Dr. Watt (Hiwatt Amp Emulator)

[Frank_NH]

Here's another amp emulator circuit from FSB that should be interesting:  Dr. Watt (high gain Hiwatt amp sim).

http://www.freestompboxes.org/viewtopic.php?f=28&t=10259&p=256681#p256681

[Chris60601]

Sweet! I'll do up the PCB with the schem they provided.

[Frank_NH]

Thanks Chris!  Any takers for the vero??

Looking at the schematic, this should be similar to the many ROG amp sim circuits (e.g. ROG Thor), and the gain will be high with the 3 JFET stages ans the mu amp tacked on the end.  Depending on the JFETs used, the 100K trimmers are probably overkill and can be reduced for better precision in biasing.  I would also add a 100 uF electro cap to the power section (after the 100 ohm resistor) to reduce power noise.

[rocket88]

i'll gladly take a go at it. it sounds freaking awesome, btw.

[Chris60601]

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[Frank_NH]

According to my JFET calculation spreadsheet, if you use J201s, you can use 50K for all three trimmers.  Also, I would use 2N5457s for the mu amp (Q4, Q5) since the JFET characteristics are less critical there.

I think this will sound pretty good - just like Pete Townshend's stacks!

[Chris60601]

LOL - you do realize that Lee (Fuzzdog) does have this PCB on his site. While I have not inspected the diffs between the schems, I gotta feeling these would be one in the same.

http://shop.pedalparts.co.uk/MegaHIWatt_-_Vintage_HIWATT_Amp_Tone/p847124_11129948.aspx

There are some similarities. The ROG circuit has the 5 trannies while FD's has 3 BS170.
Come to think of it - I actually built his (chose the Led Zep over the Townsend versions).

[Frank_NH]

The schematic at the link is not like the Dr. Watt circuit at all.  In fact, I did only a cursory check but the use of three MOSFETs suggests a similarity to the WIIO and RAH.  I built both of those and really didn't like them as much as I thought I would (too much flubby low end for me ).

So carry let's on with the Dr. Watt (which actually is sold as a complete pedal or kit at olcircuits.com).  I'm hoping to improve the design by first examining the tone stack using the DTSC.  Also, I've found from other circuits that removing one or more of the JFET source capacitors can help tighten up the lows at the expense of some gain (but this has tons of gain already).  Finally, I'm always curious how these circuits might sound at 18V - perhaps another avenue to be explored.

[Chris60601]

Right on!

On 1/7/2016 8:15 PM, Frank_NH [via Guitar FX Layouts] wrote:

The schematic at the link is not like the Dr. Watt circuit at all.  In fact, I didn't check it but the use of three MOSFETs suggests a similarity to the WIIO and RAH.  I built both of those and really didn't like them as much as I thought I would (too much flubby low end for me).

So carry let's on with the Dr. Watt (which actually is sold as a complete pedal or kit at olcircuits.com).  I'm hoping to improve the design by first examining the tone stack using the DTSC.  Also, I've found from other circuits that removing one or more of the JFET source capacitors can help tighten up the lows at the expense of some gain (but this has tons of gain already).  Finally, I'm always curious how these circuits might sound at 18V - perhaps another avenue to be explored.

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