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Messages - drdeaner

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Tape Project Machines / another mx5050 thread
« on: April 17, 2017, 01:03:50 PM »
I have read through most of the MX5050 threads about improving playback sonics via new opamps, dc coupling between stages, and power supply upgrades. Early on, I decided to abandon my Otari electronics and go with external tube playback electronics (DeHavilland)  and have been really happy with the results.I don't doubt that the high end Bottlehead preamp would be as good or better.

Recently, I revisited the Otari schematics and decided to take a stab at improving things with my B2 II machine.  I removed the first 3 opamps in the playback stages (3 total opamps for 3 stages in each channel) and installed 8 pin machined sockets in their place.  I removed the headphone opamp and installed an 8 pin machined socket.  I obtained some BrownDog single to dual SOIC to DIP adapters.  I installed 2 LT 1028 8-SOIC opamps in each adapter and plugged them into the first 3 audio playback audio stages.  I took a pair of LME49600 current buffers and kludged them into an 8 pin machined socket so they could be plugged into the headphone IC socket and provide current  but no voltage gain.  Then , I shorted (eliminated)  all of the 'lytic coupling capatitors between opamp stages because the lt1028 has extremely low dc offset and those caps seem unnecessary. And lastly, I took the audio output through the headphone jack, bypassing the final 2 opamps for each channel in the audio stage that provide balanced output.  Taking the output through the head phone jack then provides a much better cable (or headphone) driving circuit, due to the buffers.  I did not change anything in the headphone circuit, so the current buffers are driving the feedback parts that no longer set feedback.  My Otari MX5050 B2 II has the mechanical guide parts obtained from Bottlehead as well as an Anthan capstan roller.  The machine has the mic inputs disconnected and those jacks are wired for direct head output.  A pair of dpdt switches by the new tape head outputs also can direct the tape head signals back to the otari electronics. And the heads were relapped by John French with a Flux magnetics 1/2 track playback head installed.

This all came out better than hoped.  Yes, the output is lower than the balanced output but enough in my system.  The internal playback is worth listening to, which before the mod, it wasn't.  If your plan is to get into playing back tapes, this could be a path for you to get going cheap (or cheaper) and provide an easy upgrade path when your funds allow.  Let me know what you think of the idea...I have actually done several B2 IIs already. It isn't better than my tubed preamp, but it is very nice and good enough to let you enjoy those great tapes.  Of course, you could start with a working MX5050 and not upgrade the mechanical parts to reduce cost. I figured the electronic parts cost about $100.

Reel to Reel Tape Machines / Re: crown sx-822
« on: March 14, 2013, 09:01:26 AM »
I recently bought back an SX822 that I had owned many years ago.  John Haines has helped me repair the logic board, and I have decided to ditch the record/play electronics and install a tube playback electronics under the transport.  John French relapped the heads and I now have a 1/2 track and 1/4 track head on the stack, with head switching in the playback unit.  The transport makes a most satisfying "thwack" when it is put into play. Crown transports are built like tanks!

BTW, John Haines of Jemah Services is moving to Colorado in the next few weeks, and maybe getting out of the repair and parts business. He gave me his son's number in Indiana: 574-206-9080, and he may be a resource for Crown parts and repairs in the future.


Reel to Reel Tape Machines / Re: Hagerman Bugle
« on: March 04, 2013, 11:26:44 AM »
I built the bugle with the values shown above, and the EQ was way off.   I contacted Jim Hagerman and he provided the values relative to a stock phono bugle:
R10=14.3 K
R14= 226 ohm
R8= 0 ohm
remove R13 and C2 

The bugle now works great, far better than the Otari electronics.  There are 3 stages of gain, and you could vary any of them for higher gain if needed.  It is close enough as is. No, this will not equal an EF86 telefunken input stage, but it is great bang for the buck


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