Guest Posted May 11, 2017 Share Posted May 11, 2017 Just now, mwhouston said: Not in a MC Mimic. Also I have some improvement ideas for your La Gitana. PM me. (yea, that's what I meant ) Awesome, incoming Nice Pre, but clinical and bright, may suit some interested in what you have to add to it, cheers Link to comment Share on other sites More sharing options...
mwhouston Posted May 12, 2017 Share Posted May 12, 2017 17 hours ago, 125dBmonster said: (yea, that's what I meant ) Awesome, incoming Nice Pre, but clinical and bright, may suit some interested in what you have to add to it, cheers Well it took a few pairs of ears and not just mine for me to realise La Gitana tube MM phono preamp is bright. A few comments from friends helped me realise that. Not disturbingly so just leans to the bright side. Of course if your system is not as airy as it could be or your mid-range is too recessed then this would provide a balance. My 15" Beyma concentrics are a little forward in sound, I'm using one of my MC stages which is highly detailed and with La Gitana it's all possibly too much. There is an easy cure. When I was helping to develop the 4S single stage series of tube preamps I tried a pair of 12AX7s but found they sounded strained and too aggressive. I then tried some 12AU7s and found a much better balance. When I built La Gitana I swapped out the JJ 12AX7s for my then favs. the U7 but found the sound a little soft. Now I realise the U7 provided a much better balanced overall tone. But when compared to the brighter A7s felt I was missing top end. Not so the U7s just soften the treble and removed the more clinical and over detailed top end. On a short listen it sounds so much more balanced. I am using a brand new pair of top of the range Psvane 12AU7 "T" series MKIIs. I would suggest you use a high end tube to retain the clean and detailed sound La Gitana has. But each to his own. Link to comment Share on other sites More sharing options...
mwhouston Posted May 12, 2017 Share Posted May 12, 2017 (edited) Just one other great spin off for using the U7s. The A7s have a lot of gain. In my system I could nearly turn my tube preamp up. Now I can turn it up much more which gives me far better volume control and works with the better parts of the Alps Blue Velvet pot. Edited May 12, 2017 by mwhouston Link to comment Share on other sites More sharing options...
mwhouston Posted May 16, 2017 Share Posted May 16, 2017 The Oatley K272C was designed to use the OPA2134 OPAMP chip. Also there is two Jan6418 sub-miniature triodes in a portable head phone amp. I thought the sound excellent until I dropped in a Brson V5i-D OPAMP as a direct replacement. I expected an improvement on sound but not to the degree I'm hearing. It sounds so lush, rich and super smooth I'm realy quite shocked. I'm not sure of the price of these high performance OPAMPS but just from what I'm hearing I'd say it is more than worth it. Link to comment Share on other sites More sharing options...
hyper Posted May 22, 2017 Share Posted May 22, 2017 My PCBs arrived today :-) Here's the Preamp board and it's power supply board. I've already described the Preamp, so here's a bit about the PSU. The power supply board provides an unregulated +/- 20V to the regulators on the Preamp board, as well as an unregulated 16V supply for the regulator that powers the relays. The PSU has an R-C-R-C filter on each rail, to filter out any noise above a few hundred Hz even before the regulators on the Preamp board. The opamps used on the Preamp board have tremendous PSRR (power supply rejection ratio) at low frequencies, something like 120dB of rejection. They are essentially immune to low frequency ripple on their supply rails. However the PSRR drops off with frequency, so the idea is to have the PSU board take care of the high frequency noise, so the opamps only see low frequency ripple. In fact with the nice LT3081/3091 linear regs on-board, I doubt there is any noise getting thru to the analogue regulated supplies. See if I can get these built up by the weekend.. -Al. Nice work Al look forward to how it sounds? Where did you end up getting boards made? Maybe you mentioned in earlier post but too lazy to check Well done and hope the boards check out Ok, nothing worse then getting boards only to find the only non jellybean part on the board has wrong lead spacing [emoji19] Sent from my SM-G955F using Tapatalk 1 Link to comment Share on other sites More sharing options...
hyper Posted May 22, 2017 Share Posted May 22, 2017 My PCBs arrived today :-) Here's the Preamp board and it's power supply board. I've already described the Preamp, so here's a bit about the PSU. The power supply board provides an unregulated +/- 20V to the regulators on the Preamp board, as well as an unregulated 16V supply for the regulator that powers the relays. The PSU has an R-C-R-C filter on each rail, to filter out any noise above a few hundred Hz even before the regulators on the Preamp board. The opamps used on the Preamp board have tremendous PSRR (power supply rejection ratio) at low frequencies, something like 120dB of rejection. They are essentially immune to low frequency ripple on their supply rails. However the PSRR drops off with frequency, so the idea is to have the PSU board take care of the high frequency noise, so the opamps only see low frequency ripple. In fact with the nice LT3081/3091 linear regs on-board, I doubt there is any noise getting thru to the analogue regulated supplies. See if I can get these built up by the weekend.. -Al. Actually looking at the boards my guess is going to be pcbway [emoji3]Sent from my SM-G955F using Tapatalk Link to comment Share on other sites More sharing options...
Alistair W Posted May 23, 2017 Share Posted May 23, 2017 14 hours ago, hyper said: Nice work Al look forward to how it sounds? Where did you end up getting boards made? Maybe you mentioned in earlier post but too lazy to check Well done and hope the boards check out Ok, nothing worse then getting boards only to find the only non jellybean part on the board has wrong lead spacing Sent from my SM-G955F using Tapatalk Gidday Hyper, I've built up one board and gave it a quick listen while on the bench. Sounds nice and neutral, but can't say much until I swap out the old board for this one in my preamp. The rotary switch is a Greyhill one, and that's a Bourns conductive plastic volume pot - although the board also can fit an Alps Blue Velvet. For now, it makes good clean sinewaves when hooked up to the sig gen! Not much free time lately so this is going slow, as always. Never said *which* weekend I'd get the project finished!?? And yep, PCBway for the boards. Cheap, and fast delivery. -Al. 1 Link to comment Share on other sites More sharing options...
Batty Posted May 24, 2017 Share Posted May 24, 2017 My next MM phono pre will be Oatley Electronics K301 kit. Arrived today. I have separated the PSU from the pre so far, should have it together over the weekend, then it's case choice. If I like it I may put it and the Boozehound Labs Pre Pre in the same box. 3 Link to comment Share on other sites More sharing options...
mwhouston Posted May 24, 2017 Share Posted May 24, 2017 I've built one and think there was hum if you didn't seperate the PS. I thought it wasn't too bad. Link to comment Share on other sites More sharing options...
Batty Posted May 25, 2017 Share Posted May 25, 2017 Thinking maybe 2 boxes. 1 Link to comment Share on other sites More sharing options...
mwhouston Posted May 25, 2017 Share Posted May 25, 2017 38 minutes ago, Batty said: Thinking maybe 2 boxes. This is how I did mine. I had the encsloure on hand so part of the decision. http://mongreldogaudio.blogspot.com.au/2011/09/oatleymongrel-dog-audio-jfet-phono.html Link to comment Share on other sites More sharing options...
mwhouston Posted May 25, 2017 Share Posted May 25, 2017 Some other images and builds. http://mongreldogaudio.blogspot.com.au/2011/09/oatleymongrel-dog-audio-jfet-phono_24.html http://mongreldogaudio.blogspot.com.au/2011/09/oatleymongrel-dog-audio-jfet-phono_06.html Link to comment Share on other sites More sharing options...
Batty Posted May 25, 2017 Share Posted May 25, 2017 I'm thinking of upgrading the polyester caps at input, between stages and output, 0.1 and 0.33uF as they are in the signal path, any suggestions and a source? Link to comment Share on other sites More sharing options...
Batty Posted May 25, 2017 Share Posted May 25, 2017 Change of plan re the case, I have ripped the guts out of an old PC power supply and will fit it in that, nice shiny finish, plus it has an RFI socket already fitted and an earth to chassis. Just need to decide where to mount the phono sockets, top or side or input on top and output on the side or vice- versa. Pics to follow. 1 Link to comment Share on other sites More sharing options...
Batty Posted May 25, 2017 Share Posted May 25, 2017 Pictures as promised. 4 Link to comment Share on other sites More sharing options...
mwhouston Posted May 25, 2017 Share Posted May 25, 2017 Not good. SMPS. Bad, bad, bad. Link to comment Share on other sites More sharing options...
mwhouston Posted May 25, 2017 Share Posted May 25, 2017 Now I see you are just using the enclosure. Good, Good, Good. 1 Link to comment Share on other sites More sharing options...
Batty Posted May 25, 2017 Share Posted May 25, 2017 I even double insulated the mains although they are the wrong colour wire. Link to comment Share on other sites More sharing options...
betocool Posted May 25, 2017 Share Posted May 25, 2017 Can you get those mini-tubes somewhere? Any good? 1 Link to comment Share on other sites More sharing options...
Batty Posted May 25, 2017 Share Posted May 25, 2017 I have not looked anywhere to find the valves, but they are used in microphones so probably available. Link to comment Share on other sites More sharing options...
mwhouston Posted May 25, 2017 Share Posted May 25, 2017 Used in war head guidance systems. Not effected by atomic blast like SS. Link to comment Share on other sites More sharing options...
betocool Posted May 26, 2017 Share Posted May 26, 2017 @Batty, @mwhouston I was thinking more along the lines as, "can you get them from RS" and "Any good as audio signal amplifiers" 2 Link to comment Share on other sites More sharing options...
Batty Posted May 26, 2017 Share Posted May 26, 2017 I think Oatley Electronics sell them separate from the kits too. Just checked my build 20mV in 500 mV out and no distortion on a 1 KHz sine wave. 1 Link to comment Share on other sites More sharing options...
Batty Posted May 26, 2017 Share Posted May 26, 2017 Just checked the Oatley site, the valves are $6 each. 1 Link to comment Share on other sites More sharing options...
betocool Posted May 26, 2017 Share Posted May 26, 2017 Thanks @Batty, I might give them a test run given time... after I finish other projects. Cheers, Alberto Link to comment Share on other sites More sharing options...
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