AMPEX 601 Microphone Preamplifer Conversion Mic Pre RESTOMOD

[@FrankOlsonTwins]

Schematic with the parts I replaced, available here: vintagemusictech.blogspot.com/2020/03/ampex-601-schematic-and-mic-preamp.html

[@useradmin00000]

Do you know of a schematic for the 351? Or have any reccomendations as to sensible DIY mods I could achieve?

[@FrankOlsonTwins]

Hmm, I've never worked on a 350 nor 351. When approaching these projects, I try to be focused about what functions I want the units to perform, and what they are currently capable of. Also, I try to consider how they were designed to function and how far my mods can realistically deviate from those functions while still retaining the character or the design. So, for an ampex 351, I would probably do a restoration of caps and bad resistors. Clean all switches, inputs and outputs, and potentiometers(lightly, from the back of the casing). If you use it for a while, and feel like you really need a certain feature, you can consider adding the feature, but my experience is, changing one thing will probably have an effect on a different section of the preamp. Like pulling unused tubes seems like a good idea, but it can raise the tube heater voltage for the remaining tubes- not ideal. Glancing at the schematic, I personally would be interested in utilizing the playback head input somehow. A schematic is currently available here: usermanual.wiki/Document/Ampex351schematics1962.901134551 Good luck!

[@useradmin00000]

@@FrankOlsonTwins Thank you for the schematics!

[@vikrant555]

This must be a luxury buy at old times. Got to know about this through harlan Hogan's book VO. Thank you for the video.

[@FrankOlsonTwins]

Cool, good to know! Thanks for checking it out!

[@LosFicosMusic]

LEGEND~!

[@psk1461]

Sounds really creamy!! ❤

[@rars0n]

Very informative, great video!

[@FrankOlsonTwins]

Thanks!

[@fakundofrontera]

Hello, can you tell me how can i wire my Ampex 601 to play music from my computer? can i go directly with a 3,5mm miniplug wire from my laptop to the Line In input? and from the Output directly to a 12" speaker? or i need to use an amplifier from the Output of the Ampex to an Input from a amplifier?...i buyed yesterday, today i probed and its working

[@FrankOlsonTwins]

Hi, Yes you will need an amplifier to listen to music over a speaker. My best advice is to get the manual for the 601 and read about how the inputs and outputs work. That should give you a good idea if it will fit your setup or not.

[@TheGarageRecordingSC]

I really enjoyed the video, and it got me thinking. What are some tape machines out there that can be had for a decent price that have some really special preamps in it. I'd love to get my hands on one and maybe get it modified down so I could put it in some sort of a chassis, and use it for some of that old mojo. Thanks so much. 🙂

[@FrankOlsonTwins]

Thanks for the kind words! The akai M7, M8 or roberts 770, or 990 all have monoblock/tube preamps. They are a great inexpensive way to get your hands dirty!

[@TheGarageRecordingSC]

@@FrankOlsonTwins Awesome thank you for the recommendation. 👍🏻😁

[@FrankOlsonTwins]

@@TheGarageRecordingSC Glad to help. Keep an eye on ebay, my advice- buy the cleanest unit you can find, but try not to pay more than about $100 for each monoblock. They're not worth much more than that. Sometimes you'll get lucky and find a full tape machine for around $100. Good luck!

[@TheGarageRecordingSC]

@@FrankOlsonTwins You're exactly right, I've been looking around online today. 👍🏻😁

[@TheGarageRecordingSC]

I've found a really nicely cared for, Akai M8. Should I just leave it as is and use the preamps that way, or is it relatively easy to pull them out and put them in a chassis? My day job is running a metal shop so I could build something really cool. But being tube preamps, they must have some sort of dummy load if they are not connected to a speaker, correct? Or is there something built in that would allow them to just be pulled out? Sorry to bug you, this stuff just has me really intrigued. Thanks for any advice you can give.

[@cezarino]

So good!!

[@FrankOlsonTwins]

Thanks!

[@williambock1821]

I’ve done this to a few Roberts and Akai units. Hope to come across an Ampex for a decent price at some point. Probably not gonna happen anytime soon,lol.

[@FrankOlsonTwins]

Every once in a while they come up, but never as cheap as they used to. My first one was $25! It hasn't happened since!

[@platboy1789]

Can you get rode of those thick brown cables hanging off the back ? we just need the power cable ya ? i have one and id liek to remove those since im not using it in the suitcase

[@FrankOlsonTwins]

I seem to recall some of them are AC lines and some are DC lines. It's best not to just cut wires out- it can create a dangerous situation to have high voltage wires loosely clipped. Have a technician cut them directly at their point of origin inside the chassis leaving no frays or stray wires. If you don't know a technician, you can cover the ends with shrink tubing or electrical tape to make them a little more safe when outside the suitcase.

[@marcusdolby1]

I’ve purchased a stereo 601 and my tech told me one of the Power Transformers is open and the other is almost toast. I’m trying to find a replacement power transformer for it but no luck so far. Any ideas?

[@FrankOlsonTwins]

Basically you'll have to study the schematic and figure out what voltages are needed and then find a suitable replacement from a place like Edcor. You might be able to contact them directly and tell them your situation. They might be able to figure out what's needed. I'd sell the unit for parts and buy a fully working one.

[@marcusdolby1]

@@FrankOlsonTwins Thank you for all the info, unfortunately, I paid a premium price for this unit and I’m already down the financial rabbit hole that I don’t think I’ll get back unless I were to restore it.

[@FrankOlsonTwins]

Well, there's no great advice to give here unfortunately. I think your options are to either get a new transformer or replace the faulty record\playback unit(s). You could keep your eyes open for a used 601 at fleamarkets, hamfests and online of course. Prices for these units, as you know are pretty steep at this point. If you find a cheap one you could either replace the transformer or the entire channel unit. It's not uncommon to have several "parts machines" to keep a single tape machine running. It's part of tape machine culture. A third, very costly option would be to find someone who rewinds transformers and send them one or both of your power transformers to wind. Perhaps Edcor could help with this, they are usually very helpful with custom orders: edcorusa.com/

[@marcusdolby1]

@@FrankOlsonTwins Again thank you so much for the advice. I’m bringing the 601 to a close friend of mines who owns Alpha Sound and Light. He’s been repairing guitar amps and tube amplifiers for 35+ years. He said he might have transformers that will work, so maybe I will get lucky. Actually he said he’s more interested in why the transformers went bad to begin with. He’s semi retired so I feel lucky he’s going to be looking at them.

[@DamonT-jl3xs]

Hi. Thank you for the video. Any suggestions on where the safest place to install a kill switch for the noisy reel to reel motor would be. I was thinking of doing it internally so I wouldn't have to drill. But I want to retain the ability to use the reel. Thanks!

[@FrankOlsonTwins]

If you look at 00m25s someone installed just such a switch on this unit. That's probably a good spot for it, but without drilling perhaps the easiest thing would be to replace the original switch with a 3 position switch(ON-OFF-ON). You 'd have to figure out how to wire power for just the preamp, and put that on one side of the switch. The other side would be power for the entire unit.

[@felipecastrosanmartin5266]

After months of work, I could finally get my Ampex 601 to play and record. Now it’s time to recap the entire unit following these instructions. Any advice on how to change the two prong power chord for a new one?

[@FrankOlsonTwins]

Yeah, I do a couple things. Crimp(or solder) on a "ring tongue" or simlar "lug washer" on the green wire that's inside your new three prong power cable. Clean both sides of the lug with green scrubby. Drill a hole in the chassis and clean around the hole with scrubby or 600 grit sandpaper. It should look very clean. Now using a screw, nut and washer, securely fasten the lug directly to the chassis. So, order of operations would be: Put screw through clean chassis hole>>put lug onto screw, being sure the lug is contacting the chassis>>washer goes on next>>Nut goes on last. Tighten very tightly, but don't strip the screw! That's it! The other wires are black and white, which should match right up with the existing cable connections inside the 601.

[@StuffnSuch]

@@FrankOlsonTwinswhere do you connect the wire from the power switch? To the black or white terminal? The original 2 prong wiring has the black and white on one prong and the wire from the power switch on the other.

[@FrankOlsonTwins]

Honestly, without having a unit in front of me, it's impossible for me to give electrical advice. I would just say keep looking at the schematic and tracing the wiring until it makes sense. If you're not comfortable wiring it up, find someone in your area to give you a hand. Most techs could get this sorted in a few minutes, costing $50 or less. There are many forums describing this exact type of procedure(3 prong AC to power transformer hookup), the important thing is you understand what you're doing at each step. When I was learning to do this type of thing, I read as many forums as I could and asked many questions on them. It's worth spending the time to figure it out, but really it can be quite dangerous so do proceed with caution!

[@77Cardinal]

Enjoyed the video very much. I have an Ampex 601-2 (Stereo) tape deck I was given by the original owner when it was headed for a dumpster in about 1986. I've kept it stored since then waiting for "someday" when I could have it restored. I'm wondering if someday has finally come. I'll message your website with contact info and hope we can chat directly about a restomod to full operation. Nice touch using the preamp for narration. It sounds very nice. Wondering if you could mention the mic you used to record. Thanks!

[@FrankOlsonTwins]

Hey John, i got your email, I'll give you a shout next week with some details. Regarding the mic, I'm pretty certain it was an SM7B. But it *might* have been an sm58. Pretty sure it was the SM7 though, because I was really excited that it had so much gain for that mic.

[@77Cardinal]

@@FrankOlsonTwins Now that you mention it, it does look like an SM7 which is a decent dynamic but kind of under performs without a boost. It sounds really nice on your modded 601 though. Looking forward to chatting with you.

[@FrankOlsonTwins]

@@77Cardinal Oh, haha I forgot that I put the mic in the video! Yeah, definitely narrated with the SM7!

[@tw364]

Awesome thanks for posting. I have a 601 I want to convert.

[@FrankOlsonTwins]

Cool, let me know how it turns out!

[@davidhensiek2912]

I just picked up an identical unit. Would you be able to modify it for me? Great video to!

[@FrankOlsonTwins]

Hey David, I got your email. I'll send you a reply later this evening. thanks for watching!

[@jomaco1989]

Nice, any tips on adding a DI input? Where would I need to put the input jack and would I need extra parts? Cheers

[@FrankOlsonTwins]

Di Just requires a 1/4" jack that can be installed in place of the 1/8" Line input jack. I don't recall right off if it's a shorting jack or not. I don't think it was. On this particular unit, I relocated it to where the phones jack originally was(front panel), since the new owner has no need for a phones jack. No real secret to the DI on this unit. With a proper cap job and good tubes installed, the circuit is already tuned really well(Ampex engineering, after all)! If you're getting a bad mismatch between your instrument and the DI, you could use a step down transformer. That's worst case scenario though.

[@jomaco1989]

Thanks, yes previous owner had caps done so it's sounding great with a mic. I tried my active bass into the mic XLR (which doesn't seem the right thing to do, but I wanted to try anyway). I got a lot of hiss. Plugging it into a line level input, would there be an impedence mismatch? I guess an active bass might more closely match a mic input but I'm not too clued up on this, so not sure. Cheers

[@FrankOlsonTwins]

Yes, actually after conferring with the owner of the preamp- the line in isn't really suitable for instruments. Checking the schematic, it's hitting 3 gain stages, but two of them are acting as buffers/mixers, really. So, there isn't much more than unity gain happening. Now I recall- The problem with trying to create a DI from the line in is that BOTH the mic preamp and the Line in connect at 1/2 of the 12ay7 tube as a mixing stage. If you change(or remove) the resistor value in the line in path to suit a DI(there's only one) it changes the response of the Mic preamp. After a few attempts of changing this resistor, we were content to leave the line in as a low impedance input. Take a look at the schematic in the link provided above. With some effort you could come up with something suitable, I'm sure. He has been running instruments through the Mic preamp via a stepdown transformer, DI box. The Mic pre on this unit has tons of gain, so with a suitable DI box, you shouldn't be getting much hiss. If so, check your tubes.

[@felipecastrosanmartin5266]

Nice work!! Would these changes apply for an Ampex 602 with a tape transport that stills working?? Would these new electronic components affect any of the tape machine Rec-Play-Erase functions? I am planning to use it in my recording studio as a rec mic preamp, DAW>Tape Transfer unit and maybe some tape delay effects. Thanks for sharing your work for DIY enthusiasts. Greetings from Chile!!

[@FrankOlsonTwins]

Thanks for checking it out! Yes, I really just did a cap replacement service. If you're going to keep it in service, I'd recommend only replacing parts as needed. The 602 is a slightly different circuit as I recall, but still a great sounding preamp and tape recorder. Is the machine in service for you right now? Is it currently working or needs service?

[@felipecastrosanmartin5266]

@@FrankOlsonTwins The preamp works great when plugging a mic in the microphone`s input. I haven't checked the line input yet as there is some rust I need to get rid of inside the XLR connector (601 has a TS connector). I am working on the transport myself following the instructions on the manual and Jim Miller's website. Fortunately, now the mechanism is working as it should. The only thing I could not fix was the recording function, that's why I'm sending it to a technician to get that fixed and take the chance to recap the unit according to your schematic. I also have a 601 I will try to fix while the 602 is being serviced. Thanks again for your help.

[@davidtieri358]

Hey Ive got an ampex 601 Im using as a mic preamp for vocals. It sounds great, but when I sing loud into it, it has a harsh piercing treble sound. Id prefer it to have a smooth overdrive clipping sound. Do you have any suggestions on settings or switching tubes to mellow out the piercing treble? Thanks! Ps its actually the one in the "Stung By Bumblebees - 1959 Ampex 601 Studio Microphone & Guitar Preamp Repair" youtube video.

[@FrankOlsonTwins]

Hey David, I'm not near a computer but i can take a look at the schem and make some suggestions wednesday!

[@davidtieri358]

Thanks! Have you noticed similar behavior on yours? Do you think there is an adjustment I could make that would help, or maybe trying different tubes? the 12ay7 is a GE. Thanks again!

[@FrankOlsonTwins]

Hey David, I took a look at the schematic again. I have to say, the unit I modded is super mellow. The owner has been using it on different sources, and it hasn't jumped out at either of us as too bright, shrill or piercing in any circumstance. This makes me suspect the EF86 tube on your unit. If you have one(or a few) you could swap out, that might be helpful to rule it out. A screechy 12AY7 tube is a little out of character, but anything's possible. The only adjustment I can think of would be the record Equalization, however, I don't know if that's in your modded circuit. It's not in mine. If it is currently wired into your signal path, it would have a direct influence on the treble response. It looks like a little white ceramic square with a screw in the middle. By tightening or loosening the screw, it changes the amount of treble in the circuit. Hope this helps, let me know how it goes! -Frank

[@davidtieri358]

Hey sorry for the late reply, It turned out to be the cheap recording interface I was using. I got a apogee duet and i bypass its preamp completely, and the ampex 601 then sounds wonderful.

[@FrankOlsonTwins]

Good to know, thanks for checking back in!

[@tooclosetovomit6970]

Nice. Do you know how to mod it to add an effects loop?

[@FrankOlsonTwins]

Hmm, it's definitely doable with the unused gain stages in the playback section. In the circuit(available in the schematic above), it would fit in approximately where the input/tape switch is. You'd just need to figure out some mixing resistor options to get it to play nicely with the rest of the circuit.

[@ayyluckyboymike]

Rad video! I recently stumbled across an Ampex AG-600 Solid State, it appears like everything is working but I kinda wanna try taking out the preamp unit by itself and use it in my studio. Will I light my house on fire if I removed the unit and run it without the tape deck?

[@FrankOlsonTwins]

It should be fine, but I'd say keep close to it in the studio the first day or two, just to check out how hot it's getting without the included fan running. I don't forsee any trouble. Also, make sure the little bottom chassis is intact...not a great idea to touch anything inside the unit really. Good luck! Let me know how it turns out!

[@bobsbits5357]

hi have a scully 280-14 it's a lot more work to do on it the record pre amps and very bad and deck is a right of i will look good when done using alot of tascam 38 base parts as i have alot left over from doing the up and the reel of tape are about same in kgs to i can use many parts from lots of make left over as well nice job front panel and pinch roller and all front parts i am using again just the trans logic i have to remake came from a usa air base in the uk was in a very bad way i have record pre amps mag film one's used on 16mm mag film i pulled all the inside out and pimped them with tascam 38 mk 1 cards i had alot left as well i have a tube amp as well they sound ace man

[@FrankOlsonTwins]

Wow, sounds like a cool project- I was looking at scully machines until the prices skyrocketed. They were basically free at one point! I currently have a Tascam MS16 that is nearly ready to go. Everything working great except final the output on 2 of the channels(not on the cards, surprsingly). Post a vid of your Scully when you get it up and running!

[@bobsbits5357]

hi when i got it £60 uk as parts it was parts picked up some betacam sp decks for silly low money a ex hire place was going to get a big skip they had the wearhouse in my town so a worker move all the decks to my town and i buy them as i fixed them about £10 each uk getting a skip would be alot more i had reel to reel decks from 15 years old i am over 50 now bob

[@HP_____]

Tiny Chief caps are the worst. They are called Tiny Grief for a reason!

[@FrankOlsonTwins]

Haha, I'll have to remember that one!