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Class D Switching Power Amplifiers and Power D/A conversion

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Old 4th January 2010, 01:52 AM   #911
sendler is offline sendler  United States
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Default -6db

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Originally Posted by MikeHunt79 View Post
Excellent info Scott, thanks. I think I was getting series and shunt configurations mixed up in my previous post, but after reading your post shunt does look like a nice solution in this case. Shunt has 1 less switch contact in the circuit compared to a ladder configuration, which is no bad thing also.

I've already ordered a pair of unpopulated stepped attenuators, and I'm tempted to try wiring 1 up as a 4k shunt and the other as a 4k (or 10k) ladder and see how they compare... I'm still getting my head around how impedances work out between various sources and amps - it's turning out to be a little more complex than knowing Ohm's law!

I should have mentioned in my previous post that I'll be keeping the stepped attenuators very close or on the Sure PCB, but I'll be using 2ft or 3ft interconnects between the DCX and the Sure amp. I thought that it would be best to try and make these as short as I can as there will now be no op-amps in the circuit, so the DAC is now having to deal with driving the cables also. Am I right in assuming that cables have more effect when driving lower impedances?

I still have not had time to do the direct out mod yet however, but I'll try using the digital volume control first, I'm already using the DCX's volume control to pad my tweeter down -6db however. My plan is to eventually achieve the -6db gain reduction on my tweeter channels with the stepped attenuator, which is why I've opted to populate the stepped attenuators myself as opposed buying some pre-made ones.
I continue to use 8 foot cables between my direct out modified DEQ and the amps with excellent results so keeping that cable short is not as much of an issue. Trying to use a set of attenuators with one pair always offset from the others to get the -6db will be tough to get the resistors available in the exact value that you need to make the steps stay exactly matched because even with the vast range of values that are available, the exact number you need might not be. My attenuators will be within .2% across all six when they are on the same step but the next louder step might be 2.3db and the next quieter step might be 1.9 depending on the resistor values that are available so if you try to use the tweeter attenuator 3 clicks quieter than the woofer's to make the general offset, the relative levels might change .5db either way as you go through the range of listening levels. Does that make any sense? It might not be a big deal in practice but it could be more accurate to change the gain of the amps as needed to get rid of the digital attenuation. We have +6 and +9 selections built right onto the boards already with the switches. Of course there is always a catch, the amps sound better to me at the lowest gain. Eliminating R14/34 should give an increase in volume level. +6db? And sound better following a passive volume control? Not sure yet as I haven't tried it but it should be louder. It might make the TC2000 more vulnerable to pops. Aren't trade offs fun? It is worth it in the end.
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Old 4th January 2010, 04:12 AM   #912
dr_vega is offline dr_vega  United States
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Originally Posted by sendler View Post
...
You still need a cap between the amp and your control to keep the amp's DC from shorting through the attenuator. As well as the other cap to keep the dac's DC from shorting.
Scott, do you really need the cap between the DAC and the attenuator? Won't the DAC see the attenuator as a 10k ohm load, not a short?

I want to build a six channel, remote control 10k Alps pot into the DCX. I'd like to avoid a second cap in the signal chain. Isn't the input cap on the Sure amp enough?

-dr_vega
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Old 4th January 2010, 04:51 AM   #913
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Hi all diy gurus. I stumble upon this thread and am interested in this amp as well. There are several questions thou, and I am hoping that you all can help me out:

1. I wanna make this amp into a monoblock, can I just add in a preamp? Website said adding in a preamp will kill the chip. Anyone tried before?
2. Since I wanna make it into a monoblock, one of the channel will be going into an active sub. Will that kill my sub? Sub is a Active sub with 200W of power.

I thank everyone who spend the time to read and those who help. Thanks a lot
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Old 4th January 2010, 08:24 AM   #914
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a) I do not think you know what the word "monoblock" means.

b) Many users just use a passive preamp (ie. a potentiometer or stepped attenuator). It's possible to use a preamp, but you need to be a little careful so as not to send too hot a signal to the amp chip. In practice, such a signal will be very loud, so I doubt anyone has ever killed a chip this way.

c) You do not want to send an amp output to the line level inputs of your active sub. Doing so will damage the input stage of your subwoofer amplifier.
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Old 4th January 2010, 11:12 AM   #915
sendler is offline sendler  United States
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Originally Posted by dr_vega View Post
Scott, do you really need the cap between the DAC and the attenuator? Won't the DAC see the attenuator as a 10k ohm load, not a short?

I want to build a six channel, remote control 10k Alps pot into the DCX. I'd like to avoid a second cap in the signal chain. Isn't the input cap on the Sure amp enough?

-dr_vega
The dac chip has 2.4v dc on it's outputs, as the amp does on it's inputs. I don't know how it will sound or how long the chips will last to let this run to ground through 10k. Maybe you can dig out some passive cross speakers and try a fixed pad on two channels of the DCX to see. I think you will also find that you are not willing to give up the sound quality that will be lost by having a passive volume control so far from the amps. Aside from the cap issue, you can try the fixed pads on all channels of the DCX to hear the impact before starting the project with the remote ganged pots. I have started looking at these remote VolControl2 modules
.
Dantimax (elektronik) - Control_boards
.

and have ordered some Lightspeed LDR optocouplers to start work on a multi channel remote that can control 12 channels at the amps. The only hang up with this is the difficult matching of the LDRs. In the meanwhile I am content to have the DCX on the coffee table in front of me and use the digital volume control for fine tuning with the main volume control via direct attenuators at the amps.
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Old 4th January 2010, 03:06 PM   #916
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Originally Posted by TheSeekerr View Post
a) I do not think you know what the word "monoblock" means.

b) Many users just use a passive preamp (ie. a potentiometer or stepped attenuator). It's possible to use a preamp, but you need to be a little careful so as not to send too hot a signal to the amp chip. In practice, such a signal will be very loud, so I doubt anyone has ever killed a chip this way.

c) You do not want to send an amp output to the line level inputs of your active sub. Doing so will damage the input stage of your subwoofer amplifier.
Well there, TheSeekerr, if you read from my post, you'll see that I am a noob. Just that I am kinda interested in Class D amp, and always wanted a monoblock. What I know about monoblock is it is a power amplifier, with it's own PS, and it does not have the crosstalk as other stereo amps. Please correct me if I am wrong. Although the internet has a lot of information, some sites can be misleading, or didn;t really explain clearly. Hope you didn;t mind my stupidity.

b. a passive preamp? hm......does it includes line selector? What happened if I were to connect a phono stage or a DAC? will it work too?

c.thanks for the advice.

I think I should let you know too, that I am don;t have much knowledge in electronics (i am in different field), but I am interested in audio, and wanna go for DIY amps since it won;t burn a big hole in my pocket (low pay and very limited funds)

Thanks for replying. ^^ Take care
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Old 4th January 2010, 08:10 PM   #917
dr_vega is offline dr_vega  United States
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Originally Posted by sendler View Post
In the meanwhile I am content to have the DCX on the coffee table in front of me and use the digital volume control for fine tuning with the main volume control via direct attenuators at the amps.
Thanks, Scott. Now that I have, with your help (air-cores), got the Sure amp sounding pretty good, I'm working on making it more convenient.

-dr_vega
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Old 4th January 2010, 09:04 PM   #918
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Hi all,

I'm purchased two of these amps to power my mid-range and tweeters in a tri-amp setup. The mid will be hi-passed @ about 900Hz so I'm not too concerned with lower freq. resolution... Are most of these mods implemented to improve the bass response of this amp, or are there any *simple* modifications that you can recommend to sweeten up the mid/top end?

I'm horrible with a soldering iron but I'm working on it )

Thanks
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Old 4th January 2010, 10:09 PM   #919
sendler is offline sendler  United States
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Default mods

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Originally Posted by DarpMalone View Post
Hi all,

I'm purchased two of these amps to power my mid-range and tweeters in a tri-amp setup. The mid will be hi-passed @ about 900Hz so I'm not too concerned with lower freq. resolution... Are most of these mods implemented to improve the bass response of this amp, or are there any *simple* modifications that you can recommend to sweeten up the mid/top end?

I'm horrible with a soldering iron but I'm working on it )

Thanks
The mods are for the whole range. Probably more noticeable on a tweeter or mid than in the bass.
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Old 4th January 2010, 10:48 PM   #920
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Quote:
Originally Posted by DarpMalone View Post
Hi all,

I'm purchased two of these amps to power my mid-range and tweeters in a tri-amp setup. The mid will be hi-passed @ about 900Hz so I'm not too concerned with lower freq. resolution... Are most of these mods implemented to improve the bass response of this amp, or are there any *simple* modifications that you can recommend to sweeten up the mid/top end?

I'm horrible with a soldering iron but I'm working on it )

Thanks
I'm just working on getting mine together so I can't speak from personal experience, however from following the thread it sounds like the two biggest improvement can be had from changing the input caps and changing the inductors on the output. Lots of different choices for input caps. I've really enjoyed Obbligato copper caps with other tripath amps. Here's a web page for winding your own inductors, which is what people here seem to have the most luck with as far as inductors go. These should both be simple modifications, and give improvements across the frequency range. Good luck.

I also have a quick question for people using the 36volt meanwell supplies. I'm building an oak enclosure for my amp and was planning on routering in some small vent in the top of the enclosure for the amp to help keep it cool enough. Have people found the power supply to get hot as well? In other words should I vent above where the power supply goes to try and keep it running cool as well? I'm only running one amp per power supply and am going to use a passive line level crossover so each amp should have an fairly easy load. I'm guessing there is no need to vent above the power supply, but I wanted to check in to make sure.
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