[Monolith]

****WARNING****
Modifying your unit can void your factory warranty.  If modifications are professionally done, ask whether the modifications will void Carver Pro's 5 year warranty.  Modifications to power supplies can be especially dangerous.  IF YOU ARE NOT COMFORTABLE WITH YOUR SKILL LEVEL, DO NOT ATTEMPT THE MODIFICATIONS.  Modifications are done AT YOUR OWN RISK.  Sometimes the obvious needs to be stated....on with the modification discussions....


Purpose of this Thread
My intent with this post is to consolidate modifications in a single thread.  Hopefully, along with the edit feature, this can be kept up-to-date and possibly cleaned up in a better format later.


NEW Section - Modification Pictures:

Link To Gordy's Carver Amp Pictures in the Gallery[/b]


ZR1600 Main Board Photo:
Click Here ---> ZR1600 Main Board[/b]

ZR1600 additional photos are posted at:
Click Here ---> ZR1600 Photo Album[/b]

ZR1600 schematics, parts layout, and board traces are found in a single PDF file at:
Click Here ---> ZR1600 Schematics, Parts Layout, & Board Traces[/b]

Tripath Chip Datasheet is found at: (Note:  Gain, Rin, and Cin formulas are found on page 9.)
Click Here ---> Tripath TA0104A Datasheet[/b]

For Rin & Cin on ZR1600 board layout (under wind tunnel), see:
Click Here ---> Under the Wind Tunnel Layout         



Bypassing the input board altogether (suggested by 8th Nerve - tested, less grain), the parts in the direct input signal path (in order) are:

Ch1[/u]
                                    
C201----0.47uF                     
C202----10uF/35v NP            
U202A---LM833(SM).................Dual Possible replacements: OPA2604 (easiest, tested), OPA2134, AD variants                     
C215----0.47uF                    
C216----10uF/35v NP        
U203B---LM833(SM).................Dual Possible replacements: OPA2604 (easiest), OPA2134, AD variants                   
C219----0.10uF                     
C223----0.10uF                    
U203A----LM833(SM).................Dual Possible replacements: OPA2604 (easiest), OPA2134, AD variants               
R240----2.21k(SM)                     
U206B---LM833(SM).................Dual Possible replacements: OPA2604 (easiest), OPA2134, AD variants                   
R263----10.0k(SM)                       
R264----10.0k(SM)                     
U206A---LM833(SM).................Dual Possible replacements: OPA2604 (easiest), OPA2134, AD variants                    
R246----100R(SM)

Suggested by Occam (tested 10/31/03) - The above components can be bypassed altogether and the signal fed into R405/C406.  This will, however, make the high/low pass & limiter non-functional.  This leaves the following two elements directly in the signal path (suggested by Occam):
             

R405----100k(SM)         
C425----0.47uF  

R405 and C425 can be adjusted for gain when going directly into the Tripath chip at pin 5  

Click Here ---> Under the Wind Tunnel Layout         


Ch2[/u]
     
C204----0.47uF
C203----10uF/35v NP
C202B---LM833(SM).................Dual Possible replacements: OPA2604 (easiest, tested), OPA2134, AD variants
C217----0.47uF
C218----10uF/35v NP
U205A---LM833(SM).................Dual Possible replacements: OPA2604 (easiest), OPA2134, AD variants
C221----0.10uF
C225----0.10uF
U205B---LM833(SM).................Dual Possible replacements: OPA2604 (easiest), OPA2134, AD variants
R241----2.21k(SM)
U207A---LM833(SM).................Dual Possible replacements: OPA2604 (easiest), OPA2134, AD variants
R265----10.0k(SM)
R266----10.0k(SM)
U207B---LM833(SM).................Dual Possible replacements: OPA2604 (easiest), OPA2134, AD variants
R247----100R(SM)

Suggested by Occam (tested 10/31/03) - The above components can be bypassed altogether and the signal fed into R403/C405.  This will, however, make the high/low pass & limiter  non-functional.   This leaves the following two elements directly in the signal path:
 
R403----100k(SM)
C420----0.47uF

R403 and C420 can be adjusted for gain when going directly into the Tripath chip at pin 6

Click Here ---> Under the Wind Tunnel Layout         



Occam By-Pass Mod - Status: Tested[/u] (a.k.a. "where oh where to tap into the signal lines...." <--- See link immediately above this paragraph.)

If capacitors C201 (10uF NP Ch1), C202 (0.47uF film Ch1), C203 (10uF NP Ch2), and C204 (0.47uF film Ch2) are removed, this would permit convenient soldering points for soldering in by-pass wires for the incoming signals.
Click Here ----> Signal By-Pass Jumper Start Point

The signals (Ch1 & Ch2) need to be jumpered to a point after resistors R246 & R247 (respectively), which are immediately after U206, pin 1 and U207, pin 8 (LM833's) (respectively). R246 (Ch1) & R247 (Ch2) are surface mounts. It is an option to remove these and temporarily tack the other end of the signal by-pass wire to the outgoing surface mount resistor pads.
Click Here ----> Surface Mount Resistor R246 & R247 Location (two bottom surface mount resistors in photo)

The signal trace lines are routed around the wind tunnel nylon stand-off and across the front of the main board.
Click Here ----> Signal Trace Paths After R246/247 (fourth and fifth trace lines from bottom in photo)

The signal traces then go to the underside of the main board through "vias."  The signal traces on the underside of the board are about 1 inch and 3/4 inch long vertical traces that go through another set of "vias" and back to the top side of the main board.
Click Here ----> Signal Trace Paths Underneath Main Board (signal trace "jumpers" are the two vertical copper traces in center of photo)

The signal traces emerge from under the main board into the dark recesses of the wind tunnel shadow.....
Click Here ----> Signal Trace Paths Enter The Abyss (signal traces emerge from "vias" under wind tunnel)

A suggested permanent mod would be to remove the wind tunnel and the 0.47uF caps (C420/425, Ch1/Ch2, respectively) and surface mount resistors (R405/403, Ch1/Ch2, respectively) and replace them with higher quality parts that allow easier point-to-point wiring for the by-pass.



Output Board[/u]

Click Here ----> Maxim Class D Audio Amplifier Output Filter Optimization Article

Suggested by _scotty_ (untested) - Eliminate the smaller chokes from the output board altogether.  Also, possibly run the output directly from the main chokes on the main board, bypassing additional caps and chokes.


Output Connectors[/u]

ZR1600 OEM Binding Posts
Click Here ----> ZR1600 OEM Binding Posts Photo

Superior Electric BP30-2BR (tested, direct replacements)
Click Here ---> Superior Electric Binding Posts - See Page #5[/b]

Click Here ---> Allied Electronics[/b]

Click Here ----> Superior Electric Binding Posts Installed - External
Click Here ----> Superior Electric Binding Posts Installed - Internal


WBT Midlines (tested)


Fans[/u]

OEM Fan 60mm - Constant Velocity 23.5CFM (34.5db)
Click Here ---> Sunon KDE1206PTB1[/b]

Papst 612NGMI - Temperature Dependent ~ 10-22CFM (10db to 28db)
Click Here ---> Papst Temperature Dependent Fan Model 612NGMI[/b]

Papst 612NGL - Constant Velocity Fan ~ 11.2CFM (16db) (tested, much quieter than OEM fan)
Click Here ---> Papst Constant Velocity Fan Model 612NGL[/b]


Input Connectors[/u]

WBT Midline RCAs (tested)



Power Supply[/u]

ZR1600 OEM Main Bridge Rectifer - 400Volt/25Amp
Click Here ----> OEM Main Bridge Rectifier Data Sheet (MB254W) in ZR1600

Click Here ----> IXYS FRED Bridge Rectifier (#VBE 17-06NO7) <35ns, 600v/27A
M. Percy sells, possible replacement, but different pin pattern than OEM and flanges add extra width (OEM cost ~ $5, IXYS ~ $20) (untested)

Click Here ----> EDI Ultrafast Bridge Rectifier (#BRUS340W) <50ns, 400v/30A (untested, should be drop-in replacement)


Harris in +/- 15volt DC supply rectification
Click Here ----> OEM Diodes in ZR1600

Click Here ----> Harris RHRD660 Data Sheets

Click Here ----> Harris RHRD660 Installed in ZR1600


ZR1600 OEM 5 Volt Regulator L7805CP
Click Here ----> OEM 5 Volt Regulator  Data Sheet (L7805CP)

Click Here ---> Photo of OEM 5 Volt Regulator

Occam's suggested replacement:  (Tested on 12/6/2003 (MC7805ACT))
Click Here ---> OnSemi's 5 Volt Regulators - MC7805

[Occam]

Monolith,

In reality, the only ICs required for the operation of the ZR amps, as an 'audiophile' amplifier, are those found on page 5 of the pdf schematics. (plus the 7815 and 7915 linear regulators of the low voltage rails, which could be replaced with 317/337[or other] adjustable, and better functioning regulators). By 'audiophile', I mean the minimal requisite circutry needed for operation as a power amplifier. This is by no means a criticism of the CarverPro amps, it is simply an acknowledgement that much of the circutry (high/low pass, limiting, volume control, level leds...) is superfluous for 'audiophile' use, but needed for 'pro' use. At minimum, one might consider bypassing the 5 opamps/channel and 2 singnal path cpacitor pairs (np electo and bypass) in the signal path found on page 3 of the schematics, and also eliminating the 'signal present' and 'limiting' functionality. As is, the signal passes throgh these 5 opamps, whether one uses their functionality, or not... With some jiggery-pokery, one might leave the houskeeping functionality found on page 4 of the schematic, intact, without impacting the sound quality, bypassing the circutry on page 3 and the input board, and feed the dang thing with a preamp directly.

The schematic I'm referring to, can be found at -
http://www.carverpro.com/2003/products/zramps.html
upper right where it says download ZR schematics.

Additionally, IMO, the powerline filter, housed within the IEC receptitcle is there for FCC sec 15 compliance, not for improved sonic quality. It should be replaced with filtering that is less likely to saturate its small inductors and provide both compliance and improved sonics. But that costs money...

Upgrading the Input board (replaceable on the 1000/1600) is really a superfluous execise, considering the rest of the circutry, and its funtionality is there simply to provide conversion of possible balanced input to the amps requisite single ended signal (and adjustable input sensitivity). Certainly, high quality RCA inputs and those wonderful Superior BP30 binding posts would yeild improvements.

As to whether a 'streamlining' of the ZR amps would improve the subjective quality of the amps, that would depend on the users own metrics.

I've no doubt that sprinkling BG caps in the signal path and BGs and/or Jensen 4pole caps in the power supplies would also change sonic perceptions and I assume for the better, but given the complexity of the signal path, that might not be the most direct route....

Obviouly, these amps provide a tremendous material value, and my comments are not a criticism considering the intended market and economic realities of manufacture. CarverPro is running a very efficienct, low margin, high value operation.

[Monolith]

Monolith,

In reality, the only ICs required for the operation of the ZR amps, as an 'audiophile' amplifier, are those found on page 5 of the pdf schematics. (plus the 7815 and 7915 linear regulators of the low voltage rails, which could be replaced with 317/337[or other] adjustable, and better functioning regulators). By 'audiophile', I mean the minimal requisite circutry needed for operation as a power amplifier. This is by no means a criticism of the CarverPro amps, it is simply an acknowledgement that ...

I like your approach.  I will attempt to locate C405 and C406 physically on the board to see what needs to be done to accomplish this.  I'm not sure it will be conducive to some folks who like to see the green leds light up, but it suits me.  I have a bad feeling that some of the caps are under the wind tunnel next to U405 chip.  I agree that change is not always "change for the better," but it's fun trying.

Thank you for your input!

[Monolith]

Monolith,

 Additionally, IMO, the powerline filter, housed within the IEC receptitcle is there for FCC sec 15 compliance, not for improved sonic quality. It should be replaced with filtering that is less likely to saturate its small inductors and provide both compliance and improved sonics. But that costs money...

If you have some suggestions for powerline filtering parts, let me know and I will update the list.

[Occam]

The only capacitors in the direct signal path that are neccessary for the operation of the 'real' amplifier, that Tripath chip, U405, are C420 and C425(.47mmf) on page 5  of the schematic. These are absolutely required, as they not only block dc offset from the IMO 'superfluous' circutry, but also allow for the injection of the requisite bias (nominally +2.5v) provided by the required servo opamps U403 and U404 (a very nice approach to providing the required bias and elimination of dc offset at the speaker outputs. EDIT [I'd previosly suggested adding an additional passive highpass that I'd overlooked on the schematic. I wouldn't touch this lovely servo circuit anytime soon.] Those input caps cannot be eliminated!. As these caps operate with a required dc bias, much of the criticism of elecrolytics in the signal path are obviated, although this is a situation where replacement by BG type N or C electrolytics might yeild substantial subjective improvements.  A multicap RTX might be better, but I don't know how you'd shoehorn them in and they're very expensive.  The caps C405 and C406 are 'on' the signal path, and are there to shunt high frequecy noise to ground, and should remain.

[U401, a switching regulator that provides the required 100ma+, floating 12volts above the negative power rail, scares me, simply because I'm not familiar with that chip...]

Ideally, one could connect a high quality coax(s) (belden 89259 or something of equal quality, but thinner) to the positive input of the input connecter(s) on the input module, or the outputs of your (possibly modified or replaced) input module, and leave everything connected (with a big 'but! to follow), and route those coaxs to CH1Input & CH2Input, as on page 5 of the schematic. The shield(s) would be connected to the ground side of respectively, C405 & C406.  Most of the indicators, the level leds, overload, etc... would work, those functions driven by the speaker level output of the amp.

Now here is that 'but!'

1. The HP, LP, Limiter?... features would not work, and should be disabled. All that I've describe as 'superfluous' would be outside the audio chain, if you do the following-

2. You've got to cut 2 traces on the main circut board, so that the unprocessed audio signal is delivered via the 'direct' coax, and not the 'superfluous' circuitry, those 5 opamps (plus possibly those on the input module), and 2(+) capacitors,  per channel.

3. If you jumper directly from the input jacks on the input module, you give up the bridging capability.

4. You'll inevitably not get the grounding right on the first try, and have to muck about with it to eliminate loops and noise.

5. Inevitably, I'd make the amp "blow'd right up", and with such surgery, couldn't expect any recourse through CarverPro.

And the benefits are -

While not trivial for the first optimized  'minimalist' implementation, hopefully, subsequent implementations are quite easy, requiring the connection of 2 coaxs and cutting of 2 traces. Even if you bypass the input module, your drive requirement from your preamp is at most 2.5volts p-p, 1.76v rms, or if you route through the standard input module, .72v rms, into a high input impedance.

You've eliminated, per channel, 2(or more) signal path capacitors and 5(or more) opamps. It shouldn't hurt.....

And obviously there is the power supply. Replace the 1N4004s with the fast/soft recovery, or Shottkeys of your choice. Howzabout Telefunken's (Vishays) 'cause the name evokes such kewlness? The bridge could use discrete Fairchild STEALTHs! Don't know how these would sound in this specific application, but those names should certainly convey some bragging rights... And gazillions on name brand ps caps...

And if the transformer secondary on the low voltage winding permits, replace the 7815/7915 with a higher voltage pre-regulator chips, and for non critical needs drop additional voltage with zeners, and for critical needs, choose a discrete local regulator(s).

But the major changes would be architectural, taking opamps and caps out of the signal path, and they are also the 'easiest'.

About that IEC noise filter, I'm sorry I mentioned it.... but will comment after I give it some thought.

If anyone is masochistic enough to read the schematics, I'd appreciate any comments, corrections......

[Monolith]

I'm more than likely going to go ahead and replace the op amps with OPA2604's since I have them on tap already.  I will use the Harris diodes because I have them already also.  I am a little concerned about hole size on the mainboard because blackgates tend to have large leads.  I will probably do a straight value for value upgrade in quality on power supply capacitors to see the effect.  I think most people would be interested in the effects of "upgrading" their amps first, before a major redesign.  At that point, I will begin cutting to the heart of the matter as it were and completely bypass the peripheral controls (level, high/low pass, etc.)

I will try to get back with you on the servo mods.

Got the Vishay's in the CD player...

Thank you again for your comments.  It definitely adds value to this thread.

[Occam]

I believe the function of that power filter  is to filter the Tripath chip's  switching frequency (FCC Sec 15 compliance). Its amount of needed  inductace, determined by the switching freqency and the IEC's capacitors' values, and hence its potential to saturate, is substantially less than a filter who's function is to minimize the impact  of noise entering the amplifier through the AC line and from line frequency rectification. To provide a single place filter that would provide better sonics  for the amp itself, as well as keeping crap from the amp from polluting other components would be quite difficult, requiring substantially better measuring instrumentation than most of us can access, as well as substantially more expensive AC filter components.

Additionly, the amp provides the .1mmf cap accross the transformer primary, capacitive 'snubbing' accross the Tripath's rails' bridge rectifier, and provides local rail decoupling on all the integrated circuts; impressive. I'd consider, as a future possible modification, of addling additional capacitances accross the transformer's secondaries. Those values would have to be determined by 'rule of thumb' and verified and adjusted by experimentation.

 I'm curious as to what impact various external line conditioners provide.

[Monolith]

There are several posts here on AC about Dezorel units bringing the digital amps to life. Read that the digital amps are very appreciative of good conditioners.  I have no first hand experience though.

[Occam]

From 8thNerve's thread -
http://www.audiocircle.com/index.php?topic=5347

So here is a rundown of the mod package:

-WBT RCA Inputs
-Audience Auric Hook-up wire directly to an IDC connector on the main board, bypassing the input card. This allows you to put the old ribbon cable back in and use the input card at a later date if you so desire. It will also allow you to use any other aftermarket or Carver Pro cards that may be released at a later time with no soldering at all. Simply pull the new IDC connector out.

-Papst silent fan. This is the quietest fixed speed fan available in this size. From Germany.

-Audience Auric Hook-up wire from the output card to the Binding Posts
-WBT Binding Posts

All very cool! Now it's verified that the Input board circuitry can be bypassed. The next question is can the direct RCA inputs be easily routed to CH1-INPUT & CH2-INPUT as shown on pg 5 of the PDF schematic? The bypassing of those additional 5 opamps and 2 signal path capacitors/channel is still the purist's route. Admittedly, you forego the level set, highpass, lowpass, and the limiter functions, but how many of us need that functionality for our specific purposes? A 'switchable' mod, allowing either the driving the amp normally trough the original XLR/Eurobloc with all the 'pro' functionality, or a purist mode bypassing both the input cicuitry and those 5 additional opamps could be implemented by adding 4 pins, 1 added resistor and cutting one trace  /channel on the main board.  One position of the jumper bloc connecting the pins would route the signal across the now cut CHx-INPUT trace providing 'stock' functionality, and the other orientation taking the added RCA's specific input directly to CHx-INPUT and also routing those 5 opamp's final output to ground through another 100k resistor. Voila!

[Monolith]

I believe the connection point for Ch1 and Ch2 is under the wind tunnel. I'm trying to verify that.  I could not find them visually on the board.

[Occam]

I believe the connection point for Ch1 and Ch2 is under the wind tunnel. I'm trying to verify that.  I could not find them visually on the board.

SonOfABeach.... it appears you may well be right. If those connection  points are in that space as shown in your gallerey -

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=122

it might be possible to still impement that purist mod via a low profile right angle header on the main board, sitting below the tunnel and using jumper blocs that fit the headers. Dunno...

If someone in the NYC area would be kind (foolish?) enough to let me take their ZR apart, and back together, I could give a more definitive answer. I'd do the mod, gratis, if desired and if possible. If there's a willing 'guinea pig' out there, PM or email me.

[audiojerry]

Monolith and Occam,
I've been following your discussion - pretty heady stuff. Once you fella's have ironed things out and implemented the mods, please get back to us and supply a review of the sonic results.

I have the Dezorel LAF-mkII unit that has been passed about for auditioning. If you are interested, I think we can arrange to let you try it. Shipping cost would be minimal, plus a $15 audition deposit for those who have tried it. (We still need to come to a consensus on how to sell it and split the proceeds). I plan on trying it with the Sony AVD-C700ES when Sony finally makes them available.

[JCC]

Stan Warren now has two ZR's and will soon be starting his modifications. It should be interesting.

[Monolith]

Who are the lucky owners?  AC members?

[Occam]

Monolith,

I just reread your original post, and realized that you pointed out the possibility of bypassing all of the active circuitry prior to the Tripath chip.
Dang! It must have been one of my increasing frequent "senior' moments. That post is amazingly comprehensive. Kudos.

I've done a bit more schematic surfing and think that the direct input points to the Tripath chip, bypassing all those opamps, CH1-INPUT & CH2-INPUT on Page 5 of the schematics, are connected via 'J601' amd 'J602' referenced on page 3 of the PDF schematic. If these 'J's refer to wire jumpers, it might well provide an ideal access point, that one could directly access, with the simple expediency snipping those jumpers and routing the audio signal directly to the Tripath end of those links.

I don't actually have a ZR amp, but from  pictures and your comments, I believe those jumpers are located at the front of the amp, direcly underneath the cooling tunnel. Though it might require removing that heat sink tunnel (unless the jumpers were located on the underside of the main board), the existance of those jumpers?, is heatening.... If that "J" refers to jacks, so much the better.

[Monolith]

Monolith,

I just reread your original post, and realized that you pointed out the possibility of bypassing all of the active circuitry prior to the Tripath chip. Dang! It must have been one of my increasing frequent "senior' moments. That post is amazingly comprehensive. Kudos.

No senior moment! Kudos are for you!  It is my desire to update the mods list as new approaches are suggested.  Thus, the comments in the first post are from you!    Good job!

I've done a bit more schematic surfing and think that the direct input points to the Tripath chip, bypassing all those opamps, CH1-INPUT & CH2-INPUT on Page 5 of the schematics, are connected via 'J601' amd 'J602' referenced o ...

Hopefully, I will obtain this information in a week or so.  I will let you know how the board is laid out.  I dropped in some Hyperfast diodes in the 15 volt supply last night and looked the board over again.  There are parts under both ends of the wind tunnel and not easy to see.  The bottom of the wind tunnel is actually screwed to the heat sinks!     In order to remove the bottom of the wind tunnel, all heat sinked parts must be either unscrewed from the heat sinks or desoldered from the main board.

I am looking at ways to replace the main power diode bridge and had a couple of considerations.  Let me know what you think:

Click Here --->Harris Hyperfast Discrete Diode RHRP3060
Click Here --->Harris Hyperfast Stealth Discrete Diode ISL9R3060G2/P2

My main concern is in dissipating heat from the discrete diodes.  Any suggestions? The main OEM diode bridge is heat sinked to the case wall.
Click Here --->ZR1600 OEM Diode Bridge Photo

[8thnerve]

The Papst 612NGL - Constant Velocity Fan ~ 11.2CFM (16db) has proven to be quiet enough.  As long as you use rubber washers to stand the fan off from the metal wind tunnel, the fan is virtually inaudible.  It can be heard if your ear is closer than a foot from the units front where the fan exhausts, but even at that it is close to silent.

Also, if you wire directly to the main board, you will be choosing to use the amp in stereo or mono mode, unless you wire a switch of some kind right after the RCA inputs.

Any talk of the parts on the output board?  This should be easy to bypass, and should provide favorable results.

[Occam]

Keeping current thinking on the first post is an excellent idea. It is a tremedous boon for the efficiency of this thread, a centralized point for access to the 'knowledge' (such as it is...)

Re the Fairchild Stealth Rectifiers -
Variously known as Harris, Intersil and now Fairchild due to corporate machinations, they're thought to be the cat's meow by Bob Crump, who knows what he is talking about.  The 2 amps I've heard that used them for high current rail rectification (one production, one a mod) were lovely. But I've not tried them as a mod myself, so can't render any first hand comparisons. A selection guide, with the configurations and specifications can be found here -
http://www.fairchildsemi.com/collateral/igbtrectifier_sg.pdf
WARNING! its a big PDF

You could bolt 4 discrete, TO-2xx package, diodes to a purpose made heatsink, to package a pin-for-pin replacment. The heatsink would simply be made from a piece of aluminum, sufficient to provide thermal hyteresis and dissapation. It would be a central square, with 4 rectangles entending from the square's edges, which you'd bend perpendicular to provide surfaces to which you'd attach the diodes. A square sized perfboard below would position the doide leads and allow the requisite interconnections. (Note the cathodes of these diodes connect to the metal tabs, so attachment to the heatsink will require silpad or mica thermal pads.) Its easier to do than describe. Fairchild also makes dual, common cathode versions of some of these, so one could make the replacement bridge from one cc diode dual and 2 singles.

[Monolith]

You could bolt 4 discrete, TO-2xx package, diodes to a purpose made heatsink, to package a pin-for-pin replacment.

Which form factor provides the best heat transfer, 220 or 247?  I may end up ordering more than I need because of small part quantity prices/shipping/handling.

[Occam]

The Papst 612NGL - Constant Velocity Fan ~ 11.2CFM (16db) has proven to be quiet enough.  As long as you use rubber washers to stand the fan off from the metal wind tunnel, the fan is virtually inaudible.  It can be heard if your ear is closer than a foot from the units front where the fan exhausts, but even at that it is close to silent.

Also, if you wire directly to the main board, you will be choosing to use the amp in stereo or mono mode, unless you wire a switch of some kind right after the RCA inpu ...

Thanks for the info on the Papst! You make a good point about direct connection and bridged drive. Reliance on the input board's dual opamps and topology for providing the balanced signal required for bridging elicits the following proposal-

Keep those great, added direct input RCAs, that you came up with, and add another RCA specific to bridged drive needs and that switch, that would feed a balanced driver ic such as a DRV134. These chips are the darling of various BridgeKlone builders, and have an excellent reputation, for that specific purpose.
http://focus.ti.com/lit/ds/symlink/drv134.pdf

This would add the minimal circuitry need to get the job done, though 2 $100+ Jensen transformers would probably be the best route. I doubt whether CarverPro has implemented full blown differential amplifier technology on their input board required for solid state optimization of PSRR and CMRR.