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Audio Blast: Eastern Electric Minimax DAC Opamp Rolling

A Final Look at maximizing the Minimax's potentials

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Introduction to Re-Submitted Audio Blast: Opamp Rolling the Eastern Electric Minimax DAC:

The article which you are reading is a re-submission of one which discussed Opamp rolling the Eastern Electric Minimax DAC. The prior article which may still exist somewhere in the Net’s ether is to be distinguished by reference to reversed positions of placement of Opamps and red lettering to indicate reversed positions of Opamps; that article is now revised. Why? Because there is concern by circuit designers that reversal of Opamps in the Minimax may be harmful to the unit and/or other equipment. To date there has been no actual evidence that harm has been caused by reversing Opamps. The revision was due to concern in the design community over the suggestion.

Why then would I ever write such an article? I had obtained approximately 12 sets of Opamps from Cimarron Technology for utilization in the Opamp rolling testing period. At one point in the testing process I inadvertently placed the Opamps in reversed positions – yet the unit worked and sounded better! Bill O’Connell from Morningstar Audio, the distributor of Eastern Electric, was concerned over this and wanted it known that the activity of Opamp rolling would void the warranty. I agreed and made this evident in the article.

I still wondered whether to discuss the reversed position of the Opamps. I certainly wanted to as a reviewer since the sound was clearly superior, and I enjoy promoting ideas which yield greatly improved sound, especially if gotten on the cheap. I explored the situation with Eastern Electric and Cimarron and was told by both that they did not understand how the unit would work with reversed Opamps. Aside from Bill’s general uneasiness (I should have been more sensitive to that, Bill!) at no point was I told it might cause failure or hurt other gear. Combined with the fact that I had proceeded to roll several sets of ‘reversed’ Opamps without any hint of technological issues, and the resultant superior sound, I decided to mention it in the article.

I enjoy experimenting with audio gear. That is how discoveries for better sound are made. However, I am no fool and when an authentic issue arises which can wreak havoc I do not promote it. I am not taking this step of rescinding the original article from my own experiences, but am addressing the concerns of disassociated designers in the community. It would not be advantageous for me as a reviewer to pursue clearly unproductive or potentially disastrous tweaks, and when an issue arises it behooves me to act expeditiously, as I have.

When Bill O’Connell informed me of the online discussions warning of the potential for serious problems, after immediately viewing them that same night I began to post online my intent to resubmit the article sans the reversed position Opamps section. I also re-wrote the article that night, knowing that the less time the original was on the Net the better. It’s important to me that anyone who reads my articles knows that I do not seek irresponsible solutions and uninformed (as much as is possible at the time of writing) suggestions.

Upon publication of the article the DIY community, especially those with intimate knowledge of Opamps, raised the alarm that reversing positions on them could theoretically cause catastrophic harm. Seeing the danger I contacted our publisher voluntarily withdrew the article, replacing it with the one that follows, free of any mention of reversed positions for Opamps.

This sudden reaction by the community and my re-submission of the article took place in a span of less than 24 hours. I mention this to give some appreciation of the blessing of having internet involvement in assessment of technically oriented articles, and to make the reader aware that at no point have I intended a cavalier attitude toward Opamp rolling and products like the Minimax DAC. It should be noted that the alarm arose from the DIY/Modding sector of the audiophile community. It makes perfect sense that if using a modded Minimax DAC reversing the Opamps might cause harm. However, it is not a foregone conclusion that reversing them in a stock Minimax would cause harm. Despite this, I have withdrawn the original article on the outside chance that someone who as a modded minimax might incur damage from reversing the Opamps.

The reversed position was clearly better sounding than several of the properly placed Opamp combinations. Toward the end of my testing, when I found a few combinations of Opamps which were placed properly and sounded nearly as good, the issue moved toward being a moot point. The article below has been entirely reworked, all references to reversed positions expunged. Consider from now on this version as the only official Audio Blast perspective on Opamp rolling the Eastern Electric Minimax DAC. The act of Opamp rolling voids the warranty; Bill O’Connell’s comment below that Opamp rolling, “… is fine,” is not Morningstar’s blessing upon Opamp rolling, but merely indicates there is no concern regarding electronic issues arising from proper placement of Opamps. No designers in the community are wary about that. It’s the notion of reversing their positions on the circuit board (swapping dual Opamps for single) which was controversial.

This experience of exploring the unknown effects of a tweak in a design and seeing the reaction from the community has been interesting to say the least. At first I was surprised, and then agitated at the online reaction to the article. But an email from Bill O’Connell shed some light on the matter. When I informed him that the article would be rewritten and the reversed position discussion removed, he wrote (unedited):

Hi Doug,

Thank you.

You have set my mind to ease. The op-amp rolling is fine.
The singles where doubles go and vice versa had me so worried.

Didn’t you accidently stumble upon the reverse op-amp situation. It
sounded better and then just experimented. That is fine but without
knowing electrically what could be the damage is a another matter.
I worried over the long term effect and possible electrical meltdown of a
component with possibility of a fire at the extreme end but I’m a worry

I was at a audio buddies house about 18 months ago and he had picked up a
tube DAC from another company that his buddy was trying to sell him.It
was a good thing we didn’t go upstairs to the patio to have a glass of
wine and stayed downstairs for a minute. Upon turn on of this DAC the
thing started smoking and started on fire. It was flaming. It was the
scariest thing.

From that moment on, I never leave my components on when I’m not at home
anymore. I saw that and said I gotto be crazy to walk out of my house
with my tube amps sitting idle or better yet, go to the office leaving my
house for an hour while my system warms up.

Back to the story at hand, without knowing the electrical properties of
what the inside components can take and switching op-amps singles where
doubles should be, I surely was not comfortable. Schematics tell the

Thank you for caring so much,

Kindest Regards,

Indeed, it appears that the details do matter, much more so than was at first apparent to me. It was right that an outcry arose about the reversed position Opamp discussion, and in hindsight I’m very glad it did. This will be filed in my mind as a new Audiophile Law, one perhaps known as, “Know Thy Limitations in Experimenting”. I have not shied away from what I consider sensible, experimental tests in assembling audio systems. However, in the future very likely intentional reworking of designers’ circuits will not be one of them!

Douglas Schroeder, 3-26-11


This second Audio Blast article on Opamp rolling the Eastern Electric Minimax DAC is a technical discussion of the process of Opamp rolling and descriptions of the influence of various parings of Opamps in the DAC. It is replete with technical information which some readers may find burdensome. I invite those who wish to skim the article and refer to the chart and descriptions of Opamps toward the end.

I was right; the 32 bit Saber DAC Reference chip from ESS Technology is laying waste to all manner of 24 bit DACs. I only had a clue how fantastic it is until recently when I began to roll Opamps in the Eastern Electric Minimax DAC. I believe that 24 bit DACs will become largely obsolete in high end two channel audio due to the emergence of 32 bit chips from the likes of ESS and eventually competitors. The Sabre DAC chips are not used to their fullest expression in the stock unit.

Roll a set of four custom upgrade Opamps into the Minimax and you’ll become a believer in the power of 32 bit DAC processing. There has been popular acceptance of the Minimax DAC, and it has won awards, but the audio community is still unaware of this product’s extended capabilities. The whispers are circulating that it can perform on a very high level, but with Opamp TLC it’s a truly stunning sounding product fit for the highest caliber systems.

Since I write this on Valentine’s Day, as an audiophile I declare my love of Opamps. I love my wife, of course, but I really lovewhat Opamps can do for a component! I didn’t have too much insight into what precisely they could do in terms of sound enhancement until recently, when, as indicated in my previous Audio Blast on the Eastern Electric Minimax DAC, I began Opamp rolling. The past two weeks as I have experimented with these potent little power packages I have had more fun as an audiophile than I recall having in years. With an over-achieving, affordable component, tons of options and surprising results it all adds up to a compelling audiophile story.

I am indebted to Phil Maltby of Cimarron Technology, maker of Brown Dog Adapters, for his provision of Opamps for this review. He also showed infinite patience instructing me on the finer points of Opamp chips and adapters. This article will point to Cimarron as a source for the Opamps I will recommend. I have already covered the lead in to Opamp rolling the Minimax in my previous Audio Blast, so let’s jump into the fray.

Over the past couple weeks I have rolled the following Opamps into the Minimax:

Burr Brown: OPA 627, OPA 827, OPA 2134, OPA 2604

Analogue Devices: AD797, AD8620

National Semiconductor: LME 49710, LME 49720, LME 49990

Pay Attention

You are going to be bombarded with a lot of detailed information below. Do not get discouraged or fearful; it is provided so that you will be thoroughly acquainted with the Minimax DAC in terms of Opamp rolling. The real work involved is in identifying and selecting Opamps, not in placement of them.

There are a total of four Opamps required in operation of the Minimax, two pairs in locations labeled U1 and U2 located in the middle of the unit as the front of the DAC faces you; U6 and U7 are located to the right of the others. Locations U1 and U2 are to take a double channel Opamp, while locations U6 and U7 take a single channel Opamp. According to Alex Yeung, the designer, “After the ES9018 D/A conversion, there are opamps for I/V conversion and low pass filtering etc., then there are 2 independent circuits for output gain stage namely one 12AU7 that is the tube and the NE5534 that is the opamp.” Consequently, Opamps are utilized in both solid state and tube output, though in different capacities. When one changes all four Opamps, both the solid state and tube output will be affected, meaning there are two chances to hit it big in terms of improved sound.

When the Minimax DAC is opened up one sees the stock Opamps. Though they are all single chips, though the ones in the U1 and U2 positions are dual channel. One cannot identify the single and dual channel Opamps merely by their appearance; some Opamps built onto adapters for dual channel operation have one chip on an adapter and some have two chips! You will rely upon the designation of the Opamp from Cimarron to know definitively which ones are single or dual. I strongly recommend that you not open up multiple sets of Opamps from their packages, as you will not be able to easily identify them visually. Keep them segregated and work one set at a time for replacement. I have heard the suggestion that dual channel Opamps made with a single chip are superior sonically to those constructed with two chips. However, I found instances which the reverse was true.

Sourcing The Custom Opamps

In order to Opamp roll the EE DAC with any Opamps mentioned here you will need to obtain them from Cimarron Technology Inc. All of the Opamps mentioned here are assembled by Cimarron. The reason why is that the chips are far too small to fit into the sockets on the Minimax’s circuit board. Cimarron has a line of adapters for Opamps which allows the use of smaller Opamps in positions meant for larger ones. The adapters made by Cimarron are called Brown Dog Adapters. To see the adapters, go to and on that page you will see two windows labeled “SO8 to 8 Pin DIP Adapter (p/n 970601A)” and “Single to Dual Opamp Adapter (p/n 020302A)”. The SO8 adapter is used for the single channel Opamps and the Single to Dual is used for the dual channel Opamps.

The only reason it is possible to Opamp roll the Minimax DAC is because Alex used “socketed” Opamps rather than soldered ones. Therefore, anyone with no more than a bit of interest and patience can roll (swap) them! I publicly shout out a big THANK YOU to Alex for allowing this introductory DIY project! Frankly, I do not think he had this in mind at all when designing the Minimax, but it appears to have been a prescient decision.

Prices to get two pair of Brown Dog custom Opamps for rolling the DAC range from about $100-140, as the Opamps have a fair bit of price variance. Is this expensive for a few itty-bitty chips compared to an entire component? Yes, and in a way absurdly so. Are they worth it? Yes, and in a way absurdly so, because unless you are a DIY enthusiast who can mod the unit, it’s what I would call a surefire way to radically ramp up the performance!

I have been in communication with Phil about this article and they will have the Opamps and adapters for both locations for audiophiles to try. There is only one small problem; there are a lot of options! I have taken on the arduous task of conducting “rolling sessions” to assess the performance of many of the options and will here provide my findings.

The Variables Involved In The Testing

First, some comments about my testing these Opamps. You will see very shortly that there are an authentic myriad of settings and options involved in using them with the Minimax DAC. To conduct a comprehensive analysis would be prohibitive. Consider that there are a dozen discreet Opamps involved in differing locations. Add to this the allowance that one can adjust their performance via using the volume control on the DAC as an impedance selection device! I ran the Minimax DAC into the venerable VAC Signature MkII Preamplifier. When the volume control of the Minimax was adjusted it influenced the entire system’s tonality and clarity as well as gain! I determined to pick a position on the Minimax’s volume control at about 3:00 on the clock dial and leave it there throughout testing.

Also, one can select tube or Solid State output. Because of what is to my ear a more pleasing tonality I have tended to use the tube output the most. Therefore, I installed the stock tube and ran it for all tests, ensuring consistent testing. Considering Opamps, tubes, solid state or tube output, and the volume setting dozens upon dozens of variations are possible, and you can appreciate that I’m not paid to run a lab. This is an unsolicited article and I’m supposed to be doing other reviews (shhh… don’t tell Constantine!). If the first or second Opamp rolling experience had crapped out, you wouldn’t be reading this; the activity would have failed my Law of Efficacy and my conclusion would have been that it was largely a waste of time. However, the experience has been anything but droll. Opamp rolling this unit is a terrifically effective means to upgrade one’s digital source.

Ready To Roll

Before you contact Cimarron Technology you should get the Opamp extraction device called “DIP/IC Extraction Tool – S-340” made by Jonard Industries Corp. from Use it to pull and place the Opamps. It is recommended whenever digging into an electronic device like the Minimax that you obtain a wrist strap grounding cord, get that as well Locate a proper sized small Allen Wrench for the four top screws to remove the lid of the DAC or else you’ll be upset when you have the Opamps and have to scrounge to get them inserted!

Then, referencing the Cimarron Technology website you select the Opamp pair you want for location U1 and U2, followed by the Opamp pair used in location U6 and U7.

Here are the Dual Channel Opamps offered for the pair in locations U1 and U2:






Here are the Single Channel Opamps offered for the pair in locations U6 and U7:





Installing The Little Suckers

They’re small, and one or two are located under an overhanging wire, so I use the extractor to pull and place them. The tiny pins are aligned perfectly by the adapter, so you should not have problems aligning the Opamps – unless you put it in backwards! Every single one of the adapters has one spot on the top of the adapter where instead of a circle at the leg attachment point there is a square. The leg with the square attachment point always goes to the upper right as you face the front of the DAC. There are no exceptions to this; in all locations you want the adapter’s square in the upper right position. When the Opamp is seated properly with all 8 legs push down gently to slide it into operating position. The effort is in the selection and proper placement, not the pushing!

You will notice that in order to try all possible combinations one would have to conduct 20 trials! In addition, I was given several extra samples of custom Opamps, such as the Burr Brown OPA2134 and OPA2604, or the Analogue Devices AD8620. Some of these I tested and recorded results along with the others in a chart below.

I was elated to have such a comprehensive suite of Opamps, as they allowed me to find the perfect sound for my system. The suite of Opamps is itself like an ultimate system tuning tool. I obtained results with forward or recessed soundstage, emphasis on treble, midrange or bass, warmer or cooler tonality, and varying degrees of edge to the precision or clarity. It may be that nearly any set of my final recommendations for these custom Opamps will take the Minimax to a level that is likely to outperform your current 24 bit source.

The system and The Music

Speaking of systems, I used the phenomenal Legacy Audio Whisper DSW speaker system in fully active crossover mode, a trio of Coda CS Amplifiers, a Denon 2900 Universal Player (don’t laugh; this transport with the EE DAC and Opamp upgrade is clearly the best digital source I’ve ever used), the Minimax DAC, VAC Signature Preamplifier MkII, and all Clarity Cables. Even with this system there were approximately half of the Opamp tests which I felt were failures of my Law of Efficacy; they simply didn’t have enough differentiated character or change from the other excellent options to warrant a comment. Note virtually all of these Opamp sets are excellent in the Minimax DAC in comparison to sub $5K, 24 bit players. I was highly critical and discerning to find my recommended sets.

What did I listen to? A smattering of tracks which would give me a quick read on the performance parameters of the rig. There was the difficult “Barbossa Is Hungry” from the Pirates of the Caribbean: The Curse of the Black Pearl soundtrack, with tremendous symphonic energy ramping up in a hurry, with less outstanding clarity – that would test the ability of the system/Opamps to parse the orchestration. It was followed by Delerium’s Voice with all female vocals, especially focusing on Sarah McLachlan’s “Silence” and Leigh Nash’s “Orbit of Me”. Nash’s voice is a great gauge of how hot a system’s treble is running, and in this case the piano on “Silence” assisted in checking the ambience and top end performance. I worked with a couple selections from The Premier Collection: The Best of Andrew Lloyd Webber, focusing on “Don’t Cry for Me Argentina” from Evita and “Pie Jesu” from Requiem. Especially in these last two pieces I listened for how the acoustic instruments such as the harp sounded as well as how much decay and spatial information of the venue was resolved. I was looking for the voices, both solo and massed, to evoke strong emotions.

Finally, I turned to some pop/rock in Gino Vanelli’s “Black Cars” and “Just a Motion Away” to see if I could crank it up closer to live level without getting an ear bleed. Rock songs like these are good to test clarity and detail since so many times the lyrics are difficult to distinguish. One of the most difficult lyrics to cleanly render I have found to be the repeated phrase at the start of Joe Satriani’s “I Just Wanna Rock”. Try listening to it on your rig and take a guess what is being said through the distortion. With the better Opamp combos in the EE DAC the phrase became easily distinguishable.

The Opamp Chart

This chart shows the order of testing, working from the top left and moving across the row, then down one line and moving across again. Opamps which go into the U1 and U2 positions are listed down the first column. Opamps in the U6/U7 positions are listed in the row across the top.

Eastern Electric Opamp Spreadsheet Image

Noteworthy Combinations of Opamps:

Denoted as: Location, Opamp, (single/dual channel). You will Order two of each.

U1/U2 LME49990 (dual) and U6/U7 LME49990 (single)

I started this comparison with the LME49990 Opamp as my reference. It ended up at the top of the pack at the end as well. This combo has ultra-clean, ultra-distinct definition. One has to be ready for a level of detail possibly never dreamed from Redbook and streaming audio. Individuals who live for analogue will likely think it too highly detailed. But perhaps this can be addressed by using the volume control as impedance selector and or tube rolling. The odds are very good you have not heard this level of precision in a DAC in your system prior.

U1/U2 OPA627 (dual) and U6/U7 OPA627 (single)

The 627 was a very surprising Opamp, as it was not expected to perform at top level. My understanding is that it is an older Opamp design, so it should be more economical. I felt the solid state output was superior compared to the DAC’s stock tube output. As with all these special mention “finalists” the clarity and definition is superb, but this option had a slightly softened treble to allow the midrange to shine.

*U1/U2 OPA827 (dual) and U6/U7 OPA2604 (single)

It would be proper to recon this as one of the better combinations. My notes simply indicated, “Gorious! Perfect!” as it was a finalist. *The OPA2604 is not currently offered by Cimmaron. I believe it is an older Opamp; if sourced elsewhere Cimarron can use the Brown Dog adapter to make the Opamp for your Minimax.

U1/U2 OPA827 (dual) and U6/U7 OPA827 (single)

In my notes I had this as one of my “finalists”. The distinction between the absolute best pairings became very small at the end. This pairing would likely find wide acceptance in many rigs.

U/1U2 AD8620ARZ (dual) and U6/U7 LME49990 (single)

This Analogue Devices chip may be worth checking out with other Opamps in the U6/U7 position. If I had not been sent the OPA2604 (unavailable currently from Cimmaron) I might have used this combination as my reference.

*U1/U2 OPA2604 (dual) and U6/U7 AD797B (single)

This was the big winner in my system, offering scrumptious sound for both the Legacy Audio Whisper DSW and Kingsound King speaker systems. I find precious little to nitpick about this pairing; it yields a mature, “full bodied” sound with plenty of crispness and detail but without a trace of stridency. *Again, one may have to search for the OPA2604.


You will note that as we’ve moved through the chart there was no “sweep” in terms of superior performance by one company’s Opamps. National Semiconductor seems to have an edge in absolute clarity/definition. However, both Burr Brown and Analogue Devices capture the richness of timbre in instruments extremely well in the Opamps I cite.

The combinations of the distinct Opamps seem to be critical; I did not get the ultimate results from just slapping one brand of Opamps into all four slots. Sorry; it’s not that easy to get the best of the Minimax! What did I end up with for now? For my own system with the Cambridge Audio Azur 840W amp for the bass and two Pathos Classic One MkIII units handling the midrange and treble in place of the Coda CS amps I have settled on the very last option I mention: U1/U2 OPA2604 (dual) and U6/U7 AD797B (single).

My bottom line is that the EE Minimax is far beyond a great value and performer in its stock form, and is capable of elite sound with custom Opamps. I believe it is on its way to becoming a cult favorite among budget minded audiophiles in its stock form. With the Opamp upgrades it may become legendary.

The DIY crowd is often right; there are amazing improvements to be had at times through upgrades to components. In this particular instance the average guy (or gal) can get in on the action though having no specialized skills. For the price of admission to the Opamp rolling improvement it is a giveaway of several large levels of improvement to a rig. The Minimax Opamp Upgrade fairly launches your system’s digital performance heavenward like a rocket – a veritable Audio Blast – in the quality of the sound.

Readers’ Letters

If you can pass this on to Doug Shroeder, the opamp upgrade for the minimax dac from the January article made a tremendous diffenrence. Thanks Doug! – Tony Barca, 3/24/2011

Hi Doug, After reading your original article on the EE MiniMax opamp upgrade I ordered a couple of pairs of LME 49710, LME 49720 which I have been living “happily” with for the past couple of weeks.

I then stumbled upon your follow-up article and am now contemplating ordering custom opamps from Cimarron. The problem is that I can’t quite figure out exactly which part combination I need to order. As I don’t want to order these rather costly parts for nothing I was wondering if you could simplify the process for me by listing exactly what opamp/adapter combinations I need to order for optimal results.

Thanks in advance for your help with this enigma. -Michel (Montreal) 3/27/2011


God’s Peace to you,

Thank you for the lovely note. I’m glad you are giving the Opamps a try, because it is a wonderful improvement to the stock unit.

“Optimal” results for the individual will vary somewhat, however my choice that I have been very happy with using for both of my reference speaker systems is: U1/U2 OPA2604 (dual) and U6/U7 AD797 (single), but the OPA2604 is not available at this time from Cimarron Technology, where I received the sample Opamps.

I suggest you try my alternative reference set:

If you simply indicate to Cimarron Technology that you need a two each of:

AD8620ARZ dual channel opamps and LME49990 opamps,

they will know precisely what you need. If you choose to order them online notice that the single channel opamps are sold individually and the dual channel opamps sold in pairs. Tell them it is for Opamp rolling the Eastern Electric Minimax; they have intimate knowledge of this DAC.

I have been informed that the OPA2604 is available as a “drop in” chip from other sources, not needing an adapter, for about $5. However, I cannot vouch for the sound or usefulness of alternatives.

If you seek this combination, Phil at Cimarron is familiar with it and can help you.

Douglas Schroeder

Hi Doug, can I possibly trouble you regarding the nomenclature on those National Semiconductor op-amps you sourced from Digikey for the EE Minimax DAC mod? It seems there are three (3) versions of the LME49720/49710 and per the catalog, have slight alphabet differences at the end of their description.

Your article on this fine piece of equipment has inspired me to take it to the next level. Rolled in a Marconi 12au7 and am ready to go. Any assistance greatly appreciated. Thanks. – Rich Oriti 3/28/2011


The Joy of God to you. Thanks for the fine note; I’m happy to see you are enjoying the DAC and are interested in doing the Opamp rolling.

The part numbers for the Opamps you mention sourced from Digikey are:

LME49720NA-ND and LME49710NA-ND

However, I would urge you to consider the upgrade Opamps mentioned in the subsequent Audio Blast article entitled “Opamp Rolling the Eastern Electric Minimax DAC” as these are far more potent in upgrading the DAC performance. The first Opamps from Digikey provide only a fraction of the improvement possible with any of the suggestions I made in the Opamp Rolling article.

I understand that there are other sources than Cimarron Technology to acquire Opamps, but one would need to conduct their own due diligence to determine if the Opamps would be suitable and perform up to the level of the ones mentioned in the Opamp Rolling article. If you are going to order Opamps mentioned in the article from Cimarron, they will be aware of the part numbers associated with the Opamps mentioned.

Enjoy! Either route you go will be an upgrade, but I hope you can afford the top tier Opamps.

Douglas Schroeder

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