Sligthly OT: Non-HRM preamp stompbox build

[markusw]

After browsing a lot through this amazing forum I finally decided to build a Non-HRM preamp.
Boards were ordered at Olimex. To minimise noise I included a top ground plane into all of them.
I know that PCBs are not really mod-friendly but I included various possibilities for mods (like OD treble bleed).
Basically, the whole thing is run from a 230VAC to 2x18VAC toroid transformer that I put into a separate enclosure (the black one in the first pic).
With the preamp running it still has 2x19,6VAC. So with it's 50VA it's clearly overkill LOL

The HV is done by connecting a 230VAC/2x12VAC transformer back to back to the 2x18V transformer.
With 50k load on the 230VAC side it gives about 276VAC. It doesn't get warm at all. Maybe slightly above body temperature.

Heaters are run from 12.6VDC. Relays from a separate 12VDC supply.

The dropping string at the moment is 2k2/50µ 2k2/50µ 2k2/22µ 2k2/22µ.

Overall it's build according to the "Early 80's grail tone" schem by mdroberts1243 (thanks a lot btw!) with some changes:

* input resistor to OD is 180k instead of 220k
* V2A and V2B snubbers are 330p instead of 270p
* No Master bright cap at the moment
* addition of a 47n/4M7 combo to the OD entrance (removable by jumper)
* V1B grid resistor bypass cap is 470p instead of 500p
* No rock/jazz switch

Since I didn't use any shielded wire I added a couple of 10p caps to ground.
Also, if the loop is used, there is a 120p cap to ground after the master pot to simulate input capacitance of the PI.
The loop itself is very simliar to the Iron Sounds loop run except it's run from +/-18VDC.
There are two Wima MKP4 caps used at the inputs of the send and return opamp stages. However, they are bypassed at the moment, so the whole loop is DC coupled.
Opamp is NE5532 but could be replaced for e.g. a OPA2134.


Voltages (with 150k FET simulation resistor) are:

B+4 302
B+5 294

Plate voltages are

JJ 12AX7 in V1 and EH 12AX7 in V2

V1 CL1: 181
V1 Cl2: 192
V2 OD1: 183
V2 OD2: 193

With the same tubes the other way round:

V1 CL1: 178
V1 Cl2: 188
V2 OD1: 186
V2 OD2: 197

So far we tested the thing by feeding it into the PI of a Musicman RD 112 65W (via J4 High/3V in the last pic) equipped with two SED Winged C 6L6.
Tests were done with a Strat and a Ibanez 335 copy.
Fortunately, noise is definitely not an issue.
Don't know if it sounds similar to a real Non-HRM, but my guitar buddy Dan and me we were both pretty impressed of the improvement compared to the sound of the
Musicman's solid state preamp.

It was fascinating for us too that all four combinations (CL +/- PAB and OD +/- PAB) gave really useful sounds for both the Strat and the Ibanez

We will do sample clips hopefully next week.

[markusw]

Some more:

[markusw]

Finally the Musicman schem:

[dimitris]

It looks very professional.I like it.

[heisthl]

Most impressive work - I'm guessing a few hours of work went into this one (probably hundreds) - are you thinking about prodution on this?

The talent seen on this BB constantly amazes me.

[markusw]

It looks very professional.I like it.

Thanks!

[markusw]

Most impressive work - I'm guessing a few hours of work went into this one (probably hundreds) - are you thinking about prodution on this?

The talent seen on this BB constantly amazes me.

I think you're right with your estimation LOL....although I didn't count the hours it took me quite some evenings over the last few months.

Actually, I just wanted to do an experiment. I never thought about production (also because I'm happy with my job). But who knows....

Next step will be a real Non-HRM or probably better HRM because I could always use this preamp in combination with a real one....

[Bob-I]

Now that's amazing work!!

I bet she sounds great through that MM. I have an old MM 65 watt head and it's got a nice fat tone, but overdrive has to come from pedals.

Very cool project.

[blue_lu]

markus,

any soundclips?

regards from würzburg

[markusw]

Sorry, no real sample clips yet although I promised
Will do them together with my new reverb head once it is in it's cab.....I swear

[blue_lu]

marcus,

if you do the clips, maybe you could use something else than a dumble amp,

a standard fender amp maybe?

did the preamp turn your mm in to a dumble?


regards, lu

[markusw]

marcus,

if you do the clips, maybe you could use something else than a dumble amp,

a standard fender amp maybe?

did the preamp turn your mm in to a dumble?


regards, lu

Good idea! I will ask Pete to bring his Fender Super 60. Unfortunately, I don't have access to another Fender amp. What do you think?

Peace,

Markus