Hybrid Passive RIAA phono pre-amplifier

Hari Iyer

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After enjoying the outstanding performance of my passive low pass filter using audio transformers in my DAC Chip board, the next logical step was to extend the design in other areas. I was intrigued for building a similar design for a passive phono pre-amplifier. After listening for over a week in digital domain, the most obvious listening experience was the amount of micro-detail lost in the active filter. I don't know if this was because of the op-amp or how the active LP filter is designed or the choice of original components, but neverthless there was a significant loss of information vis-a-vis my passive LP filter (I thank myself for not going for an active filters for my speakers - no matter how huge the temptation was - for similar reasons of use of op-amp and component usages in the filter stage). So my first design criteria will be NOT to use any op-amp in the phono preamplifier.

The phono pre-amp design is challenging as the output from a MM cartridge is quite low (4.3mV for my cartridge). This will require some amplification for the amplifier to drive. Amplification is possible by a op-amp / tubes / transistors. Using tubes was risky as i am not a tube expert and any mis-calculation could be a disaster. Only option left was using a low-noise transistors.

I have already tested the concept using op-amp and they work after 6 to 7 iterations of my RIAA curve. But i still feel the op-amps will be loosing some micro-detail which i am not aware as of now. I have come-up with this block diagram which i will be implementing this week on a bread-board.

1655399081261.jpeg

The transistor based difference amplifier will have a gain of around 43dB which will be followed by my RIAA filter. This will be interfaced to a audio transformer for I/V conversion. The feedback to the input will also be routed via the transformer center-tap for a balanced to SE conversion.

Thanks for looking.
 
This passive preamplifier did not work as intended so scrapped this project. Now back to my previous JFET + OPAMP stage.
 
This passive preamplifier did not work as intended so scrapped this project. Now back to my previous JFET + OPAMP stage.
If you are going the op amp way, I strongly recommend a discreet Opamp.

I recently replaced a opamp in a whammy HP amp/preamp with a discreet opamp.

cant go back..
 
If you are going the op amp way, I strongly recommend a discreet Opamp.

I recently replaced a opamp in a whammy HP amp/preamp with a discreet opamp.

cant go back..
Thanks. Currently i am using AD837 in place of LM4562. I am finding the AD chip to be more organic while the TI chip is more detailed. Its matter of what you prefer.
Many years ago, i have read and article from ESP about not to use discrete opamps as they are under performing compared to actual opamps from ESP pages. Don't know how true they are though.
 
Thanks. Currently i am using AD827 in place of LM4562. I am finding the AD chip to be more organic while the TI chip is more detailed. Its matter of what you prefer.
Many years ago, i have read and article from ESP about not to use discrete opamps as they are under performing compared to actual opamps from ESP pages. Don't know how true they are though.
 
If you are going the op amp way, I strongly recommend a discreet Opamp.

I recently replaced a opamp in a whammy HP amp/preamp with a discreet opamp.

cant go back..
Which Op Amp chip did you replace, Rajan ?

.... and which discrete op amp have you used ?
 
Which Op Amp chip did you replace, Rajan ?

.... and which discrete op amp have you used ?

I replaced a JRC4560 with a Burson Audio V6, Classic

 
I replaced a JRC4560 with a Burson Audio V6, Classic

Here is the link of the ESP pages which do not consider discrete op-amp to be better than a original op-amp.

I am planning to add my Marantz HDAM discrete buffer which i had build some 3.5 years ago after my phono-stage. The reason is to isolate the phono stage from direct couple to my tube-amp and also to increase the current output for the phono stage for even more better mids and highs. Since this is already an assembled unit, its a matter of just hooking them up for a test. Check out this link for schematics in post # 13.

I may not add the op-amp gain stage but just from the P1 stage onwards. Will identify all unwanted components and scrap them in the chain too.
 
Here is the link of the ESP pages which do not consider discrete op-amp to be better than a original op-amp.

I am planning to add my Marantz HDAM discrete buffer which i had build some 3.5 years ago after my phono-stage. The reason is to isolate the phono stage from direct couple to my tube-amp and also to increase the current output for the phono stage for even more better mids and highs. Since this is already an assembled unit, its a matter of just hooking them up for a test. Check out this link for schematics in post # 13.

I may not add the op-amp gain stage but just from the P1 stage onwards. Will identify all unwanted components and scrap them in the chain too.
I am aware of ESP pages, find it very knowledgeable and used to live less than a Km away from their setup.

and I am not going to argue if their opinion is right or wrong.. I am not qualified at all...

so I am not going there abt what his comments abt burson.


No offense to you... with my next comments and questions..

Are you going to take his word for everything you want to do ? or someone else equally famous and qualified in Audio electronics ?

In that case, I could show you a lot of posts abt placebo effects (in their words) about Cables. and How some of them ridicule people getting fixated on such not so important matters.

Now, I know your mileage varies a lot on cables.

question is, will you change your approach because of a post on the net?

I rest my case...


and in any case, IF everything is "Maya", I am sure I would like to create mine the way I like it,
 
I have used variety of opamps including Burson Audio V5 and V6 in my DIY CNC phonostage. They are really good. I preferred the LME49990 opamps over any other type followed by Opa 1612.
I gave away Burson to my friend and he is very happy.

Regards
Sachin
 
I am aware of ESP pages, find it very knowledgeable and used to live less than a Km away from their setup.

and I am not going to argue if their opinion is right or wrong.. I am not qualified at all...

so I am not going there abt what his comments abt burson.


No offense to you... with my next comments and questions..

Are you going to take his word for everything you want to do ? or someone else equally famous and qualified in Audio electronics ?

In that case, I could show you a lot of posts abt placebo effects (in their words) about Cables. and How some of them ridicule people getting fixated on such not so important matters.

Now, I know your mileage varies a lot on cables.

question is, will you change your approach because of a post on the net?

I rest my case...


and in any case, IF everything is "Maya", I am sure I would like to create mine the way I like it,
Absolutely. I never take anyone on face value and did not go the opamp way by reading this article at all. To import Burson V6 isca challenge for me and if i understand the literature they go about adding current to the o/p stage to get more juice from the source which an opamp cannot do. To compensate that, i shall be using a HDAM discrete buffer with class A output stage to add around 15mA of current for more juice. Many DIYers are already doing this with tons of benefits. YMMV .
 
Last week i added the HDAM buffer preamplifier to increase the current and thereby increase the mid and high frequency gain to sound more detailed, organic and in level with the lows. The stock BC550 and BC560 had around 15mA of current gain which was not sufficient. I modified the resistors (22 ohms changed to 10 ohms) and got around 27mA. With that he mids became quite good, open but the HF was getting masked. 27mA was the maximum you can drive with this complimentary pair. I had wanted to increase current further and went with modifying the transistors from the above to on ONSEMI MJE340 / MJE350 complimentary pair - the choice was not because of any audiophile reason, but just because it was in stock with me and they can be driven quite hard. The current is now 60mA and this makes the transistors quite warmish. The 10 ohms is now changed to 2.5ohms. Now the bandwidth is quite flat and there is no masking of any frequency. I may go ahead and change the resistor from 2.5 ohms to 1.5ohms for more deep class A, more organic and airy highs. The transistor can be driven till 500mA continuous RMS current and this might go max till around 100mA. This is quite a high bias current and will need adequate heat sinking.

Thanks for looking.
 
Hari,
Can you share the circuit diagram or a link to the circuit diagram for the HDAM buffer that you are referring to ?
 
Thanks, Hari, However I am a bit confused as to which Discreet Op amp you are using with increased current ...

Your Post # 8 refers to :

1. BURSON AUDIO SUPREME SOUND Version V6

2. ESP Discrete Opamp

Further, you have referred to the ESP site as saying: "Here is the link of the ESP pages which do not consider discrete op-amp to be better than a original op-amp." But it seems that you have now shifted to a discreet Op Amp.


I suspect that you are referring to a relatively simple, non buffered output, circuit :

p07_fig1.gif
The non buffered output makes it unsuitable to drive any capacitive load (eg passive RIAA Equalisation, interconnects) or a low impedance of the next stage. There is also no overall feedback, to ensure 0 Volts output and to determine the Voltage gain of the circuit which will hugely depend on the load, and may even vary continuously with frequency, if the load is capacitive....

Hence I would go to the extent of saying that the above circuit is Not A Buffer At All! Its simply a Voltage gain stage.


The Burson Discreet Op Amps are Far more elaborate in their circuit, and more closely resemble the circuit of an Op Amp.

As Far As I Understand, "the HDAM buffer" that you are referring to is developed my Marantz and is Unique to Marantz ONLY.
Its circuit... as per internet sources ( the circuit values seem to be tweaked in different products .. below is that used in their CD63 CD player ) is completely different, using a differential Voltage Gain stage and also a (JFET) output buffer stage:

8_82_827733b0_hdam.jpg


Great to learn of your experiences of tweeting circuits and relating the changes to that of the sound quality.
 
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I have used variety of opamps including Burson Audio V5 and V6 in my DIY CNC phonostage. They are really good. I preferred the LME49990 opamps over any other type followed by Opa 1612.
I gave away Burson to my friend and he is very happy.

Regards
Sachin
My ssp really sings well with Burson V5 opamp.Its sounds musically better than Burson V4. But V4 has bigger soundstage and laid back nature. LME49990 sounds very dark but has colored sound. It seems to have fixed sound signature.
 
Thanks, Hari, However I am a bit confused as to which Discreet Op amp you are using with increased current ...

Your Post # 8 refers to :

1. BURSON AUDIO SUPREME SOUND Version V6

2. ESP Discrete Opamp

Further, you have referred to the ESP site as saying: "Here is the link of the ESP pages which do not consider discrete op-amp to be better than a original op-amp." But it seems that you have now shifted to a discreet Op Amp.


I suspect that you are referring to a relatively simple, non buffered output, circuit :

View attachment 70874
The non buffered output makes it unsuitable to drive any capacitive load (eg passive RIAA Equalisation, interconnects) or a low impedance of the next stage. There is also no overall feedback, to ensure 0 Volts output and to determine the Voltage gain of the circuit which will hugely depend on the load, and may even vary continuously with frequency, if the load is capacitive....

Hence I would go to the extent of saying that the above circuit is Not A Buffer At All! Its simply a Voltage gain stage.


The Burson Discreet Op Amps are Far more elaborate in their circuit, and more closely resemble the circuit of an Op Amp.

As Far As I Understand, "the HDAM buffer" that you are referring to is developed my Marantz and is Unique to Marantz ONLY.
Its circuit... as per internet sources ( the circuit values seem to be tweaked in different products .. below is that used in their CD63 CD player ) is completely different, using a differential Voltage Gain stage and also a (JFET) output buffer stage:

View attachment 70875


Great to learn of your experiences of tweeting circuits and relating the changes to that of the sound quality.
I am not sure whic link in post #8 are you referring. Please check post #8 the final link. Then in post #13 there is a schematic which is NOT the above which you have showed.
 
Hi Hari,

I am lost ...
Can you just repost below:

1. The Relevant Link

2. The Relevant Circuit Diagram (Not a link to a circuit diag)

Many Thanks
 
A beautiful, well-constructed speaker with class-leading soundstage, imaging and bass that is fast, deep, and precise.
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