small fans.
Best Regards, nightrush
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images resized for web. Be kind, please resize before posting.
Uhm, which exactly do you mean? Those black cables passing through the massive panel?
and yeah, thanks for resizing the pictures, I forgot to do this to all of them.
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How many have tried the BA-1 Semisouth modification?
Myself and Generg have tried it. I used just one SemiSouth R100 and he used 3 or more pairs. I got decent sound out of it. I swapped it out on the mini-A with a better sound (probably more distortion).
I don't think Papa has sanctioned a SS mod to the BA line of amps. I would think a modded front end would be essential.
well, I typed this responce hours ago before I went out but...
I would guess back in this thread somewhere you could read about useing a SS device as the follower and a Fairchild or IRF device as the current source device. Should be a worthwhile improvement. Ideally I suppose changing out bouth devices could offer even further improvement but I really have no proof or that.
I beleive GenReg may have experimented with a configuration useing the SS part.
I would guess back in this thread somewhere you could read about useing a SS device as the follower and a Fairchild or IRF device as the current source device. Should be a worthwhile improvement. Ideally I suppose changing out bouth devices could offer even further improvement but I really have no proof or that.
I beleive GenReg may have experimented with a configuration useing the SS part.
Yes I tried....
First I changed only the non-CCS parts to SS and I liked the sound very much, especially voices came in a marvelous new way.
Changing also the CCS to SS I got no clear result, more details, but also some sharp "s" in the voices.
I have no possibility to measure distortion ..... I suppose there was more.....
@tea-bag: yes, I preferred Pumpkin over the original front end, with the flexible concept variac and the others choose this is no problem...
First I changed only the non-CCS parts to SS and I liked the sound very much, especially voices came in a marvelous new way.
Changing also the CCS to SS I got no clear result, more details, but also some sharp "s" in the voices.
I have no possibility to measure distortion ..... I suppose there was more.....
@tea-bag: yes, I preferred Pumpkin over the original front end, with the flexible concept variac and the others choose this is no problem...
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That's true, Pumpkin offers some serious drive to be considered for a SS backend. I am using a cascoded front end for the BA-2 to drive bass speakers, offers plenty of grunt. Runs at about 50v.
Someday I will wire by Pumpkin together more permanantly
But placing the SemiS R100 in the signalpath of the outputstage does not seem to be a mismatch, there are many other examples here in the forum with other amps.
But a little expensive for an experiment, maybe you take for a try only two pairs per channel..... but difficult to compare then, less damping, less power might give other results.
From what little i know, finding a way to put a SS (R550 possibly)device in the 610 position stands to yield the greatest difference in sound. The need for dual j109's i believe is related to the input capacitance and the need for more drive current. I had to add parallel fets on the input of my AJ monoblocks to drive the extra fets i was adding to the output. It is interesting that you heard a difference with SS in the output stage. I would of thought being a powerbuffer operating as source follower, it would not have contributed much of its nature to the sound. I always thuoght the sound of the transistor cam largely from its gain and the associated non/linearities of the amplification. In reading the DIY OpAmp article on the Pass site, it seems you stand to gain lower distortion by cascoding the front end. It allows better control over the fets and protects them against any more voltage that may be needed for more power for Vas and ouput stage. I could be wrong across the board. I am new to all this.
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Yes, the SemiS R550 could be a possibility to replace IRF610 in the frontend of BA-1, I tried R550 in my Aleph P but I could not here a great difference, to my surprise, I was used that the SS replacement works immediately, but not in this case and I was not clever enough to calculate the input resistor network correctly.....all voltage values got very deviant from the original values, when I reduced the values to a third of original values.
the 610 has still lower input (and output) capacties (135/60) than R550 (170/20) but it might be a try worth! But no comparison to SSR100 (630/100).
the 610 has still lower input (and output) capacties (135/60) than R550 (170/20) but it might be a try worth! But no comparison to SSR100 (630/100).