PAT-4 Rebuild - It started out as a simple project.

rlee8394 · « **on:** 4 Mar 2018, 12:00 am »

Somehow, I can't quite remember, I ended up with a pair of Dynaco PAT-4 preamps. My nephew was getting into vinyl and was running his rig through an old Technics receiver. I bought him a new U-Turn Orbit turntable and gave him an Audio by Van Alstine Insight + 170 power amp. I came across the site Updatemydynaco; https://www.updatemydynaco.com and thought it would be nice to refresh one of the PAT-4 preamps. So I purchased the Blue LED light for power switch, Regulated power supply, Tone Control switch, Distortion Reducer, Phono Preamp Upgrade, and the Line Stage Kit. I installed the various kits and listened to the completed preamp and it sounded very good! Much better than the stock PAT-4. I gave it to my nephew and along with the Orbit, AVA Insight+ 170, and a pair of Dennis Murphy's new model Affordable Accuracy Monitors, he had a damn nice system.

After about six months, I upgraded his preamp to an AVA Fet-Valve with Insight + Phono board. The problem now was, what am I going to do with this updated PAT-4? I decided to sell it but felt it wasn't the best it could be. So I went back and purchased the RCA jack set as I didn't want to sell it with the old corroded phenolic jacks. Jacks installed and now the preamp was worthy of inserting into someone's system. But wait, there's more!

I guess I was bitten by the upgrade bug. I then made the final purchase from Updatemydynaco of the Toroid Power Transformer. I also purchased new Alps volume and balance controls. to complete the upgrade I stripped the entire chassis, ultrasonically cleaned the switches, boards, reflowed all solder connections, and rewired the unit with teflon wire. The result is what you see below.

This is probably one of the nicest, cleanest PAT-4 preamps around. I'll be posting this in the Trading Post for sale.
Now where is that other PAT-4????

-Ron

dB Cooper · « **Reply #1 on:** 8 Mar 2018, 05:26 am »

Nice work. Looks like you did everything upgrademydynaco offers without changing out the main pc cards. I have an SCA80 with AVA MosFet circuits in it and will probably replace the horribly oxidized RCA jacks first if I ever get around to sending it up to AVA.

Let us know about the second one, esp. if you go 'all in' and replace the main boards.

ohenry · « **Reply #2 on:** 8 Mar 2018, 05:42 am »

Ah, shades of 1974. I built that preamp and the ST-120. They carried me through four years of college and beyond. I'm sure the changes made are nice. It's good to see the oldies still going strong. Nice work.

Speedskater · « **Reply #3 on:** 8 Mar 2018, 02:11 pm »

It might be a challenge to modernize the obsolete backpanel.

hibuckhobby · « **Reply #4 on:** 8 Mar 2018, 04:01 pm »

Quote from: Speedskater on 8 Mar 2018, 02:11 pm

It might be a challenge to modernize the obsolete backpanel.

Actually, he already did with the exception of things like balanced inputs/outputs, which isn't realistic.
What I'm curious about is if a remote control volume could be added...perhaps the one they use in
their preamp kit? For me, that would be a wonderful balance of retro and modern.
Hibuck...

dB Cooper · « **Reply #5 on:** 8 Mar 2018, 04:07 pm »

If that operates by IR, probably not (unless the IR sensor could be put right behind the power switch maybe) unless one drills the front panel for it (sacrilege!). If it could be done, it would be cool though.

I think a system that makes you get off your (_._) once in awhile may actually be a good thing LOL

rlee8394 · « **Reply #6 on:** 16 Apr 2018, 10:30 pm »

db,

You have inspired me! I built a nice little jfet phono card a while ago and installed it in a spare chassis. I think it sounds pretty darn good. Anyway, your suggestion of all new cards in the other PAT-4 chassis got me thinking. I designed a jfet line card and a new precision dual adjustable power supply card. They arrived today. I then designed a new backplane jacket card for the PAT-4. All the jacks are grounded to the backplane except for the phono jacks. Finally, I designed a new board for the rocker switches. I hate having to wire all of those switches with small pieces of wire. This board will slide over the lugs of all the rocker switches except for the power switch and soldered in place. All interswitch connections are routed on the board along with the four caps and five resistors soldered on-board with pad connections for the selector switch and volume control. This board and the backplane will get ordered this week. I'll use a new Alps volume and balance controls as on this unit. The filter switch and gone controls will be bypassed. Stay tuned!

Ron

dB Cooper · « **Reply #7 on:** 18 Apr 2018, 04:55 pm »

Damn... Thats some serious DIY. Love to see some pics. With AVA essentially out of the kit business (I think they still offer the ST70 kit), there just isn't a lot of kit audio at all anymore (unless one goes hardcore DIY as you are describing). The upgrademydynaco stuff looks interesting but I haven't seen any professional reviews or bench testing. But for someone with tired circuits or groty mehanicals, they're probably a good option.

gregfisk · « **Reply #8 on:** 20 Apr 2018, 07:20 am »

Quote from: dB Cooper on 8 Mar 2018, 04:07 pm

If that operates by IR, probably not (unless the IR sensor could be put right behind the power switch maybe) unless one drills the front panel for it (sacrilege!). If it could be done, it would be cool though.

I think a system that makes you get off your (_._) once in awhile may actually be a good thing LOL

You could mount the IR receiver in front and underneath the face. They do this on TVs when you need a repeater for your audio gear that's in the cabinet.

Nice looking piece of gear, I remember lusting over this stuff as a young teenager and thinking I could never afford that.

bregez · « **Reply #9 on:** 21 Apr 2018, 03:06 am »

I have been thinking about upgrading my PAT-4 again. The last time I did was 10 years ago using Mr. Van Alstine's recommendations per Audio Basics VOLUME FIVE NUMBER ELEVEN, November, 1986. The modifications greatly improved the preamp. I am sure getting rid of all the electrolytics and drifted resistors also helped. I will keep the orange neon as I am tired of blue LED's. How do you like the new power supply board?

http://www.audiocircle.com/image.php?id=73582
http://www.audiocircle.com/image.php?id=73584
http://www.audiocircle.com/image.php?id=73586

rlee8394 · « **Reply #10 on:** 3 May 2018, 04:32 am »

So here are the completed power supply, phono board, and line-stage board. Now time to tackle the mechanical switches and controls. Need to order the new backplane jack set board and rocker board. Stay tuned.

Ron

rlee8394 · « **Reply #11 on:** 4 Jun 2018, 01:05 am »

So I've completed the build of the second PAT-4. Here are some photos:

New rocker switch pcb. Eliminates the messy inter-switch wiring.

New rocker switch pcb installed.

Interior view from front. Note new ground plane I/O jack set PCB.

Interior view from rear.

This preamp sounds very good with great separation, great dynamics, and very musical. But of course I'm biased.

Certainly much better than any standard PAT-4 out there.

I'll shoot more photos of the front with the modified faceplate and new power cord installed soon. Also need to sand and repaint the top cover. Will photograph that when complete as well.

One of the consequences of ordering new PCBs is that there is a minimum quantity of five pieces. So I have enough to build four more preamps.

I'm wondering if there would be any interest in the next four rebuilds. If so you would need to supply your own PAT-4 preamp. Now I know its hard to tell how it sounds from my description, so I am willing to send this out "On Tour" for those who would like to listen in their own environment. I would imagine you would listen for no more than two weeks and then send it on to the next participant. Seems to be plenty of PAT-4's out there, so it seems a shame to not upgrade them. Makes a fine preamp for a second system or that budding audiophile.

Let me know what you think.

Thanks,
Ron

dB Cooper · « **Reply #12 on:** 4 Jun 2018, 01:09 am »

Quote from: rlee8394 on 4 Jun 2018, 01:05 am

This preamp sounds very good with great separation, great dynamics, and very musical. But of course I'm biased.

Thanks Ron. You're Class A!

Norman Tracy · « **Reply #13 on:** 4 Jun 2018, 05:09 am »

Excellent resto-mod! Very nice PCB layout work. Leveraging the very affordable cost of PCBs into these classic chassis is a great idea.

charmerci · « **Reply #14 on:** 4 Jun 2018, 03:49 pm »

I would be more than happy to give it a listen and give my honest opinion on it.

rlee8394 · « **Reply #15 on:** 5 Jun 2018, 02:05 am »

OK, all interested parties send me a PM with your contact information, e.g. email and address.

-Ron

dB Cooper · « **Reply #16 on:** 5 Jun 2018, 02:18 am »

Is the mod 'straight line', that is, no tone controls?

rlee8394 · « **Reply #17 on:** 5 Jun 2018, 12:20 pm »

Correct, no tone controls or high filter switch. Just source, volume, balance, and the rocker switch functions.

-Ron

rlee8394 · « **Reply #18 on:** 24 Jun 2018, 10:21 pm »

Preamp on it's way to Charmerci. Have fun Charlie. PM sent.

Ron

dB Cooper · « **Reply #19 on:** 25 Jun 2018, 01:14 am »

I have an '84 vintage Van Alstine MosFet CA-80 rebuild (mine actually says Jensen's Stereo Shop on it) that I've off and on thought about sending to AVA (it's noisy and hummy now) but I've also considered gutting it and installing the updatemydynaco circuits just because I haven't built anything in ages. Wonder how a recapped 30+yo AVA circuit set and the updatemydynaco circuits would compare.