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Possible to use SHD as processor only? 2 months 1 week ago #57632

  • eisenb11
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I decided to roll the dice and get the preamp. I figure worst case, I can likely recover most/all of my investment if I decide I don't like it. I have a deal in the works and will fill in details if it goes through.

Given that we're putting the SHD up front, what are your views on how to handle the sub? I have two options:

Option 1: SHD -> preamp -> mains & sub
Option 2: SHD -> preamp & sub, preamp -> mains

For option 1, everything from the SHD is going into the tube preamp (has 2 sets of XLR outputs). I'll likely need to Dirac the system with the sub off. The sub (B&W DB3D) has it's own DSP which seems to work well. I can have the sub do room correction on itself. Then, adjust the trim on the premp to level match the mains and sub.

For option 2, I'll continue using the SHD to high pass the mains and low pass the sub. DSP on the sub is off. Then level match and Dirac both the mains and subs at once. With this, though, only the mains will go through the tube preamp so the sound will be a tube/SS hybid depending on where the sound is coming from. 

I'm kind of thinking that Option 1 sounds like the way to go, although Option 2 sounds like an interesting science project. Thoughts?

PS. Thanks so much for the help!

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Possible to use SHD as processor only? 2 months 1 week ago #57633

  • asx77
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Remember what @entripy said.. Dirac is the closest out of the DSPs to magic! No doubt in my mind, Option 2 is the way to go. SHD allows you to properly crossover your subs/mains and set appropriate delays. Use a fixed volume on the pre-amp and with the sub's internal crossover set to max, run Dirac for the lot.

Why worry about the hybrid? What you're proposing is already a hybrid with valve pre and SS power. You won't loose anything by having the sub's own solid state doing the really low stuff. In actual fact the bass should be tighter that way. 

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Possible to use SHD as processor only? 2 months 1 week ago #57634

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Sounds like a plan. Option 2 sounds like I can try to have my cake and eat it too. Wish me luck with the deal going through / no complications!

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Possible to use SHD as processor only? 2 months 1 week ago #57653

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Posting an update: good news and bad news. 

Good news: the deal went through and I purchased a used McIntosh C2300 tube pre amp. I have that paired with my current MC152 amp. The preamp is being fed by the SHD. I didn’t get around to doing a config (volume leveling, then a DIRAC run) yet. But I played with it a bit and my question is answered. I do like the tube sound. You do get a slightly elevated background noise floor when standing 2 inches in front of the tweeters, but not audible otherwise (my SS amp had tweeter noise too, just less). Hard to describe the tube sound as it’s really subtle with this setup (or maybe because I haven’t finished doing a config run), but I’d describe it as taking the edge off the sound. I listened to an old jazz recording where the transition between lyrics was really harsh and this made it sound pleasant. Tried out rap, R&B, electronics, and a bunch of other stuff and it all sounded great. No bass issues, but I’m also doing the hybrid thing and my sub bypasses the tubes as it’s connected to the SHD instead of the second output on the preamp (future science project for fun). 

Bad news: the preamp has a problem. Something strange in the left channel that’s causing a loud white noise sound regardless of input. Happens on both XLR and RCA outputs, but only left channel. The amp needs to be on to hear it, but if I turn the amp off I can “see” it because the left Vu meter keeps moving slightly even when nothing is playing or plugged in. Fortunately, I bought it from a Mc dealer so he had me drop it off at the local repair depot in LA. Now waiting for it to be repaired - hopefully doesn’t take too long but you never know with the supply chain issues today. Doubt I’ll see again it for at least 2-3 weeks - or longer depending on parts. 

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Possible to use SHD as processor only? 2 months 1 week ago #57654

  • asx77
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Glad you like it. Shame about the problem.

When I got my valve amp's, given they were second hand, after picking them up I took the covers off in a close by lay-by and saw all the power supply caps were bulging. Luckily I had arranged to drop them off at the OEM for a service on my way home from collection! These things happen with older equipment but the good thing about valve amps is that they long outlast solid state because anyone decent with a soldering iron can fix them as they're generally point to point wired. There's nothing inside it which shouldn't be next day deliver or even already in your repairer's stock cupboard. Who doesn't have a supply of resistors and capacitors?

Hopefully you'll have it back soon. Enjoy. 

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Possible to use SHD as processor only? 2 months 6 days ago #57659

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Update: Bad news and good news.

Bad news: I got a call from the repair depot and they said that everything is fine - nothing is wrong with the preamp. Went there and they had it hooked to a scope. Left and channel and right channel within 1 dB of each other. I told them to just look at Vu meter, you could see the left meter bouncing a tiny bit... The right is not moving... and it's the left side that's messed up, but they claimed that that's not unusual for tube amps and it doesn't affect the sound. Said that it's probably wifi interference or something. Brought it home, hooked it up and... left channel noise. Turned off all the wifi and wireless stuff nearby... no affect. Hooked it to another set of speakers and a different amp in a different room... same thing. Aargh. Measured 14 dB difference between left and right channels.

Good news: I figured it out. I swapped the left and right tubes and, sure enough, the noise moved from the left to the right channel. I had already tried swapping tubes earlier (there are 6 tubes in there) and apparently randomly grabbed another bad tube. Tried another tube and now I have silences instead of white noise and the 2 channels are within 1 dB of each other. So apparently it's bad tubes and this repair shop doesn't know how to do their job.

Now to get around to calibrating things and balancing in the sub.

Sounds like I have an excuse to roll some tubes... heard the Gold Lions and Telefunkens are good with this amp.

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Possible to use SHD as processor only? 2 months 6 days ago #57670

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Whenever I purchase a used piece of equipment with tubes I always replace all of the tubes with known good tubes. I do this before powering on the unit and I ignore the sellers claims. It's an expensive add on cost, but it saves lots of frustration. After I've done that, I check the tubes that came with the unit, one by one, and put these into a spares bin if they are good, and toss out those that are noisy.

I buy my tubes from a reputable seller, (tctubes.com). I don't bother going through all of their tubes on their website. I email them the make and model of the equipment and the tubes required, and they respond with several choices, with links to make ordering easy. They ship quickly and the process assures that I will have fully tested and known good tubes to start with and a spare tubes bin that contains good tubes.

I've never seen the point of tube rolling. (No criticism intended). I'm old enough to remember the tube testers that were a permanent installation in audio and tv stores when all that was available was tube gear. You walked in and tested the tubes yourself. I only have one tube amplifier now, mostly for nostalgia's sake. I really don't want to ever go back to those days again.

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Possible to use SHD as processor only? 2 months 5 days ago #57673

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Just finished doing the volume levelling and running Dirac. Wow oh wow - this was worth every penny and every ounce of frustration in getting the purchase issues sorted out. Sounds... absolutely... amazing. I'm done buying stereo stuff for a while (famous last words).

So in case anyone was wondering (like me) if Dirac goes and DSPs away all of the tubey goodness... the answer is no, absolutely not!
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Possible to use SHD as processor only? 2 months 5 days ago #57677

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I've never seen the point of tube rolling. (No criticism intended). I'm old enough to remember the tube testers that were a permanent installation in audio and tv stores when all that was available was tube gear. You walked in and tested the tubes yourself. I only have one tube amplifier now, mostly for nostalgia's sake. I really don't want to ever go back to those days again.


I'm in agreement to a point. I have the SHD straight into a pair of pure class A triode monoblocks each with two pairs of EL34s in push-pull after ECC82 phase splitter and ECC83 pre-amp valves. When I got them like you I was unsure the history of the valves so I change the lot. Asked a valve supplier in the UK for recommendations and went with that. But the TungSol ECC83s I received honestly made it sound like a blanket had been thrown over the speakers!

I spoke to the OEM and they said that tthere was little point tube rolling the output valves, but suggested the key valve wrt sound signature was the pre-amp ones so wasn't surprised what I'd found. I decided to put the original pre-amp valves in and ordered two to try from two one supplier (so said I could send the ones I didn't like back to him for a refund) and i ordered a third type from a second supplier who sent me the wrong ones at first but didnt charge for replacement so I ended up with 6 to try!! Conclusion, I have test tracks (actually just passages in certain tracks) that I use for critical listening and with the exception of the Tungsols (which were noticably bad) there was very, very, very little difference across the others. I had my favourites but tbh could live very happily with 5 of the 6. The biggest difference was the price!

I won't tube roll again but the experience now tells me that if I buy new (unlikely any time soon given my stock now!), I'd just compare the new with the outgoing valves and if there's no noticable difference then no need to try anything else.

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Possible to use SHD as processor only? 2 months 5 days ago #57678

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Tube (or transistor or op-amp) rolling is always very dependent on how the device is used in the circuit. Back when I designed tube circuits in the late 80s / early 90s I  found that the biggest place for change was in the power circuit, not in the power amp or pre-amp. But it all depends on the topology of each section.

Despite tubes being liked for the character of their non-linearities they are inherently more linear than transistors.

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Possible to use SHD as processor only? 2 months 5 days ago #57679

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Despite tubes being liked for the character of their non-linearities they are inherently more linear than transistors. 

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Possible to use SHD as processor only? 2 months 5 days ago #57680

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Current versus voltage only gives you the non-linear impedance of a device, not the typical transfer non-linearities in amplification topologies.

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Possible to use SHD as processor only? 2 months 5 days ago #57681

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What would that look like for say Triodes?

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Possible to use SHD as processor only? 2 months 4 days ago #57688

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www.aquinaudio.co.uk/valve_em_further.html

The first image is a transfer function of an ECC83 in a typical amplification stage. It could be described as a straightish bit in the middle, becoming increasingly less straight at either end.
A BJT (bipolar junction transistor) amplifier transfer function is similar, the last image at www.quora.com/What-are-transfer-characteristics-of-a-BJT for example.

The difference is the degree of straightness in the middle.You would never use a BJT amplifier circuit without copious amounts of negative feedback to linearise the straightish bit. With a tube circuit you would use far less negative feedback, or even perhaps none. You may end up with similar amounts of straightness but a tube will need less negative feedback to achieve that.  Note that both single BJT and single triode amplifier stages tend to invert, which is why the transfer functions slope the way they do.
 
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Possible to use SHD as processor only? 2 months 4 days ago #57689

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Oh Thanks that's interesting. The blurb that came with my amps describe them as low feedback designs. I guess in the 90s that was more of a thing, given more importance than it is today since these days I'm guessing the historical negative aspects of using negative feedback are all but designed out of amplifiers. 

Feels like these days there is more stigma around not using feedback. Am I right thinking that the lack of feedback means valve amps' output voltage changes slightly with impedance changes it is that not the downside?

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