# NAD Suhr Corso.



## vadsy (Dec 2, 2010)

I've wanted something new for a while, seeing the 'best/worst purchase' thread and a few smaller amps get listed I thought I'd try for a smaller head that was able to record well. I found a Suhr Corso. 

Anyone try one, have one? Love it, hate it? Do share....

full disclosure, I ordered a used one but don't know what to expect


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## TheGASisReal (Mar 2, 2020)

Sounds/feels cool in a small setting, but it has zero headroom. It's definitely a dirty-only amp, and one suited for low-volume or recording.


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## vadsy (Dec 2, 2010)

ok, Cool. I am going after a different way to record but also thought it may be neat to hear tube breakup at lower volumes. I am confused about the headroom, the YT reviews seem to show it playing fairly clean with single coils, is that misleading? is Pete Thorn a liar?


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## vadsy (Dec 2, 2010)

look how cute this little guy is. gotta wait to fire it up


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## tdotrob (Feb 24, 2019)

Nice! Looks cool. I’ve never tried a Suhr amp before.


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## Paul Running (Apr 12, 2020)

The moulded wood looks sharp...12BH7s in the output...bet ya that's got a very clean sound to it.


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## Paul Running (Apr 12, 2020)

Trying to locate a schematic for it. Do you know if it is fixed-bias or cathode bias?


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## vadsy (Dec 2, 2010)

Paul Running said:


> Trying to locate a schematic for it. Do you know if it is fixed-bias or cathode bias?


not a clue. I also would like to know the details. I'll look up a manual later (I know it isn't a schematic), mostly to make sure I don't mess up the transformers using the line out with the attenuator while running it silent. Not as much info on these as I thought there would be. John and Jim went in to some detail on TGP supposedly but I haven't found the thread yet. I want to know why it was discontinued but all the reviews seem to be fairly positive.


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## Paul Running (Apr 12, 2020)

According to the data sheet, the 12BH7 can dissipate 3.5W per triode × 2...7W for an advertised 5W amp, no BS there.


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## vadsy (Dec 2, 2010)

Paul Running said:


> According to the data sheet, the 12BH7 can dissipate 3.5W per triode × 2...7W for an advertised 5W amp, no BS there.


ok,. is that good?


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## Paul Running (Apr 12, 2020)

I believe so. 5W is enough power with efficient loads, for most audio applications.
Right now, there is not many requirements for high power applications.


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## Paul Running (Apr 12, 2020)

Sorry correction, the output uses 2×12BH7...double that power to 14W for the output, depending on the class of service, A or above...14W is plenty.

*Specifications:* One channel, 5W output (variable)
Tubes: 2×12BH7A (output), 1-12AU7 (Input) and 2 ×12AX7 (Tone and PI) Front Panel: Input, Bright Switch, Drive, Mid Switch, Treble, Gain Switch, Bass, Presence Switch, Deep Switch
Power and On/Off switch
Back Panel: AC Mains Inlet, Fuse (1A/250V (Slo-Blow), 2×8Ω spker. outputs and Line Out


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## Vincent Boissinot (Jun 3, 2017)

Always loved the way this amp looks, please let us know what you think about it!


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## vadsy (Dec 2, 2010)

here is a hokey little number I recorded during some disappointing play by the Oilers. rhythm parts were against the Leafs, we lost that one. lead parts (on the new Corso) were against the Canucks, we came back to win. jazzed up the drums a bit tonight to have some dynamics. the guitars were recorded live, drums are programmed and the bass was direct. Corso has a little compression and reverb in post, otherwise all amp


__
https://soundcloud.com/tom-jones2012%2Foilers-losing-project-2021-05-04-1111-pm


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## Paul Running (Apr 12, 2020)

The McDavid section really stands out.


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## vadsy (Dec 2, 2010)

lol. this is more of a joke track, that guy is for serious.

anyways, I'll record some proper clips of the amp in the coming rainy days. So far I appreciate it being present in the room at lower volumes, you don't have to keep feathering the volume knob under 2 to keep the walls from shaking. All the options it has for tone control at this lower wattage is very useful and something lacking on a lot of other low watt amps, seems you can always dial in the high end even with attenuation. and, yea, not much headroom, as expected. but you can get some clean-ish sounds if needed.

I also need to give the line out silent option a try, that may be the most useful part of it


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## vadsy (Dec 2, 2010)

Paul Running said:


> Tubes: 2×12BH7A (output), 1-12AU7 (Input) and 2 ×12AX7 (Tone and PI)


Can you explain the input and the tone and phase inverter here? I'm mostly confused on what the AU7 does. and how would these tubes fall if we looked at the amp in a V1, V2, etc.. sort of way?

for fun, here is some gut shots, I'm sure you enjoy this sort of thing like I do


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## Paul Running (Apr 12, 2020)

2×12BH7A (output), 1-12AU7 (Input) and 2 ×12AX7 (Tone and PI)
First drawing below: from their spec sheet VI (input) will be a 12AU7...you should be able to confirm that, top-side.
The tube next to V1, should be a 12AX7 (V2), again you can confirm that top-side. According to the spec sheet the 12AX7 serves as tone (V2) and PI should be V3...more to come.


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## Paul Running (Apr 12, 2020)

2×12BH7A (output), 1-12AU7 (Input) and 2 ×12AX7 (Tone and PI) 
Second drawing: V3(12AX7) should be the PI, with V4(12BH7) and V5(12BH7) the output tubes...confirm top-side.


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## Paul Running (Apr 12, 2020)

2×12BH7A (output), 1-12AU7 (Input) and 2 ×12AX7 (Tone and PI) 
Third drawing: output tubes V4 and V5, paralleled, 12BH7A triodes; V4, pin I (brown-wire P1), is one half of the primary for the output transformer and V5, pin 1 (blue-wire P2) is the other half of the primary for the output transformer.


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## Paul Running (Apr 12, 2020)

I notice 0.1µfd coupling caps (larger white caps), to the output tubes, for a low frequency roll-off...extended bass range.


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## vadsy (Dec 2, 2010)

wow, dude. killer rundown, thank you.

so my understanding is that V1 is often responsible in setting the amp 'gain' and changing it can have a pretty serious impact on things. if the AU is so low gain are we getting the drives from the V4 and V5 output section?


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## Paul Running (Apr 12, 2020)

vadsy said:


> the drives from the V4 and V5 output section


Yes the output has the drive power. It should be quite with a 12AU7 in the front-end...very stable with plenty of drive or fanout. I'm speculating on what the schematic entails however, I would say they have fidelity in mind...all triodes.


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## vadsy (Dec 2, 2010)

Paul Running said:


> Yes the output has the drive power. It should be quite with a 12AU7 in the front-end...very stable with plenty of drive or fanout. I'm speculating on what the schematic entails however, I would say they have fidelity in mind...all triodes.


I'll start by saying I have no intention of doing this but what would happen if we changed up the V1 of this amp for a higher gain tube?


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## Paul Running (Apr 12, 2020)

The bias would go off-center and signal distortion would result...unless the plate and cathode loads were altered. The circuit would loose stability in most cases, especially with higher gain tubes such as the 12AX7.


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## jb welder (Sep 14, 2010)

Swapping the V1 to another 12A*7 type can't hurt anything (if you decided you wanted to try). Like Paul said the bias for that stage will change shifting the operating point of the tube. That, along with the great increase in gain is going to have a major effect on the distortion character, and what is on tap from the 'drive' control.
Some guys probably start rolling tubes in that stage as soon as they get the amp. 'What, 12AU7 in the input stage, blasphemy!' 
I bet it sounds great.


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## vadsy (Dec 2, 2010)

jb welder said:


> 'What, 12AU7 in the input stage, blasphemy!'


agreed. who'da thunk it. but I'll leave it alone, no issues with it the way it is

I did switch out V1 in a Jr I have to an AT or AY even, mellowed it out and decreased the overall idle noise


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