The Mustang is a clone of a clone. I believe that the source was a Bludodrive Ojai and it's 'secrets' were not revealed by the proprietor of Bludo rather another US amp builder who came across it. I don't know if Nik has followed the information 100% - the Ojai circuit is quite specific about the use of components / tolerance especially the Pots for Input gain and Midrange. These are Audio taper pots but the taper response is 30% on Robben / Ojai amps rather than the more common 15% on standard tape pots. In practice this means that for any given setting (say Noon), the 30% taper pot is electrically further along it's travel. In simple terms, Noon on a 30% taper pot gives more midrange than a 15% pot set at Noon (similar impact for gain on the input gain control). There is no more gain / midrange available overall, it only impacts on where you end up setting the pot to achieve the sound that you desire.

The Ford Mustang is a clone of Robben Fords amp, well more accurately it's a clone of a clone - the cloned amp in question being a Bludodrive Ojai. The most obvious change is in the Presence circuit (Global Negative Feedback) which contains a 2.2 uF capacitor. This will change the tonal characteristics of the amp and give a different range of operation to the Presence control. More brightness available.

The 183 is an Overdrive special with serial number 183. It was an EL 34 based amp that was bought by a well known Gear Page forumite for a lot of cash ($50,000 has been mentioned); and he paid a US based amp builder to clone it. I think that he then sold the original amp. The 'guts' of both of these amps have been 'shared' and discussed on the ampgarage forum although there is a fair amount of disquiet over Niks use of this information - I'll stay out of that discussion.

I'm not sure about the HRM MK 2, It's a revision on the HRM so it could just be Mark 2. The Emmy Pro is a well known Two-Rock take on the Overdrive Special HRM so there is a chance that it is based on that. I haven't looked too closely at the revised diagram, the comments state that the LNFB has been removed from V2 which will give a bit more gain / loosen up the feel a bit.

The verbrator in parallel mode will change the tone because it's only the FX that are inserted into the send / return that are placed in Series or Parallel. Even in Parallel mode, the 'dry' signal from the OTS will pass through the Cathode Follower and Gain Makeup stage. Whether it's a dramatic change in tone.....that's a different thing and will depend upon how hard you drive it.

If you don't want the reverb then I think that Fuchs will sell the same thing minus reverb. I have verbrator and think that it's great both as a loop and a reverb unit. As I wanted reverb anyway it made sense. techically the Verbrator is similar to the C-Lator (Tube Cathode follower with Tube gain recovery) but it doesn't have a bright switch.

The only thing missing from the Verbrator that the C-Lator has is the Master output gain. As the OTS FX loop is driven 'post matster volume' not only is the reverb level dictated by the master volume setting, but you also can't crank the master to drive the Cathode follower hard without increasing the sound level produced by the amp. The C-Lator has it's own master which in effect becomes your overall master volume, you can then crank the amp master to get a nice compression from the C-Lator. I'm looking to fit a master to the Verbrator for this reason.

Nothing wrong with that sound, both cleans and OD are fantastic.

You know, I think that we all get a bit too critical when it comes to judging the sound of our amps - the OTS is a wonderful amp for many different music genres, granted it takes a little bit of getting used to and you have to find the 'sweet spots' but once you do, it's a real head turning sound especially when played at gig volumes.

My view now is that I'm better off spending more time on my playing (which is full of 'issues') and less time spent worrying about whether changing the bypass capacitor on V2b to 2.2uF is going to make things any better.

C- Lator is better as it is valve (tube) based and will add a bit of compression / harmonic interest when driven.


In my view you need to have the G12-65H for 'the' Robben sound...there again which Robben sound are you looking for?

My OTS is pretty much standard spec, I use a Fuchs Verbrator in the loop, drive a 1 x G12 - 65 cab and set the knobs as:

Gain = 5
Treble = 3.5
Mid = 4
Bass = 3.5
Level = 4
Ratio = 6
Master = whatever I can get away with.....4 sounds really good
Presence = 3 (I prefer this to be low for OD sounds although I admit that clean sounds better when set at 7 / 8
Internal gain trim set at around 10 O'Clock (measures 27 K Ohm on a DMM in circuit)

I use a Richie Kotzen Telecaster that has a Single Coil sized Humbucker in the Bridge (Di Marzio Chopper T). I like to back the guitar volume off a bit.

I'm not particularly going for the Robben Ford sound but it's pretty damn close to my ears, there again the RF sound that I like is the more recent "Truth" era rather than the heavier tones e.g. Blue Line.

It's been said here before that the Robben Sound is as much to do with 'touch' rather than amp settings - vary your picking attack from very light to heavy so that you control the OD level in this way. It works for me - I find that I don't like too much OD on this amp - it just doesn't work, the sound goes too mushy and I attribute that to the Skyliner tonestack. When I do want a more 'Marshall OD Tone" I kick in the PAB & Mid Boost and then back the gain off on my guitar by 75%.

Changed the slope resistor and it has made a bigger impact than I thought.

1. More gain (probably due to more lower mids getting through tone stack)

2. It cured another issue that I had with the OD sound in that if I 'popped a string' by pulling it away from the fretboard and letting it snap back, it used to give a really nasty overtone - now it doesn't.

Overall, it's improved things for me - dare I say it the OD is less harsh!!

Worthwhile checking your amp against the published layout as my amp was built by Ceriatone.

Next thing I'm going to do is to change the 3K3 resistor in the power supply to 3K9 or 4K2 to see if I can get the anode voltages at V1, V2 and V3 a bit lower....moving into 'cork sniffing' territory now but who knows?

On a general note (and I'm not having a dig at anyone because mistakes happen) but it's always worth running through the components in your amp and validating against the layout that Nik produces.

I've had my OTS for over a year now and have been very happy with it - of course like anyone you always wonder whether a little tweak here or their might improve things even more. I have just upgraded the PSU caps to F&T not sure whether it was worth the effort but whilst doing it I wanted to familiarise myself with the main preamp assembly. I discovered that the slope resistor was 220 K rather than 150 K Specification. I'm going to change this to see if it has any impact on tone - techically it's increasing the impedance of the tonestack so I'm not expecting a massive change but you never know. As I say, it's always worth double checking your existing components before looking at other tweaks.

+1 On the Verbrator, been using one for nearly a year now. Only one thing that I want to change and that is a master return level control from the Verbrator so that I can crank up the Master on the OTS to drive the Cathode Follower harder in the Fuchs....get a little compression going.

It's worth trying this (without an active boost pedal that is).

If you set the master volume to the 'loudest level' that you require and then insert a passive volume pedal to take it down from there.

You will need to choose the Pot Value in the pedal carefully - this is where my expertise runs out but I'd say that something around 500K would be good. I'm sure others will jump in and tell me that this is wrong!!

Spot the mistake - V2 is the OD valve. The impact is the same, without buffering the signal with a cathode follower, you will load V2 and compromise your tone.

I've had the same thoughts about trying this - in effect what you want to achieve is the equivalent of tunring up the amps master but through the use of either a footswitch (activate clean boost) or volume pedal.
The FX return on the OTS is post Master Volume and feeds straight into the phase inverter so it's the right place to make this change. However, you cannot successfully place FX units into this loop without using a Klein or C-Lator. The basic problem is impedance mismatch where the Volume Pedal / Clean Boost unit 'load down' the output of V2B (2nd clean triode) and the input to V3 (phase inverter). Doesn't matter how good your cables are, you will have a noticable impact on the tone (reduced highs, unwanted distortion).that's my take on the scenario.

Hywell, there is definitely evidence to suggest that lower plate voltages = smoother OD but my take is that this is likely to introduce even more compression into what is already quite a compressed OD tone - there again I could be wrong. If I were going to make changes to the OTS, I think I'd go down the route of changing it to a straight 100K configuration. This is another 'classic' version of a D-Style amp and some of the TR's are based around it. I agree that the OTS has a spikey top end but I find that it is a perfect match for my Telecaster that has a HB type pickup in the bridge.(DiMarzio Chopper T). I have the treble control on the amp set at 3.5 and still roll off more via the Guitar Tone Pot. But I have to say that I can get some fantastic expressive / woody tones out of it like this. Increasing the snubbers on V2 is the other option for taming treble content or increasing the grid resistors on V2a and V2b which will give a low pass filtering effect.I can recommend the book "Designing Tube Preamps for Guitar & Bass" book by Merlin Blencowe - do a google search on "Valve Wizard" and you should find the website which is almost as good as the book. 

I'm not too sure either but from what I can gather, the plate voltages on the OTS are on the high side compared to 'established standards' whatever they may be. The dropping string resistor values used in OTS are different to those listed in other schematics that are listed elsewhere. Many people increase the 3.3K resitor to lower the plate voltage downstream. The different plate values on a 220/150 design will vary the actual plate voltage on each triode. As these are 1% tolerance resistors I'm not aware of many people adjusting these.Hywell I wouldn't have thought that lower plate voltages would give you the Matt Schofield type sound that you like? Much more likely to end up in Robben Ford territory?