RAAL-requisite: The Official VM-1a Discussion Thread

[Makiah S]

RAAL-requisite’s all new standalone ribbon headphone amp the VM-1a features a dedicated variable mode tube circuit design exclusively for driving ribbon headphones. Capable of operating in Ultralinear, Triode or Pentode mode, this top of the line amp delivers uncompromising performance RAAL's SR-1a headphones.

This custom built amp features variable mode select for: Ultra-Linear, Triode, and Pentode Operation modes. This direct drive vacuum tube amplifier is compatible with all of RAAL-requisite’s ribbon headphones. It has selectable SR-1a open-baffle compensation and CA-1a non-compensation for both outputs. It also has a 24-step precision attenuator which is ideal for precise channel matching. On top of that, it has transformer balanced inputs (left/right) and outputs for simultaneous dual headphone operation. Toroidal output transformers and the toroidal power transformer are all magnetically shielded and epoxy cased. Lastly, the amp allows you to select between 115V and 230V voltages, which is great for those who want to use the amp in different regions of the world.



Features
Ultra-Linear
Power Output: 15W
Bandwidth Frequency Response: 20Hz - 70kHz, -3dB
Triode
Power Output: 10W
Bandwidth Frequency Response: 10Hz - 70kHz, -3dB
Pentode
Power Output: 20W
Bandwidth Frequency Response: 30Hz - 50kHz, -3dB
Specifications
Input Tube: 1x Tung-sol GTB 6SN7 Dual-Triode
Splitter/Driver Tubes: 2x Apex Matched Mullard EL34
Output Power Tubes: 4x Apex Matched Mullard EL34 Quartet
Input Impedance: 50K ohms
Input Sensitivity: 2V
Distortion: < 1%
S/N Ratio: 72dB
Weight: ~29lbs​

​

 

[FLTWS]

sub'd
The obvious question.
What is this?

 

[Ciggavelli]

sub'd
The obvious question.
What is this?

Naim dac/streamer

 

[Makiah S]

Naim dac/streamer

mmhm, Uniti Atom, it was a nice match but I like the Brciasti M3H a little more given just how resolving SR-1A and VM1a are together. So I'll likely swap out the images soon,

Also, enjoy some spoilers for an upcoming review [and forgive the lack of crop haha]

 

[jlbrach]

I am curious about this amp...I have the 1b and like it a lot...I have just gotten the Tl box and I have been listening to the sr1a out of my bakoon 13r with the converter box and I really like it...it is more tube like sound to my ears...soundstage is even wider....

 

[jlbrach]

I do hope to hear more about it

 

[FLTWS]

I did see someone mention (I believe it was on this thread) that they preferred the sound of Triode and Ultralinear over Pentode. I hope to order mine (VM-1a) next week.
I have a variety of tube and SS and hybrid HP amps, I always feel tubes have the sound I prefer. It is possible to tune an SS design to have some tube like traits/characteristics, but they never really give me that full bodied "there-ness" I hear with tubes.

I'll definitely be comparing it to my HSA-1b down the road.

 

[Roasty]

if the input sensitivity for this amp is 2v, does that mean I have to reduce the dac output/volume (by a fair bit) to accommodate it? rockna Wavelight/holo may xlr out at 5.8 vrms.

 

[justin w.]

The amp has a volume control which is going to attenuate the input signal, I assume. so if the volume control is in that traditional position then you can't have an input signal too high unless you turn the amp's volume up too much

 

[Makiah S]

The amp has a volume control which is going to attenuate the input signal, I assume. so if the volume control is in that traditional position then you can't have an input signal too high unless you turn the amp's volume up too much

I also had a chance to speak with Danny about the subject

His recommendation was to keep the volume pot at about noon and just adjust the output level of the DAC if it is available especially, if you’re using the 5.8 line outs of your Rockna over the 3-pin XLRs

The Bricasti M3h has such a feature and I find that it works successfully with the VM1a

 

[Roasty]

@justin w. and @Makiah S thanks very much for the help and information!

 

[Jon L]

Is there any reason I should not try to power my 111dB sensitive/8 Ohm compression driver with Raal VM1a amplifier? I would, of course, make appropriate adapters to connect the speaker cables correctly out of the front headphone XLR connectors.

 

[Roasty]

some early impressions on this amp.

built like a tank. really heavy and feels super solid. looks really cool on the rack.

- 1.6A fuse for 230v units may not be a good match/rating. I have blown four 1.6A fuses in the past 2 days. a 2A fuse is running well so far.

- ultralinear mode sounds very good. very clean with well extended highs. lots of depth, space and clarity. low end is not as good/strong as speaker amp to Ti1b box or Triode mode; it is fast and tight but would be nice to have more amount, punch and weight/oomph.

- triode is my preferred mode on this amp. bass is less tight than Ultralinear but is made up for by amount, extension, rumble. top end is less extended, and there is less space/width than Ultralinear mode. mid range is killer on triode mode, very lush and full sounding.

- pentode is very upfront with lots of energy in the upper mids and highs. super fast sounding but overall a bit lean and sterile/anaemic. I'd probably not see myself using this mode much.

- lots of power. with mitch filters (which I'm assuming has some -dB preamp gain), I'm running the sr1b at volume knob around 12-13 out of 24. I can get up to 15 and still be quite comfortable (ie no tinnitus) but at 16 and above its a bit too much for me.

- still early days but quick a/b comparison to my pre/speaker amp + ti1b, I'm getting better space, a more balanced presentation, and stronger bass with the ti1b than the vm1a on Ultralinear mode. on triode mode, the vm1a bass is more comparable to the ti1b setup, but I end up missing the top end detail/clarity and overall staging. if there was an "in-between" ie triode mode mids + bass with Ultralinear top end, that would be perfect!

all in all, it is an amazing unit if one wishes to have a dedicated amp for the sr1b/ca1a. there is always the price comparison to a dedicated pre/power combo, not forgetting the additional costs of interconnects, speaker cables, power cords etc. I'm not making the comparison to the price of a normal headamp because I have tried ferrum and wa33 into the ti1b and IMHO it just doesn't do the sr1b justice.

- on turning on the unit, there is a rather long wait for sound to come out; Raal mentions this is normal and is due to the autobias ramping up slowly. it would be good for future revisions of the manual to include this information.

that's it for now. as mentioned still very early days. am going to observe and see if I have any further issues with the 2A fuse, and if not, am going to try an SR purple.

some questions for the Raal guys:

is it possible to use the xlr OB compensation adaptors with this amp for even more low end? or not advisable?

for the EL34 tubes, if I swap them out, do I have to swap all 6 tubes at one go or I can do it in pairs ie one each from L and R sides of the amp, leaving the other 4 stock?

 

[Catharus]

some early impressions on this amp.

- 1.6A fuse for 230v units may not be a good match/rating. I have blown four 1.6A fuses in the past 2 days. a 2A fuse is running well so far.

Congratulations @Roasty!

Thanks for reporting your experiences with fuses on 230V. That will help me in the coming months as I fire mine up in Europe.

I am curious about the front panel printing. It looks cleaner than on my unit and what is in the user manual.

 

[Roasty]

I am curious about the front panel printing. It looks cleaner than on my unit and what is in the user manual.

you're right.. I didn't realize that until u pointed it out. and I'm kinda glad I got the revision faceplate.