Here's a very advanced CAD rendering:
I just did that on an LMxxxx I have, I forget the exact part #. Not ideal as it picks up more noise, but works enough for the testing purpose. Mixed mode feedback would be better to produce a given output impedance value. Setting it at ~80ohm might be enough to simulate current drive at ~10X load impedance.
As voltage will track impedance at a constant current, impedance peaks will produce the most power. In the case of the Fostex, the Z peaks may be around 75-100ohm IIRC, so it figures there would be a huge rise in output.
Variable Amplifier Impedance
Ok, so you modified the standard LM8xxx schematic to bypass feedback resistors then.
When Pass uses current amps, they really boost the bass output of a Lowther. See measurements in paper:
http://www.firstwatt.com/pdf/art_cs_amps.pdf
Was that mounted to the KleinHorn? I suppose this would fit my description of a "huge horn" a couple of posts back.
The impedance must have been tamed enough to boost bass evenly with the midrange.Yeah, for sure. If a current source amp is going to be used, the amp/speaker system needs to be designed around it.
It's the CHR70 version 2 I think. I took a look at the BB4.al branded version, and it looks like the same driver. Not sure though. With current source, the freq response will tend to track the impedance curve, and boom and HF peaking would be expected. If it were to be used with the Pass F2, I'd put it in a stuffed straight TL with an open end, about 1.3m tall.
RE my tweaks: I don't find the CHR70 to be at all objectionable in stock form. It is after all the markaudio starter model, and I'm simply trying to hot rod it. There is a bit of breakup hash around 10k, which is actually pretty subtle in practice, and not particularly annoying. Still, I wanted to see if I some tweaks would be helpful.
Looking forward to hearing how the mods to the TPA3116 go. I'll have to try that, after I put together the gainclone in my project queue, and fix the 3 old tube amps I already have.
It's been a long time, but I don't recall the peaks on my FF125K being that severe. It did have equivalent overall rising response. It seems like the driver was slightly downgraded when production moved from Japan to Taiwan. Mine was easily tamed with a passive network or EQ. I can't last 3 minutes with big peaks like that myself. I flatten everything. Mash it down!
These paper fostex drivers respond well to dammar and other special sauces. I think it's about time for you to try some tweaks xrk971! It is however a good idea to practice on cheap paper full range drivers before doing anything irreversible to expensive fancy ones.
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Much easier to buy a $20 3116 and swap a couple of electrolytic caps than make a gainclone and repair tube amps
That's the truth. Vintage tube amps can be lots of fun. Just figure that all the caps are shot and leaking, all the carbon comp resistors have drifted, and all the pots are broken junk. Once all that is swapped you're fine.
in the heyday of mass produced tube amps, output transformer quality was very good in general - EICO,Fisher. Heath etc had very wide and smooth response - much better than say Hammond 1650 - my second or third stereo amp was EICO's ST40 then 70 which probably sounded better than a stock Dynaco ST-70- here's John Atwood's push pull tests from 1990 Push-Pull Transformer Test
Here is an interesting "full range" driver that is not too expensive, made of paper, and has "Fostex-like" or "MA-like" peaks. It may sound fine as-is, but would be interesting to play with and add special sauce recipes to tame those peaks. For $18, a lot better than possibly ruining the nice grey charcoal bincho kenaf paper cone FF105WK.
http://www.parts-express.com/pedocs/specs/295-010-dayton-audio-pa130-8-specifications-46131.pdf
What do you guys think of the PA130-8? Kind of a high fs, so maybe as FAST would work but appears to be a sensitive full range option?
Looks good to me. Is that one you've used freddi? It's a hotspot clone. If you've heard those you'll know that they can play very loud and clear. Perfect candidate for tweaking experiments: special coatings, felt on the inside of the frame, epoxy plumber putty for stiffening - maybe even a phase plug.
I don't hesitate to tweak expensive drivers, but it's not a good idea unless you have a very good idea of what the result will be. IOW, experiment on the cheap ones.
I don't hesitate to tweak expensive drivers, but it's not a good idea unless you have a very good idea of what the result will be. IOW, experiment on the cheap ones.
Eico ST70 is way better than a stock Dynaco ST70, at least as far as high fidelity is concerned. No doubt I'll get some heat for that statement. I'd give it an edge over my old Bryston (etc) in realistic presentation.
Much easier to buy a $20 3116 and swap a couple of electrolytic caps than make a gainclone and repair tube amps
That's the truth. Vintage tube amps can be lots of fun. Just figure that all the caps are shot and leaking, all the carbon comp resistors have drifted, and all the pots are broken junk. Once all that is swapped you're fine.
Most fun is simply to do it all.
I've had tons of fun as well as frustration getting a couple of console tube amps back up to snuff. Results were worth it and I learned a lot in the process. OTOH, I like the little TDA2616 kit from Velleman as well. The most ridiculous I built was an all-DIY 4x10W class A beast that cooked a coil as I desperately tried to tame PS ripple. My main amp at the moment is ICEpower 50ASX2, real good stuff IMO. I should check out these 3116 boards to see how they compare. If I build that 2x6" X-Klam from the other thread, I could see about bi-amping it for pretty cheap with these.
There was a reason the scaling was set where it was for the CHR70 - to provide a flat frequency response and good bass extension. If you increase the width to 0.53x, there will be a sag in the response with a peak at the bass knee (due to driver Qts and Vas value). You may want to run dual CHR70's if you like the 0.53x width. I have not run sims for a dual CHR70 yet, but if you are interested in doing that let me know.
Here ya go!
Giantstairs,
Glad you like the TPA3116D2 amp! It is the perfect amp for full range drivers as we hardly ever see the need for more than 40 or 50 watts/ch.
The dual CHR70 Omnes is an interesting pairing with the Karlsonator. The bezel on MA drivers is huge - if that was my one complaint, they should be smaller in the future (probably large size needed for strength since made of plastic?). The bezel is nearly 5 in in diameter which necessitates a scale on the Karlsonator to be at least 0.75x in order to accommodate the two driver bezels. This is not exactly a mini anymore at 22 in tall - but hey, the bass performance will amaze you in this box at that size. The optimized design ended up at 0.75x for length and depth (13.2 in deep) and 0.47x in width (7 in wide). It will be a tall aspect ratio cabinet. The drivers are connected in series as the Re is 3.6 ohms for a total 8 ohm nominal load.
The SPL vs Freq looks very good with an average SPL in the bass region of about 90dB at 2.83V and 1m. The -3dB point for bass extension is about 45 Hz which is very good.
The impedance looks very good for most amps and is flat in the HF region:
The cone excursion is manageable, if you have lof freq content, a high pass filter before the amp might be needed to stay below 4.5mm.
Finally, the impulse response is about as good as you can get - very clean tight dynamics. Drums, guitar, pianos should sound very crisp and lifelike.
I hope you build it - please post pics!
Dayton Audio PA130-8 and PS95-8 are good
I just ran some sims of the PA130-8 in a 0.53x Karlsonator (single driver) and the PS95-8 in a 0.40x Karlsonator and they both model very well. Should provide a very good full bass output that will negate having the need for baffle step correction.
Spec for drivers here:
PA130-8 ($18ea.):
http://www.parts-express.com/pedocs/specs/295-010-dayton-audio-pa130-8-specifications-46131.pdf
PS95-8 ($23EA):
http://www.parts-express.com/pedocs/specs/295-349--dayton-audio-ps95-8-spec-sheet.pdf
PA130-8 in 0.53x (with 50Hz HPF):
PS95-8 in 0.40x (full range):
If anyone wants a budget driver that sounds great - these should be on their short list.
I just ran some sims of the PA130-8 in a 0.53x Karlsonator (single driver) and the PS95-8 in a 0.40x Karlsonator and they both model very well. Should provide a very good full bass output that will negate having the need for baffle step correction.
Spec for drivers here:
PA130-8 ($18ea.):
http://www.parts-express.com/pedocs/specs/295-010-dayton-audio-pa130-8-specifications-46131.pdf
PS95-8 ($23EA):
http://www.parts-express.com/pedocs/specs/295-349--dayton-audio-ps95-8-spec-sheet.pdf
PA130-8 in 0.53x (with 50Hz HPF):
PS95-8 in 0.40x (full range):
If anyone wants a budget driver that sounds great - these should be on their short list.
Attachments
I am working on the 0.53x surgical procedure now. New baffle for 5in driver installed, old holes sealed up. Doubled-up the K-aperture with second layer of foam core with constrained layer damping via liquid nails (low VOC). Looking good so far. Fingers crossed. Should have first sound soon. It looks "right" in an 0.53x - the proportions are there and very pleasing.