Thanks for all the additional input. I think the power supply will be targeted as well as the bridge rectifier, caps and resistors, as per Bombaywalla's great advice (really nice Scinnies by the way and the Cat/Symphonic must make an outstanding combination... very nice rig). ..... Thanks for your kind words, Lissnr. Indeed the combination is very enjoyable. You had asked about approx total cost - it's very hard to give you such a number as the costs vary depending how far you want to take the upgrades/modifications. One simple example: if you choose Kimber Kaps when replacing caps everywhere, you might end up paying an avg. of $15/cap. OTOH, if you choose, say, Mundorf, you could end up paying 2X or 3X more per cap. That could escalate your costs very quickly. Same deal with the other components. All the best & I/we hope that it all works out for you. The Apogee DAX are very well regarded. Keep us posted on this forum. Thnx. |
Thanks for all the additional input. I think the power supply will be targeted as well as the bridge rectifier, caps and resistors, as per Bombaywalla's great advice (really nice Scinnies by the way and the Cat/Symphonic must make an outstanding combination... very nice rig). I'm looking fwd to getting this into the shop soon and will post results asap. |
I just converted the output stage on the low frequency EQ unit for my Infinity RSIIb speakers from cap-coupled single-ended mosfet to direct coupled with OPA827 opamps, and the new output stage is much more transparent and clear sounding. The entire signal goes through this stage after equalization.
I know single-ended mosfet stages have a much better audio rep than lowly opamps, but the SiGe OPA827 is very nice sounding, and its exceedingly low DC offset lets me rid the circuit of the output coupling cap - the best cap is no cap, IMHO. |
Just for some reading material....
I've built a CMOY pocket headphone amp.
I used the OPA2134 series.
http://tangentsoft.net/audio/cmoy-tutorial/parts.html#op-amp
Somewhere in the documentation is a long list of opamps and how the author feels about them. Some are very good while others have audible flaws which some may find acceptable, others not. |
This is the one I meant, you said you had been on the old ones previously.
http://www.apogeespeakers.com/ |
I also have DSs, one currently needing repair. I am eventually going to upgrade them with better wiring and binding posts and eventually a better base. I have RELs myself but I doubt you will need them with the DSs. I had large subs when I was using them last and never felt the need to add them. Have you been on the Apogee users forum, it is quite helpful? I run my RELs off the power output of the amp, have you ever tried this? |
Great information so far and exactly why these forums are so helpful and appreciated. Yes, it is an Apogee Dax, but not the one pictured with my previous Mini Grands. I have Duetta Signatures now and the one we're discussing is an original Dax 1.
For those of you understandably unfamiliar with Apogee speakers there were 2 models of Dedicated Active (electronic) Crossovers (DA?X?) (actually 3 were supposedly developed but only #'s 1 and 2 really hit the market) which were designed to "divert around" the passive crossover components built into the speaker and act as true control centers of the woofer and midrange/tweeters as well as facilities for matching gain of different amplfier outputs when running the speakers bi-amplified (a REQUIREMENT when utilizing the Dax).This 'specialization' for only a specific few of the Apogee models is what makes it such a lure to those model owners. Over the years the Dax 1 [in the old Apogee forums] began as 'the cat's meow' for an admirably long time but with the advent of newer crossover designs by other companies (though none were ever specifically designed for any one particular brand or speaker model to the extent that the Dax's were for Apogee), other crossovers began to replace the now-aging Dax's... I myself have been using an excellent example of exactly what I'm saying: I've been the very happy owner of an NHT model X2 active crossover which is currently doing duty splitting my full range preamp output at 50hz into my Rel subwoofer and then [through the use of an 'rca splitter' on the high output jacks], sending the remaining signal to a dedicated woofer amp and a dedicated mid/tweeter amp into the [bi-wired] passive crossovers....(note there is no control for matching separate amp outputs but I've been fortunate that there seems to be a good balance overall).
The Dax 1 will add tremendous flexibility and I feel will make a worthy addition IF I can get it to today's high standards of transparency, dynamics, and all the other assets sought after in a well designed quality crossover...
Thank you for all your thoughts and suggestions so far, as I said, these are exactly the discussion points I need to have with the technician... Now all I have to do is figure out where I draw the line on the law of diminishing returns when it comes to deciding the $$$ expenditure on this. Certainly, I do realize I'm pretty much marrying this unit and I have no problem with that idea at all IF it turns out to be as good as I hope.... For the record, while not one to throw dollar figures around on these forums I will say that the unit originally retailed for $4K and that I have an 8/10 condition which I paid just under 25 cents on the dollar for... Which leads to the question inspired by Bombaywalla's excellent list of specifics above (thank you!): how much should / could having all/most of the above cost????? This hobby is relentless.... Thanks again ,everyone. |
To further Al's point, some makers are using NOS parts because they feel they are better for their particular application. Also a design may have been optimized using certain parts and the substution of "better" ones may destroy the balance achieved by the original ones. I have read several accounts in the modifiers forums of how after extensive modification with expensive replacement parts the owner returned it to the original state as being better. As Al points out new caps of the original value are the safest path to begin with. |
I second Bombaywalla's excellent comments, which I saw as I was just about to post the following:
As someone with significant experience designing op amp-based circuits (although not for audio applications), I am highly skeptical.
I would ask him what the manufacturer's part numbers are for the existing and the proposed replacement op amps. Post back with that information and I or someone else can look at the manufacturer's datasheets and hopefully develop a better idea of what the differences might be.
Also, ask him what other equipment he has tested this exact substitution on, and if that other equipment includes any electronic crossovers.
Some additional thoughts:
1)Substitution of a faster device, or a device that may be "improved" in other ways, in a proven op amp circuit design by no means guarantees improved performance. It amounts to a circuit redesign, which if not designed and tested carefully could just as easily degrade performance.
2)Op amp circuits are typically designed so that their performance is as independent as possible of variations in the parameters of the particular op amp, within the range of variation that can be expected for the particular device that is used. In other words, circuit performance is designed to be primarily dependent on the passive components that surround the op amps. Seconding 4est's suggestion about capacitors, I would expect that upgrading the 15 to 20 year old capacitors that are used to implement the crossover slopes would be more likely to make a meaningful improvement, with far less risk of adverse effects.
3)As far as I am aware technological advances in the last 15 to 20 years, that would be applicable to op amps used in audio applications, have been minor at best.
Regards,
-- Al
|
While it is true that technology has improved today compared to 1991, I would have to say that biggest trend today is that things have become more digital - HD TV, HD radio, digital modulation schemes for cellphone over-the-air protocols, digital cameras, Blu-ray DVD players, etc, etc. I.E. there is more & more emphasis put on the digital signal processor (DSP) piece of silicon inside a lot of electronics.
In the meantime, human-beings' audio range is still 20Hz-20KHz. I have looked at Analog Devices', TI's & a few other companies' standard parts catalog. Many of their standard off-the-shelf part numbers are the same as they were 10+ years ago. In fact, many of these companies pride themselves on this part - an off-the-shelf opamp part designed 10+ years ago is still for sale today (because it was a damn good performing part them & remains a damn good performing part today) & is still bringing in revenue. I even know some of the engineers who designed these opamps - they are still designing in the industry not necessarily for that same company.
So, the point here is that it is very likely that it is not your opamp that needs replacement (it very well could & it would be easy to find a similar replacement if your tech looked in the catalog) but you could definitely do with a replacement or upgrade to
* the diode bridge rectifier - use of FREDs or Schottky diodes (the sound of both of these is very different & some people prefer Schottkys over FREDs)
* a change-out of the electrolytic capacitors - use modern day computer grade or audiophile grade caps.
* a change-out of the resistors - use Caddock, Vishay, PRP, Dale, etc brand resistors or the very expensive Tantalum kind that Audio Note UK uses
* Upgrade the internal hook-up wires
* damp the overall metal chassis by using Dynamat (asphalt-based) or Cascade (vinyl based) or you can use the less expensive vinyl based stuff from Partsexpress.com
* upgrade the RCA jacks to any brand that your favour - WBT, Cardas, etc, etc.
* Make sure that your tech uses audiophile grade solder such as Wondersolder or Cardas eutectic solder or something else.
* Make sure that your tech cleans the PC board - all these years could have generated a lot of copper oxidation.
* One other thing to do is for your tech to touch-up all the solder joints just to make sure that there are not old solder joints & no cold solder joints.
I think that once you do all of this, you should have a more transparent sounding x-over. |
Oops,I may be wrong in that the crossover is possibly at 70 hz.
Another option, and maybe the best would be to eliminate the crossover for the Diva, instead using a capacitor only on the input of the amp on the highs. The slope may be different than what is there, but should sound better if done properly. My 2 cents.
Something like an older ARC tube crossover works that way- you could try one of those, as they are relatively inexpensive. |
I assume it is the Apogee DAX in your system photos. Seeing as from what I have read the crossover is at about 330 hz, I'd say there is a good chance of it being improved upon. That is if your technician knows how to do it properly. All op amps are not created equal. I do not know what it has in there. As for other things, power supplies have always been one of the most important parts of audio equipment. Anything that can be done there will be beneficial. Further more, as usual, any capacitors that have signal through them might ought to be looked at.
You may be better off buying a new one that is better all around... Bryston maybe. |
Crossover? How about a DAC? You have to give a model for us to have a clue? |
