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The THD Univalve amp is a high quality amplifier and clearly the designers and company know their craft. However, after several years of using it I found myself frustrated with its limited scope of sound. I fiddled with tone settings, speakers, and tube types. I tried Gibson, Fender, and PRS guitars and various pickups. I remained unhappy with the sound and eventually accepted the fact that the designers created something that just didn’t match the range of my tastes. You have to respect the designers for both the mechanics and electronic circuitry. The amp is solid and reliable and it does produce a unique sound, unfortunately, it’s just not exactly the only sound I want.
The THD Univalve amp is a high quality amplifier and clearly the designers and company know their craft. However, after several years of using it I found myself frustrated with its limited scope of sound. I fiddled with tone settings, speakers, and tube types. I tried Gibson, Fender, and PRS guitars and various pickups. I remained unhappy with the sound and eventually accepted the fact that the designers created something that just didn’t match the range of my tastes. You have to respect the designers for both the mechanics and electronic circuitry. The amp is solid and reliable and it does produce a unique sound, unfortunately, it’s just not exactly the only sound I want.
The circuit is full of response-shaping RC combinations that indicate the designers clearly crafted the amp to produce the sound coming out of it. My experience was that the best sound came from the amp when you’re at high volume and high distortion. Now, that’s fine some times, but I don’t want to play that way all the time. The amp at low volumes and low distortions sounds tinny and scratchy. Maybe I’m too demanding, but I expect an amp to handle a range of tones and styles and to do them all well (see the section on tube sound). Eventually, I ran an analyzer on it and the response curves confirmed that at low or modest levels, there is almost no low end (therefore the tinny quality) and the treble boost is huge. Basically, above about 150 - 200Hz, the response curve showed sharp gain increases with frequency. Even with the bass control at maximum, there was at best a thin and weak low end. Furthermore, the amp had an annoying “scratchy” quality as the tubes were driven into large-signal distortion. Normally, amps produce a smoother transition into initial breakup. The Univalve produced a non-harmonic scratchy breakup that I found grating and annoying at times. At this point you’re probably wondering why I even used the amp or why I didn’t send it back. I can only say that while it was bad at times, I kept telling myself there was no obvious reason for the limited sound range and there were qualities I liked about it. As I said, the amp presents itself as a well designed unit.
The circuit is full of response-shaping RC combinations that indicate the designers clearly crafted the amp to produce the sound coming out of it. My experience was that the best sound came from the amp when you’re at high volume and high distortion. Now, that’s fine some times, but I don’t want to play that way all the time. The amp at low volumes and low distortions sounds tinny and scratchy. Maybe I’m too demanding, but I expect an amp to handle a range of tones and styles and to do them all well (see the section on tube sound). Eventually, I ran an analyzer on it and the response curves confirmed that at low or modest levels, there is almost no low end (therefore the tinny quality) and the treble boost is huge. Basically, above about 150 - 200Hz, the response curve showed sharp gain increases with frequency. Even with the bass control at maximum, there was at best a thin and weak low end. Furthermore, the amp had an annoying “scratchy” quality as the tubes were driven into large-signal distortion. Normally, amps produce a smoother transition into initial breakup. The Univalve produced a non-harmonic scratchy breakup that I found grating and annoying at times. At this point you’re probably wondering why I even used the amp or why I didn’t send it back. I can only say that while it was bad at times, I kept telling myself there was no obvious reason for the limited sound range and there were qualities I liked about it. As I said, the amp presents itself as a well designed unit.
Eventually, it got the best of me. I tore into it and reverse engineering the circuit. This was a significant effort and the reason I had not previously done anything serious with the amp. Once I had the first two stages worked out, the picture started to fall into place. As I said the circuit contained RC networks designed to boost treble and cut bass. Again, I recognize that the designers are smart and capable people, but we just disagree on what tone we're after. Furthermore, I’m not a fan of intentionally shaping the response curve too much, when we all spend a fair amount on instruments that offer a balanced and wide spectrum of sound. The guitar body resonance, the wide range of pickup sensitivity, and the wide range of picking/playing style produce a lot of signal over the full range of audio frequencies. Granted, there is not much of significance below 50Hz and above 5K (we can even argue about that), but the response at the high, mid, and low end need to be balanced to get a pleasing tone (IMO) that enhances the efforts made in building and playing the instrument. The stock Univalve was intentionally designed to emphasize the high end. Fortunately it’s relatively simple to alter this and I am pleased to say, the results are a much more balanced tone. All the other qualities of the amp are now fully appreciated and it’s an absolute stellar package – I recommend it highly.
Eventually, it got the best of me. I tore into it and reverse engineering the circuit. This was a significant effort and the reason I had not previously done anything serious with the amp. Once I had the first two stages worked out, the picture started to fall into place. As I said the circuit contained RC networks designed to boost treble and cut bass. Again, I recognize that the designers are smart and capable people, but we just disagree on what tone we're after. Furthermore, I’m not a fan of intentionally shaping the response curve too much, when we all spend a fair amount on instruments that offer a balanced and wide spectrum of sound. The guitar body resonance, the wide range of pickup sensitivity, and the wide range of picking/playing style produce a lot of signal over the full range of audio frequencies. Granted, there is not much of significance below 50Hz and above 5K (we can even argue about that), but the response at the high, mid, and low end need to be balanced to get a pleasing tone (IMO) that enhances the efforts made in building and playing the instrument. The stock Univalve was intentionally designed to emphasize the high end. Fortunately it’s relatively simple to alter this and I am pleased to say, the results are a much more balanced tone. All the other qualities of the amp are now fully appreciated and it’s an absolute stellar package – I recommend it highly.
Note there are clips at the bottom of this page that demo the tonal range of the UNI with all the mods.
Note there are clips at the bottom of this page that demo the tonal range of the UNI with all the mods.
Revised 4/20/2011
Revised 4/20/2011
Since the time I created this site, I've done a series of mods to this amp. I order to make better sense of the changes, I'm redoing this page to separate and sequence the mods. The first two were outlined in a single page, but now that info is found on pages for ModA and ModB. A new page is created for ModC, which is the latest mod version (as of this date). I can't say enough about it. Have a look if you're adventurous. The mods are cumulative, although most of the changes are independent and you can mix-match them. The idea is to present a series of circuit changes with my reasons for each one so you can decide if they matter enough to you to make that change. A summary of the mods is below to introduce the progression of things I wanted to change and how they were done.
Since the time I created this site, I've done a series of mods to this amp. I order to make better sense of the changes, I'm redoing this page to separate and sequence the mods. The first two were outlined in a single page, but now that info is found on pages for ModA and ModB. A new page is created for ModC, which is the latest mod version (as of this date). I can't say enough about it. Have a look if you're adventurous. The mods are cumulative, although most of the changes are independent and you can mix-match them. The idea is to present a series of circuit changes with my reasons for each one so you can decide if they matter enough to you to make that change. A summary of the mods is below to introduce the progression of things I wanted to change and how they were done.
ModA is basically a frequency response modification. It will put back some bass that the stock design intentionally cuts out. The mod also decreases the treble boost in the stock design. The overall effect is a more balanced tone from the amp. Since the ModA amp has increased bass response, the power supply hum level becomes excessive, so additional filtering is added to the power supply to reduce the hum.
ModA is basically a frequency response modification. It will put back some bass that the stock design intentionally cuts out. The mod also decreases the treble boost in the stock design. The overall effect is a more balanced tone from the amp. Since the ModA amp has increased bass response, the power supply hum level becomes excessive, so additional filtering is added to the power supply to reduce the hum.
ModB is an effort to reduce the hiss and hum levels for the Roll input. Shielded wire routing and an added "Miller" capacitor are the main changes. As a byproduct of the mod, there is also some smoothing of the amp breakup sound quality. The degree of smoothing (and hiss reduction) can be controlled by selecting a capacitor value.
ModB is an effort to reduce the hiss and hum levels for the Roll input. Shielded wire routing and an added "Miller" capacitor are the main changes. As a byproduct of the mod, there is also some smoothing of the amp breakup sound quality. The degree of smoothing (and hiss reduction) can be controlled by selecting a capacitor value.
ModC is comparatively drastic. It goes even farther than ModB in quieting the amp and more importantly, it completely alters the clean tone of the amp (for the much better IMO). Naturally, it also impacts the overdrive tone, but that impact is not as drastic as the clean tone impact. The stock Univalve has a somewhat fuzzy clean tone. This mod changes that completely. I've never heard or played a clean tone like this before. I hope the sound clips make my case. It's not recognizable as a Univalve clean tone. It's a bell-like tone, but with some punch to it. The tone has unique quality all it's own. This is a signature clean sound to go with the high-drive tone it's already known for.
ModC is comparatively drastic. It goes even farther than ModB in quieting the amp and more importantly, it completely alters the clean tone of the amp (for the much better IMO). Naturally, it also impacts the overdrive tone, but that impact is not as drastic as the clean tone impact. The stock Univalve has a somewhat fuzzy clean tone. This mod changes that completely. I've never heard or played a clean tone like this before. I hope the sound clips make my case. It's not recognizable as a Univalve clean tone. It's a bell-like tone, but with some punch to it. The tone has unique quality all it's own. This is a signature clean sound to go with the high-drive tone it's already known for.
Revised 5/2/2011
Revised 5/2/2011
Other mods and stories and useful ideas that people sent me are posted on this page.
Other mods and stories and useful ideas that people sent me are posted on this page.
I'm collecting and trying to keep Univalve mod info in one place since I'm getting access to a lot of unposted info and even posted info is scattered all over a number of forums.
I'm collecting and trying to keep Univalve mod info in one place since I'm getting access to a lot of unposted info and even posted info is scattered all over a number of forums.
Revised 5/22/2011
Revised 5/22/2011
ModD is new and adds a master volume control as well as a safety circuit to prevent turn-on damage to the V2 tube. This change really "completes" the amp for me. The master volume multiplies the tone range and degree of control you have. I don't see myself doing anything more to this amp... it's just perfect now IMO. Below the mods are a series of waveform images at key points in the signal path and some explanation of what each tube stage is doing to the signal. Unleash the amp within!
ModD is new and adds a master volume control as well as a safety circuit to prevent turn-on damage to the V2 tube. This change really "completes" the amp for me. The master volume multiplies the tone range and degree of control you have. I don't see myself doing anything more to this amp... it's just perfect now IMO. Below the mods are a series of waveform images at key points in the signal path and some explanation of what each tube stage is doing to the signal. Unleash the amp within!
Revised 10/15/2012
Revised 10/15/2012
ModD is an accumulation of all the mods I’ve made to the Uni. Although the waveform images on the ModD page show what the amp does to a signal, it’s hard to translate that into what it sounds like. So here are some clips that demonstrate the range of the ModD amp. I used five different settings to sample the range of tones the amp can create. You can imagine there are also many variations in between.
ModD is an accumulation of all the mods I’ve made to the Uni. Although the waveform images on the ModD page show what the amp does to a signal, it’s hard to translate that into what it sounds like. So here are some clips that demonstrate the range of the ModD amp. I used five different settings to sample the range of tones the amp can create. You can imagine there are also many variations in between.
All the clips are made under similar conditions. I used my American Standard Telecaster with stock PUs switched to “both” except for one clip using the bridge PU. In one of the clips you’ll hear me briefly switch PUs, but it’s only for a few seconds at the end of the clip. The guitar vol and tone are max’d and it's plugged into the TLA 5051 set for slight compression at hard strums and flat EQ. That output runs into the GSP 1101 set for slight reverb and tremolo – no modeling. The GSP output feeds the UNI input at pretty much the same level as the guitar output. There is little or no gain created by the TLA and GSP – all the gain and overdrive come from the Uni itself. The Uni has Electro-Harmonix 12AX7EH’s for V1 and V2. V3 is a JJ KT-66.
All the clips are made under similar conditions. I used my American Standard Telecaster with stock PUs switched to “both” except for one clip using the bridge PU. In one of the clips you’ll hear me briefly switch PUs, but it’s only for a few seconds at the end of the clip. The guitar vol and tone are max’d and it's plugged into the TLA 5051 set for slight compression at hard strums and flat EQ. That output runs into the GSP 1101 set for slight reverb and tremolo – no modeling. The GSP output feeds the UNI input at pretty much the same level as the guitar output. There is little or no gain created by the TLA and GSP – all the gain and overdrive come from the Uni itself. The Uni has Electro-Harmonix 12AX7EH’s for V1 and V2. V3 is a JJ KT-66.
Most of the Uni settings are fixed for all the recordings. Treble and Bass are at ~1pm. Attitude is set to max. Voltage is set to HiV and NR is off. The attenuator is turned all the way down so the volume from the cab (Neo) is minimal. I’m listening to the recording monitors as I play, so the recorded signal is exactly what I hear while I play. There are only three amp variables in these recordings: the input jack, volume, and master volume. I tweak the line line-output volume control (on the back of the Uni) for each setting to more or less drive the recording interface with the same amplitude signal and make up for amp output level variations.
Most of the Uni settings are fixed for all the recordings. Treble and Bass are at ~1pm. Attitude is set to max. Voltage is set to HiV and NR is off. The attenuator is turned all the way down so the volume from the cab (Neo) is minimal. I’m listening to the recording monitors as I play, so the recorded signal is exactly what I hear while I play. There are only three amp variables in these recordings: the input jack, volume, and master volume. I tweak the line line-output volume control (on the back of the Uni) for each setting to more or less drive the recording interface with the same amplitude signal and make up for amp output level variations.
The recorded signal comes from the Uni line out which runs to a UA-25EX USB converter and I record mono tracks with Audacity 1.3. The tracks are saved as mono WAV files and loaded into Protools 9 where I cut contiguous segments out for these clips. There are no PT effects or edits in these clips – PT is only used to clip out segments. I played/recorded each amp setting for about 5-8 minutes and then just clipped out a representative segment. Excuse my playing nits… these clips are not edited and they are just the guitar, so you can hear everything. You may notice that one thing you don’t hear is SC PU hum in the seconds before or after a clip - even with the high-gain amp settings - thanks to those cancelling coils in my Tele.
The recorded signal comes from the Uni line out which runs to a UA-25EX USB converter and I record mono tracks with Audacity 1.3. The tracks are saved as mono WAV files and loaded into Protools 9 where I cut contiguous segments out for these clips. There are no PT effects or edits in these clips – PT is only used to clip out segments. I played/recorded each amp setting for about 5-8 minutes and then just clipped out a representative segment. Excuse my playing nits… these clips are not edited and they are just the guitar, so you can hear everything. You may notice that one thing you don’t hear is SC PU hum in the seconds before or after a clip - even with the high-gain amp settings - thanks to those cancelling coils in my Tele.
The table below summarizes the differences in settings for the five clips.
The table below summarizes the differences in settings for the five clips.
Tone Quality Input Jack Volume Master Vol
Tone Quality Input Jack Volume Master Vol
Clean Roll 10am Max
Clean Roll 10am Max
Full-Clean Roll Max Noon
Full-Clean Roll Max Noon
V3 Drive Rock 10am Max
V3 Drive Rock 10am Max
V2 Drive (bridge PU) Rock 3pm 8am
V2 Drive (bridge PU) Rock 3pm 8am
V2 Drive (both PUs) Rock 3pm 8am
V2 Drive (both PUs) Rock 3pm 8am
V2+V3 Drive Rock 3pm 11am
V2+V3 Drive Rock 3pm 11am
Clean – this setting is the cleanest the amp will allow. None of the stages are overdriven, so the output is as clean as possible with a Uni. This Mod Uni sounds cleaner and has more bottom end than you’ll likely hear from a stock Uni. It’s a matter of taste, but I appreciate the ability to get a clean and full-tone if I want one.
Clean – this setting is the cleanest the amp will allow. None of the stages are overdriven, so the output is as clean as possible with a Uni. This Mod Uni sounds cleaner and has more bottom end than you’ll likely hear from a stock Uni. It’s a matter of taste, but I appreciate the ability to get a clean and full-tone if I want one.
Full-Clean – this setting drives V2 to large signal swings and that produces a nice warm tone. The master volume reduces the large pre-amp signal to keep the output stage from significant distortion. I really like the ringing-bell quality to this setting. It’s probably my favorite setup for most playing. I could not get this tone from the stock Uni.
Full-Clean – this setting drives V2 to large signal swings and that produces a nice warm tone. The master volume reduces the large pre-amp signal to keep the output stage from significant distortion. I really like the ringing-bell quality to this setting. It’s probably my favorite setup for most playing. I could not get this tone from the stock Uni.
V3 Drive – this is basically like the stock Uni at medium drive. The Rock input is used, and the volume setting is kept low to keep V1 and V2 from significant distortion. Most of the distortion comes from the V3 output stage. This is the signature Uni tone although I have a bit more low end getting through due to the mods. Reducing the bass control gets back to the stock Uni tone.
V3 Drive – this is basically like the stock Uni at medium drive. The Rock input is used, and the volume setting is kept low to keep V1 and V2 from significant distortion. Most of the distortion comes from the V3 output stage. This is the signature Uni tone although I have a bit more low end getting through due to the mods. Reducing the bass control gets back to the stock Uni tone.
V2 Drive – this is a preamp overdrive tone. The Rock input with high volume drives V2 hard for lots of preamp overdrive. The master volume is dialed way down to keep the V3 output tube from distorting. This is a qualitatively different distortion from the V3 Drive tone. I really like it. It’s less “hairy” and smoother to my ear, and it’s only possible with the master volume mod.
V2 Drive – this is a preamp overdrive tone. The Rock input with high volume drives V2 hard for lots of preamp overdrive. The master volume is dialed way down to keep the V3 output tube from distorting. This is a qualitatively different distortion from the V3 Drive tone. I really like it. It’s less “hairy” and smoother to my ear, and it’s only possible with the master volume mod.
V2+V3 Drive – this again produces lots of preamp overdrive in V2, but the master volume is turned up enough to get some V3 output stage distortion as well. The master setting will control the mix of preamp and output stage distortion. With the master set to full, you’re back to stock Uni high-drive conditions.
V2+V3 Drive – this again produces lots of preamp overdrive in V2, but the master volume is turned up enough to get some V3 output stage distortion as well. The master setting will control the mix of preamp and output stage distortion. With the master set to full, you’re back to stock Uni high-drive conditions.
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