Guild G600 Aspen Acoustic Amplifier

Since I wrote an article about the Timberline series of Guild acoustic amplifiers, and another about the G300 Tamerack, when the opportunity arose to buy a G600 Aspen acoustic amplifier, I simply couldn’t resist.

Read along while I go over every detail of this cool acoustic amp from 1993 or maybe 1994 as well as why I can’t seem to pin that date down.

Intro

This is the second of the Timberline Acoustic Amps from Guild, and this is arguably the one that looks most like a “normal” guitar combo amp (though the rare G500 amp really holds that honor, but that’s an article for another time), at least when it comes to size, dimensions and overall look. Where the G300 Tamarack was short and wide, the G600 Aspen is taller and as a result looks more like the guitar combo amps that most of us are used to seeing. It kind of reminds me of the old Mesa Boogie amps with the wooden cabinets and cane grills, but this amp only compares to those Mesa boogies in the looks department because this amp is designed for acoustic guitars and is therefore 100% solid state.

There is very little information about these amps on the Internet and what I was able to find was mostly about the entire series, though I do have the schematics and user manual which are shown below in the appropriate sections. I was unable to find any artist endorsements, any magazine advertisements, and the “catalog” (more of a flyer, really) page to the right is from the same material that Grot supplied me when I wrote about the Timberline Series. I’ve since scored my own copies of this flyer but Grot still get’s the credit because he’s awesome.

As an added thrill (for me at least) after writing about the Timberline and G300 amps, I was contacted by the person responsible for designing them. Kevin Nelson who now owns and runs Gizmoe Amps worked for Randall at the time that Guild was bought by US Music and so was the key person who designed and developed these amps. Special thanks to Kevin for answering my many questions. For those of you who’ve read many of my Guild articles, Kevin is also the person who helped me regarding the 1990s Guild Brian May pedal.

If you read my review of the Guild G300 Acoustic Amplifier, the Aspen in this article may seem like a larger version of that, though it differs in some interesting and useful ways, the most obvious being that it has larger speakers and more power. The fact that the Aspen is a larger amp also lends itself to having more expansion options such as the ability to connect to an external cabinet.

This snippet from the September 1993 price list shows the four Timberline amps most commonly seen with the Aspen listed as the G600. Interestingly, the G600 Aspen does not show up in the earlier April ’93 price lists with only the G300 Tamarack, G500, and G1000 amps shown. With the retail price of $899 in 1993, this was not an inexpensive amp, but remember that there were very few acoustic amps available at the time with Trace Elliott probably being the notable exception, so Guild was breaking new ground.

Features

The Aspen is fifty watts in total and is full stereo, designed such that each channel is 25 watts.

I found the manual for this amplifier on Randall’s archive page, and kudos to Randall for keeping all that old material available. Click on the image of the manual to the right to get a local copy in PDF format. The manual explains what the many knobs do which I’ll cover in detail below in the controls section.

One of the biggest differences feature-wise between this and the G300 Tamarack is the Rototron which is a kind of better than tremolo feature that is supposed to simulate a spinning speaker like a Leslie. It’s really just a temolo, but since this amp is stereo the effect is sent from side to side which gives it the feel of a rotating speaker in a way that a mono amp really cannot acomplish.

At almost twice the size of the G300 Tamarack, this amp puts out more power, has more flexibility, and looks more like a regular guitar amp. Just based on looks alone I think the average player would choose the Aspen over the Tamarack, though some of us are just obsessive about needing complete sets of things even if we don’t really have the room for them.

Cabinet and Grill

The cabinet of the G600Aspen is oak, just like the Tamarack. Both of the Timberline amps I have in my possession came to me with the wood quite worn and it seems to me that Guild did not finish the wood or seal it in any way (I had the same reaction to the G300 Tamarack’s cabinet). In some of the pictures the case almost looks like pine or even balsa wood and that’s because it has been dried out and worn from decades of use where no one even though about treating the unfinished wood. It really doesn’t take much to care for these cabinets, either, which makes it all that much more disappointing that it seems to never get done. The amp was shipped purposely with an oil-only finish which I’m sure looked amazing at the start but after decades of people not caring for the wood properly, most of them look a bit sad.

By the way, as per the designer, those slots on the side of the cabinet are not heat vents, but are there to further  enhance the stereo effect of the Rototron. Oh, and you may notice that my amp has little wooden plugs covering the screw holes on the top. I added those – the amp does not come with them.

The cabinet is open with two wooden panels that come off, each by removing two wood screws. The bottom panel serves no real purpose aside from keeping the power cord inside the cabinet when stored there. The top panel, however, actually acts as a strain relief for the cables from the speakers and the power supply which are routed through small rough cutouts in the top of the speaker baffle. These cutouts are covered by the panel which keep it all together and looking neat. I think this is a pretty nifty idea, though it does require the removal of the panel if you want to remove the amp chassis which is really not that big of a big deal considering the rarity of such an event. Just don’t blow the fuse (more on that later).

As I wrote above and in my G300 Tamarack review, the cabinet of both amps was a bit of a mess when I got them. I took everything off of the cabinet (except for the handle which was on there for good), sanded the entire thing lightly with 300, then 400, then 600-grit sandpaper, then wiped it clean with a wet rag and then hand rubbed multiple coats of lemon oil into the wood which the thirsty wood soaked up with gusto. From what I could gather the wood was left unfinished on purpose

If you have one of these amps and you don’t know how to take care of the wood, rub it down with some lemon oil. You don’t need to sand it or do any of the crazy stuff I do – just give the wood some lemon oil and it will look tons better in no time. Hell, lemon oil-based furniture polish would be a fine choice too. Anything is better than letting the wood just dry out. My Aspen was so dried out that I had to treat it again after a couple of weeks.

The grill cloth appears to be a kind of cane weave with an acoustically transparent black mesh behind it. There is nothing special about the frame for the grill cloth, though this one did have velcro holding it on whereas my G300 Tamarack did not. I’m not convinced this was a factory addition, but it certainly could be. On the bottom right of the grill is the Guild Acoustic badge which, as I wrote in my other review, I wish you luck replacing should you ever break it. Indeed, I have a Guild G500 amp that I’m reviewing and it has a broken badge which I have been unable to replace.

All of these oak encased Guild acoustic amps originally came with covers, and the amps above the Tamarack came with foot switches. My G600 Aspen did come with the cover but the foot switch had been long lost. The seller from whom I bought it did send me a new-in-box no-name dual footswitch that works wonderfully, so there’s nothing proprietary about its workings and you should be able to use any such footswitch with a stereo 1/4″ phone jack.

Controls

The knobs on this amp are Guild G-shield knobs in gold which are pretty damn hard to find in 2019. It is very common for these knobs to have the gold foil label fall out and sure enough this amp arrived to me with three of them missing. Since Guild does not currently sell a guitar with these knobs, they don’t sell replacement knobs in gold which means I had to resort to paying too much for them on eBay, and let me tell you: I am not a fan of paying too much for things. If you find one of these that’s broken you could buy it for cheap and flip the knobs for a likely profit. Better yet, sell it to me and let me fix the amp!

Oh, and as per the designer, the knobs are all situated so that the G-shield is right-side up when the knobs are set to zero. Why? Because marketing wanted it that way. In my pics they’re all right-side up with the knobs at five. Why? Because I wanted it that way.

Here are the front panel controls from left to right:

Input

The input jack is where you plug in the guitar. I assume I didn’t really need to explain that but you never know and there are a bunch of jacks that look just like it on the back of the amp. Plugging your guitar into to some of those could be very bad so if you’re prone to mistakes like that it’s probably best to stay on the front part of the amp anyway.

Active/Passive (switch)

This enables a preamp when in Passive mode and disables it when in Active mode. I know, that seems backwards (there’s lots of weird stuff on these amps), but you set this based on what kind of pickup is in your guitar. If your guitar pickup doesn’t have a battery that means it doesn’t have a preamp and is therefore passive. Thus, you set this switch to Passive. If your pickup does have a battery, then it’s an active pickup and you set this to Active. The label for the control does not reflect the mode on the amp, but rather the kind of pickup in your guitar.

If you set this to Passive and you have an active pickup in your guitar then you’ll end up pre-amping your pre-amp and it will either a) sound really bad or b) squeal and feedback like crazy which depending on your tastes may or may not be the same as (a).

Sensitivity

The sensitivity knob is only active when the Active/Passive switch is set to Passive and acts like the volume knob on an active pickup which is kind of what it is.  Tip: if your guitar squeals when you turn this up, flick the Active/Passive switch to Active and stop using this knob. Also read the part that explains the Active/Passive switch again.

Note that the position of the Active/Passive switch and the Sensitivity knob are reversed on this amp when compared to the Tamarack. I doubt that will affect anyone who doesn’t own both, but I figured I’d point it out because I own both. Not even the mighty Grot can say that!

Level

The manual states that this sets the input level of the amplifier. Looking at the schematic, this control alters the gain of an opamp, so it’s like setting the volume of the preamp after the preamp that may or may not be engaged with the Active/Passive switch. Try not to think about it. This knob makes things louder.

An opamp is an operation amplifier and is a solid-state component that is an integrated circuit (IC) that amplifies a signal. They are more or less what replaced tubes in solid-state amplifiers. 

Treble,  Middle, and Bass

These are the tone controls. This is an amplified stage (they all are, really), but not individually. In other words, these are passive tone controls.

Plectron

The manual describes this control as “An ultra high frequency tone control used to accentuate pick attack for flatpicking or fingerpicking styles, or can be used to smooth out pick attack for jazz or mellow styles.”

This is a standalone control that’s later in the signal chain (near the master volume), and it looks to be a simple tone control but there’s some stuff going on in that part of the schematic that exceed my self-taught capability to understand. Therefore, it’s magic until someone convinces me otherwise.

Notch

The Notch filter is used to narrowly filter out frequencies in order to help prevent feedback. This dial controls the frequency that is being filtered out, and in theory if you’re having feedback issues, turn on the Notch filter and turn this knob until it stops. The Notch filter only sweeps between 100 Hz and 1200 Hz and should have a minimal affect on tone since the filter is so narrow.

In/Out (switch)

The In/Out switch enables or disables the Notch filter.

Reverb

This dial controls the amount of reverb added to the signal. To disable it just dial it down to zero or use the foot switch. As with most tank-based reverbs, a little goes a long way and setting this too high can make the amp sound unpleasant in a “please turn the reverb down” kind of way, though I must say that I like the reverb on this amp better than I did on the G300 Tamarack which is odd because they appear to be the same circuit and tank.

On the G600D (The same amp but with digital reverb), this is a Reverb Select control with a smaller knob in order to show the scale which is, Small, Medium, Large, and Gate. An excellent example of this rare model can be seen in this reverb ad.

Master Volume

This is the control for the power amp section of the amp where you’re supposed to “control the overall volume level of the amplifier.”  Since you don’t use the amp like a tube amp where you’d boost the preamp to distortion levels and lower the volume with the master, this can seem odd to electric guitarists. The fact remains that this knob is controlling the gain of the power amp and ends up being the control I use the most.

Rototron/Chorus (switch)

This switch chooses either the Chorus feature or the Rototron feature, but does not enable or disable either. Read on for more on that. If you use this amp normally (as in you’re not laying on the floor while you play), you likely won’t even see that this switch is labeled Rototron and Chorus because the Chorus label is so high on the faceplate that it’s hidden by the cabinet and thus all but invisible unless you tilt the amp back. This confused me at first because I thought this was just a Rototron switch and since “up” usually means “on”, the switch did not behave as expected.

To further add to the confusion, the LED indicator above this switch has nothing to do with this switch at all. It’s actually tied to the Depth knob. Sort of.

Depth

The Depth knob controls the intensity of the Chorus and “stereo enhancement effects” as well as the Rototron depending on the previous switch setting. From what I’ve seen playing with this amp, this effect can go from subtle to “OMG turn that off!” in very short order. A little chorus goes a long way, especially with this solid state Chorus from the early ’90s.

On the G300 Tamarack that was the end of the story, but on the G600 Aspen, the Depth knob is actually a push-pull control and you pull this knob out to enable the Chorus/Rototron effect (You choose which one with the Rototron/Chorus switch). Of course I had no idea this was the case until I read the manual, but again the face plate is labeled way up high where you’ll never see it unless you tilt the amp back pretty much so its horizontal on the floor. That label says, “Pull On”. Brilliant. I’m SO glad that Randall kept those manuals online!

When using a footswitch this knob must be pushed in.

Chorus Speed

The Chorus Speed knob controls the speed of the Chorus effect as it wavers from side to side. This is another control where I tend to keep it down low because it quickly gets out of hand. This control is only active on Chorus and has no effect on the Rototron.

LED

There is an LED with curved arrows surrounding it between the Chorus Speed and the Spin Rate knobs. This LED flashes in time with the Spin Rate setting. It’s fun to watch and I’ll admit to losing a fair amount of time playing with the knob and watching the light throb. I’m simple that way.

Spin Rate

Since the Rototron is supposed to simulate a spinning speaker, this knob controls the rate of the “spin” which is essentially the effect moving from side to side.

Power

Used to turn the damn thing off when your wife says it’s too loud at 11pm. You know, or the gig is over. Whatever.

Control Summary

I wrote in my G300 Tamarack review that the controls on that amp were laid out in such a way as to be completely indecipherable when in use.

This amp is arguably worse. The controls are more baffling, there are LEDs that don’t make immediate sense, and some of the useful labels are under the top lip of the cabinet where you can’t see them.

I did most of my testing with a guitar on my knee sitting in front of the amp with a view similar to the one in the picture. If I got any closer to the amp then I couldn’t read the labels for the knobs, and you know when that happens? When you approach the amp to change the knobs.

Electronics

All of the Timberline amps are completely solid-state and were made by Randall for Guild. The chassis is relatively well designed and simple to follow with large traces that have good separation from other traces. The power supply is split into two parts with one part being a circuit board in the chassis and the transformer being mounted underneath. There are a fair number of unused traces on the board which leads me to believe that the same board is used in the larger and more feature-laden G700 Sequoia amp, but until I get one to dissect, I can’t be certain.

In the G300 Tamerack article I noted that the OpAmps in that amp were all RC4558Ps which are famous for being in some of the original Ibanez Tube Screamers. This amp is populated with NE5532N OpAmps. Perhaps more interesting than that is the fact that the OpAmp part number is hand-written on the main board, almost as if this amp was a test unit or was somehow overhauled. This is not the only hand-written mark on the amp, either. In fact, the bottom of the chassis has a large note on it as well.

The bottom of the amp chassis is marked in similar handwriting and ink as “Model G-600 Jan 31/94, Benchtest 2-22-94, Wiring 02-294”. I assume the last number to be a typo of some sort (perhaps also intended to be 2-22-94).

There is a bit more writing on the main board as well marking other chip part numbers and some minor notes. All of this writing on the board would normally make me think that some tech worked on it years after it was made, but the 1994 date on the chassis made me wonder if these are factory marks. Maybe even some sort of prototype or early build sample. Given the difficulty in finding details about this amp, I doubt I’d ever know for sure, though I have my doubts (read on).

The NE5532N (data sheet) OpAmps in this particular amp are from Phillips and are made in Thailand for those of you who like to obsess about such things (you know who you are). Looking at these ICs, I believe they all have a date stamp of 9844nK and though I couldn’t find an official code reference, I did find this which leads me to believe that these OpAmps were all made in 1998. If true, then that means all of the OpAmps were swapped out at some time after this amp was built. It’s possible the amp was repaired, but since all of the OpAmps now match and have the same codes, I have to wonder if someone snagged all the original OpAmps to use elsewhere.

In my conversations with Kevin Nelson, he informed me that the amp was designed to use TL072 OpAmps so this one has clearly been altered. I’d also like to point out that Kevin designed this (and all the other Timberline amps) such that the OpAmps are socketed which makes working on the amp an absolute pleasure. That’s the kind of thing that cost-cutting removes, so it’s nice to see the sockets.

I will say that I think this amp sounds better than my G300 Tamarack, but it’s not really a fair comparison to begin with given the different speakers, cabinet, power, etc.

This picture shows the bucket brigade chip (MN3007), the clock generator/driver (MN3101) and the two optocoupler photocell “bugs” for the Rototron and Chorus effects.

This amp does have an effects loop which is a nice step up from the G300 Tamarack. It also has dedicated speaker outs as well as a headphone out on the back. There is also a signal out jack for each of the stereo channels for low-level signal reamping which is a nice touch. Combined, these additions make for a much more useful amp more in-line with current offerings than the smaller and less expandable G300 Tamarack.

The schematic for this amp is available in PDF format from Randall here. I’ve also sourced it locally here. If you click on the pic of a piece of the schematic (It’s part of the Chorus) to the right you’ll get a large upscaled PNG file I made of the schematic which I find much easier to read than the PDFs from the links.

Speakers

This amp has two 10 inch spakers and a single piezo horn and they are mounted at an angle facing upwards. As expected, because of the larger woofers this amp has a fuller sound than the G300 Tamarack.

The woofers are marked 052-042 along with some Eminence codes with a couple of very worn stickers as follows:

10″ (R) – 10328 8Ω 67-93230795 G1
10″ (L) – 10328 8Ω 67-93230793 G1
Tweeter – No markings

The Eminence codes break down As follows:

10328 – Customer part number
 – Speaker impedance
67-93230795 – Eminence
67-93230795 – Made in 1993
67-93230795 – made in the 23rd week
67-93230793 – The 793rd speaker made that week.
67-93230795 – The 795th speaker made that week.

G1 is an Eminence metal group number. I have no idea what that means but suspect is has to do with magnet types.

I emailed Eminence about these speakers and got this reply:

10328 was a custom designed OEM speaker that we manufactured to one of our customer’s specifications. It is an 8 ohm speaker with a 1.5″ voice coil and a 16 oz ceramic magnet. We do not rate OEM designs (that is left up to the customer to test and rate their cabinet or amp), but a conservative thermal power rating based on the voice coil diameter would be about 50 watts.

Like the G300 Tamarack, this amp has a Piezo horn, but where the G300 had a Motorola marked horn, this one is unmarked. Motorola stopped making piezo tweeters in the early 1990s, so this is probably a CTS horn as they took over production of the tweeters and sold them as KSN 1005 Super Horns.  The amp seems to date from 1994 so the horn being from CTS would make sense.

Since CTS then sold the product line in 2005 or so to Piezo Source, replacements can be bought from Piezo Source or US Speaker and the specs for the currently made unit are here. I have no idea if the new ones sound the same as the old ones.

The piezo horn is wired to left speaker and there is no crossover of any kind involved in the circuit. This was a common design at the time because these horns were advertised as not needing a crossover, though today many people insist that the behave better with one in the mix.

Sound

Given the likelihood that this amp has been tinkered with for whatever reason, it is probably unfair to judge all of the Guild G600 Aspens based on this unit, and with different OpAmps, this one it may set unrealistic expectations by presenting this amp as being representative of the model.

Of course, I made the recordings anyway. I dialed the amp in so that I liked the sound and then promptly didn’t write down what those settings were. Then I set about methodically going through the effects settings because somehow that warranted proper note-taking where the actual tone of the amp did not. I guess there are reasons why I’m not actually a scientist.

No effects

Chorus 5

Chorus 10

Reverb 5

Reverb 10

Rototron 5

Rototron 10

Chorus vs. Rototron

Chorus Hiss

For the recordings I first recorded my Taylor DN-K unplugged so you could get a sense of its natural tone. Then, about two years later, I got a Guild Artist Award from 1988 and re-recorded all of the samples using that guitar, so the sounds you hear don’t match the guitar in the picture, but I like the picture and I’m too lazy to take another one.

The first recording is of the amp with no effects active. It is very easy to dial in a darker or brighter tone with this amp and with so many knobs it would take me a year to deliver a variety of tones, so I opted to keep everything simple. At least that’s what I’ve told myself, so let’s all pretend that this is a good thing.

The recordings are pretty obvious based on what I’ve named them, but according to my notes the Rototron on 10 also got the added adjective “nauseating”, and listening to it now I can see why.

It is very easy to make this amp sound terrible. Because of the piezo horn, dialing excessive highs can be downright painful and dialing out the highs excessively can make the amp sound woofy and dull, but there is also good tones in this amp if you avoid the extremes. The effects are similarly capable of awful sounds, but by keeping within tolerances I think the amp can sound pretty great. In fact, I really enjoyed playing the Artist Award through this amp a lot more than I did playing my much brighter-sounding Taylor, though the Artist Award is in a different league than my Taylor, and that’s saying something because I love my Taylor.

Remember that these are not the original OpAmps, but I have my doubts that there would be that much of a noticeable difference if I took the time to replace them all. I actually considered it and that’s reason number 38 for why this article took me so long to publish. I even went so far as to source a bag full of vintage TL072 OpAmps in order to do so, but then I realized that I had a book to finish so the entire project just sort of languished. To make up for my failures, here’s a picture of my 1988 Guild Artist Award that I recorded the sound samples with.

Conclusion

I love the look of this amp, and it is certainly capable of producing some nice tones, though it does take some dialing in to get it to sound nice compared with modern options.

I don’t know that I’d choose this amp over a modern choice unless I wanted the warm look of the wooded cabinet for aesthetic reasons. I’ve gigged with my acoustic in the past using nothing more than my Axe-FX set on pass-thru (acting as an EQ) and my QSC K12 delivering the power and that worked quite well for me. Most acoustic players don’t haul around an Axe-FX rig, though.

The weakness of this amp is that a) I didn’t find any awe-inspiring tones, though to be fair an acoustic amp should deliver the tone of the guitar at volume, and b) the effects didn’t wow me largely due to the hiss that wouldn’t go away when they were engaged. I think the amp simply suffers from being a decades old design at this point. There’s nothing wrong with it, but modern amps can just do it better.

Where I think this amp shines is in a home office, studio, living room, or anywhere else that a tolex-covered amp wouldn’t work. This amp has style, and while it may not be my main choice on stage, it might be at home. The problem is that while I’m playing at home, I don’t need an acoustic amp. As a result it sits mostly unused. Sure looks nice, though.

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