January 26, 201610 yr On 21 January 2016 at 11:38 AM, spritzer said: The Susy needs max 10K so I had to use some of my TKD's. Hey Spritzer, just wondering, what do you mean by this? Is it a gain/stability issue to use a pot of say, 50K? Reason I ask is I'm interested in understanding what effects volume pot resistances have on amps - some people say it makes a difference, others say doesn't matter. I've had to replace quite a few old amps that have had 20 K input pots with 50 K ones just because I couldn't source any of the original ones...
January 26, 201610 yr I think japanese made R-core would be better Kitamura Kiden (北村機電) http://kitamura-kiden.co.jp/
January 26, 201610 yr For a completely different project I have a couple of Chinese ones, via eBay. Two secondaries are rated at 17.5VA each - so 35VA total. Looking at the product datasheet for Kitamura, the physical dimesions (including fixing hole spacing etc), the Chinese one correspinds to Kitamura's 25VA, so the 35VA chinese rating looks a bit hopeful.
January 26, 201610 yr Gotcha, thanks. 7 hours ago, kevin gilmore said: susy is low impedance input, so you can't use a 50k pot. 10k pot max!
January 27, 201610 yr Author 10 hours ago, Craig Sawyers said: For a completely different project I have a couple of Chinese ones, via eBay. Two secondaries are rated at 17.5VA each - so 35VA total. Looking at the product datasheet for Kitamura, the physical dimesions (including fixing hole spacing etc), the Chinese one correspinds to Kitamura's 25VA, so the 35VA chinese rating looks a bit hopeful. That is indeed the issue. The core sizes for the R's are fixed but the Chinese manufacturers don't care too much about that. As for posting pics, that won't work as out of a batch of two, one transformer might be fine while the other one is garbage. Some have been truly terrible with dangerous lead wires and truly terrifying build quality. The bottom line is that I'm staying with toroids for now.
January 30, 201610 yr Ok. Total off-topic time. So, zeroed the four-wire probes. They were 0.0012 ohms. Set to slow with 10 moving average samples. Using 100 range with a 100.000 .005% resistor. Last calibration 15 years (!) Ok, spec after 1 year (max on datasheet) is 100+40, which is ppm reading plus range. So, I think this is 100*0.01%+100*0.004% or +/- 0.014 ohms. So, my reading is 99.981. So, in spec? Maybe?
January 31, 201610 yr I tried a member's dynalo mk2 in San Jose meet today. I think it's neutral and well controlled and beats Nelson Pass headphone amp (which is shown side by side) easily.
February 14, 201610 yr SE to balanced is what you probably mean, and you can do that. you can also do SE output, but then why?
February 14, 201610 yr Perzactly. Just make sure the wires to each transducer such as the return/negative are NOT joined in the plug.
February 14, 201610 yr 4 hours ago, spritzer said: Leave the - output floating and just use the +. 3 hours ago, wink said: Yep, and let all that balanced goodness go to waste......... 14 minutes ago, kevin gilmore said: SE to balanced is what you probably mean, and you can do that. you can also do SE output, but then why? Yes, i mean SE output. I will use both SE and Balanced output but SE is always more convenient because i have 5 headphones and recable all of them will cost quite a lot. I have another questions: 1. How do i wire the ground wire of SE output jack? to one board Gnd or to the Power supply GND? 2. I searched mouser for the Op27, there are 2 variant: Op27Gp (3.42$) and Op27Ep (6.61$), the different seem like only the operating temperature, so will the Gp work fine? I also have some spare opamps (opa1641 and opa551 which can run at +/-30V), can these work as servo opamp for the Susy Dynalo? Thanks!
February 14, 201610 yr Author The ground on the Dynalo is shared but for lowest potential I'd connect the ground to the PSU. Shouldn't matter though... Too tired to look up the datasheets for those but many single opamps will work.
February 15, 201610 yr FWIW, this OP27 works on my Dynalo build: http://www.mouser.com/ProductDetail/Analog-Devices/OP27GPZ/?qs=sGAEpiMZZMvtNjJQt4UgLalm6EXZly/yGRc8RxRIZuM=
February 15, 201610 yr I used OPA445BMs on my build ,I think single OPAmps can run unity-gain stable should work fine
February 16, 201610 yr I use TL-071 or TL-081 for singles (or 72s and 82s for duals). From testing opamps in a discrete I/V stage (0 feedback, so touchy), these seem to pull the offset in faster and lower than the OP27s I had do. Particularly the 08x. I believe Justin used to use these in the GS-1 and probably in the GSX as well.
February 17, 201610 yr i have over 200 op27 in stock. where i got them, no clue. but better than paying for them. finally had to buy opa445 from mouser as i ran out. one chip dead out of the package. have not seen that in a very long time.
February 17, 201610 yr Author That is just weird. Never had that happen but the OPA445 is certainly not cheap so shouldn't even be possible...
February 19, 201610 yr On 2016-01-21 at 1:38 AM, spritzer said: As I've been promising to do for months I'm finally working on some dynamic amps. Here is something new, a Susy Dynalo with switchers... Running at +/-18V there. Are those switchers of the ready made or home made variety? Thinking about trying this, but not sure what requirements to set on switchers in this use (max ripple, for example)?
February 26, 201610 yr mwl168 did a run of them awhile ago, probably the newer SMD version. The TO92 silicon is not available anymore; I was probably one of the last to build that version and got lucky on finding some. He will probably weigh in on whether he has any left or not. Otherwise, someplace like seeedstudio could run boards for you for pretty cheap. The later board runs seem to use heavier copper (2oz and sometimes 4oz), but I've never had any problems with 1oz copper boards even with some rework. Kevin has the board files on his site. I see dynalobal12 dynalobal13 dynalobal15 dynalobal17 Not sure what the differences are between them; would have to search the thread.
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