THD UniValve Head

Nice set of features for a simple amp. Not cheap, but well built and unique in what it offers. I use it with a preamp and effects unit. Wish it had an effects loop. Plenty of power.

Use it with a Tele (5-way switching), Gibson LP double cutaway with P-90s, and Tele HH with Duncan SH2n and SH4 pickups.
Overall sound stock is not very good - excess of treble and some nasty breakup scratchy sounds when you drive it hard. In the clean settings its OK, but lacks full sound. I eventually made serious mods to the circuit.
Check out my mod at http://sites.google.com/site/stringsandfrets/Home
The result is absolutely stunning - the amp performs beautifully. If you have a Univalve and you're not happy - try the mod - its so worth your time.

Seems reliable - well built in many respects. There were some issues with the Hot Plate control getting dirty and noisy, but I've cleaned it once (per THD service bulletin) and it's been fine since. I've had the amp for over 3 years.

Reasonable. I wish THD were more open about the circuit schematics. I have searched for them and finally just dissected it myself. They could have saved me a lot of time.

Now that the amp is modified, I would not trade it for anything I've ever heard or played through. Again, see my pages for info on the mod
http://sites.google.com/site/stringsandfrets/Home

Its pricey new, but there are a number for sale used now that you can get for less. It's worth picking one up if you do the mods.

Unsure of year, but serial is 1352. I have owned my Univalve for 12 months now and am ready to write a report.

I play all types of guitar music and have owned a raft of lesser amps - Marshalls, Fenders, Roland, TubeWorks - nothing comes close to this class A single-ended beauty. I consider it a serious musicians tool, not something that will give the instant gratification many manufacturers need to push.

The controls are adequate for the purpose - but you have to spend time learning the amp and to get the best out of your guitar and speaker combination, try different valve combinations - no other valve amp has this flexibility.

I use two guitars:
Electric is a PRS Custom 24 with a Dragon in the neck position and HFS in the bridge (I used to own five guitars - Gibson, Fender, Ibanez however after owning the PRS for 2 months I discovered I only need one electric guitar)

Takamine - sorry forget the model - 6 string acoustic with piezo pickup.

I have several effects but generally only use a MI Audio Neo Fuzz (buy one!).

I use high quality Mogami cables with Neutrik connectors.

This amp makes no noise - even fully cranked....

Sound depends on the type of tubes you choose to use, also the speaker cabinet.

Some combinations I like:
Want it clean - ECC81's for INPUT and DRIVER, 5881/6L6CG for POWER
Want it dirtier - ECC81's for INPUT and DRIVER, EL34/EL84 for POWER
Want it woody - 12AX7 for INPUT, ECC81 for DRIVER, 5881 for POWER
Want it woody/dirt - same as above but sub EL34 for power
Want it Yum - 5751 for INPUT, ECC81 for DRIVER, 6L6CG fo POWER

I don't enjoy the sound through an open backed cabinet is much as the sound from a sealed cabinet.

Clean is wonderful, distortion is crystal clear - even at high volumes, you can hear each note of highly distored chords - this is the nature of class A.

Many people comment that this is the best sounding amplifier for my acoustic guitar - really is magical and through the Univalve actually sounds like an acoustic guitar! This again is the nature of Class A - it is pefectly suited to the anomalies of acoustic guitars.

You have to learn how to use this device.

All I can say is one night, mid-gig, mid-song, I felt the rhythm guitarist trip over whilst doing his silly Pete Townsend imitation and turned around in time to see my 2x12 cabinet, with UNIVALVE atop falling over forward.

The amplifier hit the floor from nearly 3 feet up. It bounced. A peculiar fart was emitted from the speakers, and we kept playing. The Roadie picked up the speaker cabinet and left the THD on the floor, upside down, while we finished the last 40 seconds of the song.

At the end of the song, we picked everything up - all still powered up and running, put the amp ack on top of the cabinet, and got into the next song.

That was eight months ago. I found that one of the valves used in that 'experiment' died soon after and was buried with full military honours. The amp didn't seem to suffer any consequences.

I dropped a Marshall from 6" once getting it out of the car and it cost over $180 to get repaired.

Never had to deal with THD.

My tech did a review when I purchased it and recommended I purchase a new 12ax7. No issues h could see.

Been playing for over 30 years.

If someone steals it and I find them, we'll be having our own, very special "Good Friday". Then I would sell their hair to a wig maker and use the proceeds to immediately purchase another Univalve.

I had tried a Mesa Boogie and Ampeg - both were nice, but I found the Univalve had so much variety through the ability to instantly change a valve. There was NO COMPARISON with new Marshalls or Fenders I tried - but hey, brand and image is everything in the big, wide, wonderful music instrument industry!

The only thing I would change would be to include a footswitch for selecting high or low impedance inputs.

Serial number 1681. The amp debuted in 2001 to positive reviews. I picked this one up used, in excellent condition in 2008 from a private party. Featurewise, it's Class A, single ended with the unique (as far as I know) ability to accommodate a variety of preamp and power tubes without the need for rebiasing. In my book, you can't get any more versatile.

I've read the other reviews and I'm baffled by the negative (harsh) comments. In fairness, I play my amps as clean as possible, preferring distorting pedals to ad whatever "grit" I need at any particular time. So here's my setup: mostly single coil, Fender-style guitars (my current favorite is a Warmoth Fender with Fender noiseless cobalt PUs) straight into this amplifier's "Roll" input (low gain) without the attenuator active, High Voltage, "Attitude" at 12 o'clock, volume at nine, treble at 3 (this is a really bright Strat) and the bass at nine. It's like an eargasm. That means an orgasm for your ears. Duh. Crystalline, warm, three-dimensional, living and breathing notes spilling out of this thing in a way that makes every other amp I've ever owned sound flat and brittle, including my prized Fender Pro Reverb. I confess. I don't even know what kind of tubes are in this thing at the moment. It sounds incredible. Fantastic. Unbelievable. Spine-chilling. Warm, Breathy. I could sell every other amp I own (I started doing so today, after playing through this amplifier) and be perfectly happy.

Seems well built. No reason to think it's not reliable, but I can't offer an opinion on this topic.

No opinion. Buzz seems pretty positive on THD in general.

I've owned a lot of amps. I tend to buy, sell, buy, sell and buy, then sell. This one's a keeper.

Simple design with some twists. Low and high inputs, volume, treble, bass, "attitude" knob (adjusts the signal strength to the driver tube),full power/attenuator switch, the attenuator control, which is actually a THD Hot Plate (think Marshall Power Brake), hi & lo voltage switch, and a simple (but effective) noise reduction circuit. On/standby switch, and of course, mains power switch. Rear panel consists of speaker out jack, switch to toggle between 2/4 ohm, and 8/16 ohm speaker loads. Also a line out jack with its own level control. Single channel, no FX loop. Amp has the ability to accept any octal based power tube (6L6, EL34, 5881, KT66, KT77, KT88, KT90, 6CA7, 6550, and even 6V6,(amp must be set on lo voltage), and an EL84, with a yellow jacket adapter. Also, any 9 pin tube can be used for the pre-amp, and driver tubes, such as 12AX7, 12AU7, 12AT7, ECC83, etc. All this adjustability to tailor the overall character and response of the amp.

Well, this is where it gets harsh, literally. This is the 2nd Univalve Ive owned, and I had forgotten why I sold the first one, but was reminded after owning this amp again. I really cant understand why players seem to be gushing over themselves about this amp. I tried at least 20 power tubes (some duplicates, like 3 or 4 different EL34's) and an equal amount of pre-amp/driver tubes, and though the amps character DID change, I was NEVER able to get rid of the harshness of the overdrive/distortion in this amp. Its not the speaker cab (2-12, half open, half closed back cab, with G12H-30 Celestions)that causes this. It might be transformers, it might just be circuit design. There really is no clean sound, unless the guitar is plugged into the low gain input, and then the amp sounds somewhat weak. Its strong enough in the high gain input, but again, harsh sounding, especially in the lower registers of the fingerboard. Its not that the amp necessarily sounds BAD, it just sounds dry, and "grainy", and excessively bright; the amp does lack bottom end, regardless of tube choice. I ALWAYS had to run the bass full up, and the treble basically at zero, or 9 o'clock position at best, and even then, the low end was barely acceptable. Once the attitude is turned up, the brightness increases even more, along with the aggressiveness of the amp. Its an appropriately named control. It is a fairly loud amp, and it has a LOT of gain, just not quality gain IMO. The attenuator and the noise reduction work as advertised, but decrease the responsiveness, and attack of the amp considerably. Hi/low volt switch cuts the output approx in half, and also knocks down the responsiveness.

No reliability issues. It does seem to be built very well.

I spoke to Andy Marshall (THD amp designer) and he seemed very friendly and helpful. He recommended trying KT66, or KT88 tubes, which I did. Neither cured the harshness, or lack of bottom end punch.

Ive played guitar for 35 years, and have owned a LOT of different amps and guitars. Quite honestly, Im selling this amp this coming weekend, and I cant wait to get rid of it, and would NEVER buy another one. Im not opposed to trying other models of THD amps, such as the Flexi-50, but the Univalve is something I wont buy again. (and I got this amp DIRT cheap, at Guitar Center when they had an inventory clearance). There was a reason this amp wouldnt sell, at any more than what I paid for it, because no one liked the way it sounded. Im firmly convinced that there was nothing actually WRONG with this amp, as my previous Univalve had the same grainy tonality. Its just the nature of this amp.

This amp has one channel but it has a two inputs, one of which adds a gain stage for those who play with a lot of distortion (or weak pickups). You cannot AB the inputs because when you are plugged into the low gain input it defeats the high gain stage or something like that. There is no effects loop or headphone jack which would both be nice, but there is a switchable line/instrument out with a volume control, and when no speaker is plugged in, the amp supplies a dummy load, so it could easily be run into a headphone or practice amp, or your stereo's aux in, or any higher powered slave for that matter. You could plug it straight into a Twin. It has a Hot Plate -- kind of like a power soak -- which works best at mid volume, but gets a little tinny when you really crank it down. The amp can run any octal ouput tube with the same pin-out as a 6L6 (6V6 up to 6550), so you can fiddle with the ouput power and tone, and with an efficient speaker it would be loud enough for small clubs with the stock EL34, but I'd just recommend getting the tone you want and running the line out or a mic to the house system.

The features I was looking for in an amp were flexible tone, tube overdrive regardless of volume, and NO hiss or hum. I have vowed never to carry anything heavier than 30 lbs again, so I didn't want a combo. My favorite time to play is late at night, and when I am not playing a note, I DONT WANT TO KNOW THE AMP IS THERE, just like when you pause a CD player, you don't want to hear your stereo making extraneous noises. I tried new Vox and Line 6 modeling amps and tube amps. The modeling amps with a 12AX7 seemed good at first, but then I could hear the hiss being gated out. I also tried the new Fender Princeton Recording Amp and was impressed with the features. Any of these would have been good choices for playing live, but all failed the hiss test. I wound up buying the Univalve because it passed the NO hiss test (there is a noise reduction switch that is not a gate) and the tube overdrive criteria, but I had to do some experimenting to get the flexible tone.

There is really only one feature I wish this amp had that I can't invent a workaround for, and that is a drive control to let you adjust the amount of gain you are adding if you use the high gain input, so for now I don't use it, but I haven't tried any tube substitutions yet.

You will never get through all the sounds this amp can make once you start substituting preamp and power tubes. Plugged into the high gain input, noise reduction off and cranked you can make this amp a little more noisy, but nothing like a Mesa -- sorry, but NO hiss was one of my main criteria here, so there isn't much to criticize.

The amp is heavier on the mids than I like for playing either bright jazz or funk rhythm, but just right for lead. At first I thought I was going to have to use a second amp for rhythm, but I solved my problem as follows. My pickups are active EMGs on a strat. I plugged into the low gain input, turned the amp all the way up and set the controls for a good searing lead. Then I put a Danelectro Fish&Chips graphic EQ pedal between the guitar and amp (read the Harmony Central review on this little cutie), cut the mids out and dropped the master gain on the pedal for a 10 - 15 dB cut, just the amount I needed to dial back for clean rhythm tone. If your pickups aren't as hot as my EMGs, you could probably do the same routine in the high gain channel. The result is just like channel switching, EQ in for rhythm, EQ out for lead. You can use the hot plate to adjust overall volume.

I would use it without a backup. The tubes and controls are mounted on the chassis, but this amp does have printed circuit boards in it. Things are spaced out nicely inside, and power resistors are up off the board. I prefer point to point wiring but that would put it way out of my price range. My compromise will be just to open it up once in a while for the first few years and make sure the circuit board isn't getting brown (heat damage).

I bought this amp used on craigslist -- no warranty -- and had never played one before. I noticed that the hotplate cut out when the knob was turned all the way up. I called the Seattle factory and talked with the guy who designed the amp, Andy Marshall. He emailed me instructions on how to clean the rheostat complete with pictures. He offered just to do it for free if I brought the amp in. The instructions were good enough for me, but if you don't want to open your amp up, you could print them and take them to a tech.

If you take an amp back into the isolation room in your favorite music store you will learn more about it than you can on the show room floor with all those other players wanking on the Marshall Stacks. I have been playing since I was 10 and building amps since I was 12 (49 years old now). I have built and owned dozens of tube amps and I had pretty much come to believe that more gain stages equal more hiss. I cannot figure out how THD made such a NO hiss amp, so if I lost this one I would have to just buy another. Granted that I had to use a $40 pedal to make it act like a channel switching amp. I think my amp building days are over because of this one.

Great.....but no reverb! i give it a 10 because of the tube swapping and no biasing, which to me means no amp tech charging me money.

great tube saturation. i've been playing this amp for a year now, and i can tell you this: i've been the type to buy an amp play it for a year, sell it on ebay, buy a different amp and continue the same routine. i've been doing this for about 10 years now. i've had fender custom shop amps (bassbreaker) marshall jcm 800, ton's of blackface and silverface fenders, and many other amps. i always would get tired of the tone in a year or so and sell them in order to be able to afford another one. the only one i could not sell was a blackface twin that is the best twin i've ever heard (i've owned 6)
well a year later and i'm still in love with the tone that the thd gives me. if i get tired of the EL 34 sound hell i just throw in a 6l6 or a 5881. i will not be selling this amp, if a guy like me who is so fickle about tone can still fall in love with the tone every day for a year and not want to sell it, then that should speak volumes about the univalve. speaking of volume the 15 watts is perfect, i keep the volume turned all the way up and i'm never to loud but never get lost in the mix. you can hear some recordings i've made with the univalve at myspace.com/toddpirk all the songs on that site were recorded with the univalve. i used different tubes for each song too.

i give it a 8 b/c the light keeps blowing, bad fuse or something, but it does not affect anything it's just a light.

never dealt

been playing for 18 years, i think i will always be an owner of thd amps from now on, i love it! the price is just so good too, they could easily charge more for these amps and still sell them. i do wish at times it had reverb but thats what my fender twin is for i guess. great amp that univalve.

It has a lot of features, the hotplate is ok but as they all do at near max attenuation, robbs character severely. The lack of any loop on a techy sort of head like this bugged me to. You might think it would degrade the tone so it was left off? The hotplate should be left off too if that's the case. The high low inputs are vastly different in volume. While the high gives good volume, it's only good for a high gain tone. I have 5 watt amps that give twice the volume of the low gain input. If my ratings seem harsh, they're only in relation to the price of this amp.

It is a medium-to-high gain amp really and does little else worth mentioning. The tone was dissapointing and harsh, not musical at all. My array of 9 assorted power tubes changed the amount of gain but not that harsh, grainy honk. I have honestly gotten FAR tastier tube tone from a Sanamp Classic through a clean Fender Twin or Musicman RD50-112. That setup also takes a giant dump on the Univalve at speaking levels. I play Floyd Rose Mexistrats with USA electronics, Duncan little 59 HB's in the bridge pickup and Warmoth stainless steel fretted necks. I tried a ts808 with the Univalve which sounded OK but I was dissapointed that it was so much better than the amps tube grind. For the price and description, I didn't think I should need an OD pedal.

No problems at all. But I didn't keep it 2 months.

I've been playing over 30 years. I know classic tone, how to tweak knobs and adjust settings. I have several speaker and cab options. I tried everything. I loved and still love the look and portabillity of the THD amps. They look so damn cool but fell WAY short of my expectations in the tone department. The sound clips on the site were nothing like the actual tones available. I packed up my pile of new JJ's, the amp and the gigbag and sold it as fast as I could. I got my cash back before the word was out. I have owned Many tube amps, Mesa Mk3, Marshall DSL100, Fender Prosonic, Twin Reverb, Traynor yba-1, GK 250ml, and more. I have never unloaded any amp as fast as I unloaded that Univalve. My advice, try one first if you can or get a good price cause you might be selling it fast. It doesn't get good tone for the price, plain and simple. I doubt I'll ever try another THD amp.

The UniValve has 2 channels (Rock and Roll), but they are not switchable. Aside from that limitation, the amp is incredibly versatile, allowing you to freely interchange tubes (power and preamp) without rebiasing. The amp also has high and low voltage settings, as well as a built in THD Hotplate attenuator, so you have tremendous control over output level.

I own both the UniValve and BiValve, and they are my favorite amps of all time (and I've been playing for 30+ years). I cannot fathom how anyone could rate the UniValve low on "sound quality"! By experimenting with different combinations of power and preamp tubes, you can pretty much create whatever tone you like. No, it may not sound "exactly" like a Fender or "exactly" like a Marshall, but I don't care because I think it sounds better. And, if you should become tired of the Uni's tone, just change the tubes -- Fantastic. The UniValve (and BiValve) is also very responsive to pedals.

THD prides itself in state of the art PCB construction, and when you look inside, it appears every bit as well made as any boutique PTP amp I have ever seen. For 2 or 3 years now, I've played it 3 or 4 days per week, and have never had a problem. As an aside, it's also one of the most aesthetic amps I have ever seen -- sometimes I just want to stop and stare at it!

Playing classic rock 30+ years, and have owned too many amps and guitars, always looking for the perfect "tone." I've sold off a lot of good ones (vintage and boutique), but will never part with my UniValve (or BiValve). Moreover, at under a grand, this amp is a downright steal.

The 80 plus reviews here will give you the details here. I bought mine in 2006 with the Avatar cabinet deal. This is not my only tube amp-it fills a nice void with the features it has. I like the Hot Plate, I like the responsiveness of all the controls. Do not use the noise gate switch and yellow light at all.

They did switch the "THD" logo on the front from steel to white plastic. No big deal, but I liked the metal logo better...and yes you can put the top grill on with a KT88 in there.

I rarely use the "Roll" input. Sounds a bit thin with either my Strats or SG (or other humbucker equipped guitar). Big difference in volume between the two channels....i.e. if you leave volume at 'noon' setting, it is louder on the "Rock" input than the "Roll". No big deal. I run it with a JJ KT88 and JJ preamp tubes. This set up gives me a great Ronnie Wood Faces Strat tone and with a slight tweak, a great Duane Allman sound for slide and leads via the "Rock" channel. It does what my other tube amps do not. I have Groove Tube Soul-O 75 with GT6L6 GE tubes and a Savage Macht 6 with EH 6V6 and 5751's in it....so it fills in there. I also like it with EL34's-but not 6L6, 6V6 or the EL84's with the yellow jackets. Don't kill yourself buying and switching tubes like mad, I know that is the idea here with the Univalve-but pick a sound you can work with and go with it.

Very reliable and light. Be careful if you have kids, they can get their little fingers in there when you aren't looking! Tubes look cool to kids and the purple pre amp tube covers are tempting. No issues here. Have not had to change the little yellow/orange bulb.

Great. They forgot the power cord in mine when it shipped. Called Ed at THD, told him I got from Avatar (even if you do order through them, it ships direct from THD), he sent out next day. Never dealt with them other than that.

I love this amp. Fairly cheap for all the features you get for different applications. I would definitely check out the Avatar deal, their cabs are great for the money. I ended up running my GT Soul-o 75 through the Avatar 2x12, and now run the Univalve through a Mesa 1x12 3/4 back. Good for guys who have/want multiple amps...I just do not like the Roll input as much as the other. Maybe if I fiddled around with tubes all day, I would find a combination that would work for me using that input-I am sure I could.

Very versatile amp, you know the features

I guess it depends what you like. I found three combinations that were stunningly good, and a couple that were just average. Overall though it sounds great. You really have to tinker with it, it took me a week to find a combination that worked for me. I wish it had a master vol. I don't like the hotplate sound very much. Gives off a little hum, but nothing offensive noise-wise.

No problems. Excellent construction.

Very good support.

Great overall