Buzz, I bought 500 pcs. batch from Mouser and 90% of them are in 13-14 mA range. The rest is 1-2 mA higher or lower.
Since I don't like gate current, degeneration is mandatory (5-10R). I use them with Id of about 10mA at Vds of about 10V so heat is not a problem. Actually I didn't have a single failed BF862 with Pd of 150mW - for more you'd probably have to cool them. A small area of copper at the Gate is enough to keep them coll enough.
Since I don't like gate current, degeneration is mandatory (5-10R). I use them with Id of about 10mA at Vds of about 10V so heat is not a problem. Actually I didn't have a single failed BF862 with Pd of 150mW - for more you'd probably have to cool them. A small area of copper at the Gate is enough to keep them coll enough.
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Using juma's post 53rd schematic to draw a buffer with input selectors. Hope he don't mind
The size is 56 X 85 mm.
I am curious that should I put each 0.1uF on the voltage rail near to the buffer? Or just one unit 0.1uF on the PSU is enough. 78L05 regulator feeding G6K-2P-5VDC relay with 1n4001, I doubting will this work nicely?
PS:
I am using SK-13D07 slider for selecting input. I wonder if the connections correct compare to datasheet
The size is 56 X 85 mm.I am curious that should I put each 0.1uF on the voltage rail near to the buffer? Or just one unit 0.1uF on the PSU is enough. 78L05 regulator feeding G6K-2P-5VDC relay with 1n4001, I doubting will this work nicely?
PS:
I am using SK-13D07 slider for selecting input. I wonder if the connections correct compare to datasheet
Attachments
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Tube pre amp and F5
Hi fellow Diyer's
need a little help from my friends'
I have been using my F5 for quite some time now using a SONY digital processor as preamp. Sounds very good I'm happy with the set-up. but would like to try the sound of the TUBE , for cheap. Just to have a taste of what the buzz is all about, I bought a 2nd hand Little dot MK III pre /headphone amp .which is nice using it as a headphone amp. I have measure the DC offset of the tube amp and it's in mV so I think it's fine to connect it to F5 just to quickly check. I was happy I like what I'm hearing.
The next listening session, very eagerly, I turned everything ON, CD player, Tube pre and F5 in that order, I forgot that I need to let the Tube pre to warm-up first and stabilized. DISASTER... in a split second my Fostex BLH speaker fried really good!! cone is stuck and voice coil open circuit. Whaaa!!! Can anybody in the cummunity help me with my problem? I like this tube pre and F5 combination but don't know if it's alright / or a SIN to put a coupling cap infront of F5? what value? Any help is appreciated.
Thank,
Reytnz
Hi fellow Diyer's
need a little help from my friends'
I have been using my F5 for quite some time now using a SONY digital processor as preamp. Sounds very good I'm happy with the set-up. but would like to try the sound of the TUBE , for cheap. Just to have a taste of what the buzz is all about, I bought a 2nd hand Little dot MK III pre /headphone amp .which is nice using it as a headphone amp. I have measure the DC offset of the tube amp and it's in mV so I think it's fine to connect it to F5 just to quickly check. I was happy I like what I'm hearing.
The next listening session, very eagerly, I turned everything ON, CD player, Tube pre and F5 in that order, I forgot that I need to let the Tube pre to warm-up first and stabilized. DISASTER... in a split second my Fostex BLH speaker fried really good!! cone is stuck and voice coil open circuit. Whaaa!!! Can anybody in the cummunity help me with my problem? I like this tube pre and F5 combination but don't know if it's alright / or a SIN to put a coupling cap infront of F5? what value? Any help is appreciated.
Thank,
Reytnz
Use a good quality 1uF capacitor, and connect a 1M resistor from the cap input to ground.
This is what you wrote.
Read it again and you tell us what's a sin and what's a good thing to do?
Another idea for a nice preamp suitable to drive F5 (post #55 and onwards) :
http://www.diyaudio.com/forums/analog-line-level/206532-if-you-dont-have-sit-fake-2.html#post2950967
When used to drive F5, C4can be 1uF and R9=1Meg. For C3 (10uF) I successfully used SMD (0603) COG cap.
http://www.diyaudio.com/forums/analog-line-level/206532-if-you-dont-have-sit-fake-2.html#post2950967
When used to drive F5, C4can be 1uF and R9=1Meg. For C3 (10uF) I successfully used SMD (0603) COG cap.
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If you mean the proposed C4 value (1uF), it's determined by F5's input resistance (101k) and by our wishes:
- to avoid high-pass filter at amp's input by using too small a value ;
- not to use very big value because good caps are cheaper when smaller .
Hi Juma,
I'm looking for a suitable preamp for my new F3 and I like your design from post 53.
Currently I drive the F3 with my Naim NAC72 with its 22dB gain, not enough for the 12,5 dB from the F3.
How much gain has your design as posted and which gain is possible without disadvantages?
thanks & cheers
Thorsten
I'm looking for a suitable preamp for my new F3 and I like your design from post 53.
Currently I drive the F3 with my Naim NAC72 with its 22dB gain, not enough for the 12,5 dB from the F3.
How much gain has your design as posted and which gain is possible without disadvantages?
thanks & cheers
Thorsten
tp147,
you should consider more than just the gain - F3 puts out just 15W at 8 Ohms which translates into 11V RMS at 8 Ohms. F3 has gain of about 12dB (4V/V) and that means that it needs about 2.7V RMS at its input for full power.
If you say that NAC72 with 22 dB (12.6 V/V) gain can't drive F3 to full power it means that your source has less than 200mV output and that looks strange.
Think once more and analyze where's the problem:
1. low power (just 15W from F3)
2. low output from your source (less than 200mV)
3. low output level of your preamp (can't deliver 2.7V RMS into 10k load which happens to be F3's Zin)
The preamp mentioned in post #110 will work great with 6-12dB gain and it can put out 8V RMS into 10k load.
you should consider more than just the gain - F3 puts out just 15W at 8 Ohms which translates into 11V RMS at 8 Ohms. F3 has gain of about 12dB (4V/V) and that means that it needs about 2.7V RMS at its input for full power.
If you say that NAC72 with 22 dB (12.6 V/V) gain can't drive F3 to full power it means that your source has less than 200mV output and that looks strange.
Think once more and analyze where's the problem:
1. low power (just 15W from F3)
2. low output from your source (less than 200mV)
3. low output level of your preamp (can't deliver 2.7V RMS into 10k load which happens to be F3's Zin)
The preamp mentioned in post #110 will work great with 6-12dB gain and it can put out 8V RMS into 10k load.
OK, thanks for reply juma.
I will check some params out, may be there is something wrong with the F3.
I only changed the power amp from NAP250 to F3. The NAP 250 has a gain arround 30 dB and with the NAC72s volume nob at 10-11 o'clock it is louder than with the F3 at full turned on
thanks & cheers
Thorsten
I will check some params out, may be there is something wrong with the F3.
I only changed the power amp from NAP250 to F3. The NAP 250 has a gain arround 30 dB and with the NAC72s volume nob at 10-11 o'clock it is louder than with the F3 at full turned on
thanks & cheers
Thorsten
That's completely OK - NAP250 delivers a lot more power (80W at 8 Ohms) than F3 (15W). If your loudspeakers are not very efficient (more than 95dB/1W/1m), the F3's low power is the main cause of your dissatisfaction and no preamp will cure it. And if your speakers happen to have 4 Ohms impedance the situation will be even worse - at 4 Ohms the NAP250 will deliver more power and the F3 less (10W at 4 Ohms).
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I guess the main problem are my speakers arround 90 dB!
I'll build some speakers > 95 dB soon, driven fully active, so I gather some poweramps right now and a preamp with active x-over.
I'm not really unsatisfied with the F3, but it was a big surprise when I connected first time and I raised my eyebrows due to the low volume - I didn't expect this in this range.
I'm not used to hear music at the highest levels, but this would be a little too less
thx & cheers
Thorsten
I'll build some speakers > 95 dB soon, driven fully active, so I gather some poweramps right now and a preamp with active x-over.
I'm not really unsatisfied with the F3, but it was a big surprise when I connected first time and I raised my eyebrows due to the low volume - I didn't expect this in this range.
I'm not used to hear music at the highest levels, but this would be a little too less
thx & cheers
Thorsten
Juma,
I have been looking at yor circuit post53 and I think I have a spot where it will help me. I now have a dcb1 hooked to my F5 and for all the sources except the iPad I have plenty of gain. My idea is to build your circuit and put it between one input and the b1. The power can come from the dcb1. I'll leave off the volume pot and the input cap. Now my question, and I'm sure this will show my inexperience. In the schematic the source of the 2sk170 is hooked throughout the potentiometer to the drain of the 2sj74. In the copper trace from post 3 it looks like the 2sj74 is reversed. Same for the output pair. Where am I going wrong in my understanding?
Evan
I have been looking at yor circuit post53 and I think I have a spot where it will help me. I now have a dcb1 hooked to my F5 and for all the sources except the iPad I have plenty of gain. My idea is to build your circuit and put it between one input and the b1. The power can come from the dcb1. I'll leave off the volume pot and the input cap. Now my question, and I'm sure this will show my inexperience. In the schematic the source of the 2sk170 is hooked throughout the potentiometer to the drain of the 2sj74. In the copper trace from post 3 it looks like the 2sj74 is reversed. Same for the output pair. Where am I going wrong in my understanding?
Evan
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