HISTORY OF THIS AMP HEAD & ACOUSTIC "THE COMPANY"
WOW!
I am seeking new homes for some of our OLD muso's equipment that our audio post production facilities had around either as "loaners" or fun gear for the staff in our "down time"
I have provided a LOT of information because I am trying to be helpful to someone who may be considering this amp head, my career background is electronics which means my focus is on the electronics when I looked over this gear.
NO muso's equipment for gig work is going to be "pristine" after 50 years or more but I was pleasantly surprised with the condition of this ACOUSTIC 450
Although I am providing a "flood" of information about this equipment, it is still provided on an AS-IS basis but I tell it like it is, if there is something not right, you will be told!
The "sound" of this amp is of course of vital interest to the player but I have NOT plugged in a guitar for testing!
Why?
Because I have no instruments left at the house and no bins so I had to make do with a sound source (microphone for low level and CD player for line level) and tested using a vintage ROLA (UK) 12" loudspeaker. All the details about my testing are further down in the TESTING section of this description ...
HOWEVER, there is a TON of videos/demos on Youtube so have a listen ...
This is a pretty ordinary demo but I hope it gives you an idea Then there is this demo video - much better in my honest opinion
But wait there's more!
Try this video from the duo Death From Above 1979 - they are devoted users of the ACOUSTIC 450 amp!
I go into a lot of detail in this advertisement, not just for fun (but for me it is fun anyway) but also, who on earth would consider buying something without knowing EVERYTHING possible? That would be like selling a car with the description "it's got 5 wheels, goes and is white" - doesn't tell you much!
I know some don't like all this information (it hurts their brains if there are more than 140 characters involved!) but please please try and read through the WHOLE description, there is a lot of information to give ....
I have found some excellent information HERE that does describe in much detail the use and "sound" of these amp heads in general (and the quirks*) and I am very much in appreciation for the author's very detailed information ... his information provides many insights into the use of this amplifier, not just the technical info. I wish I could give credit to the author/owner of the website but a name is not mentioned anywhere (that I could find) But it is a VERY informative site with information about many different pieces of gear.
*I mention "quirks" READ the article I have linked to above, it references the switch "GND-REV" on the front panel (just below the Power ON-OFF switch) The switch actually changes the connection of the AC power!
This switch does NOT reverse signal and signal ground (like a Phase Switch). It swaps over the Active and Neutral AC connections in the power supply with respect to the amplifier's ground.
This is NOT a good thing, electrical standards have changed since the 1970's so at the very least, NEVER flip this switch or better still - disable it. Any amp tech can do this for you and it is not a complicated procedure.
I remind the new owner once again, NEVER flip this switch as you could be putting your safety at risk.
In many respects, my description is only adding to his already excellent work and the information here is specific to this amp head I have here right now.
The Designer/Manufacturer of this gear was Acoustic Control Corporation, a small startup operation in California USA and that came to gain quite a reputation in the world of guitar amps. HERE is some wiki stuff about them.
ACOUSTIC CONTROL CORPORATION - Amp Head
Model: ACOUSTIC 450
Designed & made in USA
Circa early 1970's
Serial # 6005
Multi AC input voltage options, currently set for 240V operation lead is 4 metres long (heavy duty) with a standard Australian 3 pin GPO plug fitted
Power Earth is connected
Twin input front panel jacks
Multiple rear panel "sends", foot pedal controls etc - all on standard jack sockets
2x Jack socket outputs to your bin(s)
DIMENSIONS:
650mm long x 190mm high x 320mm deep
WEIGHT:
15Kg
Luggable because of the very strong handle at one end
Designed for lead or bass guitarists
Cruises along providing an ear-splitting 170 Watts average output with the knob at "10" or 450 Watts on peaks, meaning if you push the amp hard it will not crumble into a horrible sonic mess!
Various tone adjustments are provided such as Brightness, 5 band EQ and a separate Low-Mid-High tone adjustment setup.
Distortion effect is built in (NOT Reverb as I saw one advertiser call it!)
Actually, many of the features are already very well described by the author at Home Music Recording Studio so there is no point in repeating the information here.
FIRST IMPRESSIONS "THE LOOK"
Amazing clean!
Case is undamaged, all eight feet are present and undamaged (four when lying flat in use and four at one end for upright storage/travel)
All metal corner protectors are in place and undamaged
Overall vinyl (original) is NOT cut or scratched either - Black stipple vinyl. NO vinyl lifting from the particle board framework, this was put together properly and with attention to detail.
Metal carry handle at one end (Black finish) does have some paint flaking - easy to recoat if this bothered the new owner!
FRONT PANEL:
All controls/knobs and switches on the front panel are originals and not damaged or broken
REAR PANEL:
All sockets and connections look original (Switchcraft) and are undamaged. Power lead (fixed in position) is undamaged
Output transistor covers (six little ducks all in a row, Bingo!) look undisturbed and are a complete set.
ALL labelling (front and rear) is substantially undamaged and easily readible - this looks to be high quality screen printing onto the aluminium panels, heavy print and durable
Let's dig down a bit further ....
EQ FRONT PANEL
With gear of this vintage ALWAYS look behind a panel that has sliders! Easy to miss but vital. I unscrewed the 4x EQ panel screws, removed the slider knobs and OMG! but no surprise, the dust cover FOAM has completely disintegrated. This is quite normal for OLD foam it turns to dust over time and leaves little bits of itself everywhere. Touch it and it just crumbles under your fingers.
So, I sucked out all the foam remants, spray cleaned the slider tracks and have created a brand new foam dust cover.
The slider knobs have no cracks or damage to the slot used for securing to the slider pot shaft - great!
LETDOWN POINT #1: While the build quality is great, I was disappointed with the arrangement used to secure the front fascia to the front panel. The fascia has 6x plastic standoff's moulded as part of the fascia. These standoff's have a very simple wide thread and from INSIDE the frame you screw on pressed metal nuts! It works to hold the front fascia onto the front panel but it just doesn't have the "toughness" of the remaining build quality and in fact one standoff had broken away from the moulded fascia and a further two standoff's are missing altogether! I glued the one standoff back into place and it works fine now but I cannot do anything more about the two missing standoff's.
This means that the fascia IS secure but it feels a little "loose" down at the power switch end of things because it is not secured properly.
THE CASE:
I have already described the OUTSIDE of the case (which is extrordinary and described above) so lets go inside, shall we?
INSIDE THE CASE:
The following describes my "impressions" and observations, NO service work has been undertaken other than a little cleaning and a couple of measurements - read more ...
I am well over my servicing days and am not interested in undertaking any service of this amplifier and in fact (at this time) it does NOT need servicing but it would be sensible to have an amp tech caste their eyes over it for your own piece of mind.
Immediately I noticed the simplistic design which is very well constructed (by hand) anodised aluminium, screw together so it is easy to get to the "tight" spots inside.
The sub modules of the amplifier are easy to identify, three quality single sided boards and access for service work is a snap, if ever this was needed.
Discrete "through hole" components are used (no SMD here!)
Very clean inside, and I checked for signs of brittle insulation on the wiring, none.
The large AC Power transformer is fully shielded AND has the copper flux band to reduce stray flux outside the magnetic circuit formed by transformer windings and the core i.e reduce magnetic fields from the AC transformer affected nearby circuits.
Slide switches mounted near the transformer are used to select various AC input choices (nice for a 1970's USA product to have multi-voltage capability) - it is currently set for 240V AC and I have left this setting alone.
Look at that monster of an electro for the DC filtering! Damn it's a big one.
Details of that electrolytic capacitor are: General Electric Type: 86F2157M1 7800uF 100V DC (125V Surge) 85C Temp rating. There are no signs of leakage or bulging - if ever leakage was to occur, BE VERY CAREFUL! This is an era when PCB's were often used in capacitor manufacture, mainly capacitors used for fluoro lighting and industrial equipment but it still pays to be careful if the casing has failed (which it hasn't!) PCB's are nasty and hazardous to human health, stay away from them and if you must deal with PCB liquids, there are Federal Government guidelines on the proper way to handle these LOOK HERE
Digging down deeper, here is a blow by blow printed circuit board report
THE BOARDS IN DETAIL
ALL of the front panel pots are connected directly to this board, direct soldering (no flying leads)
Surprised that shielded cable has not been used from the front panel jack sockets (INPUT 1 & 2) down to this board. The jack sockets are Switchcraft, as you would expect. I don't like the way those sockets are grounded though, inside the front panel the black paint coating has simply been scrapped away (not so well either) and it might be a good idea to make sure more bare metal is pushed up against the jack sockets (although I did not experience any hum issues)
The jack sockets were a little dirty so I have given them a clean up and I am happy that they can be relied upon but if you wished to be ultra-cautious, I do have BRAND NEW Switchcraft sockets to suit listed HERE
Quality EVOX MMK metallised poly caps extensively used and just took a quick look at a few of the small signal transistors, most appear to be Motorola, gold leads.
I actually pulled off the spade connectors on the rocker and main power push switch to test them, particularly the power switch as the 'action' felt not so positive as you get with a nice fat toggle, but ALL switches, including that power switch, tested fine.
LETDOWN POINT #2: I really was disappointed with that Power ON-OFF switch (push ON push OFF) the action is not so positive in my opinion but it works fine AND the soft red glow of the Neon lamp inside the switch is reassuring!
The pots used for the level controls etc (all in a row with black knobs) are SPECIAL. It's not the value or even the size that makes them special but they have a welded bracket on the rear which is soldered to the PCB, support only - it has no electronic function. On the front side, the shaft has TWO flat spots, not one. These shafts allow the special push on knobs to fit securely and tightly. The pots are all Clarostat's (USA), the 137 77xx series and the manufacturers ID and values are stamped into the metal casing. Clarostat was taken over by Honeywell years ago.
The black knobs which fit onto these shafts are plastic but where the shaft fits there is a spring metal "clip" and this provides the very secure grip of the knob to the shaft - no grub screws or collet arrangements.
All knobs are remarkably clean and the vertical white pointer line (with a white dot on the top) is completely unworn on all knobs.
The Preamplifier PCB (170043-C) topside looks to be unmodified and has no obvious service work undertaken. This might be a good thing or not, the cap's should generally be fine but those OLD carbon resistors might be something to look at ONE DAY!
The PCB underneath (solder side) has had something done to it, a mod perhaps. One Motorola small signal transistor (looks to be a 2N5460, it's hard to read, a diode which I would take a guess is germanium (thin, black and looks to be glass encapsulated) and a small electrolytic.
Because on the topside nothing has changed, no missing components or through holes which are empty, I am guessing this is a mod not service work and I am thinking this mod revolves around the distortion circuit.
The EQ PCB (170044-C) is located next to the preamplifier board. Note those large fat brown "things" on the copper side where the EQ slider pots are located (see the photograph) are not trimmer pots but inductors (fully encapsulated) - they do not have a manufacturers name on them, just a number - each is different. The slider pots for the EQ are mounted directly onto this board and as mentioned above, have been properly cleaned when I replaced the dust cover foam.
Next is the MAIN AUDIO PCB (170051-A) with the drivers and sockets for the power output transistors. I carefully examined ALL components for stress (discolouration etc) and nothing seen. Again, so clean, I was amazed. In fact the overall condition inside is pretty damn good, this surprised me quite frankly.
REAR PANEL:
Clean and without damage
Lead supports at each end are undamaged
ALL jack sockets are clean/shiny
Fuse holder is fine, fuse is intact
ALL power transistor top covers are securely in place with no signs of heat stress
LOOK, I know, talk talk talk - so what does it sound like?
TEST SETUP (Crude but you work with what is to hand!)
Due to a lack of a guitar or a bin or two, I used a dynamic mic as a low level sound source and a CD player as a line level source.
Speaker connect was a nice fat 12" Clarion (8 Ohm) I had around, single jack at the rear.
NOTE: The rear panel has two jack sockets for your loudspeakers. These are wired in parallel, that means if you are connecting 2x 4 Ohm bins then the effective load for the amplifier is 2 Ohms - these ACOUSTIC 450's can handle a wide load impedance but just watch you don't drop the load impedance too low.
POWERED UP
Neon lamp (inside the power switch) indicates steady (old Neons can go a bit "flashy" or not work at all - this one is fine)
First I looked at the output to make sure there were no hidden nasties there (high DC voltages!) - all fine.
Measured the main supply rail (across the big fatty cap) and it is 89V - all good.
At turn on there is a very brief "hum" which rapidly disappears, idle running there is NO HUM THAT I COULD HEAR AT ALL
I then used both input jacks to run some audio through the amp...
The audio (whether it was the mic or the line source) was very good - clean and NOT distorted at all.
Plenty of volume, even though I was just running an 8 Ohm loudspeaker
I then changed all the tone controls, EQ etc and made sure that changes to the audio occurred - all fine here too (and NOT noisy while being rotated or slid)
Now, keep in mind that when I say the audio is NOT distorted you can of course introduce distortion and I turned this on - Oh yeah, this also works although with a complex sound source it really doesn't sound good! A guitar would have been much much better to play with on this feature.
In summary, after all these years with us (and seeing a few gigs along the way) this amp head is in really great condition AND IT WORKS!
It is "as original" with practically no alterations since it left the factory in the 1970s
Great "bang for the buck" (selling in US for around US$700 these days) and the amp is easily able to "tame" that drummer who likes to dominate the band!
REMINDER:
Keep in mind that FREE SHIPPING is automatically offered in the checkout area, anywhere around Australia.
International buyers will have to pay shipping costs though (sorry NZ, I know a lot of interest is in this gear from "across the pond")
