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    PAT 4 Pre-amp needs help

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    wazowski

    Posts : 25
    Join date : 2010-12-28
    Location : Cleveland, OH

    PAT 4 Pre-amp needs help

    Post by wazowski on Sun Jan 16, 2011 8:36 am

    I have a PAT-4 pre-amp as well as a PAT-4A. I believe the PAT-4A is factory wired, but I am not certain of this regarding the other. Both need some work, as the pots are noisy and the selector knobs no longer work properly. Some of the switches are bad as well. I would like to try to rebuild one of them, using the remaining one for parts, if needed. Is there a source out there for either NOS or reproduction parts? I checked with Dynakitparts but no luck. Are these units even worth the trouble? I plan on using the finished product with my ST-70.

    Right now I have my ST-70 paired with a vintage Yamaha C-60 pre-amp that I was running with it's M-60 counterpart. I like the combination so far.I would welcome any comments or advice. Thanks.

    Bugs

    Posts : 91
    Join date : 2009-04-17

    Re: PAT 4 Pre-amp needs help

    Post by Bugs on Sun Jan 16, 2011 1:32 pm

    I have a PAT 4 that I gutted for the chassis. I'll check when I get home and see what I saved.

    Best

    ejc

    Posts : 32
    Join date : 2010-10-16
    Age : 65
    Location : Connecticut

    Re: PAT 4 Pre-amp needs help

    Post by ejc on Sun Jan 16, 2011 3:31 pm

    [quote="wazowski"]I have a PAT-4 pre-amp as well as a PAT-4A. I believe the PAT-4A is factory wired, but I am not certain of this regarding the other. Both need some work, as the pots are noisy and the selector knobs no longer work properly. Some of the switches are bad as well. I would like to try to rebuild one of them, using the remaining one for parts, if needed. Is there a source out there for either NOS or reproduction parts? I checked with Dynakitparts but no luck. Are these units even worth the trouble? I plan on using the finished product with my ST-70.

    [quote]

    Roy, ebay and mouser.com should be able to help.

    I am nearing the end of rebuilding a PAT-4. It has been a fun and interesting experience.
    Best is that it is sounding pretty nice.

    Roy supplied several parts - I/O board, Attenuator, Used selector switch.
    E-bay - there's a guy who sells new power supplies and capacitor kits.
    Mouser - parts - I picked up the metal film resistors here.

    Pots can be cleaned. I eliminated the tone controls. Volume control replaced w/ a 24step attenuator.

    Good luck with your project.

    ejc

    Posts : 32
    Join date : 2010-10-16
    Age : 65
    Location : Connecticut

    Re: PAT 4 Pre-amp needs help

    Post by ejc on Tue Jan 18, 2011 9:26 am

    wazowski wrote:I have a PAT-4 pre-amp as well as a PAT-4A. I believe the PAT-4A is factory wired, but I am not certain of this regarding the other. Both need some work, as the pots are noisy and the selector knobs no longer work properly. Some of the switches are bad as well. I would like to try to rebuild one of them, using the remaining one for parts, if needed. Is there a source out there for either NOS or reproduction parts? I checked with Dynakitparts but no luck. Are these units even worth the trouble? I plan on using the finished product with my ST-70.

    Right now I have my ST-70 paired with a vintage Yamaha C-60 pre-amp that I was running with it's M-60 counterpart. I like the combination so far.I would welcome any comments or advice. Thanks.

    Yesterday, I finished my PAT-4 project, it was a long day! (Aside from a repaint of the cover which will be done today). I recapped and swapped resistors for metal films. It is now done.

    Very Happy with the results. It is quiet and sounds great. I suspect the recapping got rid of the last bits of noise. This is a totally differeent unit than what I started with and was basically a rebuild. I did not change the transistors.

    My next stop will probably be to have a tech throw it on his bench to see how it specs out.

    Sal

    Posts : 221
    Join date : 2009-02-05
    Location : Central New Jersey Dynaco-ST70.com

    Re: PAT 4 Pre-amp needs help

    Post by Sal on Tue Jan 18, 2011 9:43 am

    It just so happens I have a PAT-4 on my bench, brought it back to life with a heavy dose of Deoxit. It has a hiss on both channels but otherwise sounds nice. Is that the problem you had before recapping? I unsoldered some caps to find the culprit but I guess a recapping is in order...

    Sal

    ejc

    Posts : 32
    Join date : 2010-10-16
    Age : 65
    Location : Connecticut

    Re: PAT 4 Pre-amp needs help

    Post by ejc on Tue Jan 18, 2011 10:04 am

    Sal wrote:It just so happens I have a PAT-4 on my bench, brought it back to life with a heavy dose of Deoxit. It has a hiss on both channels but otherwise sounds nice. Is that the problem you had before recapping? I unsoldered some caps to find the culprit but I guess a recapping is in order...

    Sal

    This was a step by step experience. And every step was a learning experience and brought improvement to the unit.

    The total cost including the PAT-4 ran $232

    1st I got rid of the power supply and picked up a new one on E-Bay.

    2nd I bypassed the Tone Controls and cleaned all switches and controls.

    3rd I pulled the Vol Control and replaced it w/ a 24step attenuator. This caused me to remove the Loudness Switch from the circuit. I could not figure out how to tap the attenuator to reconnect it.

    As I went along I was also replacing the solid core wires with stranded wires. I discovered all sorts of broken wires and poor solder joints along the way.

    I/O jacks went next to be replaced w/ Roy's I/O board w/ gold RCA jacks.

    It was about here that I discovered the broken selector switch, replaced with a used one (also from Roy).

    I am now using the Loudness Switch as a Selector for CD/AUX.

    I still had some hum/hiss at this point (prior to recapping). I had a hard time figuring it out. I finally grounded the PAT-4 to a wall outlet and that seemed to take care of it (sometimes the most obvious solution is overlooked).

    I was experiencing some cross talk on the Aux/CD switch, some SHORTED RCA plugs on the unused input took care of that.


    I did not bother connecting the Tape Head and Special connections from the PC Board.

    Final phase was the resistor replace with 2% metal Oxide and the Recapping.

    Now the only noise I have is on the Unused and open Special and Tape Head positions on the selector switch.

    Every step of the rehab brought noted improvement and a smile to my face. Very Happy


    Sal

    Posts : 221
    Join date : 2009-02-05
    Location : Central New Jersey Dynaco-ST70.com

    Re: PAT 4 Pre-amp needs help

    Post by Sal on Tue Jan 18, 2011 12:04 pm

    Thanks for the info, the PAT I am working on has a hiss, not a hum. Its very low but never the less its still there. Grounding did not take care of it when I tried it last night.

    Sal

    ejc

    Posts : 32
    Join date : 2010-10-16
    Age : 65
    Location : Connecticut

    Re: PAT 4 Pre-amp needs help

    Post by ejc on Tue Jan 18, 2011 5:20 pm

    Sal wrote:Thanks for the info, the PAT I am working on has a hiss, not a hum. Its very low but never the less its still there. Grounding did not take care of it when I tried it last night.

    Sal

    Is the hiss on all inputs?
    Are you using all inputs?
    You might want to use shorted RCA plugs on unused inputs.
    Bad/leaking Caps?
    Shielding problem?
    My unit had several bad solder connections and broken wires when I got it. Discovered them as I started working on the unit and they would break off as I touched them.

    Just got back from the shop. Distortion levels were low under .05.
    He suggested I change the Ceramic Cap on the On/Off Switch to eliminate On/Off Thump.
    Stopped @ The Shack on the way home and picked one up. Thump now gone.
    He found voltage across the chassis. My ground wire got rid of it, but I decided to run a 3 prong cable for ease. Pulled one out of the basement along with a new Chassis grommet and the transient voltage is gone. Along with it the hum.

    Finally I sprayed the cover gloss black.

    Now I think I'm done.

    tubes4hifi
    Admin

    Posts : 1292
    Join date : 2008-11-30

    Re: PAT 4 Pre-amp needs help

    Post by tubes4hifi on Thu Jan 20, 2011 2:39 am

    Wazowski -
    the Yamaha is a MUCH nicer preamp than the PAT4, but for anyone who wants to restore a PAT4 or a PAS3 (I know, one is SS, one is tube) I have access to MOST all of the parts
    such as switches, and all the front panel controls. As was mentioned I've also got a PCB replacement to upgrade all of the rear panel input & output RCA jacks.
    There used to be someone on ebay selling rebuilt PCBs and/or capacitor replacement kits.
    For the PAS3 folks, I've finally also sourced replacement tone controls and all other parts EXCEPT the blend switch. The blend switch should be bypassed anyway, I doubt anyone uses it.

    GP49

    Posts : 735
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: PAT 4 Pre-amp needs help

    Post by GP49 on Thu Jan 20, 2011 11:42 am

    tubes4hifi wrote:
    The blend switch should be bypassed anyway, I doubt anyone uses it.

    I need something that functions like it, for paralleling channels when playing mono records. Straightwiring it with a simple SPST switch across the channels works. However, I also prefer to be able to select one channel or the other (noise, distortion and record-damage clicks may be more prevalent on one channel or the other) so the blend switch remains, on my modified PAS.

    tubes4hifi
    Admin

    Posts : 1292
    Join date : 2008-11-30

    Re: PAT 4 Pre-amp needs help

    Post by tubes4hifi on Sat Jan 22, 2011 4:34 pm

    so what you really need is called a MODE switch, where you can select stereo, left channel, right channel, or left+right mono, that can easily be done with a 2P4T rotary switch, essentially nearly identical to a selector switch.
    I traced out the connections for the BLEND switch once and it is NOT a simple switch, it was customed design and does several different types of connections depending on the setting.

    GP49

    Posts : 735
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: PAT 4 Pre-amp needs help

    Post by GP49 on Sat Jan 22, 2011 10:56 pm

    Correct. A stereo-mono switch (100% blend) is easy to do and involves no contacts interrupting the signal path at all, thus no degradation of the signal.

    The Dynaco blend switch allows selectable blending to reduce "ping-pong" effects from too-wide speaker spacing or poor recording technique. I doubt that either would be an issue today. In the PAS-2x/3x era it also had a modification to provide ideal blending necessary for the Dyna three-speaker loudspeaker setup but that's not relevant today, either. However, any of these functions can be accomplished without interrupting the signal path, just like the stereo-mono switch.

    A switch that permits selecting one channel or the other does require signal-path interrupting switch contacts. This presents the possibility of signal degradation at the switch contacts; it's just something one has to decide upon and choose. Someone who never plays mono records won't need that.


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