High gain opamp based preamp for low output MC cartridges.

[j!m]

Use the standard MM gain configuration of 43dB SE, 49dB balanced for both high output cartridges.
It's not clear to me if you want a LO MC value as well. The standard configuration will provide 63dB gain SE, 69dB balanced, which should be acceptable for the 0.4mv output (also at 3.54 cm/sec 1kHz) or 0.56mv (5cm/sec) . This is c. 8dB higher than the cartridge that I use. The overload margin at miss-tracking will be c. 8dB, which should be OK.

OK I have plugged in 43 dB into the Gain Calculations excel sheet and I get R8 value of 28066.26 ohms and R9 value of 7267.07 ohms. Therefore, I chose 28k for R8 and 7.3K for R9; (deviation is 0.09%) for 43.02 dB calculated overall gain. 28k is easy enough to find, but on Digikey anyway, the 7.3k is a bit harder to get. Is this value typically stocked with other vendors? And did I calculate correctly before I dig for something I can work around?

Thank you again.

 

[wyn palmer]

OK I have plugged in 43 dB into the Gain Calculations excel sheet and I get R8 value of 28066.26 ohms and R9 value of 7267.07 ohms. Therefore, I chose 28k for R8 and 7.3K for R9; (deviation is 0.09%) for 43.02 dB calculated overall gain. 28k is easy enough to find, but on Digikey anyway, the 7.3k is a bit harder to get. Is this value typically stocked with other vendors? And did I calculate correctly before I dig for something I can work around?

Thank you again.

No need to use the calculator. The 43dB gain components are listed in the BOM and the component values are as listed on page 18 of the build notes. The two gain configurations that I suggested are the standard ones defined in the documentation.

 

[j!m]

OK I missed that tree amongst the forest completely...

However, is it possible either the chart on 18, or the calculator page, is incorrect? Calculated R8 is 28k and on the parts list R8 is shown as 5.11k. Also, R9 is calculated at 7.3k and shown as 30.1k . Roughly the same sum, but transposed values it seems. Does this matter? If so, which is "correct"?

 

[mkane]

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

 

[wyn palmer]

OK I missed that tree amongst the forest completely...

However, is it possible either the chart on 18, or the calculator page, is incorrect? Calculated R8 is 28k and on the parts list R8 is shown as 5.11k. Also, R9 is calculated at 7.3k and shown as 30.1k . Roughly the same sum, but transposed values it seems. Does this matter? If so, which is "correct"?

As I do not know how you have configured the gains I cannot comment. I believe that quite a few people have constructed the "43dB" MM stage- even if I have not- and I just checked the schematics. R8 and R9 are correctly valued. The approximate gain value for the first stage in this case is 27dB.
As for the calculator, that was not my work, but I did check it out some time in the dim and distant past.
In fact, the values in the BOM are not actually 43dB, but including cartridge losses etc. it's about 43- 43.6dB, as determined by simulation.
If you plug the circuit values into the calculator it reads 44.3dB, but that is an approximate, crude, value.
R8 and R9 are correctly labelled in the schematic and board, and are correctly valued at 5.11k and 30.1k, respectively. You can verify this with the calculator.

 

[j!m]

That's what I'm saying: the total sum resistance is not under question (they are nearly identical), but rather, the (possible) transposition of R8 and R9, in one of the two.

So, in the calculator, R8 has the larger value and R9 has the smaller value. On the page 18 chart, R8 has the SMALLER value, and R9 has the LARGER value, so opposite the calculator. That's what I was pointing out, or questioning is all. The location of these two may not matter, and it may matter. Since I don't know, I'm just checking...

EDIT_ I just grabbed a board and looked at the backside trace, and... I have no idea...

 

[wyn palmer]

That's what I'm saying: the total sum resistance is not under question (they are nearly identical), but rather, the (possible) transposition of R8 and R9, in one of the two.

So, in the calculator, R8 has the larger value and R9 has the smaller value. On the page 18 chart, R8 has the SMALLER value, and R9 has the LARGER value, so opposite the calculator. That's what I was pointing out, or questioning is all. The location of these two may not matter, and it may matter. Since I don't know, I'm just checking...

EDIT_ I just grabbed a board and looked at the backside trace, and... I have no idea...

I do not know what this is a response to. R8 is marked 2.8k on the board and has one terminal to ground. This becomes 5.11k in the 43dB gain case.
Do you have the first stage gain in the calculator set to 27dB?
Have you put the 5.11k/30.1k values for R8/R9 into the calculator together with the 27dB gain for the first stage into the calculator?
If you are still confused please post a snip of the calculator as you have configured it.

 

[HalfApt]

...However, is it possible either the chart on 18, or the calculator page, is incorrect? Calculated R8 is 28k and on the parts list R8 is shown as 5.11k. Also, R9 is calculated at 7.3k and shown as 30.1k . Roughly the same sum, but transposed values it seems. Does this matter? If so, which is "correct"?

I made that spreadsheet calculator from formulas Wyn posted way back in this thread. The calculator works correctly if you read the documentation.

There are 3 pre-defined gain structures for the first stage opamp: 27, 32.3 and 40.5dB. You need the choose the one most appropriate for your desired overall gain (low, medium, high). The spreadsheet instruction says "Pick front end gain", click the cell and you can choose one.

For the numbers you came up with (28066.26 & 7267.07 ohms), you left the first stage gain at 40.5dB setting (leaving only 2.5dB for the second stage). First stage of 40.5dB is only appropriate for MC carts needing 60+ dB of overall gain.

Pick the first stage gain at 27dB, and you'll get R8 = 5931.77 & R9 = 29401.56. 5.9k & 29.4k are the closest standard values, producing actual gain of 43.05dB (0.09% deviation).

 

[wyn palmer]

I made that spreadsheet calculator from formulas Wyn posted way back in this thread. The calculator works correctly if you read the documentation.

There are 3 pre-defined gain structures for the first stage opamp: 27, 32.3 and 40.5dB. You need the choose the one most appropriate for your desired overall gain (low, medium, high). The spreadsheet instruction says "Pick front end gain", click the cell and you can choose one.

For the numbers you came up with (28066.26 & 7267.07 ohms), you left the first stage gain at 40.5dB setting (leaving only 2.5dB for the second stage). First stage of 40.5dB is only appropriate for MC carts needing 60+ dB of overall gain.

Pick the first stage gain at 27dB, and you'll get R8 = 5931.77 & R9 = 29401.56. 5.9k & 29.4k are the closest standard values, producing actual gain of 43.05dB (0.09% deviation).

Thanks! As I wrote, the formulas do not take into account certain losses in the circuit that can only be properly explored by simulation, so there will be a small difference in gain between the optimized 43dB design and the spreadsheet driven design. This does not alter the applicability of the spreadsheet or the accuracy of the values posted for the optimized design in the BOM.
As has been stated before- it is recommended that the documentation be thoroughly read before embarking on the project.

 

[HalfApt]

Thanks! As I wrote, the formulas do not take into account certain losses in the circuit that can only be properly explored by simulation, so there will be a small difference in gain between the optimized 43dB design and the spreadsheet driven design. This does not alter the applicability of the spreadsheet or the accuracy of the values posted for the optimized design in the BOM...

Thanks Wyn! I understood that the BOM values for 43 & 63dB were simulation optimized. And that the calculator was for convenience when desiring a gain OTHER than 43 or 63dB.

Are there any corrective factors that could be applied to bring the values closer to reality? I can try to incorporate them into the spreadsheet.

Will the value sum (35333.33) always produce the correct 3180uS time constant, even if the gain is off a bit?

 

[wyn palmer]

Thanks Wyn! I understood that the BOM values for 43 & 63dB were simulation optimized. And that the calculator was for convenience when desiring a gain OTHER than 43 or 63dB.

Are there any corrective factors that could be applied to bring the values closer to reality? I can try to incorporate them into the spreadsheet.

Will the value sum (35333.33) always produce the correct 3180uS time constant, even if the gain is off a bit?

Yes, the TC will be correct- that math is precise. The gain errors are mostly due to the actual equivalent models of the cartridge plus load Rs etc and really can't have a "correction factor" added. The finite gain-bandwidth product of the opamps is another factor that is included, but it is amenable only to statistical simulation, and it has an effect only at the the extreme high frequencies, and only a small one at that. The overall difference is in the order of a dB, which really is not important as the errors mostly occur at the input. The calculator/math computes the value for an ideal cartridge, and ideal opamps, but unless we really want to make it much more complicated, no correction can be added for a real one.
As has been shown by the confusion that has arisen on more then one occasion when the off recommended (simulated) gains are being calculated by builders, more complexity in the model would not necessarily make the outcome better.

 

[MichaelLK]

I haven't posted much, but as a proud owner of the phono stage I did want to jump in and say that this thing completely blows away anything I've had before. It has me going back to all my favorite LP's and hearing them in a new light. I liken it to the difference between listening to a recording and listening to performances, as if some sort of film has been removed. The fast rise time and transient response make for a very rhythmic presentation and every tiny detail is audible without being spotlit. Equipment - ET 2.5 tonearm, Ortofon Cadenza Bronze cartridge loaded @ 75 ohms, VPI TNT turntable. Muse Model 3 Signature preamp, Son of Ampzilla amp, Audio Artistry Vivaldi speakers. Thanks Wyn.

 

[chapps]

I haven't posted much, but as a proud owner of the phono stage I did want to jump in and say that this thing completely blows away anything I've had before. It has me going back to all my favorite LP's and hearing them in a new light. I liken it to the difference between listening to a recording and listening to performances, as if some sort of film has been removed. The fast rise time and transient response make for a very rhythmic presentation and every tiny detail is audible without being spotlit. Equipment - ET 2.5 tonearm, Ortofon Cadenza Bronze cartridge loaded @ 75 ohms, VPI TNT turntable. Muse Model 3 Signature preamp, Son of Ampzilla amp, Audio Artistry Vivaldi speakers. Thanks Wyn.

May I ask, which version are you using? I mean, is the unmodified preamp boards? Also, can you tell me what power supply etc. that is part of the build.

I know Sachin was selling a version of Hypnotoad boards...or maybe THE same boards. Is this the same or have mods been made extensively ???

Thanks.

 

[wyn palmer]

May I ask, which version are you using? I mean, is the unmodified preamp boards? Also, can you tell me what power supply etc. that is part of the build.

I know Sachin was selling a version of Hypnotoad boards...or maybe THE same boards. Is this the same or have mods been made extensively ???

Thanks.

I'm reluctant to answer for Mike, but I shall as I do know the provenance of his phono stage.
It's the latest build of the design described in this thread, with the recommended switching power supply and filter.
It is NOT Hypnotoad's design, but rather this one without the extra output gain stages.

 

[chapps]

.

I'm reluctant to answer for Mike, but I shall as I do know the provenance of his phono stage.
It's the latest build of the design described in this thread, with the recommended switching power supply and filter.
It is NOT Hypnotoad's design, but rather this one without the extra output gain stages.

Oh no, I was not checking any provenance. No way, and that's not me. I got a the modded HypnoToad I mentioned, but I would like to give to my brother who would like to have one.

If this is another design, then great, I would like to get this too to compare. That's all. I saw the review and well it got me interested.. Can I get Mike's version pre-assembled since I don't have the bandwidth to put together from a kit? Can you please PM with details?

Thanks, and sorry about any confusion

 

[wyn palmer]

.


Oh no, I was not checking any provenance. No way, and that's not me. I got a the modded HypnoToad I mentioned, but I would like to give to my brother who would like to have one.

If this is another design, then great, I would like to get this too to compare. That's all. I saw the review and well it got me interested.. Can I get Mike's version pre-assembled since I don't have the bandwidth to put together from a kit? Can you please PM with details?

Thanks, and sorry about any confusion

I'm sorry but I don't sell assembled boards. I do sell boards at cost. This is not a business but, in a sense, an act of community. However, the assembly of the boards themselves is quite straightforward and the build guide is quite comprehensive after numerous revisions based on actual builder experiences. There is also a set of Mouser carts for the various options and I am always willing to provide guidance during the process.

 

[maxhifi]

I finally got around to finishing mine off, have been using it for months minus the LED and three of the inputs. Here is the internal photo someone requested previously

 

[wyn palmer]

It's been a while since there have been any posts in this thread.
In the meantime non AK interest remains and as a result I have a few boards available.
In addition I plan to make some additional tests once my new Autoranger 2 automatic/programmable attenuator is assembled.
In particular the intention is to repeat and expand upon measurements made using multiple input test tones using REW and my ADI2 PRO FS ADC/DAC.
In this test many (hundreds or more) separate tones are used to better approximate the case where the amp is handling real music, and the resulting intermodulation distortion is measured. The total signal level is controlled so a measure of real SINAD is obtained. The correlation of this measurement to audio quality is reputably quite high, but it is not a test that is typically performed.
I did do this test a while ago, but did not record the result in the dropbox for this project, and I plan to correct that omission.

 

[EngineerNate]

Setting up my electronics bench is next on my list of house projects... Hopefully I'll have an update on my build in the coming months. Lord knows we all need some leisure projects to distract us from current events!

I promised my wife when we moved into the new house I'd not be doing any electronics on the kitchen table. I kept that promise but not having another space setup to do them in has resulted in some serious delays in those endeavours.

Wyn, let me know what you need added to the Dropbox and I'll take care of it.

 

[PTL-Pioneer]

Hi all, sorry for dropping in at the end here, looks like I got some reading to do
What kind of cost is the circuit board etc?
I'm looking at preamps and phono stages I'd like to try some DIY.
Apologies I do know this is a lazy post, I'll get reading this thread properly, bookmark added!