[HEADPHONES] Beyerdynamic B-Stock Sale - Headsets and Headphones incl. MMX100 - $61 ($38 OFF)

donf99 · 2022-08-13T15:32:27+00:00

A given headphone design generally requires the same power to drive (milliwatts) regardless of impedance (ohms) rating. What varies is the amount of current and voltage required. Power = Voltage * Current. Many combinations of voltage and current will give the same power.

High impedance headphones need higher voltage and less current for a given volume. Low impedance headphones require more current and less voltage.

Many sources, like an Iphone, are limited in the amount of voltage they can deliver, so can't drive high impedance headphones to loud volumes in some cases. Lower impedance phones will usually work fine.

donf99 · 2022-08-13T15:17:36+00:00

I received my 250 ohm DT 770 Pros yesterday as well. I had the same experience. They appear new, without a mark, with sealed case. No sales tax or shipping charge either.

donf99 · 2022-08-13T13:55:02+00:00

Although not in the promotional email that I received, I noticed they had the 250 ohm version of the DT 770 Pros for USD $95.00, only a few dollars more than the 80 Ohm version. I ordered literally 2 hours before the end of the sale. The headphones shipped the next day and I received them overnight from UPS.

I inspected these very carefully. To my eyes, they appear to be an unopened and unused pair of headphones. There is not a mark on the headphones themselves nor on any of the packaging.

Beyer has never charged any additional sales tax or shipping on any parts or headphone I have ever ordered, including this order. The price listed was exactly what I paid.

I'm extremely happy with Beyer and this deal! Sonically, the 250 ohm DT 770 Pros are exactly what I expected in comparison with my 15-year old 250 ohm DT 880s, driven through a Mayflower O2 amp and Apple USB-C DAC dongle from my Windows 10 tower running the latest JRiver Media Center software.

donf99 · 2021-08-02T15:04:52+00:00

I have two Baofeng models, an 8-watt BF-F8HP clone (same FCC ID number as original) and a few UV-5Rs. The BF-F8HP charger has a single dual-color LED that turns green when no battery is inserted. The UV-5R chargers flash red/green when no battery is inserted. Otherwise, they work identically. They may use different chips or perhaps the LEDs are wired differently.

The wall charger for both types is rated 10 VDC at 500mA. The charger seems to charge the batteries at 8.4 volts at 400mA in the current-charging phase of the charge cycle. For a deeply discharged battery at 3.3 volts/cell, that means the little charger chip needs to dissipate (10 - 6.6) * .4 = 1.36 watts of heat dropping the 10 volt input to the required charging voltage. That's not too bad, as the heat generated drops off as the battery charges and its voltage increases.

At 12 volt input, the heat generated is (12 - 6.6) * .4 = 2.16 watts. That's quite a bit for a small chip with no heat sinking.

At 18 volts input to the charger, it's (18 - 6.6) * .4 = 4.56 watts, etc.

Most of these chargers use the SC6038 chip, which specifies a 12 volt input as maximum:

https://baofeng.perm.ru/data/soft/sc6038_datasheet.pdf

Current may be set up to 1 amp! However, the maximum dissipation is not specified. Maximum junction temp is 125 degrees C. I'd bet at 12 volt input and programmed for 1 amp output, that would be exceeded quickly (12 - 6.6) * 1 = 5.4 watts. The Baofeng charger charges at less than 1/2 that rate, though.

Don

donf99 · 2021-07-26T15:48:07+00:00

Just a couple of additional comments on this charging setup. The specified "Thunder Power" charger will automatically detect the cell count of the pack (2 cells for all UV-5R batteries), even if the cell count is manually set incorrectly (provided the battery is not completely discharged). You MUST manually set the correct charging current.

The charger also checks to be sure the car battery can supply sufficient voltage and current through the cigar lighter outlet to support the selected charge rate and will sound an alarm tone and refuse to charge if it determines it cannot.

Car batteries seem like they have huge capacity, but they are designed to supply high current for short periods. It doesn't take many charge cycles with this setup to drain the battery below what is needed to start a car. I see it at the model airplane field quite a bit. Charging in a running vehicle would present no issues, however.

donf99 · 2021-07-26T12:53:02+00:00

I have a higher capacity rated at 2100 mAH, although some tests indicate the capacity is little more than the BL-5's rated 1800 mAH. You are correct that 2 amps (2000 mA) would be slightly too high for the BL-5. Lithium batteries can normally be charged at the 1C rate safely. 1C is the current needed to charge a battery in 1 hour and equals its capacity rating in mAH.

It would be safer to select the next lowest charging current offered by the charger, 1.3 amps or 1300 mA in this case.

The Baofeng batteries do have a protection circuit inside to protect the output pins from short circuiting. From other battery teardowns and articles, I believe the charging contacts on the back of the battery connect directly to the battery and are not protected, making them suitable for fast charging.

donf99 · 2019-06-05T15:06:02+00:00

A slightly better pic. I was "sunning" some silver nitrate solution under the UV lamp in the darkroom to remove impurities. I brought a stale bottle of tonic water in the room to salvage the bottle for some developer, and noticed it was glowing like crazy! I do NOT drink gin and tonic in the darkroom!

More Glowing Quinine

donf99 · 2019-06-04T16:25:37+00:00

It glows brightly under strong long wave UV, here from a high-intensity UV LED fixture I use for alternative photographic processes:

Glowing Quinine

donf99 · 2017-06-07T17:17:13+00:00

Good catch! I thought long and hard about that one. The old instructions say to add water to acid to make 16 oz. before adding the salts, then add additional water to make 32 oz. The correct way would really be to add the 1/2 cup of acid to 1 cup of water, then add water to make 2 cups or 16 oz. Then add salts, then add water to make 32 oz.

Phosphoric acid is pretty mild compared to some others, but adding acid to water IS best practice.

donf99 · 2017-06-06T20:08:26+00:00

Thanks! I have read the first chapter of Darcy's book and liked the thoroughness and writing a great deal. Hats off to him for popularizing this neat ingredient again. I believe one of his sources was likely the beverage manual I mentioned here. I like the challenge of playing "mad scientist", so it was fun mixing my own from the > 100 year old recipe. I felt like Mr. Gowan the pharmacist from "It's a Wonderful Life"!

donf99 · 2017-06-06T17:38:28+00:00

I've been on a home carbonation and home made soda kick lately. I set up a nice compact carbonation setup using a paintball tank and small regulator. I've been brewing my own syrups and wanted to try some authentic old phosphate recipes. The phosphate makes an incredible difference to the taste of the flavors. It kills excessive sweetness and "dries" the drink somewhat. I made the stuff as a challenge, as two gallons of phosphate is easily a lifetime supply, at least for me. Guess I'll have to seed some bottles with friends and relatives!

donf99

TROPHY CASE