Low noise regulator for DAC & clock

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batteryman

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Joined 2011
#1
I was thinking of getting a couple of these on the TI development board for £20 each. ($22). The board has jumpers to set the output (1A) from 1.4 to 30V.

http://www.ti.com/lit/ds/symlink/tps7a47.pdf

http://www.ti.com/lit/ug/slvu741a/slvu741a.pdf

Not a plug in replacement for a 78x series and ridiculously over sized and priced but specs are good. (the size is probably due to the ground plane being the heatsink)

I am struggling to find noise figures for the Dexa regulators I have fitted to my dac pcb but I need a low noise regulator for the low jitter clock I am fitting to the cd transport (actually a Philips CD480 from which the I2S & master clock are derived for Iancanda's I2S board.)

Burson regulators don't seem to be stocked by anyone in the UK and I won't buy anything from Tentlabs due to their inability to supply in a reasonable time.
 
#2
The Burson regulator won't come close to the TI device in terms of noise, (Analog Devices have some very low noise devices as well,discussed on diyaudio forums).

https://linearaudio.net/sites/linearaudio.net/files/V4 JW F7.pdf

Superpower Super Regulator by Belleson

I am a fan of development boards, I use Linear Tech's "True RMS Converter" in a tarted up HP403C voltmeter. Some of the DAC and ADC boards from TI are really great for quick implementation of test equipment. ADI has impedance measurement development boards, DDS boards...i think they're a great way to save time and money.
 
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#3
Yes there are some excellent low noise regulator chips but all far too small for hand soldering. Its sad that semicon manufacturers are phasing out through -hole products and even soic versions are becoming rarer too.

Development boards are great if usually a bit costly - I've used Microchip's Bluetooth and Can development products which saved a lot of time.

Numerous Ebay sellers list 78xseries alternatives using the same TI TPS7A4700 chip but cost more at $25 + $10 shipping to the UK making the TI board good value.
 
#4
Do you plan to feed the Clock board via the main PS plug or by the 3 pins area on the side of the board ?

There is also Mravica here, if he has keeped his price as low than 2 years ago , his TSA board are a good choice too (it has the rectifier and main filter cap embeded)
 
#5
Eldam said:
Do you plan to feed the Clock board via the main PS plug or by the 3 pins area on the side of the board ?

There is also Mravica here, if he has keeped his price as low than 2 years ago , his TSA board are a good choice too (it has the rectifier and main filter cap embeded)
Click to expand...

I haven't decided whether to fit another transformer into the CDM480 for the new clock board or use the existing psu. Given the excellent line regulation probably be okay to use the existing supply before the 7805?

The smoothing caps need upgrading and I'll probably replace all the electrolytics as well. I will also remove the TDA1541 to reduce the current consumption. The new clock will connect to the SAA7220 clock input as well as be taken via a UFL cable to the I2S board in the DAC.

A member has been in touch and has the TPS7A in 78x series pitch, and soon, also the even better spec LT3045 (only .5amp but this is enough). His prices are good ~ $20-23 so I plan on buying a few in a couple of weeks.
Ian
 
#6
have you a link please ? I need one as well !

Notice than if you use the Ian's isolator before his clock, you must feed the clock from an another power supply than one which share the ground from the input stage. The TSA regs should ideally be as close as possible from the load...

I will not loose too much time to use the SAA Philips filter as it' abig source of jitter itself. (it may waste all th einvestments you made before).

cheers
 
#7
Eldam said:
have you a link please ? I need one as well !

Notice than if you use the Ian's isolator before his clock, you must feed the clock from an another power supply than one which share the ground from the input stage. The TSA regs should ideally be as close as possible from the load...

I will not loose too much time to use the SAA Philips filter as it' abig source of jitter itself. (it may waste all th einvestments you made before).

cheers
Click to expand...

I'm not planning on using the isolator initially.
I'll probably feed the clock into the SAA7210 directly rather than through the 7220.

This will eliminate the 7220 from any effect on the I2S signals from the 7210.
 
#8
To inject the clock, you need a 50 ohms tiny coax and not too big between the MCLK and your chip... 4" for instance.

Waiting the regs, one thing you could in the mean time for the fun is to putt a bigger outputt cap to the 7805 : it likes having a resistiv load, so don't hesitate to putt some good capacitance with a normal cap (all but something with a low ESR here : 100 uF to 1000/2000 uF). It lowisch the impedance outputt level !

For the 12/15 v of the analog stage, try to find some 220 uF blue Nichicon SX from an other old Philips CD or in the one you have (replace the SX with some brand new Nichicon KG for instance and keep the old Sx to the outputt of the old regs of the analog stage (better sound and 3D stage quaranted!) ! They used to putt from memory 47 uf Nichicon VX, but you winn a lot to add the Sx (don't putt something brand new with a good ESR at the outputt as well).
 
#9
Consider using the LT3042

Here's a comparison of the LT3042 vs the TPS7A47. The LT3042's PSRR is also significantly better.
 

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#11
jackinnj said:
Here's a comparison of the LT3042 vs the TPS7A47. The LT3042's PSRR is also significantly better.
Click to expand...

Yes, I'm going for the LT3045 78x substitute which will be available from a member next month, so have dropped the TPS7A from my plans.

Reading between the lines on the datasheet, there is a potential stability issue if you do not adhere to LTs recommendation for the 10uf ceramic output capacitor - a quite expensive part apparently but very low esr & esl are essential.
 
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#13
batteryman said:
Yes, I'm going for the LT3045 78x substitute which will be available from a member next month, so have dropped the TPS7A from my plans.

Reading between the lines on the datasheet, there is a potential stability issue if you do not adhere to LTs recommendation for the 10uf ceramic output capacitor - a quite expensive part apparently but very low esr & esl are essential.
Click to expand...

You should be able to use a 1206 tantalum
 
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