U got me confused there
ok thx for help guys, I'm a bit of a newb and this is just my second amp I've ever built! first one was lm1875 and I'm my self in grade 12
yes high schooler...
50K linear pot or this stepped atten should be good DACT Type 21 Stepped Attenuator Potentiometer 50K 300B - eBay (item 120473999989 end time Apr-24-10 11:05:02 PDT)
heatsinks use 2 (HSK) HS-TWD here Heatsinks - Medium, One Surface
heatsinks use 2 (HSK) HS-TWD here Heatsinks - Medium, One Surface
guys said that 10k would be better, is it right? or should i still go with 50 k?
thx for Potentiometer link and I dont really have to worry about heat sinks, I got box of them in school, we took apart over 10 PC's last year in my class
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With the stepped your stuck with whatever the steps are and not in between.
For instance you may have a setting that is okay but a tad to loud but the next setting below that is not loud enough like on some tv sets with digital control volume.
Again it is a matter of prefernce,I like having full control over were I set the volume instead of a predefined step unless it was calibrated in say .25db or .1 db steps.
For instance you may have a setting that is okay but a tad to loud but the next setting below that is not loud enough like on some tv sets with digital control volume.
Again it is a matter of prefernce,I like having full control over were I set the volume instead of a predefined step unless it was calibrated in say .25db or .1 db steps.
I wouldn't worry too much about using 50K as the real impedance is loaded down with the chip amps 22K input. Using a pot you don't have discrete steps so it's smoother in adjustments compared to a stepped switch.
On 2nd look the 21 stepped atten look cheapish ... not sure about the contacts wearing down with use and contaminants. Pots come with variable quality as well.
On 2nd look the 21 stepped atten look cheapish ... not sure about the contacts wearing down with use and contaminants. Pots come with variable quality as well.
Yes ,infinia,I agree they don't look to be of very high quality and would probably start to fail after the first year or two .
Good decent quality selector switches that can handle being turned constanly don't come cheap.
Just the same as I have to replace the switches on my guitars ever few years,especialy on my fender stratocaster, I have replaced that one three times already in the last ten years. jer
Good decent quality selector switches that can handle being turned constanly don't come cheap.
Just the same as I have to replace the switches on my guitars ever few years,especialy on my fender stratocaster, I have replaced that one three times already in the last ten years. jer
But you would want to use an audio taper pot rather than a linear taper pot for a volume control.
Here is why, http://www.angelfire.com/electronic/funwithtubes/Amp-Volume.html
. jer
Here is why, http://www.angelfire.com/electronic/funwithtubes/Amp-Volume.html
. jer
Also you would want to use an audio taper pot instead of a linear taper pot for a volume control.
Here is why,http://www.angelfire.com/electronic/funwithtubes/Amp-Volume.html . jer
Here is why,http://www.angelfire.com/electronic/funwithtubes/Amp-Volume.html . jer
Most commercial LOG pots are really not that accurate and tracking is almost always bad. So better to buy a good linear one that tracks better and modify it with the amplifiers input impedance. see ESP - A Better Volume Control
haha ok.
thx for help jer
I actually have stereo 100k audio Taper sitting in my locker in school so I might use that
got it when I was building my headphone amp
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I would love to see the circuit diagram and powersupply schematic and speaker specs of the two setups you used to compare. If you could be so kind please?
Power supply and 3886 vs others
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36V DC 9.7A 349.2W Regulated Switching Power Supply - eBay (item 160296854927 end time Apr-28-10 23:25:50 PDT)
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If I ever built with the 3886 again I would definitely use two of these rather than a linear supply. The cost is not that much more than a linear supply at the give away price they are being offered, and the sound is much better. More open and faster. When I first got the Sure 2X100, I hooked it up to one leg of my big dual mono active filtered linear supply that I had been using for all of my AB amps. Dual 24-0-24 150va transformers, Schotky diodes though I later switched to MUR860 in my 8 channels of TDA7250 amps as they sound a little smoother. 220uf of smoothing precedes the Linear Tech voltage regulators which drop 4v down to 29v rails. I added these as a last step and the active regulation does take away a slight edge from the sound. You should try it. This feeds 40,000 uf of Panasonic filter caps, bypassed with stacked film. I had Pi filter series coils in my supplies but comparative listening revealed that there was no advantage and the slight resistance was in fact vaguely rounding the leading edge of kick drum so I jumped them. Don't bother with Pi filters. They are a good way of wasting most of the upstream cap. Heavy wire, star ground, to the amps. I have used the same power supply to evaluate all of my amps over the last 12 years. In order of preference: TDA7250, Hypex, BA100 with two 3875, 3886, AKSA, Velleman modules with TIPs, TDA7294(terrible), along with a few commercial amps such as the Arcam Delta290( my previous to DIY workhorse) and the Behringer A500(terrible). I didn't need the TK2050 to show me that the single 3886 was not the best sounding amp. The bridged/ balanced 3875 is still installed in the photo. They sound way better than a single 3886 if you have a true balanced dac chip such as the direct out modified AK4395 I run as my source in the DEQ2496. I would recommend BPA200 as the minimum if you want to use the 3886 and would probably also recommend the 3875 over the 3886. The 3886 sounds a little remote and uninvolving on it's own. It sounds like there is just not enough power or class A bias current flowing from one chip.
My speakers have been the same and still sound very revealing. DIY Usher two-ways with foil coils and foil bypass on the caps. Air foil or Nordost speaker wires. 1701a interconnects and digital cables. Volex power cords. Everything has been tried and compared and tweaked for 15 years of DIY. Isn't the internet amazing. We live in a golden age. I could fill a book with all of the different components I have listened to including opamps(don't have any in my system path any more. Not that I hate them) caps and resistors, cables, room tuning, source and volume control topology. If you have a revealing system, everything matters. Many stubbornly held myths have been shattered. Surface mount resistors sound way better than through hole. Hard drive out through a firewire sounds better than my best cd transport. And the latest, Switch mode power supplies and class D sound way better than linear and class AB. If you are willing to run a wide open output filter, the Sure 2X100 is in a whole other league of transparency and speed. I was almost ready to order a run of boards for a TDA7250 amp and actually have chips and heat sinks, when I tried the 2X100 on a whim because of the low price. $60 per channel with a huge, 9 amp supply and you can wire it up and have it playing in 10 minutes with all of the connectors on the board. Finally all of my electronics are set and I can begin work on a pc cross 4 way speaker. My current signal chain is:
Hardrive
firewire cable
M-Audio Firewire 410
Belden 1701a spdif cable
Behringer SRC2496 for upsampling to 24/88
1701a aes/ebu cable
Direct out modified Behringer DEQ2496 with the dac chip swapped to AK4395 for EQ and dac.
8 foot 1701a analog interconnects
4k shunt type stepped attenuators for quiet listening or no attenuators with digital volume control for serious listening. ( the TK2050 chip set can run at very low gains with full stability so the system gain is good for me right out of the box at 16V/V to run digital volume control at -3db for loud listening with no attenuators.)
Modified Sure 2X100
8 foot foil/air 12ga. speaker cables
Murphy Usher two-way speakers. 6ohm average?
Highly treated 16x14x8.5 foot room
Part of the advantage that I hear with the TK2050 amp may come from the switch mode power supply that I am using. The MeanWell S-350-36 turned down to 32v.
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36V DC 9.7A 349.2W Regulated Switching Power Supply - eBay (item 160296854927 end time Apr-28-10 23:25:50 PDT)
.
If I ever built with the 3886 again I would definitely use two of these rather than a linear supply. The cost is not that much more than a linear supply at the give away price they are being offered, and the sound is much better. More open and faster. When I first got the Sure 2X100, I hooked it up to one leg of my big dual mono active filtered linear supply that I had been using for all of my AB amps. Dual 24-0-24 150va transformers, Schotky diodes though I later switched to MUR860 in my 8 channels of TDA7250 amps as they sound a little smoother. 220uf of smoothing precedes the Linear Tech voltage regulators which drop 4v down to 29v rails. I added these as a last step and the active regulation does take away a slight edge from the sound. You should try it.
This feeds 40,000 uf of Panasonic filter caps, bypassed with stacked film. I had Pi filter series coils in my supplies but comparative listening revealed that there was no advantage and the slight resistance was in fact vaguely rounding the leading edge of kick drum so I jumped them. Don't bother with Pi filters. They are a good way of wasting most of the upstream cap. Heavy wire, star ground, to the amps. I have used the same power supply to evaluate all of my amps over the last 12 years. In order of preference: TDA7250, Hypex, BA100 with two 3875, 3886, AKSA, Velleman modules with TIPs, TDA7294(terrible), along with a few commercial amps such as the Arcam Delta290( my previous to DIY workhorse) and the Behringer A500(terrible). I didn't need the TK2050 to show me that the single 3886 was not the best sounding amp. The bridged/ balanced 3875 is still installed in the photo. They sound way better than a single 3886 if you have a true balanced dac chip such as the direct out modified AK4395 I run as my source in the DEQ2496. I would recommend BPA200 as the minimum if you want to use the 3886 and would probably also recommend the 3875 over the 3886. The 3886 sounds a little remote and uninvolving on it's own. It sounds like there is just not enough power or class A bias current flowing from one chip.My speakers have been the same and still sound very revealing. DIY Usher two-ways with foil coils and foil bypass on the caps. Air foil or Nordost speaker wires. 1701a interconnects and digital cables. Volex power cords. Everything has been tried and compared and tweaked for 15 years of DIY. Isn't the internet amazing. We live in a golden age. I could fill a book with all of the different components I have listened to including opamps(don't have any in my system path any more. Not that I hate them) caps and resistors, cables, room tuning, source and volume control topology. If you have a revealing system, everything matters. Many stubbornly held myths have been shattered. Surface mount resistors sound way better than through hole. Hard drive out through a firewire sounds better than my best cd transport. And the latest, Switch mode power supplies and class D sound way better than linear and class AB. If you are willing to run a wide open output filter, the Sure 2X100 is in a whole other league of transparency and speed. I was almost ready to order a run of boards for a TDA7250 amp and actually have chips and heat sinks, when I tried the 2X100 on a whim because of the low price. $60 per channel with a huge, 9 amp supply and you can wire it up and have it playing in 10 minutes with all of the connectors on the board. Finally all of my electronics are set and I can begin work on a pc cross 4 way speaker. My current signal chain is:
Hardrive
firewire cable
M-Audio Firewire 410
Belden 1701a spdif cable
Behringer SRC2496 for upsampling to 24/88
1701a aes/ebu cable
Direct out modified Behringer DEQ2496 with the dac chip swapped to AK4395 for EQ and dac.
8 foot 1701a analog interconnects
4k shunt type stepped attenuators for quiet listening or no attenuators with digital volume control for serious listening. ( the TK2050 chip set can run at very low gains with full stability so the system gain is good for me right out of the box at 16V/V to run digital volume control at -3db for loud listening with no attenuators.)
Modified Sure 2X100
8 foot foil/air 12ga. speaker cables
Murphy Usher two-way speakers. 6ohm average?
Highly treated 16x14x8.5 foot room
Attachments
I have it in my close future plans to get a shure module and test it a bit.
just as a side note.
Sorry if I am misunderstanding.
But when you say BA100 do you mean BR100. like in 2 modules in bridge mode? that is what i understnd from images. not 100% sure what you mean with bridge/balanced
BR 100 - lm3886 - should only be used into 6ohm load when using +-24 DC powersupply else chips are overdriven. they both effectively see 3 ohm loads
BR 100 - lm3875 should not be used in loads lower than 16 ohms with supply +- 35V
might be fine for slightly lower load (12ohms) resistance with your +-29V supply but nothing CLOSE to 6ohms.
lm3875 is limited to a MAXIMUM of 5 amp.
For BR100 lm3875 using a 6 ohm (average) load each lm3875 will effectively drive into 3 ohm loads which is NOT adviseable for best THD and longevity. BAsically they would be permanently very close to SPIKE current and temperature protection even at lower volumes.
Please note page 4 for voltage and load table for parralel and bridge modes using lm3886.
http://www.national.com/an/AN/AN-1192.pdf
just as a side note.
Sorry if I am misunderstanding.
But when you say BA100 do you mean BR100. like in 2 modules in bridge mode? that is what i understnd from images. not 100% sure what you mean with bridge/balanced
BR 100 - lm3886 - should only be used into 6ohm load when using +-24 DC powersupply else chips are overdriven. they both effectively see 3 ohm loads
BR 100 - lm3875 should not be used in loads lower than 16 ohms with supply +- 35V
might be fine for slightly lower load (12ohms) resistance with your +-29V supply but nothing CLOSE to 6ohms.
lm3875 is limited to a MAXIMUM of 5 amp.
For BR100 lm3875 using a 6 ohm (average) load each lm3875 will effectively drive into 3 ohm loads which is NOT adviseable for best THD and longevity. BAsically they would be permanently very close to SPIKE current and temperature protection even at lower volumes.
Please note page 4 for voltage and load table for parralel and bridge modes using lm3886.
http://www.national.com/an/AN/AN-1192.pdf
Ba, br
BA= bridge amp, as in BPA with out the P. I didn't bother with the two parallel chips as this was just a test. Built point to point. BR? what ever you call it. Just a quick test circuit to try them bridged since I have a balanced source so no need to create the balanced signal with a diff amp or DRV134. A successful test. Two chips sounds way better than one. Four will be better than two. That's why I am recommending at least BPA200 with a balanced source for the 3886/3875. I never told anyone to build BR100.
BA= bridge amp, as in BPA with out the P. I didn't bother with the two parallel chips as this was just a test. Built point to point. BR? what ever you call it. Just a quick test circuit to try them bridged since I have a balanced source so no need to create the balanced signal with a diff amp or DRV134. A successful test. Two chips sounds way better than one. Four will be better than two. That's why I am recommending at least BPA200 with a balanced source for the 3886/3875. I never told anyone to build BR100.
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