Preamplifier (tube) to match my full-range speakers and 45 SE/DHT amplifier.

[Lautreamont]

Dear everyone,

The upcoming weeks are exciting, as I will be receiving my new full-range speaker drivers (12" Rullit-inspired alnico drivers with the original Telefunken frame) and a custom-made 45 SE/DHT amplifier with Finemet output transformers, C3m driver tubes, a choke power supply, and interstage coupling with amorphous transformers. Initially, it will include a volume control so I can use it as an integrated amplifier, but in the future I would like to add a separate preamplifier to the chain.

First, it would be helpful to elaborate on the role of a preamplifier and what it can potentially bring to an audio system. My understanding is that some people believe the preamplifier is a crucial element, while others don’t necessarily feel it adds significant value.

Second, I want to remain within the tube-based approach, and I’m leaning toward commissioning a custom-built preamplifier. I’ve been quite fascinated by the blog “Glow in the Dark,” where I discovered many talented builders, including Oliver Sayes, who is also the maker of my upcoming amplifier. I have considered finding a used Shindo preamplifier or ordering one from Yamamoto—the latter being more convenient, though the delivery time is difficult (six months).

I’d like to know which components, circuits, and tubes are considered the best for preamplifiers—whether that means DHT designs like the 27 or 10Y or other topologies. A clearer explanation of the options would help me focus my search.

Important information:

• I listen mainly to classical and jazz, mostly smaller ensembles, though I occasionally listen to orchestral works.
• My listening room is relatively small (about 25 square meters).
• I will be using full-range speakers and the amplifier mentioned above.
• I care deeply about natural sound, as I am an amateur musician.

 

[THD+N]

Since Sayes is building your amp, why not your pre-amp?

 

[paul_b]

Hopefully you have a powered subwoofer to go with this. My experience with the Finemet/Audiofeast transformers is a rather profound lack of bass.

The C3M in triode mode has a few hundred picofarads of miller capacitance. That in parallel with your cables will provide a bit of a load to a preamp, so an active linestage would be a very good idea.

 

[Techu Shi]

@Lautreamont, you're moving pretty quick to be considering Shindo already! Get the 45 in play and see how you like the sound before adding more tubes.

A preamplifier gathers signals from your various sources and handles volume control. It usually adds some gain between sources and the amplifier (active linestage functionality) but it doesn't have to. It can also add 'tone' to the signal being input to the amp, most often via use of tubes.

Running a source into your amp and using its volume control should let you know if you need an active linestage. As @paul_b mentioned above you probably could use one with your amp. Rather complicated to explain all the reasons in a single post.

Preamps usally have two poles as far as tone. One school tries to add nothing to the signal, just deliver it as if the preamp isnt there. These are usually transformer based or SS The other school uses tubes to add 'tone'. These can be placed in front of a big old SS amplifier, hopefully giving you the warm tone of tubes with the massive power of SS. Or they can add additional tone to your tube amp. Shindo combines his tube pre-amps with tube power-amps to get the full Shindo sound. There are no end of combinations of tubes people will put together that way.

"The pre amp is the most important part of the system." Usually people mean that it is doing the most delicate amplification, from the very small line level signal. If it does a bad job it doesnt matter how good your power amp is, the resulting sound is bad. I personally think its an overstatement but not by much. If you're going to use a preamp its not the place to skimp.

Finally Id suggest you study up on impedance matching before purchasing any preamp because youve been told 'this one sounds good'.

As far as tube selections, circuits and parts for a tube pre Id take a look at simplepleasuretubeamps , Aric Audio | Audio Excellence , and a few other high-end builders to see what they're doing these days. Perhaps someone else here could suggest some example sites as well.

 

[RPMac]

That “Glow in the Dark” guy opens a deep rabbit hole.
Don’t ask how I know….

 

[Techu Shi]

That “Glow in the Dark” guy opens a deep rabbit hole.
Don’t ask how I know….

Yeah, he seems like a 'first drug' to a lot of people, me included. Very pretty photography, very effusive language.

At this point I have mixed feelings about his site though. On his home page he states he'll only post 'overwhelmingly positive impressions' and that "this is not a review site." Good enough, but internet searches generally dump you right to the 'review' (commentary?) page where no such disclaimer is posted.

After listening to some of the exact same amps ( he sells his 'review' amps on USAudiomart, or at least has done so in the past ) I no longer trust his opinions. They didn't jibe with mine on sound and build quality at least. Given his niche, small-scale and custom amp manufacturers, you'd expect a few duds but you'll never get that from what he posts.

 

[THD+N]

More audio hyperbole at its thickest. If you are designing, building and selling amps, you should also have some kind of test data to show some level of performance. Usually there is none, which makes their opinion mean very little to me.

 

[Lautreamont]

Since Sayes is building your amp, why not your pre-amp?

Sure, that would be most convenient and I might end up with that. For now I would like to get to know more about preamplifiers in general and what components that are considered important.

Hopefully you have a powered subwoofer to go with this. My experience with the Finemet/Audiofeast transformers is a rather profound lack of bass.

The C3M in triode mode has a few hundred picofarads of miller capacitance. That in parallel with your cables will provide a bit of a load to a preamp, so an active linestage would be a very good idea.

Honestly I do not. I spoke to Oliver Sayes' about my concern about insufficient bass and he recommended me to choose large 6W finemet output transformers, so I hope that will be helpful. I have chosen a 12" speaker model but I'm very well aware that a full range speaker will not cover the whole frequency spectrum, so I won't deny that perhaps in the future, I will have to consider for integrating a permanent bass solution. Luckily I don't listen to very bass-heavy music, but I know that bass is the foundation and an important element in all music.
Today I listened to the string works of Alban Berg and I would love to have a more intimate experience of the Juillard string ensemble.

I assume that I need a phono stage since I use a turntable and prefer moving coil cartridges. Can you confirm that I should not use a linestage, please?

@Lautreamont, you're moving pretty quick to be considering Shindo already! Get the 45 in play and see how you like the sound before adding more tubes.

A preamplifier gathers signals from your various sources and handles volume control. It usually adds some gain between sources and the amplifier (active linestage functionality) but it doesn't have to. It can also add 'tone' to the signal being input to the amp, most often via use of tubes.

Running a source into your amp and using its volume control should let you know if you need an active linestage. As @paul_b mentioned above you probably could use one with your amp. Rather complicated to explain all the reasons in a single post.

Preamps usally have two poles as far as tone. One school tries to add nothing to the signal, just deliver it as if the preamp isnt there. These are usually transformer based or SS The other school uses tubes to add 'tone'. These can be placed in front of a big old SS amplifier, hopefully giving you the warm tone of tubes with the massive power of SS. Or they can add additional tone to your tube amp. Shindo combines his tube pre-amps with tube power-amps to get the full Shindo sound. There are no end of combinations of tubes people will put together that way.

"The pre amp is the most important part of the system." Usually people mean that it is doing the most delicate amplification, from the very small line level signal. If it does a bad job it doesnt matter how good your power amp is, the resulting sound is bad. I personally think its an overstatement but not by much. If you're going to use a preamp its not the place to skimp.

Finally Id suggest you study up on impedance matching before purchasing any preamp because youve been told 'this one sounds good'.

As far as tube selections, circuits and parts for a tube pre Id take a look at simplepleasuretubeamps , Aric Audio | Audio Excellence , and a few other high-end builders to see what they're doing these days. Perhaps someone else here could suggest some example sites as well.

Thank you for the informative response and for sharing your thoughts. It makes great sense. I will spend my time learning more about preamplifiers and getting to know my 45/46 SE/DHT amp.
I see that there is a common appreciate for the 26 tube. I will study it more extensively this evening.

Yeah, he seems like a 'first drug' to a lot of people, me included. Very pretty photography, very effusive language.

At this point I have mixed feelings about his site though. On his home page he states he'll only post 'overwhelmingly positive impressions' and that "this is not a review site." Good enough, but internet searches generally dump you right to the 'review' (commentary?) page where no such disclaimer is posted.

After listening to some of the exact same amps ( he sells his 'review' amps on USAudiomart, or at least has done so in the past ) I no longer trust his opinions. They didn't jibe with mine on sound and build quality at least. Given his niche, small-scale and custom amp manufacturers, you'd expect a few duds but you'll never get that from what he posts.

I like his website as well but I have to remind myself that I shouldn't believe everything I read. I try to find people that share the same understanding of sound like me. I have met a lot of amateur musicians - like myself - and a lot of these people actually knows how instruments sound. Listening to their ideas are fascinating and typically something I try to validate through listening and confirming on the internet.

So if you are being cautious with Glow in the Dark, are there other great websites to get inspiration?

 

[RPMac]

I like a lot of what is on Glow in the Dark….because I have tried it.
I listen to an all Direct Heated Triode system thanks to Bottlehead, especially @paul_b who built my Stereomour with a DHT driver(3B7 which is arguably not the best example).

It’s your choice as to what sounds right/best to you. No two rooms are the same. No two sets of ears are the same. Reviews are someone else’s opinion in their room.
It’s a fun journey, good luck 👍

 

[rogerfederer]

Yeah, he seems like a 'first drug' to a lot of people, me included. Very pretty photography, very effusive language.

At this point I have mixed feelings about his site though. On his home page he states he'll only post 'overwhelmingly positive impressions' and that "this is not a review site." Good enough, but internet searches generally dump you right to the 'review' (commentary?) page where no such disclaimer is posted.

After listening to some of the exact same amps ( he sells his 'review' amps on USAudiomart, or at least has done so in the past ) I no longer trust his opinions. They didn't jibe with mine on sound and build quality at least. Given his niche, small-scale and custom amp manufacturers, you'd expect a few duds but you'll never get that from what he posts.

i used to live in northern VA and met kevin, the glow in the dark guy, via craigslist. he was giving away a set of open baffles he had built and i was the lucky guy (i later gifted them to someone else). i used to take new amps i had bought over to his place to test them out on his speakers.

his day job then (and i assume now) is being a photographer (hence the gorgeous photos). when i knew him (i moved away from VA in 2020, but have emailed him a few times with questions/ideas) glow in the dark was entirely a non-profit hobby for him. he was genuinely interested in the amps and speakers and his enthusiasm was real. perhaps this has changed, but (as far as i could tell) he had no financial connection with the makers of the gear he featured on the site and sold pieces as new ones came in (don't think he is wealthy).

 

[fmena]

How much gain do you need?

 

[Lautreamont]

i used to live in northern VA and met kevin, the glow in the dark guy, via craigslist. he was giving away a set of open baffles he had built and i was the lucky guy (i later gifted them so someone else). i used to take new amps i had bought over to his place to test them out on his speakers.

his day job then (and i assume now) is being a photographer (hence the gorgeous photos). when i knew him (i moved away from VA in 2020, but have emailed him a few times with questions/ideas) glow in the dark was entirely a non-profit hobby for him. he was genuinely interested in the amps and speakers and his enthusiasm was real. perhaps this has changed, but (as far as i could tell) he had no financial connection with the makers of the gear he featured on the site and sold pieces as new ones came in (don't think he is wealthy).

I have spoken with Kevin a few times and he seems like a genuinely nice guy.

How much gain do you need?

I don't know but the gain with c3m will not be high. It has input impedance of 100k and input sensitivity ~2.5v. I would like to know if there will be requirements for my amplifiers in terms of choice preamplifier.

I hope it's enough for the 98dB+ efficient speakers...

 

[paul_b]

I have spoken with Kevin a few times and he seems like a genuinely nice guy.


I don't know but the gain with c3m will not be high. It has input impedance of 100k and input sensitivity ~2.5v. I would like to know if there will be requirements for my amplifiers in terms of choice preamplifier.

I hope it's enough for the 98dB+ efficient speakers...

The C3M has a mu of about 40 when triode strapped. Your amplifier gain will be capped out at about 18dB, but will likely be a bit less than that, maybe 15dB is a reasonable estimate. If you put 2.5V into an amplifier with that much gain, you will get 25W out, so I would suggest that the input sensitivity will be more like 1.5V rather than 2.5V.

Yes, you will need a phono preamp.

No, the Finemet output transformers are not a good recommendation for full range output.

 

[Lautreamont]

The C3M has a mu of about 40 when triode strapped. Your amplifier gain will be capped out at about 18dB, but will likely be a bit less than that, maybe 15dB is a reasonable estimate. If you put 2.5V into an amplifier with that much gain, you will get 25W out, so I would suggest that the input sensitivity will be more like 1.5V rather than 2.5V.

Yes, you will need a phono preamp.

No, the Finemet output transformers are not a good recommendation for full range output.

Hello Paul

This is very unfortunate. In other words, I will not be able to use Oliver Sayes' amplifier as a single unit without risking to destroy something?

Apparently I have been too naive. I thought that efficiency of the speakers was the single most important thing to consider when choosing amplifiers to match your speakers. On the contrary I would be careful putting my speakers on with my Sansui, since it a lot of power for those delicate drivers.

So. I think I can still be able to adjust the transformer if I talk with Oliver Sayes immediately.

 

[krca50]

C3m datasheet from Siemens gives data for triode as Ug2-g1 : 19

C3g datasheet from Siemens gives data for triode as Ug2-g1 : 41

 

[Lautreamont]

C3m datasheet from Siemens gives data for triode as Ug2-g1 : 19

C3g datasheet from Siemens gives data for triode as Ug2-g1 : 41

Can you elaborate? I'm not sure if I understand the data.

I was under the impression that C3g and C3m were some of the finest driver tubes available and the latter, the C3m, is used by both Treehaus 300B amplifier (with finemet transformers) and by Shindo and Yamamoto. I was also under the impression that both driver tubes had the gain of a pentode and distortion same as only the finest triodes like E80CC.

Some important questions:

1. Is the problem here the Finemet output transformer that is a bad match with a full range driver?
2. Are C3m driver tubes actually not capable of driving my speakers alone without a phono stage?
3. If I were to change the C3m I could perhaps go for C3o or C3g?
4. Or is it simply the fact that there are not a preamplifier in the chain right now...

 

[Lautreamont]

The C3M has a mu of about 40 when triode strapped. Your amplifier gain will be capped out at about 18dB, but will likely be a bit less than that, maybe 15dB is a reasonable estimate. If you put 2.5V into an amplifier with that much gain, you will get 25W out, so I would suggest that the input sensitivity will be more like 1.5V rather than 2.5V.

Yes, you will need a phono preamp.

No, the Finemet output transformers are not a good recommendation for full range output.

Sorry for the numerous posts. I'm trying to study the technical aspects whilst reading your reply. My understanding is that the actual stage gain depends on the load (plate/load resistance, interstage transformer turns ratio, coupling arrangement, and how the output tube behaves). That means that the single mu figure is necessary but not sufficient to predict whole-amp gain or power.

 

[paul_b]

C3g and C3m tubes, perhaps the best small signal tubes ever made.

I was looking at C3G rather than C3M, my apologies. The M does indeed have lower Mu, half the transconductance, and slightly higher Rp. These are not the characteristics that one would desire when picking a tube to drive an interstage transformer. It will exaggerate the bandwidth limitations of an interstage transformer, and you'll end up with very low gain. If you use something on the level of the Monolith IT-01 or the LL2762, this could work, but the vast majority of the interstage transformers on the market are intended to look like a ~5K load, and that isn't a great choice with the C3M.

 

[krca50]

Can you elaborate? I'm not sure if I understand the data.

Paul B probably unintentionally wrote that C3M has a Mu about 40 when triode connected.

Ug2-g1 relationship is the Mu when pentode is triode connected.

So for C3M - Mu : 19

For C3G - Mu : 41

I did not check what further Paul B calculated in dB.

The point being that depending on the phono pre gain & other spurces gain - possibly the line stage gain can use C3M tube in triode ( just looking at the Mu / theoretical amplification factor to put it simply, which in the same region as 6SN7 tube fo example, no other data taken into account ).

----------

You have speakers with 98 dB+ efficiency.

Next is to now how much gain the power amplifier has ( don't know this for SE designs, usually PP and SS amps have something like 23-26,5 dB gain ).

From there You could make some rough estimates how much gain You should have from sources and then do You need line preamp with no gain or some gain & how much would that could be.

The thing to be avoided is to have a line preamp with too much gain which in practice leads to volume control being usable only in first 20% of rotation from minimum.

---------

You have on big advantage as i see it : speakers are as they are ie. very efficient, power amp is or will be custom built so any other part of the source or preamplification stages can be done to Your requirments.

This part : power amp & sources should be under consideration with so efficient speakers and it benefits to learn more before commiting some build. To learn more is to know more what You want, not just technically speaking but also what kind of sound You want.
It is also worth discussing all these things with possible constructor.

------

To summarize this long post : for listening records You need a phono preamp.
That phono preamp could be done to include selector & volume control or this can be done as separate units.
Power amp could also be done to include selector & volume control.
If using MC cart with Step Up Transformer or some other way - phono preamps tend to have somewhere around 50 dB gain or more.
If this is the case then the "line preamp" should not have much like 18-24 dB gain, more like somewhere 6 - 8 dB gain or lower.
This leads to implementation with tubes that have lower Mu factor like 12B4A tube ( just an example )...or some DHT tube.


With 98 dB speakers there is somewhat limited amount of gain in various devices ( the sources usually are not the problem ), especially in a separate control unit called "line preamp".


P.S. With 96 dB speakers personally i do not have much "room" to wiggle in a line preamp regarding gain but will need something of the sort regardless of technology or tubes used. From a turntable at the present situtation is little better but from digital sources it would require no gain approach ( these with MM cartridge & phono with 40 dB gain ).


Sorry for the long post.

 

[Lautreamont]

Thank you for taking the time to elaborate on this issue.

I currently have the following equipment:

• Turntable with SME tonearm and moving-coil cartridge
• Pro-Ject Tube Box S2 (RIAA) to amplify the moving-coil cartridge
• Sansui integrated amplifier
• Speakers

I will soon be changing both speakers and amplifier (to an Oliver Sayes 45/46 SE/DHT amplifier with a volume knob). I will also purchase a preamplifier (phono stage) later on, but for now I want to settle in with my new amplifier, get to know it, and meanwhile gain a deeper understanding of preamplifiers and my options. This leads to the following statements/questions:

---

a) My understanding is that I can use my Oliver Sayes SE 45/46 amplifier by itself (with the volume knob he is installing) to drive my 98 dB speakers and my line-level sources right away.

b) Ok. So if I want to play records using my turntable, will the Pro-Ject Tube Box S2 be sufficient and can it work as a temporary solution before receiving a dedicated preamplifier?

c) If I can use my turntable + Oliver Sayes amp + Pro-Ject Tube Box S2 to listen to vinyl, then my understanding is that adding a separate preamplifier later would be for reasons such as:

• wanting a different sonic character
• needing multiple input switching
• wanting lower output impedance / the ability to drive long cables
• needing more gain (perhaps?)

If b + c are possible then it seems the discussion about the C3m, mu, gain, and preamp gain is not about whether it will actually work, but about optimizing gain structure.

---

A follow up question could be that if I were to adjust or change components in the Oliver Sayes' amplifier, I need to address this issue now before it's too late.

Please bear with me if I’m causing more confusion—I’m still a beginner trying to learn the fundamentals. This is very helpful for me.

Thank you for your patience!