Budget preamp with quality volume control

@kr4 Silly me. Schiit gears are the same. I was confused at the time when I include the Benchmark and Cambridge all-in-one units in the group comparison.  I have taken out which category. Thanks.

@jtcf Rogue entry level tube preamp RP1 is more affordable, feature packed and has received favorable reviews. Look promising but, with the similar money, I stumble across also well-received Integrated amp Pharaoh mk 1 (hybrid tube preamp used) for sale.  Do you have experience with it? 

@audioman58 Thank you for the coveat on the Alps / Bourne pot. Regarding AGD Master 19, I just listen to MidFi Guy channel where he stated, on the positive side, wide SS, smooth, polite and affordable price but, on the flip side, not as precise, of clarity as its competitor almost like "tube amp in the solid state form." So, it seems there are coloration / distortion applied on notes through the amp, and that is sort of contradicting to transparency, neutral attributes I prefer from a preamp. But your recommendation is appreciated. I do have an eye on its big brother Master 9 though which AGD claims to be neutral and least color sound (but same claim is on Master 19 as well), but it is sort of difficult to come across reliable review on these Chinese made product.

I am going to put Rogue RP-1 (used slightly over a grand), and Freya + too, in my list for now and expand the list to cover pricier units.

Great. One of the reason I did not include Freya + in my list is because I do not want to bother with tube replacement in the long run. But Schiit says they have longer lasting alternative called solid state tube, LISST, that triggers my interest. What do you feel about them, @audioman58, @ditusa and @riie if you don’t mind? Do they really sound good as claimed? If not, what are the good choices? 

Yes, @zlone, interestingly I thought about that too. For example, I was really in self debate as to how much weights I should place on "remote." Nowadays not having remote for a stereo system is a crime but then the quality of remote is also an issue too like Topping’s. Aside from that, quality of volume control and power supply are certainly two other criteria should receive heavier weight. I sort of address the power supply issue by adding a proper cost to the units not having linear / xformer power supply.

@tomcarr Toppings are raved by many reviewers / users including the class A rating by Stereophile (for Pre90). At the same time, one of the popular reviewer (do not wish to mention his name) critizes the A90D actually sounds only mediocre. In particular, he emphasizes the initial attack from A90D is impressive, weighty but that is pretty much it. There is no significant micro dynamics and reverberation coming after that, making the amp sound too analytical / surgical. My question to you is do you feel that is a general sound traits of Topping based on your listening experience?

Thanks, @rtrlover.  By reading its description on PS Audio website,

"At this instrument's heart is the analog GainCell. Rather than using additional sonically-degrading elements inserted in the signal path to control volume, the GainCell eliminates this problem without additional circuitry in the signal path by varying its gain in response to front panel controls."

I assume that the volume control is applied in the analog stage but not 100% sure.  Especially, if I was not mistaken, Paul has mentioned that he think the digital attenuation is a better way for volume control.  Do you know?

@zlone  Good to know the universal remote work on the Freya+. I will probably get one if I do clinch the Freya+ but I am still torn between several candidates mainly Pre90, Freya s/+ and Rogue RP1.

The passive preamp Schiit SYS is first thing I tried. Although many people have attested it is a good sounding preamp, I found the low end notes thru it are softened. High end notes are restrained and less airy. On the paper, the SYS’s output impedance is as high as 5k ohms so the ratio of load impedance to its output does not reach the desired 10. It has impedance mismatch issue. I am not thrilled by it and that is the reason I am only looking at the active preamp with gain.

Neverthless, I will keep looking into Khozmo preamp while its spec. seems not available even on its own site. Thank you for the recommendation.

@audphile1  I have looked that option earlier.  Since I have hard time to pay $1000 for 1st Watt B1 buffer preamp, the only option I have looked is the Zerozone Pass X1-B Buffer Preamp from Aliexpress for around $230 incl. shipping.  But unfortunately, ZZ pass x1-B only works with Pass amp. If you know other source pls let me know.

@zlone My amps should be fine with Freya.  Two are 33k and one 20k. Thx

As mentioned earlier, after trying out Schiit SYS, I no longer consider passive preamp. I suspect the degraded SQ, i.e., soften lows and restrainted less airy highs, is resulted from the mismatched impedance. In addition, the headroom becomes fairly limited because of signal loss. Most of passive preamps have pretty high output impedance and unavoidably create mismatch issues with my amp (20k ohms - 33k ohms). I could not locate the specs for Pacette passive linestage even on their website but suspect its output imp. is no exception. But thank you for the thoughts.

@pwayland I could not find that gain stage info in the manual for my Parasound amp. The control on the back are the unity gain control whose function, as you know, is to throw away some of the preamp output to get the main volume control in the region one likes best (gain staging process). I am not sure if I could simply get rid of it but I could max it out so there won’t be any variable resistor in the signal path. Then I could use Active preamp without gain in lieu of with gain (like you said) to adjust the volume. At the mean time, I could also bypass the digital attenuator in DAC by switch the volume to the "fixed" mode to avoid sound degradation. By reading the specs, the SPL Volume 2 as you have suggested or several Schiit products such as Freya, Asgard 3, Jot 2, or Magnius on my list will serve that purpose in addition to impedance matching. These Schiit products also come with active w/ gain so is handy when needed. Thank you that really helps me to eliminate a few other choices.

Btw, while reading the tech info. (as shown below) in SPL Volume 2 manual, it really explains what I have experienced with the SYS... It is actually a much better passive preamp compared to the cheap in-line attenutor I purchased for the sub. I therefore decide to retain SYS for my sub. instead.  

Active or Passive?

It is claimed that passive circuits are less signal influencing and more puristic and therefore better. Well, that is not so.

A passive control element such as a potentiometer in the signal path, which is not electronically buffered, influences the frequency response and phase position. Both change continuously as you change the volume.

This is exactly what does not happen with an active control.

As many of you know, the basic relationship between the signal transfer (in terms of voltage) ratio to impedance between output (source) and input (load) is

Vi / Vo = Ri / (Ri+Ro+cable impedance), where V = voltage and R = impdenace

For a standard 75 ohms interconnect cable, without loss of generality, if your preamp output imp. is roughly comparable to the cable impedance, Vi / Vo = Ri / (Ri+2Ro). As a rule of thumb, it is desirable to have Ri is at least 10 times higher than Ro. The corresponding Vi / Vo = 83%. There will be 17% signal loss, acceptable (see below for the coveat) but not ideal. If Ri is 100 times Ro, the Vi / Vo ratio will be 98%, only 2% signal loss and will be deemed ideal.

In @jpasko01 case, i.e., Freya -> Bryston 4B3, Ri = 100 Ro and therefore the signal loss is only 2%. The pariing should work like charm. In the case of a passive preamp SYS (Ro = 5000 ohms) into my Parasound A23 (Ri = 33k ohms) where the ratio is merely 6.6, the Vi / Vo = 33000 / (33000+5000+75) = 87%. This 13% signal loss is significant enough to cause noticeable sound degradation that I heard. This demonstrates that the ratio of 10 is just a rule of thumb, the ratio should be as high as possible like 100 to be ideal. Since I have not seen a passive preamp impedance is lower than 5k ohms, practically only the active preamp is possible to achieve an ideal impedance match.

@tyray Thank you.  I also like what I see from this review. How do you like its DAC?  In particular, how are the soundstage width and depth?

https://positive-feedback.com/Issue72/wyred_mpre.htm

@zlone is correct. The reasons, as shown in the "measurement" section, are (for Freya)

The active balanced output impedance was the same with or without the tube stage operating. It was close to 810 ohms at 1kHz and 20kHz but increased to 6900 ohms at 20Hz. The buffered unbalanced output impedance at 1kHz and 20kHz was inconsequentially higher than the specified 75 ohms, at 90 ohms. However, it rose to 3100 ohms at the bottom of the audioband. With the tube stage operating, the unbalanced output impedance was 3267 ohms at 20Hz and 1200 ohms at 1kHz and 20kHz.

Especially on the low ends from either output, the output impedances are much higher than the specified 75 ohm.  Frequency dependent impedance, interesting, needs to be watched for.  Lean something each day.  Thank you.

I actually enjoy to read about the hardship that Steve Huffman went through when he heard the transformer buzz/hum from his over $10k Luxman and then found the Puritan 156 to finally tame it down. My Parasound amps have a bit transformer hum as well that I need to 2 ft close to hear it but is enough to trigger my irritation.  I was doing the similar things, i.e., DC offset and Monster power conditioner, trying to get rid of it but without success. It is tempting but I could not justify spending $2k to cure the hum of $1k amp.

I found a used mPre selling for $700.  Is it a fair price? It is such a pity that its DAC section only supports up to 24/96 (usb) and 24/192 and no DSD. Well, let me sleep on it.  

The classic Adcom gfp 750 and Apt Holman recapped can still be found at a affordable price but Ayre k1x or Threshold Fet 10e would cost over $2k.  They must be the crown jewels top of the line back then.  Thanks for the recommendations.

+1 @mitch2.  Thanks for the elaboration.

In-line attenutor is just a fixed output passive preamp as opposed to passive preamp with variable levels of attenuation. Not clear what "Indus" is but if Rothwell refers to their in-line attenuator, the output impedance is stated as 3750 ohms, a bit lower than the Schiit SYS (5k) but still high enough to reduce the impedance ratio (approx. 8.6) down below the desired 10. Note that the cable I was using is merely 12 inch long and my Parasound amp has a reasonably high 33k ohm input impedance. It is still likely the company’s in-line attenuator will impact on the sound quality as SYS does. As such, I have no longer considered the passive preamp or in-line attenutor option.

Some active (with gain) preamps also have attenuation function in addition to amplication, such as SPL Volume 2 (-4 dB) and some others. All the Schiit active preamps starts from a "amplication factor" (Schiit refers it as "gain") of 1 which gives no volume (dB) increase/decrease. The formula is 20*log(amplication factor). So amp. factor of 1 give 0 dB. When the amplication factor is less than 1, say, 0.63, change in volume is 20 log(0.63) = -4 dB (like SPL Volume 2 mentioned above) indicating that the preamp is actually performing attenuation. Those active preamps with gain is exactly what I am shooting for.

Yeap, it is under my radar. Did you find the tube in RP-1 changes the sound signature as compared to SS pre? I often heard the tube (for other preamp) just serves as a buffer and does not change the sound at all. But I hope that is not the case here. Also, have you tried the tube rolling before and does it change the sound?