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rick57 16th September 2005 03:19 PM

300B like 845
 
300B SEs are in some ways very nice, eg to my ears perfect for choral pieces; but Iím mostly a rock listener.

I donít want distortion or sand, I want to build a tube amp with three priorities:
Great dynamics in drumming and other transients, effortless power and just a little richness.

I recently heard this muscular sound in a commercial 845 SE (using I believe custom Stevens & Billington trannies), but itís outside my price range.
Iím new to DIY so 1200 volts is not a good idea now; and even if it were, the parts cost of a good 845 (or 211) is high!

What gave the 845 an effortless powerful sound, is it:
- just the higher watts (but itís only about double ie 3 dB over a 300B),
- the higher volts Ė I doubt it,
- the ratio of amp power to speaker sensitivity (an 18 watt amp driving 90 db speakers) Ė I donít think so
- something about the tubes (Shuguang 845Bs) Ė possibly
- generous power supply capacitance - maybe
- good OPTs - quite possibly

Some of the above plus others Ė probably Ė but which to focus on and do?

So I thought, when driving 98 dB speakers (G ribbons and PHL 3451s), it should be possible to do a 300B SE at a lower cost than an 845, that still has an effortless powerful sound. More ballsy and kicking with some smoothness than angelic. Maybe 33-50% lower cost, maximum say roughly US$ 750.

Ultra wide bandwidth not needed (using subs below 100 Hz, and I canít hear over 14 kHz). This should make it easier to get dynamics.

Suggestions please:

- Which 300B tubes and parts, esp OPTs? Maybe James or Bartolucci.
- What circuit?
- Likely to be using Aikido line stage - only 2-stages strongly preferred.
- Use 2A3s as driver tubes?
- Use interstage trannies?
- Parallel-feed??
- What PS?

KRís 300BXLS is powerful, Steve Rochlin liked it, but mixed other opinions. I just learnt of KRís 842HVD; apparently in a Cary 805C they provide ďmore punch and better bassĒ - but $500/ matched pair Ė extra cost of both is not justified for what Iím after ditto!

I donít want to pay double for tubes, so as to allow money for really good iron.

* What not to do?


Thanks

kmtang 16th September 2005 03:42 PM

Pararllel 300B SE power amp
 
2 Attachment(s)
Hi,

What about the Audio Note parallel 300B SE Power Amp? It should give you sufficient power. The Hammond 1640SE OPT is a good candidate for this amp.

Here's the schematic:-

tubelab.com 16th September 2005 04:21 PM

I have built several amps over the past 40 years both tube and solid state. Even though I listen to a wide variety of music, 2/3 of my CD and 90% of my records are rock and I like it LOUD. I have a 300B SE amp and an 845SE amp and a 300B push pull amp. All are zero feedback designs. I am very economy minded in my amp construction, so all of the output tubes are Shuguang, and the transformers are nothing special, with the exception of the Electra prints in the 300B. I currently have all three amps set up so that swapping is a one minute operation.

I find that the transient response that you seek flows effortlessly from the 300B push pull amp. In fact this is my favorite amp to use for highly dynamic music like techno. When the drummer whacks the rim of the snare with the stick the shot shoots right through your head. It has the strongest bass of the 3 amps. It also does Jimi at full volume quite well. Good for Van Halen, Metallica and other LOUD music.

The 845 SE is not as "in your face" as the 300B push pull. It is best for less dynamic and more vocal music. It does Jimi quite well. I use it for Moody Blues, Fleetwood Mac, and similar music.

The 300B SE is the most detailed of the three amps. It will bring out subtle details thet the other amps miss. It is set up to use a variety of output tubes, and has the best sound with 45's, but only 2 watts per channel.

I believe that the "in your face" bass of the push pull amp is a function of the amps output impedance. This in influenced by a number of factors, including most of the items that you mentioned. Tubes, output transformers, circuit design, power supply, and choice of load impedance.

I would advise you to listen to a 300B pudh pull amp, if possible before making your final decision. I have been searching for a single amp design that incorporates the best aspects of all three amplifiers, but it has eluded me so far. I have prototyped an 833A amp with over 100 watts and this might be it.

See the web page for more details:
http://www.tubelab.com/

Gabevee 16th September 2005 06:46 PM

Well... you force me to toot my own horn....

My 300B amp is within that price range. I also listen to rock, and wide dynamic range classical (Beethoven. The original rocker!), and everything in between.

What do I use to get the good dynamics and wide freq response? Beefy power supply, solid state rectification, large filter capacitance (330 uF) and One Electron OPT. If you are going to spend 90 bucks apiece for the Hammond, you would be better off with the One Electrons for a few dollars more. Literally about 95 bucks apiece. Oh, I use cheap 59 dollar Chinese 300Bs. Sound is amazing. JJ/Teslas for 90 bucks each should be phenominal. I may treat myself to those in a couple of weeks.

In my 300B amp (pictured upper left corner) I use a 300 volts 250 mA transformer. If you can find one with more current, use it. I use solid state rectification for three reasons, 1 the recovery is much quicker for dynamics. 2 The drop is only about 2 volts for maximum B+. 3 I use the 5 volts which would normally be used for the tube rectifier for the 300Bs.

This amp has been the talk of the "Oswalds Mill Tube Tasting" for years. Last year I did a proof of concept for my design and played, while they played soft chamber music and blues, Boston's "Foreplay/Long Time". It blew everyone's mind (including mine!) how it sounded great without breaking up. BTW, I play it on speakers that are about 86dB efficiency, and it was my 4.5 watt prototype... But the speakers at the Mill are I believe 98dB horns. My production kits have a 350 volt power transrformer for 7-8 watt output (the B+ is about 380 volts).

The issue here... I would not be easily inclined to share the schematic. Sorry. But with these ideas, you can make a pair of mono blocks for yourself. My amp is a stereo and the way I have designed it gives it its unique tonal character, and deep strong bass. All with no NFB.

I also use the 12AT7 for preamp/driver. One half is a simple preamp, gain of about 20, and the second half is a directly connected cathode follower delivering about 3-4 mA for the signal, if the tube really needs that much. But the follower keeps the preamp at its full gain for maximum output. The only caveat there is that you may need to experiment with different brands of 12AT7. I use the Phillips NOS. I recently bought a pair of JJ/Tesla, which normally sound terrific to me, and heard some IM distortion. That is a negative to me when not using NFB. Of course, they may have needed tim e to break in.

Hope this helps!
Gabe

Zen Mod 16th September 2005 11:02 PM

who need schematic after that post ?

:D

rick57 17th September 2005 12:57 AM

kmtang

Any Audio Note should sound pretty good. But Iíve heard mixed reports about parallel SE amps Ė often not quite the SE magic.

And ANís Ďbaseí 300B SE alone is US 1400, way over budget.

Apart from about 845 SE power, any reason you suggested this?


tubelab

An interesting comparison. Iíll try to locate a local 300B push pull.
Using subs below 100 Hz, only the upper bass matters.

I guess a 300B PP would cost more than a 300B SE Ė extra tube, cheaper OPTs, more parts Ė how much more, and how much in total?

I imagine your 833A could be a BMW M5 of an amp .

As a reference, which might have more of that Ďmagicí sound do you think Ė a 300B PP, or say a 30 watt (SE) Aleph SS??



So far most of the focus has been on other topologies. Apart from Gabe -

Solid state rectification - if recovery is quicker for dynamics -would be better.

ďB+ is about 380 voltsĒ vs 450 volts - is that for longer life?

12AT7 for preamp/driver. Your emphasis appears to be best value.

Your kit is $750, I was intending to spend about that on parts eg really good OPTs.


Iíve heard that to make an 845 sound like a 300b, drive it with a 300b:
* What driver for a 300b would give it most drive?
* What about a 6550 driver in triode mode connection, and a 6C45PiE upfront? :bigeyes:


Anyone from the scratch building 300B SE circles Ė whoís built a 300b that really rocked?

rick57 17th September 2005 10:43 AM

Anyone tried an 6SL7 and an EL34 per channel (like the Sophia Electric 300B Mk. II)?

kmtang 17th September 2005 11:44 AM

Hearing is believing
 
Different amps would have different characters. I built 300B, 2A3, and 45 SE amps myself. I tried using different driver in the 2A3 amp. I also tried employ different types of capacitor for the bypass of the power supply.

Therefore, it is fun being a DIYer who can experience various circuitries/components and find out the which one suits your taste.

Lastly, I would say there's no such thing is perfect in this world. This would be an endless game seeking for the perfection.

rick57 17th September 2005 03:21 PM

Iím not suggesting that thereís there's such a thing as perfection.

Iím saying for a 300B SE, rather than detail or sweetness, if the priority is muscular/ effortless powerful sound - how do you achieve it?

Brett 17th September 2005 04:01 PM

I really hate to be boring, but just go with the Allen Wright PP1C (fits all your criteria and cheap to build too) and add a CCS in the tail of the ouputs if preferred. Excellent performance and if you really want the 2H you can tweak the balance of the front end to get it. Just do a better PSU than Allen's.


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