c12mech Posted December 17, 2012 Report Posted December 17, 2012 I was looking at the Schitt Audio Mjolnir amp and noticed that it has an 4-gang Alps RK27 for volume control. Does anyone know where I could find these. I see some motorized ones on ebay but am not sure if they are real. I don't really want to spend more on a stepped attenuator than the rest of the whole project cost.
n_maher Posted December 17, 2012 Author Report Posted December 17, 2012 Ebay used to be one of the few sources for the 4-gang Alps pots. I'd avoid the motorized ones unless you really want a motorized pot. If you want I can check at home, I might have a spare 4 channel pot kicking around that I have no plans for that would be reasonably priced.
spritzer Posted December 17, 2012 Report Posted December 17, 2012 I believe the 4-gang can be ordered through the distributors as the new Senn amps use them as well. I didn't want to deal with all that so I went the Alpha pot route.
Pars Posted December 17, 2012 Report Posted December 17, 2012 I've got a motorized one (Alps RK27) kicking around that I don't have plans for. I'll have to see if it is 50K or what though. Let me know.
Lil Knight Posted December 17, 2012 Report Posted December 17, 2012 http://www.ebay.com/itm/Alps-RK27-Pot-Quad-audio-taper-50K-for-balanced-/190408038623?pt=LH_DefaultDomain_0&hash=item2c553418df
c12mech Posted December 18, 2012 Report Posted December 18, 2012 Thanks guys. Nate and Pars, let me know what you have. I am working on a Shalco stepped attenuator for my Beta 22 but would like to have some sort of volume control other than my pc. After that it will be moved to a balanced SSMH amp I have in the works. One of those dumb things I just want to do for fun. I know it defeats the whole premiss of the SSMH but I want to do it anyway.
n_maher Posted December 18, 2012 Author Report Posted December 18, 2012 If I remember correctly the gain is pretty substantial and not adjustable on the SSMH so going balanced would not only defeat the purpose but might render the amp useless. I checked Pete's article and can't find a gain spec'd but you might want to look into that issue a bit more before sinking more $$ into the project. One of the more technically inclined here can probably look at the schematic and figure it out for you but I'm not your man for that.
c12mech Posted December 18, 2012 Report Posted December 18, 2012 Thanks Nate, I will look at that a little closer before I do anything else.
n_maher Posted December 18, 2012 Author Report Posted December 18, 2012 A bit of searching in the original head-fi thread seems to indicate that the gain of the standard (19J6-based) SSMH is 15 so if you build a balanced version you're going to have a gain of 30 which would be insane.
dsavitsk Posted December 18, 2012 Report Posted December 18, 2012 (edited) Gain is a little less than mu of the tube. Might be 15 at the current level used. Tying two SSMHs back to back as a "balanced" amp is a bad idea in terms of, well, everything. If you want to build a balanced amp, build a balanced amp. But don't build two non balanced amps and think that putting them together makes something better. Also, conveniently, the 6J6 tube is built to be used as a differential pair. Edit -- and a shunting pot (Config B below) will allow you to use an off the shelf 2 gang pot, sound better, be better balanced, and will cut the signal by ~6dB. Edited December 18, 2012 by dsavitsk 1
c12mech Posted December 19, 2012 Report Posted December 19, 2012 Thanks for all the info guys. It was really just a thought I had but with this information I see it would be ridiculous to even try. I do like the idea of that shunted pot. It looks pretty simple to do as well. I have to see if I have any 2-gang pots laying around.
dsavitsk Posted December 19, 2012 Report Posted December 19, 2012 I don't mean to badmouth balanced -- I prefer differential topologies. I just mean to badmouth the building two amps and calling it balanced approach. But a 6J6 based hybrid balanced amp could be a good thing. It probably just won't look all that much like the SSMH.
c12mech Posted December 19, 2012 Report Posted December 19, 2012 The more I think about it the more I like the idea of trying the 6J6 approach. The only reason I thought of the SSMH was that I had some extra parts laying around. maybe I will just do another one and give it away or put it on my desk at work.
RudeWolf Posted December 29, 2012 Report Posted December 29, 2012 Just did some biasing to my Parasound 1600 (one channel had a nasty 0.5V DC offset). Turns out that despite using really nice (for that time) opamps Parasound decided to use rather cruddy MOSFETs as current buffers for the IV stage. Therefore I'm thinking to swap them out for a BUF634 buffer that would most likely give better linearity and no danger of DC offset. Have any of you got experience with using this chip as a current buffer in similar applications? I could whip up a smd diamond buffer but I have a hard time seeing practical benefits of this.
luvdunhill Posted December 29, 2012 Report Posted December 29, 2012 (edited) ^ I'd probably keep the FET current buffer. You can get really low distortion this way, depending on the topology. Anyone know of a place that can beat PcX's price on TKD 2CP-601S 10K? Edited December 29, 2012 by luvdunhill
n_maher Posted January 23, 2013 Author Report Posted January 23, 2013 Parts help needed - somehow in my last Mouser order I forgot the 2 N-channel MOSFETs that I need for a KGSS power supply. Anyone have a couple spares kicking around that they could send my way. They are, predictably, the last two damn parts that I need to fully stuff the boards... @c12 - I do have a one of the 4ch alphas if you are still interested. Just drop me a line and we'll figure something out.
luvdunhill Posted January 23, 2013 Report Posted January 23, 2013 Nate, let me check in the morning.. I should have plenty.
naamanf Posted January 23, 2013 Report Posted January 23, 2013 Parts help needed - somehow in my last Mouser order I forgot the 2 N-channel MOSFETs that I need for a KGSS power supply. Anyone have a couple spares kicking around that they could send my way. They are, predictably, the last two damn parts that I need to fully stuff the boards... @c12 - I do have a one of the 4ch alphas if you are still interested. Just drop me a line and we'll figure something out. What part exactly? Might have some kicking around.
n_maher Posted January 23, 2013 Author Report Posted January 23, 2013 The part that I've used in the past is FQPF8N80C. They're in stock at Mouser but I'm just trying to avoid another order, if I can help it.
eggil Posted January 23, 2013 Report Posted January 23, 2013 I have a few fqpf8n80c. How many do you need? Shoot me a pm.
dsavitsk Posted January 23, 2013 Report Posted January 23, 2013 For future reference, Digikey no longer has a minimum order requirement, and they will ship small orders via USPS First Class mail. For something like two FETs, the shipping will cost less than $2.
n_maher Posted January 23, 2013 Author Report Posted January 23, 2013 Thanks Doug, that's good to know.
Mister X Posted February 3, 2013 Report Posted February 3, 2013 Anybody have any ideas for a panel mountable male 30 pin iPod type connector? I found a connector that would be perfect but it appears I would have to order it direct from the manufacturer and then design a break out board for it..... http://www.wellco.com.tw/PDF/IPODConnectors03.pdf Sparkfun has one that would do the job but it's pretty huge... https://www.sparkfun.com/products/8295?
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