Rotel RCD-971 Mods

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Background and mods

My first CD player was a Phillips CD820 mk2, an early 90's bitstream player. I didn't buy it as a serious source, just something to play the the few discs I had acquired. In fact, I couldn't listen to it for more than an hour without getting very irritated with the sound.
Truth to tell I didn't even try to extract the best from it, and rarely used it over several years.

With new vinyl becoming scarce, and titles limited, I thought it was time to look more closely at a digital source. Due to the recent emergence of the high definition SACD and (impending) DVD-A, I decided to buy in at the low end of the CD market until the new technologies settled.

I bought the Rotel RCD971 mainly on the basis of its widespread excellent reviews in the audio press (serious auditioning of anything in this city is impossible).
I was expecting something great but initial auditioning in my system was a disappointment. Out of the box, the sound was un-dynamic and the stage width shrunken (even compared to the 6yo Phillips). Fortunately these aspects improved greatly as the player 'ran in'. While listening fatigue was much reduced compared to the Phillips, the Rotel failed to 'come to life' in my system. I found the bass slightly overblown and images a bit bloated.

I came across a reference to the LC Audio CD player modifications and thought I'd give them a try. The basic mods offered by LC Audio (at the time) were a replacement master clock, the Lclock XO and substitution of the stock OPA2604 opamps with AD825 modules. I have fitted both. (See opamp substitution update below!)

I won't go into detail about the mods, the links above give full details and specific installation instructions for the Rotel RCD971.
I did, however, have to use a different location for the clock. The large 10000uF cap on the rear of my clock board would have caused the clock board to foul the top cover, if using the position shown in LC Audio's instructions. (Maybe they changed to a different cap at some stage.) The position I used is just about the only other free space available in the compact case of the RCD971 .

The picture below could be better. The clock board is mounted vertically, with the large cap bridging the HDCD chip and supported with a piece of cork and double sided tape. The board itself is secured with double sided tape on both sides. The 825 modules are to the right-hand side of the PCB, mounted close to their four power supply caps.

The modded Rotel RCD971:
modded RCD971

Opamp substitution

After installing the clock and AD825 opamps, I posted my results at Tweakers Asylum. A contributor, Thorsten Loesch, suggested I try the LM6172 opamp (one of his favoured devices).
I did and found the results excellent. The highs were a little more pure and the soundstage had great clarity and definition. The 825's were a little fuller and warmer sounding but both the AD825 modules and LM6172 sounded superior (IMO) to the stock OPA2604 regarding clarity and definition.
The LM6172 was just a little too lean sounding in my system, so I went with the more 'full-bodied' AD825 modules.
I've drawn the RCD971's output schematic, capacitor additions dotted in.

Update 9/03 - I've reverted back to using the LM6172!

The above comparison was made when using the 8150 integrated amp and before numerous acoustic treatment additions. With the CDLAD/8200P and room treatment, the system gained a richer, cleaner and more expansive sound. The AD825's subjectively bigger bass and midrange weight (perhaps the result of a more closed-in top end) began to bother me a bit in this setup.
When I put the LM6172 back in the Rotel, I found myself much preferring it.
The LM6172 had the more naturally balanced (i.e. realistic) mids and open top end. It also offered better bass articulation, in fact more detail and nuance from top to bottom. The superiority of the LM6172 is surprisingly large in my current system.

Thoughts on the Lclock XO upgrade

The Lclock XO upgrade had a broadband effect on the sound of the stock player. Everything sounds more cohesive and it even reduced the bloated bass I complained of in the stock player (this surprised me!). There was more 'snap' to transients. That mechanical fatiguing quality, that CD sound can exhibit, is reduced.
Is it value for money? I definitely think the improvements are worthwhile.
On a dollar comparison basis, I think the opamp upgrade is better value but won't provide the same benefits.

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