Kits useable with a M500 300B Monoblock amp

[ThorstenL]

Hi,

Originally Posted by bprager

One thing I do need to ask, I have studied the WE91 mod schematic and gone to the link you provided. I have read that info and downloaded the other appropriate mods.

However, the basic mod appears to be the introduction of a 10uf cap in front of the choke, with the movement of the 220uf caps to after.

This is nothing really to do with the "91" Design, it is a modification to the powersupply derived from my "Lady Day 91" Project, which is a slightly different but parallel take on the Lady Day 91.

I would suggest to use this in combination with the WE Style connection of the 300B Cathode shown earlier)

Originally Posted by bprager

While this is clear, I have read comments about the "full" We91 mod.

The "Full WE91 Mod" being referred to is I believe based on this article:

Tube DIY Asylum: Oh no - YAWE91B300BA (Yet Another WE 91B 300B Amplifier) by Thorsten

This can hardly be called a modification, it basically requires the full stripping down of the chassis and a full rebuild to a new circuit.

The Diyhifisupply Lady Day 91 has been reviewed a few times, so you can refer to these reviews as to "what it sounds like" (and before you ask - the 6SJ7 is not a good substitute for a WE310A in my books).

DIY HiFi Supply - Ladyday Signature 300B SET 91 - The Ladyday and Billie shootout! - Review By Clive Meakins

Around the World: DIY Systems from the Other Side of the Globe

Something also possible useful may be this little article:

FAQ -- Which Amp Is Right For Me? | Diy HiFi Supply

I would say that the M500 with the hybrid Mu-Follower and gridchoke goes a long way to provide the same grip on speakers and the macro dynamics of the original Lux (the Lux 91 is another step up). I would probably add a 4.7K/4.7uF "snubber" (aka DR.P) across the coupling capacitor, this gives a little more dynamics in the lower ranges.

At the time when both the 6SL7 Mu-Follwer driven Lady Day and the Lady Day 91 where quite hot new items there where users that compared both and preferred one or the other. Those with very high efficiency speakers (Lowther Horns, big Tannoys, Bastanis Prometheus etc.) generally preferred the 91's while those with medium efficiency speakers (eg. AN-E's and the like) generally preferred the 6SL7 driven versions.

I hope this helps to make a call which way to go.

Ciao T

[bprager]

Thorsten, just to give some perspective, my speakers are very high effieciancy (102) speakers rated at 12 ohms, and they have a very flat impendance curve.
If that would lend a preference to certain mods, please let me know.
I am assuming that conversion of the amp I have to the 91 using the 310A is not practical.

As I will be making a lot of changes based on what we have talked about, plus recommendations from the links you have provided, I thought I would tweak the resistors to the highest grade that made sense, since there are so few.
I was going to switch them to the Japanese premium carbons that DIY carries. If you feel that the Tantalums would be better, let me know and I can switch or order both.

I am also assuming that the caps on the power supply board would not be an avenue to tweak, both in quality and in capacitance. In some of my earlier experiances (with much different tube amps), switching out the PS caps to higher quality, and higher value caps, led to a quieter and more stable/powerful supply.
Do you think that might be true for the M500?

Anyway, just to sum up: Based on your extremely kind suggestions and links, I will add the filament heater, power supply mod + WE cathode connection, Hybrid Mu,and a few other smaller cap changes.

Possible additions might be the resistors (since I'm already there) and the PS suppuly caps (again, I'm there and its not difficult if you think it makes any sense).

Since noise doesn't seem to be an issue, additional shielding doesn't seem needed and conversion of the 6SL7 to a 310A or a interstage transformer I assume is not possible/practical with this amp.

If this looks like a good understanding of what we've discussed, and you agree with my assumptions, I'm good to go.

If you have a chance, a comment on the resistor changeout and PS supply would be appreciated, however I want to sincerely thank you for all you have done. It has really been educational and I look forwards to the "new" M500's.

If I hadn't already gone this direction, the new amps would be high on my list and when these have some more hours on them, I suspect they will move to another room and I will be taking a very hard look at the latest and greatest. Its hard to beat great design and great prices at the same time!

Thank you very much, Bruce Prager

[ThorstenL]

Hi,

Originally Posted by bprager

Thorsten, just to give some perspective, my speakers are very high effieciancy (102) speakers rated at 12 ohms, and they have a very flat impendance curve.
If that would lend a preference to certain mods, please let me know.

Your speakers are very suited to a "91". However...

Originally Posted by bprager

I am assuming that conversion of the amp I have to the 91 using the 310A is not practical.

It has been done, but it means stripping down the Amplifier almost completely and re-building it.

Originally Posted by bprager

As I will be making a lot of changes based on what we have talked about, plus recommendations from the links you have provided, I thought I would tweak the resistors to the highest grade that made sense, since there are so few.

I would suggest to make the grid-stopper (in series with the grids) carbon composite (Allen Bradley, Xicon) or Takman Carbon if the others are unavailable.

As the Cathode resistors of the 6SL7 are bypassed their quality is not very critical, almost anything will work okay.

For the Gridleak resistors (from Grid to ground) I would suggest Takman Metal film, though again, this is not super critical. If you use the Gridchoke for the 300B this Gridleak resistor is omitted.

For the 47 Ohm in the Powersupply line (output stage WE connection) is best a 2W Kiwame.

If you do convert the Amplifiers to 91's then use Tantalums for the Anode Load on the 310A and on the 300B Grid Circuit, in that circuit these are quite critical sonically.

Originally Posted by bprager

I am also assuming that the caps on the power supply board would not be an avenue to tweak, both in quality and in capacitance. In some of my earlier experiances (with much different tube amps), switching out the PS caps to higher quality, and higher value caps, led to a quieter and more stable/powerful supply.
Do you think that might be true for the M500?

You can just replace the PSU Cap's, sure. But since the demise of Black Gates there is very little in any format that fit the existing PSU Boards and wiring in capacitors with extra long leads into the existing PCB's (as often seen) is a really bad idea as it adds ton's of inductance over the original capacitors which generally makes at least the objective results (and to me also the subjective ones) much poorer than even cheap generic electrolytic capacitors.

However if you instead apply the PSU Modifications listed as "91" modifications and you apply the WE Connection to the 300B Stage using Film Capacitors (12uF & 47uF) you get a much bigger upgrade while reducing the impact of the powersupply much (to a larger degree than the PSU Cap changes could provide).

Originally Posted by bprager

Anyway, just to sum up: Based on your extremely kind suggestions and links, I will add the filament heater, power supply mod + WE cathode connection, Hybrid Mu,and a few other smaller cap changes.

Yes, I think this will do best in terms of effort and money spend.

Ciao T

[bprager]

Thanks for all your help. I was wondering what advantage their is to using an interstage transformer in place of the driver tube. That seems to be one of the differences between
Audio Note 300B's and most others. I saw that DIY sells an interstage, but obviously felt using the 310 was better overall in their amp.
I would think the transformer would be more linear, however, I don't know about the sound, whether it would become a bit analyltical compared to an all tube design.
I was just wondering if that was a potential design that was looked at when you designed the latest Lux amps.
Thanks again and look forwards to getting started on my mods.

Bruce Prager

[Pit Hinder]

Bruce,
I will get shot for this, but...you pay crazy money for amps just because they are sold as "300B´s and make friends with your bank manager".

Ask Thorsten L about some Chinese 300B s, or about what can be done with (wonderfully underrated) EL34 or EL84. Paradise.

[bprager]

I have some wonderful scott amps that are el34 or el84. But I like 300B.

I have looked at the chinese 300B's, and have had a Cayin which was wonderful.

But due to economic conditions, I had to sell it and now am looking for a more reasonable amp. I found a used Billie, and am looking to optimize it as the total cost to optimize the amp, even to all of Thorstens suggestions, brings the total cost to way under the cayin amp. And the cheaper chinese amps have extremely mixed reviews.
So I don't think this is a crazy idea.

BP

[Pit Hinder]

There you are. I don´t know the Billie, but I know Brian´s quality standards - you are one lucky man.
I still have his Basie preamp...any stranger panhandling on Main Street can have everything I own, but not that.

Pit

[ThorstenL]

Hi,

Originally Posted by bprager

I was wondering what advantage their is to using an interstage transformer in place of the driver tube.

There is no advantage as it is not possible to do so. An interstage transformer essentially takes the place of the interstage coupling capacitor. You still need a driver tube however.

Most interstage transformers are 1:1 so they do not really offer any different signal as capacitor coupling. Of course, interstage transformers have a number of additional sources of non-linearity over a capacitor. Depending on how it is done the resulting Amplifier can be better or worse.

I have found that most interstage transformers are by far too limiting in bandwidth and have iron based cores (amorphous iron is still iron) which I dislike in transformers for low level signals. Tango and Tamura (James too IIRC) do offer some permalloy interstage transformers which I do happen to like, but a pair of these approaches "donating a kidney for cash" territory and still need some trickery in implementation.

I generally try to work without interstage transformers as a result.

The key difference between capacitor coupling and interstage transformer coupling is that the impedance at the grid of the output tube progressively increases as the frequency lowers, which means that at high power levels the grid current from the 300B is handled better.

My personal "budget" alternative to this is the use of a gridchoke together with "DR.P" (Damped Resonance Parallelfeed), which goes a long way to redress the situation or indeed "my latest trick" (Yes, that was Dire Straights on Brothers in Arms), which I call the "Bushido" circuit. It forms the core of diyhifisupply's lates generation of 300B Amplifiers, the Lux and Lux 91 but cannot easily be applied to your Amp's.

Originally Posted by bprager

That seems to be one of the differences between Audio Note 300B's and most others.

No, not really. Very few AN-UK Amp's ever used interstage coupling and AN-JP never used any IT coupling. In fact, AFAIK non of the AN-UK 300B AMp's use interstage transformer coupling and only the AN-UK Ongaku and Ankoru use IT coupling.

Here a schematic of the quintessential AN-JP Amp, the Ongaku:

Audio Note Japan (Kondo) Ongaku

Originally Posted by bprager

I would think the transformer would be more linear

Why would you think that?

[/QUOTE]I was just wondering if that was a potential design that was looked at when you designed the latest Lux amps.[/QUOTE]

Above I noted that there where/are significantly different sonic traits for the Lady Day in the 91 (WE 310A Pentode driven) and standard (6SL7 hybrid Mu-Follower with Gridchoke) configuration.

The 91 Style Amplifiers I have worked with all excel in delicacy and detail as well as in "tone", by far more so than any others (this parallels the Yamamoto Amplifiers with their Pentode drivers), however they start compressing and clipping fairly early.

The Amplifiers with low impedance triode drive (be it using low impedance triodes with or without interstage transformers or using such circuits as the hybrid Mu-Follower) always seem to offer a more robust presentation, they do not shrink from big orchestral climaxes and handle big bomblast Rock well, but they do not seem to offer quite the same redition of detail, space and tone.

Of course, ideally we want a combination of both. The two Lux amplifiers attempt to deliver exactly that and manages quite well I think.

If you read the review in 6moons, the Lux 91 went up against the Border Patrol 300B Amp's, which are IT coupled and are designed by a guy from the general original audio innovation clique - which later also gave rise to Audio Note UK and Audion UK among others.

My "Bushido" circuit performs both subjectively and objectively much better than any IT I ever tried in terms of linearity, bandwidth and ability to handle grid current and it frees us up to use any voltage gain stage we like, including the 310A.

However, this circuit and design is not applicable to your Amp's (sorry), you don't have enough tube sockets and space inside etc.

Ciao T

[bprager]

Thanks for the explanation. I asked as on the Audio Note kit page, they have a mono block kit that uses an IST and suggest that it has advantages over a non-IST design.
As you say, you can design amps many many ways, and you get advantages and disadvantages, as well as prices differences that can many times explain the advantages very quickly (the "you don't really need any kidney's pricing").

I'm planning on the MU circuit. The DR.P mod you mention, is that part of what I'm doing already with the Gridchoke mod or is it a additional mod for me to consider?

Not a big deal either way, but my philosophy is that once I'm in there and its not going to cost me a body part, I may as well do all I can so that I can mod once and enjoy forever.

My other comments regarding IST's basically came from what was on that page for the amp (I think they call it the Mono interstage if I remember correctly). My thought on the linearity was based on the premise that you would not be driving the IST near saturation levels and that a transformer (well-made) would not be subject to the sound differences that occur with caps due to the large number of different materials and designs that occur with them.

Of course, that is also why I wondered about it being a bit analytical, as those difference in caps can be judiciously used to tune a amp to the sound you prefer. I believe in neutral amps, but am not one who believes any departure is a flaw. Rooms and ears are anything but neutral and for me, the idea is that the music should be enjoyable. If its not "accurate", people have been arguing what that word even means even today.

I went with the Billie because I have developed a real love of 300B amps, seconded by small tube amps like the Scott 222 series. I prefer the slight added warmth in the mids (so long as it doesn't get syrupy) and the Billies have that quality. The only issue I have had is that the highs are sometimes a bit hot with my speakers, (which is why I'm going with the AN copper coupling caps) and hope the mods will tame that issue without destroying the underlying detail, and keep the wonderful mids I love.

Much of my experience in modding or maintaining amps have been with the Scotts which are very different than the Billie's, particularly as the Scotts are integrated's.
Its actually nice to be working on a circuit where you have some room to work and tracing the schematic is so much easier.

I really appreciate the detail in your responses as they have given me a much better understanding of 300B amps like the Billie, which will be highly useful in both modding and maintaining it as I intend to have it for some time to come.

Best regards, Bruce Prager

[ThorstenL]

Hi,

Originally Posted by bprager

Thanks for the explanation. I asked as on the Audio Note kit page, they have a mono block kit that uses an IST and suggest that it has advantages over a non-IST design.

I do not think it would be approriate to make specific comments about specific products from a competing manufacturer here. But I would look at what AN-UK and AN-JP do in their best 300B Amplifiers...

Originally Posted by bprager

I'm planning on the MU circuit. The DR.P mod you mention, is that part of what I'm doing already with the Gridchoke mod or is it a additional mod for me to consider?

DR.P means you connect a snubber (I would suggest 3.3K & 3.3uF) across the coupling capacitor (I would use 0.33uF or 0.47uF with the above snubber).

Originally Posted by bprager

My other comments regarding IST's basically came from what was on that page for the amp (I think they call it the Mono interstage if I remember correctly). My thought on the linearity was based on the premise that you would not be driving the IST near saturation levels and that a transformer (well-made) would not be subject to the sound differences that occur with caps due to the large number of different materials and designs that occur with them.

Hmmm, transformers have many problems of their own. airgapped transformers have very limited primary inductance, which limits their LF response, also, air-gapped transformers rarely use permalloy cores, so their sonic merit is quite limited simply by the core material (worse if they do not use 0.05mm steel laminations).

Equally, they need to be quite large physically (to handle substantial DC current) and need high impedances, which means winding for good HF response is at the best very difficult. Of course, few transformer winders attempt to make IT's that offer the same wide bandwidth as capacitor coupling routinely allows. Due to the "law of the 400k" this tends to work okay sonically, even though the bandwidth is obviously limited, if the transformer is designed well.

Compared to for example to a CCS Load with a gridchoke an interstage transformer will usually have much worse (lower) impedance at low and high frequencies, only in the midrange can it offer similar linearity.

In addition, there is usually a claim that interstage transformers removes coupling capacitors. This is of course patently untrue, refer to Lynn Olson's "Current Loop" presentation at ETF (available at nutshellhifi.com) for more.

So, in the end IT coupling can have some advantages over capacitor couplings, but most of these can be attained using other means as well.

Making a good Interstage transformer costs as much if not more than making a good medium power output transformer and even then the transformer is unlikely to match the bandwidth of other options. If this is a possible problem or not depends on musical tatse and speakers used (e.g. those with Speakers that omit low bass and high treble will not notice the problems, other very well might).

Originally Posted by bprager

hope the mods will tame that issue without destroying the underlying detail, and keep the wonderful mids I love.

The "Hot high frequencies" are mostly (IMHO) down to tube choices and the heater supply. Try some good NOS 6SL7's and warm or neutral sounding 300B's. If the Amp has it's original tubes, these sound quite steely and bright.

With my Billy Kit I did not listen to the supplied Chiense tubes (O&J aka Valve Art) for long, the chinese 6SL7's where pulled within twenty minutes of listening. I used with the Stock Billy Svetlana 300B's (sounded quite close to WE) and some nice NOS 6SL7's, I liked the Ken Rad ones very well. I also rather liked the TJ Tubes.

The Heater supply modification tend to reduce edginess and grainyness.

The Powersupply Mods and WE connection of the output stage extend this, the WE connection also gives a more solid presentation and more of the oh so famous "black background".

The Hybrid Mu-Follower adds more detail and slam.

Gridchoke and DR.P extend slam and make the Amp subjectivealy capable of playing notably before compressing or breaking up.

Ciao T