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38.112.26.42
Here's the circuitInput stage
WE 102L (@40K plate resistance, 1.1ma, 150V plate): 82K plate resistor, 100uf BG N coupling cap, MQ hi-nickel grid choke, 1.8K bias resistor bypassed with 1000uf BG
Driver stage
WE 101L (@5K plate resistance, 10ma, 160V plate): 250H plate choke, 68uf BG N coupling cap, MQ RIT-jr 5K 1:1 interstage, 1.3K bias resistor bypassed with 2000uf BG N
Output stage
WE275A (running at 50ma, 250V plate voltage): Tamura F5003, 1.21K bias resistor bypassed with 47uf BG VK
Power supply
Dual 6CJ3 choke input power supply. BG WKZ PS capacitors.
I understand that the Tamura F5003 has a reputation of weak bass, but in this amp the bass is so far off (rolling off in the bass really early) that I am scratching my head wondering if one of the earlier stages is also contributing to the sonics.I have tried various capacitor swapping in the input and driver stages so I hope someone can spot a design mistake or suggest a circuit change to boost the mid/lower bass region.
A side question, do tubes that are almost gone have weak bass?
Much appreciated!
Follow Ups:
Wow, many thanks for all the suggestions!I'll try to describe the circuit in more detail.
1. The interstage transformer (IT) is parallel feed so the BG coupling cap is used to remove DC from the primary. If I understand correctly, the RIT5-jr cannot have DC voltage on the primary or secondary.
2. In the secondary of the IT I am using a circuit from Asano's book. The "hot" leg of the secondary is connect to the grid of the 275A. The ground leg of the secondary is grounded through a 47K ohm resistor. A 1uf cap is connected from this point to the center point of the 1.21K cathode bias (I have a hum pot there). I understand this trick is from the WE amps (91B, 86B?). This change from connecting the secondary ground leg directly to ground did not affect the bass appreciably but made the midrange and high much nicer.
3. The power supply uses two stage choke input filter, each stage has 10H 100ohm chokes. I use a small 0.68uf cap on the rectifier output to tame the buzz on the first choke. A 20uf is between the first and second choke. The 47uf WKZ BG is after the second choke and goes to the output stage. Additional RC are used between the output and other stages. 18ga wire throughout.
4. One of the reasons I chose the 5K impedance IT is from reading the spec sheets for the Tango interstages. They show the response curves of the interstage transformer with different Rp. For instance, for a 10K 1:1.5 transformer, a 10K Rp gives the flattest high frequency response. A 7K Rp gives a high frequency bump. The bass penalty on the 10K Rp didn't seem significant enough to be consistent with what I am hearing. But I will try to replace the IT with a resistor and check out what happens. Is there anyway I can make the 5K IT work, perhaps a bass boost circuit? The reason I am asking is that I have engravings on the chassis that can't be changed.
Cheers
Hi,Well you seem oblivious to telling us what the power transformer is. If its only a 50 mA rated one, you are off on the wrong foot from the start. Find one that is about 150 mA as a minimum. The power transformer can well be the beginning of whats wrong with your bass.
Next, since single ended amps are " tuners" you need to pay much more careful attention to your wiring. 18 gauge is definitely not good enough for ground runs. Ground wire needs to be a minimum of 12 gague, as the audio signal flows through it.
You can experimentally execute this, right away, and you will ( hopefully ) hear what I am talking about. Across ALL your power supply sections' grounds, add jumper wires, you know, clip leads like you get at Radio Shack, and just listen to what that does to the body and bass of the music. As goofed up as your supply is, and it is, you still might be able to hear bass improvement.
If you are on a budget, convert all ground wiring to 10 or 12 gauge ROMEX electrical solid copper wire, with one stand of Kimber TCSS litz in parallel to it in your 45 SEer.
Unfortunately, you have a third problem. In addition to your still undefined power transformer, 10 HY 100 ohm chokes do NOT belong in any Type 45 triode amp. The choke is a driven component, hence, it is even more critical to the amp's ultimate resolution on playback than the power transformer.You want chokes that are 10 ohms DCR, or less, and with a small core, and 1/2 HY or lower in inductance. Such chokes preserve the timing of music through the single ended power supply, higher values of inductance and DCR most certainly cannot and will not do this !! I will give you a URL to read below that reflects my own direct experience with a SE globe 45 amp, only three weeks ago.
Just be aware of this : NONE of everyone else's helpful audio circuit changes means anything, UNTIL you get a good supply in the amp !! You start an amp with a well-designed supply as it is of paramont importance to the sound in a Triode amp's design.
Jeff Medwin
The whole idea of a reservoir cap is to act as the termination of the PS, as far as the amp is concerned. It is supposed to be like a "wall" between the amp and the power source. If the reservoir cap is sufficiently large and of good enough quality, then everything that comes before it in the PS (the 'boiler room', so to speak) will be inaudible. That includes the power tranny, rectifiers, smoothing cap(s) and choke(s). Their job is simple, namely, to supply a nice clean, smooth, reliable B+ of the required voltage to the reservoir cap.In the straightforward case of supplying power for class A amps, current demand doesn't change significantly and any small variations in demand are easily absorbed by the reservoir cap. DCR in the 'boiler room' of the PS is really not an issue, capacitor input filters work fine, everything is nice and simple! The only challenge is ripple, but judicious application of sufficient inductance and capacitance in the right places can reduce that to the point where it becomes inaudible. And if that doesn't work, shunt regulation can save you (don't knock it, it works).
On the other hand, the more complex problem of supplying power to class AB amps, where the current demand varies with signal level, is more of a challenge. This is where low DCR and choke input filters suddenly become important, to minimize voltage sag. Again, regulation can be a great help, but I digress!
My key point is that a power supply has no business sounding like anything. If you find that components before the reservoir cap are affecting the sound of a class A amp in any way, it's because your reservoir cap isn't doing its job properly, and that is where you should concentrate your efforts to improve the PS. It really is as simple as that.
Ray,Its YOUR whole idea of a power supply and what you say is really outdated, misleading to this poor poster, and very wrong. Class A amps and single ended amps need just as good a supply as AB amps, if not better!! Particularly single ended amps where the supply is embedded in the audio circuit.
Of course, I will bet you 1,000,000 dollars you have never even TRIED the type of supply I have proposed, so you are speaking from inexperience with both types.
Have you not learned anything from my over two years of posting about this complex subject??
YES, I am aware of what you profess, but I am also aware, after personally building BOTH types of supplies, with 80% of my builds Class A1 BTW, that you have got it wrong. You have it wrong on ALL counts, including the need for low ripple on the 45 output stage of course. Thats pretty funny. I couldn't have paid you to write a better post on what NOT to do. One good trait, you are consistent.
Have you built such a supply for a Type 45 that I descibed? 'Bet not!
L1/C1/L2/C2 are $10.79 for each L and under $13 for each C !! The only real cost is a decent power trannie, but one may relax that part's criteria some, as its the Ls that must be driven, not the Power Trannie !! One must think in dynamic terms with supplies, not in static terms as you did above...its all wrong Ray, sorry. Been there done that, and it truly sucketh.
Just read my 245 post's listening description...'think I fabricated it - and profess it publically ?? I'm not that stupid. Ask Messers John Swenson, C.Y, Nickel Core, and Dr. Y. Chung....they too are delighted . Why remain living in the dark ages??
Tell you, and ANY potential detractors what, ........... just build and listen to the supply I previously described re: the 245 amp's report. Use very heavy gauge ground and B+ wiring, and we will put an END to ANY of this bickering and wasting of bandwidth up here.
***** Its easier to build it and listen to it, than to post outdated "theoretical" supply dogma - that doesn't sound good. ******
Keep an open mind, heart and ear. Enjoy !!
Sincerely, Jeff Medwin
And certainly not intended to mislead anyone. Just my own point of view, based on what I have learned from a number of recognized sources on the subject, my own experience and plain common sense as I see it. Is it really wasteful of bandwidth to post my own honest opinion, just because it happens to differ from yours? Don't forget, this is a public forum.
Ray,The brickbat theory only applies when the capcitance is supplying current the PSU cannot deliver. If the cap does this, it discharges, and the timeconstant of recovery is based on the transformer. The transformer will be in circuit during this time, and so will be audible.
Thanks to the transient nature of a music signal, this happens an awful lot more than the theory suggests, unless your PSU is huge. Thats one of the key reasons why many DIYers upgrade the PSU, and things typically sound better....
Just my experience of the situation.
Owen
Never heard it called that before :) I do favor a fairly big reservoir cap, up to several hundred uF if it seems appropriate. I know this goes against some other people's PS design philosophies, but I'm unaware of any real downside.Certainly, if the reservoir cap gets drained despite having high capacitance, possibly by frequently repeated heavy transients in the music, then it has to be quickly replenished. That's where low DCR in the tranny, rectifiers and choke(s) obviously scores. However, I do not see the point of low C and low H.
Is that what you meant?
Ummm, a SE amp is going to have the PS seeing a *VERY* variable signal. Cut the final off, and demand from the PS goes to zero. Swing the grid full positive and demand doubles.I think you were talking about Class A PP amps. Even those see a rather interesting AC component.
Sure, SE doesn't balance like PP and the demand on the PS will be modulated by the signal. However, the reservoir cap absorbs this modulation, if it's doing its job as a decoupling cap, rendering the net DC demand essentially constant. We rely on decoupling caps at every stage, including the final.
The big final reservoir cap absorbs the modulation all right, and it also absorbs the MUSIC SIGNAL in a SE amp ....thats why we now design with all Cs under 50 uF, and maybe even under 40 uF.'Same absorption applies to high value ( over 1/2 HY ) and high DCR ( over 10 ohms ) chokes ( loses the music ) .... and absorption of the music signal through the SE supply also occurs with inadequate gauge wiring ( loses the music ).
Your thinking ( and posting ) is only static Ray, its outdated / incorrect now in relationship to optimized SE audio amplification, it needs to become dynamic.
Jeff Medwin
"The big final reservoir cap absorbs the modulation all right, and it also absorbs the MUSIC SIGNAL". To my understanding, the modulations ARE the music signal. They're meant to be absorbed, otherwise you have inadequate decoupling. Where the "hot" end of the OPT primary goes to B+ it should be the same as ground, so far as the signal is concerned. If it isn't, we have a problem.I'm not sure what you mean by "low C". Fifty or more years ago, 16uF caps were commonly found doing service as reservoir caps. Now, that's what I call outdated! Fortunately for us, it's now much easier than it was then to make big caps with high working voltages, so we are free to make our choice based on our needs, like the 40uF-50uF caps to which you refer.
'Same absorption applies to high value ( over 1/2 HY ) and high DCR ( over 10 ohms ) chokes ( loses the music )' I don't know where you get this from. As I explained, a good reservoir cap stops the signal dead. Whatever comes between the wall socket and the reservoir cap (be it the usual power tranny, rectifiers, smoothing cap(s) and choke(s) or a bank of car batteries) should make no difference to the signal.
The grid choke on the earlier stage will give you a mild boost in the upper mids and highs suggesting that the overall bass is weak. A grid choke should really only be used on a power tube to compensate for a weak high frequency throughput. With an IST a choke cannot be used of course.I would still change the driver tube to a 2A3 and retain the IST using the present arrangement. The weakness at the moment is that there will not be enough drive using a hi Rp tube. You really need an Rp of around 300 ohms to make this work. I use the 2A3 driving a Tango NC14 5k:5k and it will drive a 211. I have also used a 6C19 pushing 50mA to drive a 300B with plenty of headroom. What you have now barely works and has no headroom whatsoever and will sound weak on dynamic passages.
JohnR
"WE275A (running at 50ma, 250V plate voltage): Tamura F5003, 1.21K bias resistor bypassed with 47uf BG VK"That would give you a -3db point of about 5cps. The signal will not get all the way back to flat until 50cps. This might be part of the soft bass problem but only part of it.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
First off, congratulations for putting together a very high quality SET system. Definitely not for the faint hearted.
To help you with the bass aspects, we need to work backwards from the power tube.
The Ck value is far too small at 47uF for quality bass.
You do not mention any 20-30 ohm resistors placed between the filament and the Rk resistor thus I must assume that you have connected Rk directly to one pin.
This could be better arranged using a pair of 20 ohm resistors to ensure that the filament is correctly ac balanced with regard to the audio signal path. Once these are fitted then a pair of N type 330uF caps can be placed between the tube pins and ground so that proper ac balance is achieved. There is also another reason as follows.The IST output should be connected between the filament and the grid and to NOT use the cathode resistor Rk.
This arrangement will give you maximum gain and the absolute maximum signal clarity. Local feedback is removed thus obtaining the benefits of fixed bias but without the hassle of another power supply.
To allow the grid leak to function, a coupling cap has to be fitted between the top of the IST secondary and the grid.
The grid leak is placed between the grid and the grounded end of Rk.
A grid stopper is not required here.
The IST secondary must not be loaded nor frequency corrected despite much advice to do so. Doing so ruins the sound.
If you are against using a coupling cap here then you will have to go to fixed bias.
A 0.22uF VCAP will give you everything that can be desired. You can also use the lower voltage BG caps but beware of the voltage swing needed for full power not forgetting dynamic signal overloading and associated clipping.The OPT that you have selected will give you good extension of the highs and good *air* but not necessarily at the expense of bass output and low end punch. Very often the extended and very clean highs will fool listeners into thinking that the bass is missing. My experience of SET is that clean and extended highs are relatively easy to obtain; deep and extended bass is very much harder to achieve and comes down to the driver stage having enough current and system overhead to handle the large voltage swings. If there is not enough overhead eg minimum of 6dB, the dynamic range will be compromised and the sound stage collapses on high impact bass notes.
When you get it right, the amplifier will not sound like a tube amp at all. Once that is correct then the amp can
be voiced to suit ones own musical tastes.Now to move on to the driver stage.
You will find that the Rp of the tube is too high to drive an IST indirectly since as I understand it, you are using an ac coupled input to the IST itself. A genuine IST 5k:5k is designed for dc consequently has an airgap. It needs between 15 and 30 mA to function correctly therefore will not be able to respond properly to ac only high value low bass signals.
There is also the issue of unwanted crossover distortion as the core flux changes direction - it is not meant to.
The good news is that a high Rp triode can drive one successfully since they l function very well with a typical pentode such as the 6V6. As an example, a 6SN7 can drive one, Rp of 7K6.
To recapituate, a plate Rp of 5K can successfully drive a 5k:5k IST when connected correctly.Other points raised
Coupling caps - using large value BG high end types is unusual but can be made to work well. The exception is where there is NO dc polarisation as in a location such as an IST to a grid. They will fail given enough operating time.
These caps are not chemical, they are electrostatic as a consequence, they do not use metal for the windings therefore the inherent ESL is very low. The ESR is also very low which is why they work out to 100kHz.
I have used the 50uf/50 volt NP type for CD player output and they are clean and fast but only if polarised by at least 10 per cent of their rated voltage. I have a sub woofer that used ordinary electrolytics between the opamps
and all of the caps failed due to no dc voltage. The designer wrongly assumed that the ac ripple current would support
the low frequency signals. Worthy of note, the non-polarised types also failed in this application. I talked with the manufacturer and they said yes we know.May I suggest that whilst the overall circuit choices are excellent, it is unlikely that you will be able to use the amp over the full 8 octaves therefore some rework may be necessary.
I would propose changing the driver tube to a 2A3 and arranged to drive the IST with 30mA. An IST is normally operated with the quoted mA rather than at say 50 per cent of its rated current.
A 2A3 working into an IST and driving any of the usual power tubes will give you the delicacy that the remainder of the selected tube set is capable of.
An alternative is to retain the driver tube since high Rp power tubes have an inherent sonic delicacy that is hard to give up and change the IST to one having a primary impedance of at least 10k.
I hope that this helps you.
Regards JohnR
Nice post. Can I ask you a question about DC polarisation of caps. Do film (polyprop and foil) need to be polarized?
I'm thinking of the caps in my passive RIAA filter that are after the coupling cap and therefore are not being charged with DC.
I am thinking that I should use caps that are rated at a high enough VDC so I can move the coupling cap to the other side and keep those caps charged.Thanks, Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
film and foil caps do not need polarising voltages. You should look at inner/outer foil being next to a metal chassis due to noise pickup. Incidentally, when a foil cap is tied down to the PCB substrate they will collect noise as well therefore should be lifted off the board.My experience of no dc electrolytics and BGs show componenet failure in the longer term. An NP type cap, BG electrostatic or chemical type will fail since the electrodes do not correctly form themselves in the absence of some dc potential. The pruveyors of NP type caps will tell you otherwise however, I have had to change a few becasue of this.
Regards
JohnR
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Use the 2A3 as you suggest, and just end the amp there !!Jeff Medwin
Blackgates take time to break in. Data available around the web suggests 40 hours. My experience is that it takes more like 80 to 100 hours
AND FURTHER
You know when they finally do break in because a full octave or more of bottom end suddenly appears.As the Hitch Hickers Guide says - don't panic, leave it running a couple days and if you still have no bass you can panic then.
Cheers,
Ian
5 K is too low for your plate resistance. With Rp=Rl you get 6 dB rolloff at transformer's low rated frequency. If your driver tube is worn, its Rp may way higher than you think, which will add insult to injury.You need at least 15 K interstage for good bass in your circuit. Or you may want to use a driver tube with lower Rp, for example 45.
Hello,I take it this is a Single Ended amp. Lets start at the beginning, which is NOT the input stage, but rather, your power supply. Most SE amps are deficient here and the power supply is critical if you want to obtain stunning bass response.
Could you please tell us a lot more about the amp's power supply :1) What is the DCR of your power transformer's secondary winding, plate to plate??
2) What is the DCR, and the inductance, of your input choke?
3) Do additional chokes follow the input choke? If so, what is their DCR and amount of inductance ?
4) What sort of gauge wire do you use for the B+, and how about the grounds' gauge?
5) What amounts of capacitance do you use after each L ??After we examine the supply, I would re-compute the roll-offs of any cathode resistors which are bypassed with a cap. You want the roll offs to be at about 4-8 HZ and also not stacked at the same frequency, but lets just review the supply first, since its the beginning of the amp !!
Jeff Medwin
You have a lot of Iron there.Yes, used up tubes will sound weak and lifeless.
I would do an experiment on your driver stage. You have a choke load going into an interstage transformer. Try one or the other. A simple test is to throw in a plate load resistor on the driver to note the change. You could even try pulling the choke and the interstage to listen to it iron free (with a cap). If this does not work, go through and pull your grid chokes to see if they are contributing. It looks like you went for the full montie.
Also, what is up with using 100uf and 68uf "coupling caps". Am I right that you are using these as signal passing, interstage DC blockers. Try some lower value coupling caps. Ask Mike L what he would recommend.
_______________________________
Long Live Dr.Gizmo
Many thanks for the suggestions.The reason the phenomenon seems very odd to me is that I've done the same topology (i.e., plate chokes, interstage, grid chokes, though with different tubes) before and the results were quite excellent. So I am thinking that may be I misspecified the circuit?
I forgot to mention that the rest of the frequency spectrum sounds excellent, somehow just the mid/low bass is very weak/subdued (the difference is like full range vs mini-monitor).
My choice of coupling caps is odd but I've determined that in my system the best sounding coupling caps are the Black Gates VK or N series (as good as or better than V-cap, old AN silver foils, Mundorf Silver/Gold, etc.). The only BGs with high voltage ratings also are high values so I have to use the 100uf and 68uf ones. I really like the 22uf 350V VKs.
Cheers.
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