Is dedicated PreAmp with Oppo 105 needed?


I think I've a decent HT setup but still feel there's something missing. I watch movies 70% & listen to music 30%.

Since Oppo provides pretty clean sound, wondering if upgrading to a dedicated PreAmp will make any difference. If it does, what would you recommend in say $1000-$2000 range? I intend to bypass the Video & connect straight to my Plasma on HDMI 1.4a.

Thank you!
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LRC Speakers: Tyler Acoustics Linbrook System II
Surround Speakers: JBL S312
Amplifier: Parasound Halo A51
BD:Oppo 105
Tape Deck: Nakamichi RX-505
Room: 16x18+ with some open area, so sound can bleed
hitsofmisses
Look at the NuForce AVP-18.
If you want to inject real tonal beauty,great dynamics and weight into your system give this pre amp a try. It is a tube based preamp. ModWright SWL 9.0 SE with tube power supply, they are around $1500 used.
The ModWright SWL 9.0 SE is only two channel.
I want atleast 2 XLR i/p & preferably 5 XLR o/p if possible. I'm also open to used & refurbed.

I've been doing a bit of research on various forums. How is Classe 600 or Anthem D2? I've also heard good things about Onkyo PR-SC5508/09, Herron Audio VTSP-1, Integra DHC-80.3, Theta Casablanca, etc.

How do they compare to the NuForce AVP-18 & ModWright SWL 9.0 SE?
That's a mixed bag. The Classe 600 is ancient by prepro standards. The same can be said of any Theta CB that would fit your budget. The Onkyo/Integras are OK. The Herron is stereo only. Of the pack, I would go with the Anthem D2 if it is a somewhat later version or a D2V.

You need to define your needs a little better.
Audio Advisors was selling NuForce MCP18s for $599. A steal. I bought one and never looked back. it is very very quiet and does nothing wrong.
Look at the Emotiva XMC-1, this is a VERY capable multi-channel preprocessor and offers the XLR connections you seek. It's only $1995 with 30 day in-home trial and a 5 year warranty - w00t!!

https://emotiva.com/products/pres-and-pros/xmc-1

-RW-
Kr4: You need to define your needs a little better.

I'm not sure what additional info I can provide. I need it for HT 5.1 setup with atleast 2 XLR i/p & preferably 5 XLR o/p.

Thank you!
Hits,

I'm a little confused about your system and desires:

1. Do you currently have no preamp in your system and exclusively use the Oppo 105 as a preamp?

2. If so, and you use your tape deck for music playback, how is it connected to the Oppo?

I currently use an Oppo 105 in my system and know it has very limited inputs. This works for me since for music I only use 2 sources: the Oppo's internal player for optical discs and a NAS that contains ripped files of all my CDs and a handful of hi-res FLAC files. I use the Oppo's wireless USB connection for all NAS file playback. But I don't understand how an analog tape deck could even be connected to the Oppo.

In my opinion, the only reason to use a separate dedicated preamp with an Oppo 105 is if your system requires additional analog inputs. The preamp section really does, as advertised and reviewed, perform at a high-end audiophile level.

I originally used a quite good dedicated tube preamp, a VTL 2.5 unit with 4 NOS Mullard tubes inserted for the standard issued Russian or Chinese tubes, when I first inserted the Oppo 105 in my system. A new VTL is slightly above your stated budget with an MRSP of $2,500 (add $200+ for 4 NOS tubes of your choice) but it has plenty of analog inputs and a HT bypass switch/inputs. This preamp, combined with my class D amp, performed beautifully for 2-channel music playback and I never thought I'd not include it in my system. Also, I had just inserted a 'new' set of NOS Mullards about a month prior when I purchased and inserted the Oppo 105 in my system. Needless to say, I was not planning on not using it.

However, just to be fair and objective, I compared the sound of my system with and without the VTL playing several very familiar CDs. Letting my ears decide, and with an admitted bias toward using the VTL, I reluctantly was forced to conclude that all tracks sounded just as good without the VTL in the audio chain. The sound was a touch warmer and more dimensional through the VTL but it became clear that these qualities were added to the sound. The Oppo was very neutral but had no trouble portraying warmth and dimensionality (think 3D and very real) when the recordings had these qualities.

So, I removed and sold my beloved preamp about 6 months ago. I can honestly state I haven't missed it since.

You certainly don't need a preamp/processor, such as an Anthem or Emotiva, since the Oppo's line stage is likely better and also has a very good internal surround processor that utilizes the highly regarded Saber DAC chips; separate chip sets for up to 7.1 decoding of DTS/Dolby Digital surround and another pair for 2-ch music digital-to-analog conversion.

My point is that a $1-2k dedicated preamp really won't result in better 2-ch music performance. Each will add its own qualities to your music but that's a lot of money for basically a buffer stage. I'd only suggest a dedicated preamp if you required additional analog inputs or listen to vinyl. I decided to adopt the most direct approach and eliminate all unneeded components and cabling.

The above is just my impressions on my system and your mileage may vary.

Thanks,
Tim



Hi Tim,

I do not have any preamp and exclusively use the Oppo 105 as a preamp.

Currently, the tape deck has been disconnected but I've lots of rare tapes that I would like to listen.

I was also thinking of the same but was not sure if PreAmp had any impact on the sound quality.

Thank you!
I'm not sure what additional info I can provide. I need it for HT 5.1 setup with atleast 2 XLR i/p & preferably 5 XLR o/p.

I got that. What else do you want it to do?

Hitsofmisses hi.

Your Oppo has a digital domain volume control, are you using it's 5 channels direct into your Parasound Halo A51, and the sub output into your sub?
As this is the way I would use it, so long as the digital volume control is at or above 75% of full output, if lower you may run the risk of bit stripping, which is not harmful just robs a little definition the further down you go from 75% of full.

From What/hifi measurements
"Please ensure you enter the setup menu and set volume to “Variable”, then lower the volume control to an initial setting of 45-50 before powering on your amplifier or active speakers after factory reset. Volume setting is retained in memory when the player is put in standby. So volume at power on remains the same as volume at power off.

Output impedance 7.1 board L/R front channels 100Ω

Output impedance dedicated stereo board L/R channels 100Ω

Output impedance 7.1 board all channels except L/R front 200Ω

Recommended amplifier input impedance is 47KΩ (Industry standard)

Peak output level: 2.1 Vrms (RCA / Phono)"

All these output impedances and 2.1output volts are a perfect impedance match for the inputs of your Parasound Halo A51 and whatever sub you use.

Cheers George
Hits,

Since you currently use your Oppo 105 as a preamp and it has no RCA audio inputs, you would require a stand alone separate preamp to be able to hook-up other components such as your Nakamichi cassette deck.

The preamp would be installed between the Oppo and your amp/amps. You have your choice of either RCA single-ended or XLR L+R outputs on the Oppo that you'd need to connect to the preamp's L+R inputs. The L+R outputs on the preamp would then be connected to your amp/amps.

If you do buy a preamp, remember to make sure it has the proper (RCA or XLR)input and output connections to match the Oppo and your amp/amps.

FYI,
Tim
kr4
I’m not sure what additional info I can provide. I need it for HT 5.1 setup with atleast 2 XLR i/p & preferably 5 XLR o/p.

I got that. What else do you want it to do?

Sorry, I think this is what you’re asking. :)

I use primarily for HT (75%) & 25% for Music that are heavy on vocals. I’m leaning more towards Tube based Pre-Amps since I like the warm soundstage. From all I’ve read so far, Oppo’s video processing is very good so I can bypass video on Pre-Amp & connect directly to my 1080P Plasma TV. 
[email protected]: Did I answer your question correctly.

Since the Parasound has 5 XLR inputs, do I need a preamp with all XLR output or an RCA would do?
And does it make a big difference if I connect Oppo via XLR/RCA combo than the HDMI for audio?
If you want to play your tapes, just buy a decent analogue to digital converter, rip your tapes to your NAS, and then sell your Nakamichi. You do not need a separate pre amplifier - your Oppo is perfectly fine for that. If inserting a pre amplifier changes the sound, the pre amplifier is at fault. By definition it cannot improve the sound, and only degrade it.
@hitsofmisses - wow 2-1/2 years later! I think the only thing that will work for you is the Parasound P7 multi-channel preamp.  The P7 does have XLR outputs.  I would recommend using XLR if you can.  It does provide better sound quality and also has higher gain.  

The only alternative is to get some type of HT processor.

The idea that “if inserting a pre amplifier changes the sound, the pre amp is at fault”. This is totally incorrect and goes against all audiophile ideals, it is based on on ideal that if a piece of equipment is good than it will sound no different from any other piece. The truth is that almost every audio device out there sounds slightly different. One of the purposes of a preamp is to help “shape the sound”. It is a tool that can be used by an audiophile to help achieve their goals for the type of sound they want.

I have have heard the Oppo 105 straight to an amp. It sounds good, but it can be slightly dry. A tube or Class A preamp can help add richness and engaging sound.
Well, my audiophile ideal is a completely neutral system that does not get in between me and the music as recorded. I do not want to be a surrogate mastering engineer, or take the place of the musician. I know this is an impossible ideal, but I at least will not add anything that changes the sound.
@ Kr4: "I got that. What else do you want it to do?"
I want to connect my Nakamichi Cassette Deck & want to enjoy a richer, warmer sound of Tube.

@ Willemj: Ripping the cassettes to NAS is an option but I’m keen on spending that much time. Besides, I love how the cassette assembly of RX-505 comes out & to see some moving gears.

I am willing to stretch my budget a little bit. 1.) How is Classe SSP-800 or something from McIntosh MX series or  Krell ( Showcase 7.1/  S-1200/ HTS) or Bel Canto (Pre6/ 2-3 units of DAC 2.7/ DAC 3), etc. whichever sounds better & can process relatively current Dolby & DTS format?

A Tube PreAmp driving all the HT channels will be cost prohibitive. 2.) Instead, can I just insert a Stereo Tube PreAmp driving the front two speakers & connect remaining directly to the Parasound A51?
3.) Or how about Modwright or other similar upgrade to Oppo 105?

Thank you guys!
5 months & no replies?

Anyways, I searched a lot for a decent multi-channel, audio-only preAmps. Apart from Classe (SSP-800, CT-SSP), Krell ( Foundation, S-1200, HTS) & a few McIntosh MX series, there are not many (desirable) options. However, there’s a lot of very good Stereo only preamps. And most have very positive feedback for Stereo only over multi-channel PreAmps.

Is there any way I can connect both, the Oppo 105 & Nakamichi RX-505 Cassette deck to the existing Halo A51 - 5 channel amplifier via Stereo only PreAmp to enjoy HT & Music both?

I might be overthinking here but I was wondering:
1.) On Oppo 105 can I use "XLR/ Stereo Out" >> to connect any Stereo PreAmp >> Parasound Halo A51 Amplifier & connect the remaining 3 channels (C & L/R Surround) directly to the Halo A51 (bypassing a PreAmp) to enable both Stereo & HT listening?
This way, I don’t have to buy another Amp for Stereo only and/or reach out in the back of the A51 to toggle "Input Select" switchm which is not convenient.

2.) Another option I was exploring was to connect Oppo via Toslink to a Multi-Channel PreAmp. But google search indicates that it does not have the bandwidth to carry the lossless versions of Dolby TrueHD, DTS-HD Master Audio, or more than two channels of PCM audio.

Toslink interface is BAD BAD BAD.  Don't use it unless you absolutely have to.  Digital COAX is always superior for any digital audio.

That being said, the Krell S1200 is a great preamp/processor, but only if you mod the power supply by soldering in huge 15,000uf capacitors.  The stock power supply is undersized, in my opinion.  Stock, it will give good sound, but it's a bit thin/bright in a way.

You are correct in that putting a preamp between the Oppo and the A51 can be done to improve 2-channel audio.  Look for one that has a HT bypass input, so that you can still use volume control from the Oppo.  What is your budget? 

Is there any way I can connect both, the Oppo 105 & Nakamichi RX-505 Cassette deck to the existing Halo A51 - 5 channel amplifier via Stereo only PreAmp to enjoy HT & Music both?
No- they have to be switched separately so that one source does not load the other.


@auxinxput: If I’m using S1200, I don’t need to use the Digital COAX. I can use the XLR/ RCA too, right? And wouldn’t that be better?
Do you recommend S1200 over other Classe & Krell Multi-channels preamps?
Do you know what type of capacitor will I need? Is it an easy switch? It’s been a while but I think I can do a bit of soldering.

@atmasphere: So basically, I will have to buy a preamp & a dedicated amp just to play the cassettes on RX-505 in Stereo only mode? Well, that sucks. In that case, it’s better to get the multi channel preamp. Hopefully, it won’t compromise the sound so much compared to Stereo Only.
@hitsofmisses Sound compromise is the name of the game.

If you don't want to compromise the sound so much, 2-channel equipment is the way to go. I would look into integrating it into your HT system; maybe look at a HT processor as an input to your 2 channel preamp and amp rather than a dedicated HT integrated amp; IOW using the amp and preamp to run your main speakers.

The reason is your HT will benefit from the improved performance of separates! 5-channel amps tend to run all 5 channels off of the same power supply, and that sort of thing is often audible as less authority and less detail.

If you do the power supply capacitor mods I will describe, I think the S1200 will be superior over any other multi-channel preamp/processor.  And yes, you can connect XLR/RCA analog audio directly to S1200 as well.  The S1200 uses fully discrete Class A analog stages (no op amps).  Below is a picture of the S1200 audio board, you can see the 8 separate audio stages for each of the 7.1 channels.  Each one of these would be a single opamp in another processor.

https://photos.google.com/photo/AF1QipOOZfHv-_iCrjXTkT3JayjSMG8FCYsl1DBGeygF


As far as I know, the only other processor that uses discrete Class A stages in Bryston SP3.  However, the Bryston is not as good in my opinion.  It is voiced differently.  It has a massive main power supply with big caps.  However, their analog circuits do not have any local capacitors.  As a result, the sound is very laid back, but with massive bass.  In the Krell board, you can see tons of local power supply capacitors for each analog stage (SMD caps).  These local capacitors give the Krell enormous amounts of resolution and attack in the midrange and highs.  Unfortunately, the main power supply on the Krell is undersized, which is essentially starving these Class A analog circuits.  The result is weak bass and a thin/bright sound for the mids/highs.

The Krell Foundation would not require any of these mods as it has very good power supply caps.  However, as far as I can tell, it uses op amps for audio stages and would not be as good as S1200.  The Classe SSP-800 also uses op amps.  So does McIntosh.

Below is a picture of the basic internals of S1200:

https://photos.google.com/photo/AF1QipOAbERmjfNnzPMRpWFmk_9qKW84yLNtow4FbGjA


The bottom board has 4 separate power supplies (each marked by a pair of capacitors).  The top HDMI/video board also has its own power supply.  On the bottom board, the first three power supplies are all shunt regulated.  Power supply on the left is +5V for the ESS sabre dac VREF power supply.  The two in the middle are for the +17V / -17V for the analog stages.  The one on the right is for +12V (and probably +3V) for digital sections and uses conventional LM78xx regulators (not shunt).  We really don’t care about the power supply on the right as it is just fine.

My mod does not replace any existing capacitors. It just adds additional caps into the mix.  Below is a picture of my mod.  For reference, the blue module on the bottom of the picture is the potentiometer for the front panel knob.

https://photos.google.com/photo/AF1QipOiGwC8a6DljI_Gy9hD0Dw9Rg8Q8AMVBI4yVEuJ


For the left DAC VREF power supply, I use a Nichicon KW 10,000uf 10V capacitor in parallel with a Vishay 0.1uf MPK (part BFC241641004) for stabilization.  I basically solder capacitor leads directly to the board pins for the AC/DC diode converter block (which is bolted to the case floor).  These are the outside pins of the 4 pins.  Make sure you solder the cap polarity correctly (negative to negative polarity and so forth).  Use a digital multi-meter to confirm polarity of the pins.  This mods basically adds capacitance to the DC sections of this power supply.

For each of the middle two +17V/-17V power supplies, I use a Nichicon KW 15,000uf 35V in parallel to a Nichicon Muse KZ 470uf 50V in parallel with a Vishay 0.1uf MKP.  The 470uf helps with the quick voltage needed for midbass punch while the big 15,000uf ensures the continues voltage required b Class A circuits is never starved and helps with strong deep bass.

In addition, I always recommend a mandatory fuse upgrade.  I like Furutech rhodium fuses for the highest resolution neutral sound.  If you have a very warm sounding amp/speakers, you could use a Hi-Fi Tuning Supreme to increase the attack/resolution.

You can use the S1200 as purely a 7.1 channel analog preamp if you want (using 7.1 audio from Oppo).  However, the Krell is absolutely excellent when doing tv/movie decoding using dolby digital / DTS, etc.  Be aware that the S1200 has had common problems with the DSP board which affects decoding of audio over HDMI (unstable audio with dolby digital, DTS-MA, loud pops when changing modes, etc.).  Krell has engineered a version 2 of the DSP board which fixes all the problems, but requires you to send the unit in for replacement and new firmware.  I’m not sure of the cost, however.

Using the S1200 as a DAC is not really great unless you have 24/48 over digital COAX.  The digital clock in the Krell is temperature controlled and is optimized for 48khz audio (for movie soundtracks).  It is absolutely excellent for this.  However, if you have 44.1 or 96 or 192 audio, it’s better to use a DAC.  The Krell will play high res audio over HDMI, but it is compromised.  It is compressed with no dynamics (compared to COAX) and does have a shouty or blare effect on the upper midrange.

Oh, if you plan to use Krell 1200 for video, look for a "S1200U 3D" model.  This is the last version they made and has the latest HDMI video board.

Sorry to go on and on in this.   There are actually a couple of S1200U 3D models up for sale on usaudiomart for $2800. Wow!  low price, actually. 

In most cases I agree with atmasphere's comment that a separate 2-channel preamp will be better (in most cases) than any HT Processor.  However, this Krell S1200 with my power supply mod is pretty freaking amazing, in my opinion.  I would actually put it up against many other 2-channel preamps (unless we are looking at Krell Illusion/Phantom with separate power supply level).

The S1200 does not support 4K video over HDMI (only 1080p).  If you don't care about this, then I would say S1200  would be the best ht processor choice and also great preamp for 2-channel analog sources.

Atmasphere also commented that 5 channel amps have shared power supply.  That is definitely a restricting element if you watch high volume movies.  When you are listening to 2-channel music only, it is less of a problem.  However, a separate Parasound A21 for left/right would definitely be an improvement.  Though, an S1200 preamp/processor would be a better first step.

Oh, and upgrading the main fuse in the A51 or A21 amps to Furutech rhodium will increase the body and make the sound less thin.

For education, the Krell S1200 can do lossless decoding and playing of the following audio formats, but only over HDMI (which is fine since you're using Oppo 105 as a source):

- DTS-HD MA (bluray)

- Dolby TrueHD (bluray)

- Dolby Digital Plus (such as Netflix streaming).

The S1200 is absolutely excellent in decoding and playing the above formats.  For all other decoding, such as old school Dolby Digital, DTS and 2-channel PCM, it is better to use digital COAX to transmit this.

@auxinxput: Can't open any of the pics.
The reason I would avoid running the Oppo directly into the amp is the volume control. Running it at lower volumes reduces resolution.

I would run a line section and use the Oppo with the volume up all the way, then use the volume control of the line section to set the right level. This technique works well- the improvement in resolution is easily heard.
Since I intend to pass Analog Audio (only) from XLR/ RCA (stereo & 7.1) of Oppo BDP-105 to Parasound Halo A51 amp via a preamp:

What you guys think of Parasound Halo C1, C2 or P7 preamp? I think they all have sufficient options for analog audio input & provides XLR output for the A51. 
Out of these 3, is there any model which will do a better job than another? 
I think with P7, you can not do room calibration using a mic. In that case wouldn’t a C1 or C2 would be a better option even though they are a bit outdated? 
Also, how do they compare to Krell S1200U? 

If you are a looking for a pure analog only preamp, the P7 is the best.  The C1/C2 are older and appear to have switching power supplies and power supply banks are not good enough.  The P7 has superior linear power supply and architecture.  It will not be nearly as good as Krell S1200, but it is very good for the cost!!

If you are looking for HT Processor on the cheap, there are better solutions than C1/C2.  Look at the Anthem Statement D2, which are going for just over $1k.  They are still older, but much better than C1/C2.

Marantz AV7702 or AV7703 are in the $1k to $1.5k range and are very good (better than the P7 because of the discrete analog circuits).  If you can stretch to $2k, the Marantz AV8802a is excellent. (look on ebay for these).

Of course, none of these are as good as S1200, but in the end, you get what you pay for.

Hello Auxinput:

Does the S1200 beat the HTS 7.1 in preamp mode?  Also, curious about your mod to the s1200.  Have you done this mod to other's (s1200s). I have the HTS 7.1 still cranking out in preamp mode sounds excellent, powerful.  Let me know.

Thanks,

Mdtrec

P7 and be done with it. Otherwise throw your money into a separate preamp and amplifier that kicks butt over your Parasound and Oppo stuff. Most audiophiles have a separate setup for music. HT Passthru is an option with the P7 to get the best of both worlds. Halo P51 can't hold a candle to a good 2 channel setup. Like you said, only 30% Music.
All, I appreciate this threat has been going on for a little while but as Krell S-1200 and Oppo-105D show both up whithout wanting to sidetrack - quick question: Has anyone managed to successfully connect them via HDMI (I use Kimber HD19). I get image but no sound, interestingly the same happens with my XBox One S (where I have disabled 4K Upsampling as well as HDR to avoid handshake issues). I get analogue signal from my phone pre-amp and realized that the display of the S-1200 does not say waiting for audio signal - anyone any ideas what could be off? Thanks. A.
How does Krell S1200 compare to Denon AVP-A1HDCI preamp for Analog audio? That's one beefy preamp.
Or the McIntosh C45, MX132, MX150?
Hello Hits,

     You really still haven't resolved your issue after about 4 years?

      I find this unacceptable and would like to help you finally resolve things.
     It seems to me you just need to buy a good new or used 2-ch stereo tube preamp with a HT Bypass switch and not a multiple channel preamp like some of the preamps (called prepros because they combine preamp functions and surround sound processor functions).  
     You have no need for this since your Oppo 105 will perform the functions of a surround sound processor and you just need to add the functions of a 2-ch stereo preamp for music playback.  A tube preamp will add warmth, texture and 3 dimensionality to your music playback and the HT Bypass switch will allow you to select surround sound playback from the Oppo.

     Please let me know if you'd like my further assistance.


Thanks,
   
 

@ noble100: Thank you for your consideration & reaching out to help.

There are multiple reasons why I haven’t jumped yet: 1.) I’ve limited knowledge. I came across very few multi-channel analog audio PreAmps/ PrePros (online) and even lesser number of comparison reviews/ opinions. 2.) I had some financial difficulties due to job loss & other factors. And I do recognize my budget is limited for what I’m expecting to achieve 3.) I’m extremely picky & would like to do things right the first time.

From what I’ve read, the sound straight from Oppo 105 can be very digital or clinical. That’s why, I’m looking for a Tube or Tube like sounding Pre/Pros that is good for both Stereo & HT (multi-channel) listening.

Not sure how a 2-ch stereo preamp with a HT Bypass works. But ideally I should be able to connect Oppo’s Stereo XLR/ RCA for music & 5 out of 7.1 RCA Audio for movies to my Parasound A51. Regularly toggling the "Input Select" switch is not an option. https://www.parasound.com/a51.php
Hello Hits,

    No problem, I'll help you out as much as I can.
    I actually use an Oppo 105 in my system, too. I use my system about 60% for HT (TV and movies) and 40% for 2-ch stereo music. I currently use the Oppo as the preamp without a separate 2-ch stereo preamp but previously used a VTL tube preamp with a HT Bypass switch to add a bit of warmth, texture and dimensionality to music. Here's how a 2-ch stereo preamp with HT Bypass works:
    For preamp connections, the Oppo's stereo XLR/RCA left and right outputs would be connected to the preamp's "processor" inputs. The preamp's left and right "processor" outputs would be connected to two of the Parasound A51's input channels.  The Oppo's rear left/right rear surround and center channel rca outputs would remain connected to three of the A51's rca inputs.
    The final step required is using the Oppo's remote and going into the "SETUP" menu, selecting "Audio Processing", scrolling down and selecting "Stereo Setting" and then selecting "Front Left/Right". This just instructs the Oppo to send any 2-ch stereo info on a disc, such as a CD, to its Stereo XLR/RCA left and right outputs.
    For music, you leave the HT Bypass switch in the 'OFF/OUT' (not engaged) position and only the left and right stereo channels are played back on your main speakers.
    For TV and movies, you leave the HT Bypass switch in the 'ON/IN' (engaged) position and only the front left and right surround channels are played back on your main speakers along with the center and rear left + right surround channels being played back.
    As I mentioned earlier, I originally used a VTL 2.5L preamp, that utilizes four vacuum tubes and has a HT Bypass switch, in my system for music playback and its ability to quickly be switched to playing back the front left and right surround channels for HT. At the time, I also used a set of four expensive Mullard NOS (new old stock) replacement tubes in the VTL preamp and a Parasound AVC-2500 surround sound processor.
      Several years ago, in an effort to streamline my system, I decided to compare the performance of my system with and without the VTL preamp and Parasound surround sound processor. I found that my music sounded just as good to me without the VTL/tubes and that the 5.1 surround system actually sounded better to me decoded by the Oppo's internal ESS Sabre dac chips and with the Oppo's audio outputs connected directly to my amps. I attribute this excellent performance mainly due to the Oppo 105's exceptionally high quality audio section, dac chips and design.
      My main intent of describing all of this to you is to stress that you're unlikely, in my opinion, to find a better performing preamp than the one already existing in your Oppo 105. The VTL 2.5L tube preamp I formerly used is a very well reviewed and high quality preamp that costs about $2500 new with the standard Chinese or Russian tubes and another $200 for the aftermarket set of four Mullard NOS tubes I believe further enhances its performance.
      I've proven to myself that using a separate high quality tube preamp is definitely capable of altering or flavoring the sound of all the source content played through it and that the specific tubes utilized are also capable of further tailoring the sound to match one's preferences.           However, I ultimately discovered that the combination of a high quality music recording, played through a neutral high quality solid state preamp (like the Oppo 105 represents by adding or subtracting nothing from the inputted signals) and amplified by a neutral high quality solid state amp (like a high class D amplifier represents by adding or subtracting nothing from the inputted signals), is a more honest and simpler alternative method of achieving extremely good sound quality performance in my system.
    So, my question for you is what direction would you prefer to take? Would you like to buy an expensive new or used tube preamp and prove what I discovered for yourself? Or would you rather take the more honest and simpler alternative path of utilizing neutral high quality components, such as a more neutral high quality multi channel amp, to achieve extremely good sound quality performance in your system?
    I should warn you that an honest and neutral high quality system will not hide or mask anything. Optimum results require very good quality music recordings and any of your music that's not well recorded will suddenly become painfully obvious to you. But good recordings will sound extremely good and you'll also more clearly notice the sonic effects of any changes to your system, even smaller changes such as upgraded power cords or cabling.
    I'll stop here and await your impressions and questions thus far before continuing any further with my assistance.

Thanks,
  Tim

Not sure how a 2-ch stereo preamp with a HT Bypass works. But ideally I should be able to connect Oppo’s Stereo XLR/ RCA for music & 5 out of 7.1 RCA Audio for movies to my Parasound A51.
You don't actually need a HT bypass switch. You can use any preamp with a home theater processor. If there is no HT bypass you simply set the volume control to a particular position and let the HT processor handle the rest.


Since the Oppo and your amp are balanced, it makes sense to use a balanced preamp. I don't agree with Tim's assessment above though- a good tube preamp will give you a more neutral/natural presentation than solid state and will be less irritating in the high frequencies.  This is because solid state in general has higher ordered harmonic distortion that is more audible than it is with tube gear. I don't like the 2nd harmonic 'warmth' coloration that is often blamed on tubes but if your preamp is fully differential and balanced that harmonic will be absent. In general though tube preamps have far less of that sort of thing than amps so its not a big deal.

What might be a bigger deal is how the preamp handles balanced lines. There is a standard for balanced operation called AES48 (Audio Engineering Society file 48, although the standard was around long before the AES itself). Very few home preamps with balanced operation (tube or solid state) support this standard! The standard is quite useful as the interconnects used with the preamp won't impose any sonic footprint (that is part of the reason the standard was devised)- you won't have to audition cables to get the system to sound right and be neutral. When the gear does not support the standard all bets are off. So its a good idea to check with the manufacturer to see if their preamp supports the standard. When asked, it should be simply 'yes' or 'no'; if the answer gets much longer than that there's a pretty good chance that the manufacturer doesn't support the standard and may not even know what you are talking about (FWIW our gear does support the standard). One of the aspects of the standard is the input impedance of your amplifier will not be an issue- any device that supports the balanced line standard should be able to drive a low impedance line which might be only 600 ohms, so the typical 10K to 47K input impedance of most solid state amps will be a breeze.


If the preamp you select employs an output transformer then you will have to pay attention to loading the transformer for optimal bandwidth. I mention this because in the balanced standard, the output of the preamp floats with respect to ground; each side of the output signal (pins 2 and 3 of the XLR) reference each other to complete the circuit rather than ground. This is done to prevent ground loop problems. A transformer is one way this is accomplished; the only other way I know of is the method we patented, which is direct-coupled.
Hello atmosphere,

     Thank you for pointing out accurately that a HT Bypass switch is not technically necessary on a preamp since using the proper unity gain position on the preamp's volume control can be used as a substitute.  I was trying to keep the ease of use and concept understanding as high as possible because I wasn't sure of Hits' technical knowledge and audio experience.
      I've always really enjoyed listening to music played back via a high quality completely tube based system even though I realize it's not completely accurate and is imparting a 2nd harmonic warmth or coloration to the music.  Years ago, I understood that tube distortion tends to become audible on even ordered harmonics, that sounds much more pleasant to us than solid state distortion that tends to become audible on the odd ordered harmonics.   But I was building a combination stereo music and 5.1 surround HT system and knew that an all tube system was impractical.
      So,  I originally added the VTL tube preamp and swapped the standard tubes for NOS Mullard tubes in an effort in my system to attain the 2nd harmonic 'warmth' coloration that's often blamed on tubes, and that I liked, because I thought it was the only method to add that characteristic to my system's sound on stereo music playback at the time. 
     I began by pairing a good quality tube preamp with various good quality class AB solid state amps.  I never considered utilizing an amp to attempt to improve the sq performance of my system until I purchased an inexpensive Class D Audio SDS-440-CS amp that was a revelation to me.  This amp had extremely low measured distortion levels and the most accurate and neutral quality that I'd ever experienced in an amplifier, like the audio ideal of 'a straight wire with gain' with nothing added or subtracted from the inputted signals.  I considered the stunning neutrality of this class D amp a revelation and it began my thinking of the possibilities. 
     I only discovered a while later, through personal experimentation, about the alternative method of using very well recorded music sources played back via high quality and very neutral components along with very detailed and revealing speakers.  I found out that this type of system would also reproduce music in my room that possessed the warmth, detail, texture and three dimensional palpable qualities I really enjoyed experiencing when listening to music.
      It only required the combination of a neutral high quality preamp (the Oppo 105's preamp section), a neutral high quality amp (the Class D Audio amp and subsequently a pair of D-Sonic M#-600-M class D mono-blocks) and detailed and revealing speakers(a pair of Magnepan 2.7QRs) to achieve the sound qualities I previously thought only a tube preamp could provide.  
     Now it's just a matter of whether the recording is of a sufficiently high quality level to have captured the natural music qualities of warmth, detail, texture and other palpable characteristics. I think I couldn't achieve these results using my VTL tube preamp because it wasn't neutral enough but I realize you may have good ideas of how to accomplish these sound characteristics using a combination of more neutral tube components.     
     It's a bit of a compromise that the better the quality of the recording, the better the music sounds but I consider this prerequisite completely natural, logical and acceptable given the outstanding sound quality results. 

Thank you,
   Tim
  
Based on @atmasphere & several others suggestion, I've dropped the idea of getting a HT PreAmp. 

For a while, I explored the idea of getting 60s & 70s Fisher Tube receiver/ amplifier. However, since I don't have experience troubleshooting (I can do soldering), I would not like to get stuck with a set of expensive, dead equipment that I cannot use. The repairs on this can go upwards of $500 + Parts + S/H. 

Instead, I'm thinking of spending extra upfront & getting a used tube Stereo PreAmp or an Integrated for around $3000. It will sit in-between the Oppo 105/ Nakamichi Cassette Deck & Parasound Halo A51 Amp. 

Based on all the positive reviews, Atma-Sphere would be my first preference. However, they're very hard to come by used & definitely haven't seen anything in my budget. Apart from that, I've also read positive reviews about PrimaLuna, VAC, Conrad-Johnson, Audio Research, McIntosh, Cary Audio, Stanely, etc. They all have some good & some products to avoid. 

Any recommendation on Brand or a specific model over others?
If you can do single-ended one preamp in your budget is made by Don Sachs.  Another is made by Backert Labs
Schiit Freya Plus. Return privileges if you don't like it.  I'm betting you'll keep it.

Tom
Sony ES TA-P9000ES 5 channel audiophile class preamp.
@atmasphere: I looked at both the sites & the price of their products. Don’t you think I’ll get more value for my money by getting a used VAC or CJ or ARC products then paying the same amount for a brand new product from them?

@tomcarr:  I don’t think Schiit products are in the same league. 
I looked at both the sites & the price of their products. Don’t you think I’ll get more value for my money by getting a used VAC or CJ or ARC products then paying the same amount for a brand new product from them?
@hitsofmisses You often get more for the money buying used! So yes :)