Continued sidetrack discussion from "Tiniest Portable amp I can build" - nikongod microtransformer-based impedance step-down box

[Eee Pee]

Kick butt, it works perfectly, but just a tiny smidge too loud, but not too loud I can't listen.  Excellent!
 
I guess if I really had to I could use the iTunes volume slider to reduce volume, and go into not bit perfect mode, but it's so close I don't think I have to.
 
Gonna let the DAC warm up a bit and have at it all weekend!  Thanks again!
 

 
One hour later edit!
 
Senn 595 @ 50 ohms is about spot on.  Sweet.

 

[scootsit]

I know this is an old thread, but did you guys see these at RatShack, seem to be rated for much, much more power and perhaps be a little nicer.
http://www.radioshack.com/product/index.jsp?productId=2295111&znt_campaign=Category_CMS&znt_source=CAT&znt_medium=RSCOM&znt_content=CT2032230

 

[nikongod]

Quote:

I know this is an old thread, but did you guys see these at RatShack, seem to be rated for much, much more power and perhaps be a little nicer.
http://www.radioshack.com/product/index.jsp?productId=2295111&znt_campaign=Category_CMS&znt_source=CAT&znt_medium=RSCOM&znt_content=CT2032230

 
I haven't seen those locally, but have used "70v" speeko transformers for other stuff. 
They are kind of huge. 
They (70V speaker transformers) do make decent output transformers to fix OTL amps though. If you filter through the bottlehead CRACK thread you can see what I mean

 

[scootsit]

Sounds good, I think I may try a few of the others.

 

[jdkJake]

Got to love thIs:

"Hook up your speakers behind 4 ohm, 8 ohm or no impedance"

 

[scootsit]

Quote:

Got to love thIs:
"Hook up your speakers behind 4 ohm, 8 ohm or no impedance"

I saw that. I went to Radio Shack today and looked at them. They only had two of the ones Nikongod first mentioned, so I decided not to go for it. I figure I'll need at least 4. But, I'm honestly pretty happy with my CMoy running on my ipod line-out with a gain of 2ish. I am considering going down to unity gain, because right now, I'm getting the volume knob up to about 9 or 10 o'clock, and my opamp can handle it. In short, I'm thinking I just don't need this.

 

[jcx]

if you don't buy them out the RS probably won't order more, in fact probably won't order more anyway unless you ask

 

[scootsit]

Quote:

if you don't buy them out the RS probably won't order more, in fact probably won't order more anyway unless you ask

I really hate shopping at radio shack. I'm thinking of just ordering some better transformers from mouser.

 

[jdkJake]

You will probably need to hit up multiple Rat Shacks to get enough of what you are looking for. They are wildly inconsistent with their stock levels. Since there are more of them than even the largest fast food chains, it should not be difficult. In my case, there are twelve of them within 12 miles of where I live! Almost hard to believe they can support that density mainly on cell phones and RC toys, but, they seem to be able to do it.

 

[scootsit]

I was able to get 4. I asked them to order more, and they basically said no. I'm guessing two in series would be better than two in parallel per channel, right?

 

[scootsit]

I got 10! I put two into one of the old altoids gum cases, very small. Maybe the size of two tic-tac containers. Sounds really good, I notice an improvement on my iPod. The iPod I have has an output impedance of ~7z, so it's not reducing the output impedance (the transformer output is 8z). But, the increase in current seems to make a difference, I just can't quite put my finger on what it is, other than that I enjoy it more with the transformers. I have 8 more and an empty altoids case that I am going to fill soon, just haven't had the chance.
 
I think Radio Shack is discontinuing the transformer, so get em while you can! Any store can have other area stores ship them over for free, that's how I got mine.
 
Nikongod, you mentioned bringing one of these builds on a plane, was that in a carry-on or in checked baggage? I'm travelling soon and would love to have this for my multiple layovers.

 

[scootsit]

Well, I built the 8 transformer version, and it sounds great. I had a thought though. If you put all 4 in parallel, wouldn't that drop the output impedance to around 2z, and keep the ratio the same input and output. It would drop the input to around 250z, but that still should be high enough. Is there any downside to doing it that way?
 
Also, I'm thinking of putting this on the output side of a small DAC, like the skeletonDAC, I could even eliminate the output caps then. That would be pretty nifty.

 

[wakibaki]

You might be interested in this thread:-
 
http://www.diyaudio.com/forums/solid-state/177520-opamp-transformer-headphone-amp.html
 
...about a transformer-coupled opamp headphone amp I was messing around with before I became really interested in headphone amps. It contains some really interesting modifications suggested by Elvee regarding linearising the design by taking feedback from after the transformer.
 
I believe the model of the transformer is pretty good.
 
Gain is 3 and THD 0.0054%
 

 
 
 
w

 

[jdkJake]

Well, I built the 8 transformer version, and it sounds great. I had a thought though. If you put all 4 in parallel, wouldn't that drop the output impedance to around 2z, and keep the ratio the same input and output. It would drop the input to around 250z, but that still should be high enough. Is there any downside to doing it that way?

Also, I'm thinking of putting this on the output side of a small DAC, like the skeletonDAC, I could even eliminate the output caps then. That would be pretty nifty.

Excellent. Glad to hear you went forward with experimenting with these. I did not know RS would ship between stores for free, that is good intel.

I think you should give your all four in parallel concept a try and see how it sounds. You could also build it such that you only use one of the primaries on each transformer in the same serial/parrallel configuration you have right now. This would drop the input impedance to 250k while leaving the output at 8k. This would be an eight transformer version of the switchable box I built a few pages a go. I like the 250k:8k as there is less attenuation, which, is helpful for some material. Figure out how to put a 4PDT switch in there and you can have both configurations with a flip of a switch.

You could also try four single primaries in serial and leave the outputs in the serial/parallel configuration. Lot's and lot's of possibilities. Might be interesting to build these up on a punch board first to allow testing of various configurations until you find the one you like best.

 

[scootsit]

Quote:

Quote:

Well, I built the 8 transformer version, and it sounds great. I had a thought though. If you put all 4 in parallel, wouldn't that drop the output impedance to around 2z, and keep the ratio the same input and output. It would drop the input to around 250z, but that still should be high enough. Is there any downside to doing it that way?

Also, I'm thinking of putting this on the output side of a small DAC, like the skeletonDAC, I could even eliminate the output caps then. That would be pretty nifty.

Excellent. Glad to hear you went forward with experimenting with these. I did not know RS would ship between stores for free, that is good intel.

I think you should give your all four in parallel concept a try and see how it sounds. You could also build it such that you only use one of the primaries on each transformer in the same serial/parrallel configuration you have right now. This would drop the input impedance to 250k while leaving the output at 8k. This would be an eight transformer version of the switchable box I built a few pages a go. I like the 250k:8k as there is less attenuation, which, is helpful for some material. Figure out how to put a 4PDT switch in there and you can have both configurations with a flip of a switch.

You could also try four single primaries in serial and leave the outputs in the serial/parallel configuration. Lot's and lot's of possibilities. Might be interesting to build these up on a punch board first to allow testing of various configurations until you find the one you like best.

Well, at the moment, I'm happy with them as is. The only thing I would consider is reducing output impedance, for example by putting all four in parallel. JCX seems to have a pretty good reason(s) for doing the series parrallel configuration. I'm sure all of you guys are more knowledgeable than I. I may try them in the future, but again, I got the feeling that Radio Shack was done selling these (no stock online or jin many stores). Have you brought yours through security onto a plane? I'm nervous it will be confiscated, adn no radio shack will have the parts to rebuild it.