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In Reply to: RE: Anyone Use a Series Resistor in their BGT to Limit Current? posted by Maxamillion on November 17, 2015 at 08:42:58
I built a BGT in a project box with a 47,000uF, 16V Panasonic T-HA main cap and a 4.7uF Solen PP bypass cap, and an Energizer 9V Alkaline battery.
I added an internal 9V battery tray to make battery changes easy, for comparing the sonics of different battery types and for checking voltage/replacement at end of battery life.
I inserted a 20 ohm resistor between the battery tray + and the cap + to limit charging currents to 400mA max. I also added an on/off switch across the resistor - when the switch is ON the resistor is bypassed, so initial chargeup can be done with with switch OFF (resistor in). Can also use the switch to check sonics with and without the resistor.
External wiring is 9.5 gauge Cardas copper litz in teflon, terminated in a copper geophone clip.
Letting the cap charge up and form overnight - listening tomorrow.
Follow Ups:
After two days of listening, this is what I hear:Punchier, deeper bass with the BGT. Perhaps a little more bass detail. This is the most obvious difference.
Slightly cleaner overall presentation, but a subtle effect, not nearly as obvious as the above.
Didn't hear much difference with the resistor in or out of circuit. At times I thought there was a slight "thinning" of the sound with the resistor, but it may have been imagined.
So I'd say it's well worth the minimal effort.
I tried adding another BGT (my original junk box prototype) to the system but heard no
additional effect. It seems one BGT is enough in my system.I also tried moving the BGTs around to different locations such as source, preamp, amps, speakers. Again, the sound was the same at all locations, which makes sense to me as the grounds are all connected to form one continuous ground from source to speakers.
Anyway, that's my BGT build and evaluation. YMMV, as they say.
Edits: 11/27/15
After a few days of listening thanks to the long holiday weekend, I noticed a brightness on some songs that had not been present previously. I thought perhaps the PP bypass cap might be to blame, so I removed it, and the brightness went away with it. I still have the punchier bass and dynamics but without the brightness.I think the bypass may have been creating a resonant tank circuit that artificially magnified the treble; modern electrolytics like the Panasonic T-HA series have very low ESR on their own and really don't need bypasses in power supply applications, in my experience. The ESR of a 47,000uF T-HA is .02 ohm at 120Hz and .018 ohm at 20kHz, quite good figures across the audible frequency range.
Anyhow, thought I'd relate my finding. I'm quite happy with just the 47,000uF electrolytic and a 9V battery.
Edits: 11/30/15
that description sounds what most people think a Solen cap sounds like!
I've had very good results with them as filter caps instead of electrolytics. As a tweeter cap they are harsh, though. The Tempoelectric cap review finds the same, good in PS but not so good in x-overs.In any case, I have plenty of treble energy as is, I don't need to boost it at all.
Edits: 11/29/15
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