THD Flexi 50

stephen sawall

Well-known member
The design was all about getting British voiced distortion and a great clean from one amp.

With the switches there are a number of clean voices to choose from.
I like the clean sounds I get with the boost on best.

No matter how distorted you run the amps preamp and or poweramp you can use the volume on the guitar to get a good clean.

I feel a Hot Plate with the amp is very practical because a lot of the sounds from this amps are about the power amp being turned up.

The tone controls are not very interactive and have a large range that works.
Baxandall bass/treble. Very strong mid control.
No presence but the cut is similar but does not add gain.

The clean to clean break up on the amp is amazing.
I am sure the huge dynamic range of the amp helps.
When using a pick or my fingers it responses more to my right hand more than any other amp I have played on.

Headroom is not something that I have had a problem with.

What preamp and poweramp tubes you use gives different colors and headroom.
Setting the bias a little hotter or cooler also changes things.

This is a comparison of a Flexi 50 to a JMP
.It would be similar comparing it to a lot of amps.....

You well want a Hot Plate or what you like to use with these amps.
We are talking about power amp distortion here.

The Flexi has more bottom and low midrage if you want, the Marshall's sound kind of thin side by side with the THD.

The mid range on the two are different. Both sound good in a mix/live.
There is way more dynamics and control with your right hand with the Flexi.
The Marshall well be more compressed with a equal range of gain.
The Flexi may be the most dynamic amp made for guitar.

The Flexi has more gain on tap as it does have a boost.
You can get more gain than a single channel 800 with the boost on the Flexi.

You can put a lot of different tubes pre/power in the Flexi.
Without much time spent doing it.

The clean sound in my ears has a lot more of that old Fender tone, feel.
You can back off the volume on the guitar down to clean and does this with every guitar I have put into it.
With a Marshall if you back off too much it just gets thin and weak.

The tone controls on the Flexi have a huge range and sounds good with a lot of range.
Many voices that all work very well.

There are more voice options with the THD.
Input - Hi/Lo
Bright - on/off
Boost - on/off
50w/20wMaster - on/off
These are all tools I use.

You can get in the ball park of many English tones, even the Vox tones.
I did say ball park. That is with the right pre/power tubes.

The harmonics that come from the Flexi are unreal. I have only heard a few amps that come close.

The THD is very well built and I run it full blast without thinking twice about it
if I want that tone / gain/ feel.

Good luck finding a Marshall that does not have some bad mod done to it. If you don't know THD stands by there amps.

The problem with the effect loop is the same as all amps that get a lot of the distortion from the power amp. Distortion after the effect does not sound good with a lot of effects.

My father fixed amps on the side when I was a kid (70's,early 80's).I have played thru a lot of the classic amps.
The harmonics, punch, attack envelope, tone range and most of all the way it reacts to my right hand.The dynamics are key to the way I play.
I feel the Flexi is equal or better than anything else I have played on for a lot of things.
THD builds my favorite amps.

The Marshall sounds like a Marshall and I love that sound.But I do not miss the ones I have had that much, even my JMP and Super Lead. The Flexi just does a lot more.


Well-known member
Necro but I want to know if you still feel the same way about the amp after all this time and if anyone here has any feedback?

Btw are there any mods that people know of worth mentioning?

stephen sawall

Well-known member
I just saw this today.

I still use the amp all the time.
Personally I feel the Bivalve gets closer to the Marshall thing.

I have four THD amps. Each one has its own sound. The thing about THD amps is the amount of harmonics.

Flexi 50 - Does English crunch and Fender Tweed stuff. Class AB.

Bivalve 30 - probably the most gain. Not high gain. But can get very aggressive. Class A. Has all the odd and even harmonics.

Series One Plexi - a 1969 JMP clone, 50 watt small box. Voiced with Dave Friedman amp that Dave uses to voice everything. Personally it is the best sounding Marshall type amp I have heard. Lots of glass and really nice attack.

Deco 36 - 4 x EL84, 2 x 12AX7. Cathode bias (self bias). Class A or AB depending on settings. Doesn't sound like any other EL84 amp.
There was two prototypes built about 15 years ago. Andy Marshall recently built me a one off. This amp will go into production. He has parts to build a few hand wired right now.