Is there a magic way to decrease the gain of this amp without increasing the negative feedback? I want to avoid a volume pot on the input.
Like increasing or decreasing R23/24 or R25? I am using 4.7k for R25 now.
My iTunes volume control is at minimum for background music and will blast into distortion at higher positions. I prefer to use only the top end of the digital volume for critical listening.
Thank you,
Rush
Like increasing or decreasing R23/24 or R25? I am using 4.7k for R25 now.
My iTunes volume control is at minimum for background music and will blast into distortion at higher positions. I prefer to use only the top end of the digital volume for critical listening.
Thank you,
Rush
If you use V grade JFETs (Idss about 15mA or more) at input and increase their source resistors (to 15R) it will lower the OLG (because your Id will be higher and Rd will have to go down) and decrease the CLG (150/15 instead of 150/10) in approximately same amount so that GNFB stays the same. It might lead to necessity of cooling/cascoding input JFETs, but you are aware that there is no such thing as a free lunch, right ?
There are possible further steps in second stage, but it's the same general direction - decreasing the OLG. How will it sound? You'll have to test - I chose the values of elements according to my taste...
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UTC Transformers A26
Juma,
I really don't want to change the sonic quality of this amp, so I will hold off changing the parts you suggested.
I was poking around on diyAudio looking for a single ended to balanced solution for a friend of mine and found this transformer solution using a Jensen JT-11P-1 used primary toward the source and thus a reduction in gain.
So I looked around the shop and found a pair of UTC A26 transformers laying around. They are 30K / 500 ohms. The primary and secondary are split windings. One of the transformers is open on 1/2 the primary winding (7 & 9 pins) so they aren't much good for the intended purpose and thats is why they were laying around. I measured a 1K sine wave at 3.7 volts on 1/2 the primary and 1 volt on the secondary so I thought I would try it in front of this amp to reduce the gain and see what it sounded like. I put a 4k7 ohm resistor across the secondary (500 ohm) and wired two interconnects in/out and gave it a go. The wires are about 2 feet long total.
It sounds pretty good. I can turn the iTunes all the way up (when the wife is gone) and no distortion and it is plenty loud enough.
I can switch back to using Audiruana (it doesn't have a volume control).
So far the trade off of the transformer and the better audio player is paying off!
My system consists of the following:
Mac Mini (2.66 Ghz, 8 GB RAM, 40 GB SSD (OS disc), 500 GB second HD (music storage disc), server OS boots 64 bit) external 12.92 VDC linear regulated power supply for the mini with film by-pass caps on output
Ayre QB-9 USB DAC completely stock
Juma/Pass modified Hafler DH200 (160k uF, 17 VDC power supply, surplus transformer)
Snell E (original issue).
I use RAM Disc set at 4 GB and load Audiruana and my music selection for that night into RAM and play it from there. I have heard the Ayre player is even better but cost $35. I am saving up.
Next is to build more amps and go active. I will be able to deal with the gain more easily then.
Comments always welcome.
Rush
Juma,
I really don't want to change the sonic quality of this amp, so I will hold off changing the parts you suggested.
I was poking around on diyAudio looking for a single ended to balanced solution for a friend of mine and found this transformer solution using a Jensen JT-11P-1 used primary toward the source and thus a reduction in gain.
So I looked around the shop and found a pair of UTC A26 transformers laying around. They are 30K / 500 ohms. The primary and secondary are split windings. One of the transformers is open on 1/2 the primary winding (7 & 9 pins) so they aren't much good for the intended purpose and thats is why they were laying around. I measured a 1K sine wave at 3.7 volts on 1/2 the primary and 1 volt on the secondary so I thought I would try it in front of this amp to reduce the gain and see what it sounded like. I put a 4k7 ohm resistor across the secondary (500 ohm) and wired two interconnects in/out and gave it a go. The wires are about 2 feet long total.
It sounds pretty good. I can turn the iTunes all the way up (when the wife is gone) and no distortion and it is plenty loud enough.
I can switch back to using Audiruana (it doesn't have a volume control).
So far the trade off of the transformer and the better audio player is paying off!
My system consists of the following:
Mac Mini (2.66 Ghz, 8 GB RAM, 40 GB SSD (OS disc), 500 GB second HD (music storage disc), server OS boots 64 bit) external 12.92 VDC linear regulated power supply for the mini with film by-pass caps on output
Ayre QB-9 USB DAC completely stock
Juma/Pass modified Hafler DH200 (160k uF, 17 VDC power supply, surplus transformer)
Snell E (original issue).
I use RAM Disc set at 4 GB and load Audiruana and my music selection for that night into RAM and play it from there. I have heard the Ayre player is even better but cost $35. I am saving up.
Next is to build more amps and go active. I will be able to deal with the gain more easily then.
Comments always welcome.
Rush
FAKES
Yes, I got the 2SK2013 and 2SJ313 from utsource. They were fakes. I replaced them with transistors from Zhou Fang and the amp is very thermally stable now.
Seemed like a good idea at the time. utsource has refused to take them back as well as the 2 pair of 2SK1530's and the 2SJ201's. They are all fake as far as I can tell. The face of the "P" channel transistors are sanded and faintly stenciled with the part number.
Yes, I got the 2SK2013 and 2SJ313 from utsource. They were fakes. I replaced them with transistors from Zhou Fang and the amp is very thermally stable now.
Seemed like a good idea at the time. utsource has refused to take them back as well as the 2 pair of 2SK1530's and the 2SJ201's. They are all fake as far as I can tell. The face of the "P" channel transistors are sanded and faintly stenciled with the part number.
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Can you post some picture from the fake parts please.
Also it would be great to warn everyone on the forum not to buy parts from them.
Probably start a new post fake parts (counterfeit) from "utsource"
If they are so PIGs they does not take back the fake parts not even the one U didn't used yet is good to people get warn about them.
Greetings
Also it would be great to warn everyone on the forum not to buy parts from them.
Probably start a new post fake parts (counterfeit) from "utsource"
If they are so PIGs they does not take back the fake parts not even the one U didn't used yet is good to people get warn about them.
Greetings
FAKE PARTS
Not the best photos.
The real 2SK2013/2SJ313 from Zhou Fang are the single on the left.
I don't have any real 2SK1530/2SJ201 to compare.
The "P" are sanded and restenciled, can't tell what they did to the "N".
utsource offered me $8 refund on the $67 order. $2 each for the 2SK2013/2SJ313 and $5 each for the 2SK1530/2SJ201 plus $3 PayPal.
Not the best photos.
The real 2SK2013/2SJ313 from Zhou Fang are the single on the left.
I don't have any real 2SK1530/2SJ201 to compare.
The "P" are sanded and restenciled, can't tell what they did to the "N".
utsource offered me $8 refund on the $67 order. $2 each for the 2SK2013/2SJ313 and $5 each for the 2SK1530/2SJ201 plus $3 PayPal.
Attachments
Hello
Yes on the smaller parts 100% can see it is counterfeit, even the grade (letter) Y,O,etc missing!
The biggest problem even large electronic stores sometimes buy the parts where they get them cheaper.
I bought here in Toronto Sanken transistors ($17 with tax), at the first power up exploded! Almost broke into 2PC.
I went over and over on the PC board and I didn't found any mistake. At that time more than 60 people built that amp, and I used the same PC boards.
Also I ordered 30PC from MCM Electronics 2SK246GR. When I started to match I couldn't. Out of 30PC 30 was garbage.
I ordered 2SJ103 to and that was OK.
Greetings gabor
Yes on the smaller parts 100% can see it is counterfeit, even the grade (letter) Y,O,etc missing!
The biggest problem even large electronic stores sometimes buy the parts where they get them cheaper.
I bought here in Toronto Sanken transistors ($17 with tax), at the first power up exploded! Almost broke into 2PC.
I went over and over on the PC board and I didn't found any mistake. At that time more than 60 people built that amp, and I used the same PC boards.
Also I ordered 30PC from MCM Electronics 2SK246GR. When I started to match I couldn't. Out of 30PC 30 was garbage.
I ordered 2SJ103 to and that was OK.
Greetings gabor
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ok, thanks
my goal is a 'simple' bass guitar amp
driving it with BA3 FE, maybe
so I thought, do I really need another pair of jfets in between
with the 2013/313 and another pair of outputs, I could run it at higher voltage
from what you stated ealier it works on lowered bias too, with slightly more distortion
which in this case wouldnt be a big problem
the thing is, I have the devices
but was just a crazy idea
ofcourse I could consider to cascode the jfets instead
but Im still looking
my goal is a 'simple' bass guitar amp
driving it with BA3 FE, maybe
so I thought, do I really need another pair of jfets in between
with the 2013/313 and another pair of outputs, I could run it at higher voltage
from what you stated ealier it works on lowered bias too, with slightly more distortion
which in this case wouldnt be a big problem
the thing is, I have the devices
but was just a crazy idea
ofcourse I could consider to cascode the jfets instead
but Im still looking
if you're going to make that , driven with BA3 FE , then use simple follower IRFP output
BA3 FE have more than enough gain for purpose
in fact , when I recollect my lousy memory - isn't it made exactly for that ?
but then - preamp stage , with gain,volume,tone control duties is another issue
BA3 FE have more than enough gain for purpose
in fact , when I recollect my lousy memory - isn't it made exactly for that ?
but then - preamp stage , with gain,volume,tone control duties is another issue
you got all the major points
BA3 FE would be part of the front pickup/gain stage
basicly, a power amp with high gain input would be optimal
with instrument amplification, everything seem to be upsidedown
but maybe the thought of using BA3 FE have turned into my main problem now
well - it seems worth of dedicated thread
you really need to think about it as two parts project - power amp ( BA3 FE + follower IRFP output stage with desired power ) plus guitar type preamp ;
invented long time ago , and - by my knowledge and experience with several guitar players and their equipment during last few decades - that concept is hard to beat
now - Mr. Mod , please behave and stop trolling da perfect on topic thread ......
you really need to think about it as two parts project - power amp ( BA3 FE + follower IRFP output stage with desired power ) plus guitar type preamp ;
invented long time ago , and - by my knowledge and experience with several guitar players and their equipment during last few decades - that concept is hard to beat
now - Mr. Mod , please behave and stop trolling da perfect on topic thread ......
