DVD Player audio performance mods

[akshayjha]

Hai Akshay,

What Op-Amp chips do you suggest for replacement.

N.Murali

OPA2107 looks like the best dual opamp option, for now

 

[akshayjha]

1. Instead of the 47uF/16 on 2107's PS & Gnd, go 220uF/16.
2. For biasing, would suggest to go easy & more like 12/6 = 2k at starting. If you get good results, move to 1.8k. 1.5k only if you put a heatsink on top of 2107 as the opamp will get quite hot.

Cheers!

Have you ever done an AB test with/without the class A mods.(keeping other variables constant). Had you performed the Class A mods on the OPA2107.

Cheers.

 

[spirovious]

Farnell India: Farnell India | Farnell India - world-leading distributor of electronic and maintenance, repair and operations products.

Prices of some products are very high-

say stereo jack here for Rs.70 & MX in local around Rs.15 to 20
LUMBERG|1503 09|SOCKET, 3.5MM JACK, R/A, STEREO | Farnell India

 

[akshayjha]

Prices of some products are very high-

say stereo jack here for Rs.70 & MX in local around Rs.15 to 20
LUMBERG|1503 09|SOCKET, 3.5MM JACK, R/A, STEREO | Farnell India

Yup, they are a bit expensive compared to the local markets. But they do have some amount of QA and can source/sell in India. I wouldnt advice buying usual components from Farnell.

 

[akshayjha]

The MX local jacks absolutely suck, the contacts wear out soon and don't retain their shape.

It does cost a dollar and a half - I think it's a reasonable cost, actually, if you want the thing to last longer than a few months.

I second that opinion

 

[akshayjha]

But the TRUE results come when you take adequate care to ensure PSU is stiff, decoupled with MKP.

Yup. The PS needs to be as stiff as possible, as little ripple as possible. I wonder how a class A power amp sound with regulated power supplies!! :clapping: havent seen any class A with regulated power supplies

When I was doing the Class-A biasing test runs, I had put in a trimmer and started with only 3mA and kept increasing to 8.5mA to see the results. Above, 7mA, only if you heatsink the chip esp for usage in our high temperatures ambient climatic conditions.

And guess who guided me towards zeroing-in on the right sort of value? Grand ole Nelson Pass!
Of course, I used a +/- 15V supply and later a +/- 18V 120VA toroidal.
When I opted for the 18V PSU, I discarded the 2107 and went for the 627BP on browndog, heat-sinked, with at 8mA bias.
Astounding results!

Hey thats great info. Thanks.
Eventually what bias current did u find most suitable for the OPA2107 or is it that higher the current better the sound? Do u know of any good links for op-amp class A operation other than the google links. Any reference book for eg. I havent read much bout class A op-amp operation and theres no circuit analysis that I've come accross.

And guess who guided me towards zeroing-in on the right sort of value? Grand ole Nelson Pass!
Of course, I used a +/- 15V supply and later a +/- 18V 120VA toroidal.
When I opted for the 18V PSU, I discarded the 2107 and went for the 627BP on browndog, heat-sinked, with at 8mA bias.
Astounding results!

What type of regulation did you use? How many op-amps did you power with the 120VA supply? Isnt that a bit too much for a few opamps.

Cheers

 

[akshayjha]

You might be interested to know that a notable preamp uses a 300VA transformer (I forget the name but it will come back to me), and has a standing current draw of over 150mA, which is as much as a NAD 355 power amplifier section. Nelson Pass's BOSOZ preamp draws around 300mA at idle, and the minimum recommended transformer is 100VA.

A pre-amp may have more power consumption because the circuitry should preferably be class A throughout plus there may be relays, LEDs etc to drive. Use of a 120VA power supply for a single OP-AMP is simply overkill IMHO. Thats the reason why I asked how many op-amps does it drive..

has a standing current draw of over 150mA, which is as much as a NAD 355 power amplifier section. Nelson Pass's BOSOZ preamp draws around 300mA at idle, and the minimum recommended transformer is 100VA.

150mA / 300mA. Is that input AC current.

Cheers

 

[akshayjha]

I noticed a big improvement when I went from 15VA to 30VA for an I/V stage that draws less than a watt (all opamps, mind you).

Hey, Thanks a lot for sharing this info.
Were you using regulation at 15VA/30VA. Were you able to make any ripple measurements. A well designed regulated 15VA PS may work far better than a non regulated/poorly designed 30VA PS IMHO.

 

[akshayjha]

@ akshayjha : When it comes to PSU, I always believe in overkill. The 120VA was only driving DAC chips & buffer. I/V was internally done within the DAC chipset. Buffer was a single Dual opamp.

120VA was +/- 24V, regulated down to +/- 18V for Buffer Opamp while further regulated down to +/- 12V for the DAC chips analog feed. A separate 30VA +/- 8V Raw and +/- 5V after regulation fed digital sections of the DAC circuit and input sections.

Well if the 120VA supply had other things to power then thats absolutely fine. 120VA to source a few mill-amps @24VDC is way way way overkill IMHO. The law of diminishing returns would kick-in way below.

It gives me great joy to see ppl doing some comprehensive DIY projects in Bharatvarsh.:clapping:

Regards.

 

[akshayjha]

An Update:

Tried a few tweaks with the filter design of the o/p. The MFB low pass filter works best with the following components R1:10K, R2:10K, R3:18K, C1:390p,C2:100P.

I tried a few variations in the filter circuit components but the above values seem to give the best audio improvement(to my ears).

Has anyone tried these mods yet?

Cheers.