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Follow Ups:
I can't fine the spec on the 10y, but I wouldn't. When I went from a 100K on my 300b to a grid choke there was a world of difference. And it was all good. Once the grid is over driven, the larger the DCR in the grid circuit, the more the tube is taken out of bias and the longer it takes to recover.If you're going to use a resistor, I would think the smaller the better as long as the driver stage can handle it.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Dear Tre,Thanks.
Let me eleborate. The preceeding (voltage) stage has a Zout of slightly less than 25K. I do have a 4800H grid choke, but @ 4hz this gives a Xl of about 120K. I want to maintain a 1:10 ratio between Zout and Zin, so this will not do.
Hence my question for the 250K grid-leak, which I want to breadboard, just to compare the 250K grid leak vs the 4800H grid choke. Compared with a 100K grid leak, I will be better of with the choke I guess.
On the breadboard I also want to experiment with a choke bypass R to lower the Q, and even a 100K in series with the grid choke.
I cannot 'tune' this on paper, so I just want to listen and compare.
Regards,
NC
"I do have a 4800H grid choke, but @ 4hz this gives a Xl of about 120K. I want to maintain a 1:10 ratio between Zout and Zin, so this will not do."But it's 250k at 8Hz!
How low do your speakers go? :)
The speakers go down to DC (for a little while at least), problem is that I don't hear much out of the speaker below 30Hz or so... ;-)Point taken, but I just want to avoid any 'anomalies' in band. But, as Naz mentioned, I also might like a small 'bump' in the 20-30Hz region, indeed balancing the rolloff.
Thanks all.
NC
Hi NC,I have little doubt that 250K will work but like Tre I'm a fan of grid chokes and would opt to use that 4800H choke of yours any day. I wouldn't worry about the lowish impedance at 4Hz. This will cause slightly poorer linearity but at 4Hz who cares, you'll never hear it. The benefits of the grid choke far outweigh this and I'd be VERY surprised if any value grid leak R sounded better. The coupling cap value has a large bearing on the Q as well so you should experiment with this as well as parallel R. Smaller C value will increase Q. Series R is a waste IMHO but it's always good to see the effect for yourself.
Regards,
Naz
Only thing I differ in is, I'd like to avoid the R and would increase coupling cap some but perhaps not as much as the math suggests. A slight rise at 20 hertz peaking around 7 hertz or so isn't such a bad thing. Given what most can afford in speakers I doubt it will be a problem. Due consideration to a rumble filter might be in order for vinyl lovers. I stressed a lot about but in the end things have worked out nicely.So like Naz says....go with the grid choke and don't think twice. Look at the choke's reactance at higher hertz and ask yourself what resistor can match that....and then factor in the lower DCR to keep that output tube happy....as da hammer said, "you can't touch that".
Russ
Hey Russ,Just to clarify, I agree with all you've said, including elimination of the R. In providing some general comment on the options I wasn't clear enough on that point. Also, depending on the headroom of the amp, and the speaker combo I'd even tune for a peak a higher frequency like 20 - 30 Hz. This can add a nice fullness to the presentation making vocals, woods, drums and the like much more pleasing ... relaxed and natural IMHO without muddying the mids. The purists might have a problem with it but I say you are only balancing the rolloff anyway.
Regards,
Naz
i'll agree with you as long at that peak is well damped. This happens naturally in an output stage from the speaker, but in the case of a grid choke, you can get some pretty sharp peaking without adding external parts to "smooth" things out.
You know I am playing with speakers....I will use an evil op amp crossover at first but line level passive will be the goal. The high pass (250 hertz) of the band pass filter (to midrange) could be done nice and easy with coupling caps and cathode bypass caps in the power amp. But if I have grid chokes on the output tubes won't trying to create a roll off with coupling caps just raise my resonance point with my grid chokes?
Russ
P.S. You had mentioned a way to not have bass muddy the mids before...is this one of your tricks?
Actually, it can work for you. A lower value cap not only increases the frequency of resonance but also the peak amplitude. In doing so the LF rolloff is also much steeper so with some experimentation I think this will work very well for you. Although in itself its not one of my "tricks" I have found it extremely useful in boosting Low frequency response without muddying the mids (I suppose it could be termed a trick after all).
Fundamentally what I've been advocating is the use of one or more (good) subs with a very steep HF rolloff to keep them right away from the mids. Sometimes it even pays to set the Xover point to a very low frequency, like 40-50 Hz if the slope isn’t steep enough. I can understand people's distain for subs if this is not done, but done right you would never live without them. I think a grid choke can be very beneficial here.In my system I take the signal from the OP of my Phono/Pre direct to my SE845 amps to run the Midbass/ESL combo with a full range signal. The OP of the Phono/Pre is paralleled off to drive the SS Active Crossover (which has a very high input impedance) and the Crossover is only used to drive the SS sub amps. The Mid/HF output is ignored. I can't remember if the Crossover has an 18db or 24db / Octave slope but in any case I use a Xover frequency of 60Hz and still find myself further boosting 30Hz by 4db and cutting 50Hz by the same to effectively achieve a higher slope. If it had a 50Hz Xover option or a steeper slope I’d use it.
There are some interesting things that happen when done this way and I've seen you write about one of them. The added bass actually seems to improve the HF response and definition. It also adds weight to vocals and other instruments even though there is minimal effect on their expected fundamental frequency range. Tonally it is far more pleasing and natural sounding. In fact I strongly suspect that tonal balance has far more to do with achieving a harmonious (and real) sound than distortion (within reason of course).
IMHO there is a whole octave of music missing without the use of subs or speakers that will work effectively down to 20-30Hz … even with Vinyl! Exaggeration, but you get what I mean.
Cheers,
Naz
Are you married to the driver with the highish output impedance?Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Dear Tre,Actually yes...
If you look at 'her' picture, you will understand why...
Regards,
NC
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Have Fun and Enjoy the Music
"Still Working the Problem"
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I have been using 22K on my 801A running in plain class A1: input stage with a transformer.Ciao
Gianluca
Good Gluca,My mentor, Bob Fulton in 1984, told me to use R's to ground on output stage DHTs of 20K or less, and get a driver stage that can pull it, OR, use iron with low DCR to ground.
Jeff Medwin
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