Preamp with Tone Control or only Volume control

[avesbilal]

Thanks you everyone finally ordered Preamp built by Bibin from DAC just now.

Hope I will like it...

Eagerly waiting to audition it with my LM3886 power amp.

One more question to everyone.

My LM3886 has a coupling Cap (WIMA 1 UF), and the preamp from DAC has a input and output coupling Caps.

Should I remove the coupling caps from my LM3886 power amp?

Regards
Bilal

 

[avesbilal]

I checked with bibin and he confirmed that I have to remove the coupling cap from my power amp, but still have to have more views from others about my below mentioned question.

what will be difference with the cap in Power amp and without it, am I taking any risks buy trying to compare the difference with or with cap?

My LM3886 has a coupling Cap (WIMA 1 UF), and the preamp from DAC has a input and output coupling Caps.

Should I remove the coupling caps from my LM3886 power amp?


Thanks for all the great help from all you experts till now.

 

[kaushik]

Yes they are on the way.... Tube PreAmp & PowerAmp will be available shortly. Already started working on it. Let us also join PM Modi's Make in India Campaign.



I agree with this... Each OPAMP has its own character....

Thats a great news many DIYers will get encouraged .
in a ways we will save the industry buy promoting diy highQ audio
people will demand FLACs and many indian artists will get paid for selling good flacs

 

[sarathssca]

I recently built a preamp with two opamps (one is buffer stage) OPA2134 with option to set the gain using 4 way DIP switch and integrated Regulated (LM317 & LM337)CRC power supply. SQ is really awesome...very detailed. There is no tone control and I only used a pot to control the volume.





Thanks,
Bibin

Hi Bibin,

Could you please tell the power requirements for this preamp?
how much voltage and current drawn for this?

Also for volume control what pots are recomended?

thanks and regrds
s sarath

 

[bibin3210]

Hi Bibin,

Could you please tell the power requirements for this preamp?
how much voltage and current drawn for this?

Also for volume control what pots are recomended?

thanks and regrds
s sarath

Hi Sarath,

12-0-12 VAC/500mA

For pot you can use 25K or 50K audio tapper.

Thanks,
Bibin

 

[mbhangui]

I also built this preamp with a good cabinet from Bibin. I have connected this preamp before pass B1. Have also built DCB1. Will post photos later in the DCB1 thread.

I want to do some op-amp rolling with this and my Xonar essence one DAC. Any idea how to buy online LME 49990 opamp along with dual soic dip8 adaptors? Which site do you folks use for buying electronic components?

 

[sarathssca]

Hi Sarath,

12-0-12 VAC/500mA

For pot you can use 25K or 50K audio tapper.

Thanks,
Bibin

Hi Bibin,

Any idea what is the DC power used here, the DC current drawn?
I am thinking to use a DC-DC converter for powering preamp.

thanks and regards
S Sarath

 

[bibin3210]

Hi Bibin,

Any idea what is the DC power used here, the DC current drawn?
I am thinking to use a DC-DC converter for powering preamp.

thanks and regards
S Sarath

The built in CRC Regulated power supply using LM317 & LM337) is sufficient for this preamp.

I think the output of regulators are set to +/- 12DC. Current I am not sure, I need to check.

Thanks,
Bibin

 

[mbhangui]

Hi Bibin,

Any idea what is the DC power used here, the DC current drawn?
I am thinking to use a DC-DC converter for powering preamp.

thanks and regards
S Sarath

If you are using OPA2134, the quiescent current is 10 mA per chip. It can deliver 40 mA per channel. So 80 mA per chip. Two of these chips, so I guess 160 mA would be the max current draw.

 

[avesbilal]

Hi everyone,

Is it worth to use a toroidal transformer for this board or EI core is sufficient? First I was thinking to have this board it in my power amp itself where I have toroidal transformer with 12-0-12 + 24-0-24, but now I'm thinking to build a separate preamp, so have to buy a transformer separately for this board. Please help me out..

The reason I'm asking this question is because the price difference in EI core and toroidal transformer is a lot.

Regards
Bilal

 

[spirovious]

Any idea how to buy online LME 49990 opamp along with dual soic dip8 adaptors?

I got from FM Omishra who is from Pune.Also Sachu88 had in past.Contact them and find if they have one.

 

[bibin3210]

Hi everyone,

Is it worth to use a toroidal transformer for this board or EI core is sufficient? First I was thinking to have this board it in my power amp itself where I have toroidal transformer with 12-0-12 + 24-0-24, but now I'm thinking to build a separate preamp, so have to buy a transformer separately for this board. Please help me out..

The reason I'm asking this question is because the price difference in EI core and toroidal transformer is a lot.

Regards
Bilal

Hi Bilal,

There is nothing wrong in using EI transformer as far as it can provide required voltage and current.
I have been powering the same preamp board with EI transformer for quite sometime now.

Thanks,
Bibin

 

[mbhangui]

Hi everyone,

Is it worth to use a toroidal transformer for this board or EI core is sufficient? First I was thinking to have this board it in my power amp itself where I have toroidal transformer with 12-0-12 + 24-0-24, but now I'm thinking to build a separate preamp, so have to buy a transformer separately for this board. Please help me out..

The reason I'm asking this question is because the price difference in EI core and toroidal transformer is a lot.

Regards
Bilal

There is high capacitance coupling between the primary and secondary windings in an EI and toroidal transformers. You should actually look at R-Core transformer for such projects. If you use EI/toroidal, you will need good filtering in the power supply to filter out the line noise. You could put an EI now and later upgrade to r-core later. If you use EI try finding one with physically separate bobbins for the primary and for secondary. In fact a better designed EI can outperform off the shelf toroidal.

http://www.soundstage.com/maxdb/maxdb071998.htm

 

[avesbilal]

Thanks for your replies..

Does EI transformer doesn't cause interference? Or is it negligible?

What advantage R-core have over toroidal transformer? I see getting a toroidal is easier then R-core. I see Bibin has toroidal transformer which are recently added on his website (which is good). When I asked in the local market for toroidal transformer they had black faces (like I'm asking a spare part of a space ship)

 

[mbhangui]

Thanks for your replies..

Does EI transformer doesn't cause interference? Or is it negligible?

What advantage R-core have over toroidal transformer? I see getting a toroidal is easier then R-core. I see Bibin has toroidal transformer which are recently added on his website (which is good). When I asked in the local market for toroidal transformer they had black faces (like I'm asking a spare part of a space ship)

I had the same experience hunting for r-core transformer in Pune. But at least for toroidal transformer you can buy it online from quite many sites. r-core is impossible to buy online from any of the indian sites.

I have used EI in low gain circuits without any ac hum coming into the circuit. You can take precautions like keeping the transformer, power switch as far away possible from the preamp board (e.g. on diagonally opposite sides of the cabinet). For something like a phono preamp, I would make the power supply outside the phono preamp cabinet where only the dc cable from the power supply comes and connect to the cabinet. See if you can get an EI transformer which has two bobbins where the primary is on the top bobbin and the secondary is on the bottom. Take a look at this http://p.globalsources.com/IMAGES/PDT/S1117436340/EI-Transformer-PIN.jpg

Though toroidal have low magnetic flux leakage and hence high efficiency, toroidals have high interwinding capacitance. High interwinding capacitance means wide bandwidth coupling between the primary and secondary windings. This may not be what you want in an audio power supply, as it implies that all kinds of noise as well as 50/60Hz can pass through the power supply. r-core have the primary and secondary windings on totally separate bobbins and hence have low interwinding capacitance.

http://www.shilchargroup.com/electronics-telecom/r-core.aspx?pg=pr&sid=rc

 

[mbhangui]

I think we should request Bibin an enterprising entrepreneur to have EI, toroidal, r-core transformers at diyaudiocart (I can see toroidal already available) or have a way where our members can put in a request, pay in advance, group buy, etc.

I my school days, philips used to make good quality EI transformers (primary and secondary on separate bobbins), good finish of the EI cores and terminals instead of wires. The philips EI transformers used to look beautiful. The philips transformers have disappeared from the market. All we have now are the locally made EI transformers with horrible finish. The toroidals on diyaudiocart have a good finish though. Even the cheap chinese wall adaptors have transformers with good finish. However they just use barely enough copper windings on the primary and the primary blows off with the slightest higher than normal AC supply.

 

[spirovious]

I think we should request Bibin an enterprising entrepreneur to have EI, toroidal, r-core transformers at diyaudiocart (I can see toroidal already available) .

There is one already -
DAC - 60VA R-Core Transformer

 

[bibin3210]

There is one already -
DAC - 60VA R-Core Transformer

This is out of stock at present. The demand for this was very low, hardly 4 or 5 pieces gone in the last 10 months I guess. Will try to get new stock soon.

We are working on adding a new page (kind of service) in which user can configure custom power transformers (EI and Toroid) and OPT for SE and PP as per their requirement and place order. Also a similar kind of page will be there for inductors. The new feature will be migrated to the production server soon.

Thank you all for you good support and positive feedback.

Regards,
Bibin