scratchin my head!

[shooter]

I’ve got a build request that has me scratchin my head!

1 Must be light n small, customers example, a small crate 25w SS
2 Must be 40ishwatts
3 Must be good tone with NO distortion
4 Must have a dedicated balanced line out 3prong to feed into the PA which is how the audience hears him,  not from the amp.
5 Must be able to have a separate volume/mute for the amp which he uses as a stage monitor.
   The volume/mute of the amp cannot affect the line out volume but the tone he hears in the amp he wants on the line out.  He doen’t care tube or transistor, just good tone (yeah I know:) and loud enough so he can hear over the drums n electric bagpipes (usually on either side of him).

Here’s my idea so far.  Start with Doug’s stereo preamp, bridged input, with dual gang tone pots but fix the gain on one channel for line level out, no vol knob,  the other channel tweeked for no compression feeding a monoblock SS brick type poweramp.

He’s in a Celtic band that is quite popular in the area.  He sets the rhythm n tempo with an F body Gibson or a highly modified LOOT?(humbuckers, vol n tone)  the other 6 members are the  “lead” players.

Any ideas/help would be appreciated

thanks

[SILVERGUN]

I'm gonna chime in because I'm in the middle of a similar situation, and I have a couple ideas for you....
- Small, light, easy to build would be a 5E3 cab ...."monitorize" it with some tilt back legs http://thebluesalligators.narod.ru/olderfiles/1/5E3_DELUXE_STYLE_CABINET_3.pdf

- See Sluckey's website for his Tweed Deluxe Reverb, and go to the end of his documentation where he upgrades to 2- 6L6
http://home.comcast.net/~seluckey/amps/tdr/tdr.htm
- Then just take his "AB763 Deluxe Lite" schematic and tweak for cleanest signal,( 'maybe' eliminate the cathode bypass cap on the second gain stage, or use a 'boost limiting' resistor.....etc., etc.)
http://home.comcast.net/~seluckey/amps/misc/AB763_Deluxe_Lite.pdf

- Extra lightness can come from a Celestion G12 Century Vintage
I bought one of these and I feel that it shines on the clean channel, and is just a great deal as well:
http://www.parts-express.com/celestion-g12-century-vintage-12-8-ohm-neo-guitar-speaker-60w--299-464

- Lastly,,,,I recently found a thread where one of our guys suggested this xfmr for creating a simple XLR out:
https://taweber.powweb.com/store/balun.jpg

Since it just creates a copy of the output signal, you'll still have your speaker out volume, and then this additional XLR volume control to feed the PA (if I'm seeing it correctly)

The one thing this doesn't address is an absolute mute (but I'm not sure why that's necessary)...but I guess you could do a built in switchable load resistor   

Hope there's something in here that's helpful.

[terminalgs]

it sounds like you really don't know for sure what level of on-stage volume he really wants.   40W clean... is a heavy tube amp combo! Is there any way you can put a couple of amps in front of him?  what kind of  AB763 amps do you have for him to test out?

speaker selection will be important.

any chance he'd go for just a pre-amp, and use the house PA monitors ...as monitors?

he could have a preamp with two line-outs for the house PA: one "audience", and one "monitors" that he can kick on and off with a foot switch..  this has the advantage of house PA clean monitors regardless of required volume.. downside,, special instructions for sound guy about to what to put in the house, and what to put on stage (do they travel with their own sound guy?)

[EL34]

40 watts and light/small don't go together when it comes to tube amps
Tube pre amp is a good start


Don't know what to suggest for a power amp unless it's solid state

[terminalgs]

The one thing this doesn't address is an absolute mute (but I'm not sure why that's necessary)...but I guess you could do a built in switchable load resistor   

After the preamp, once the audio signal is on two separate paths,  a foot switched light source (led or neon) can control an LDR that mutes the signal on one of the two paths.

[SILVERGUN]

How about using an OT with at least 2 secondary taps and use one tap to run the weber xfmr driven XLR .....and the other tap to a switchable junction of load resistor (mute) OR speaker?

[shooter]

Thanks guys, it about has to be a SS Pwramp section, which should be easy enough there are a lot of 2Xwhatever blocks, I have a vintage 12" enininance that is sparkly with very little weight.  Mesa uses a fet type mute in front of the pa section so that will be the starting point I think.  I just have a hard time with all SS hence the tube pre.

He currently uses the pa monitors but says that's not working well for him, vocals n other distractions?
I did copy that LXR idea posted here and think that's the way to go.  Since it's clean, no PA distortion, I figure all the amp tone will be developed outta the pre, mirroring 2 channels seems to be my biggest challenge.

Doug I know it says it's your personal build but is the turret board you used in your preamp available for sale?

again, thanks for the links n ideas

[HotBluePlates]

I’ve got a build request that has me scratchin my head!

1 Must be light n small, customers example, a small crate 25w SS
2 Must be 40ishwatts
3 Must be good tone with NO distortion

The customer just described a 60-100w solid-state amp.

You simply can't get around tube amps being heavy on account of the transformers, if nothing else. If it must be lightweight, solid-state wins.

If the customer wants zero distortion, there's no benefit to using tubes. Clean tube amplification sounds the same as clean solid-state amplification. When there is a tonal difference, it is because one or the other is distorting in some fashion, even if it just sounds like "warm clean" instead of "stark clean".

The customer probably gets to his end goal faster and cheaper by auditioning and buying a solid-state item off the shelf.

[shooter]

You're right, the one oddity is he wants to control amp volume without effecting line out so I can't simply come off the speaker or anywhere post volume.  He has a ultra Chorus '90s fender that I just repaired but says that's to heavy, so, because of time n other factors I ordered a clone stereo Marantz 7 preamp kit, 2 12au7s, and a 70Wrms SS monoblock.  the preamp is line-out ready so I'll use ganged pots n build a fender style tone stack, proto-type it then tweek for his idea of "sound".  Should have a working proto-type in about a week, then see what yellow brick road I wind up on!

[HotBluePlates]

4 Must have a dedicated balanced line out 3prong to feed into the PA ...

You're going to need a transformer to do that, because all signals inside the amp are unbalanced.

5 Must be able to have a separate volume/mute for the amp which he uses as a stage monitor.
   The volume/mute of the amp cannot affect the line out volume but the tone he hears in the amp he wants on the line out. 

Then what he wants is a preamp that develops the tone and sends a balanced signal to the PA. And then a 2nd output of the preamp goes into the on-stage amp.

So not an all-in-one amp with a balanced line out, but 2 separate devices to work together to accomplish his goals.

[shooter]

Yup, the challenge is gonna be balancing the 2 pre's so what comes out of each is "close enough"
I got this xformr example from this forum but I'm having a hard time sourcing it.

[SILVERGUN]

Last item on this page:
https://taweber.powweb.com/store/magnetic.htm

[shooter]

Thanks silvergun, don't know how I missed that, I was just google searchin "wbalun" without much luck.  The preamp kit is do today, cleaned off my bench, twitchin, what a great addiction!

[SILVERGUN]

The timing of this is amazing....this amp is still open on my bench, but is up and running and the XLR out sounds great

I made it's own separate board with eyelets for the pins jumpered to turrets for the connecting wires

[shooter]

silvergun you happen to know if the pin spacing is the standard .1" pc or .156" or none of the above?  I was gonna use the RS 2X2 ic board if it's a .1"  otherwise try n find room on the preamp board so I can keep leads short.

[SILVERGUN]

Well,,I'm not positive,,,but I tried it on one of these boards and the pins on one of the the short sides lined up with the two red circles @ .4"
But the pins on the other end wouldn't line up with those holes that are marked with red X's in pic

It would have been easy to bend the pins to get the fit, but I preferred the look of the homemade board

[Willabe]

Be very careful trying to bend any pins on the small tranny. IMO I think it's a bad idea.   

The old saying is 'gotta break some eggs to make an omelet.'  Eggs are cheap if you mess up, but....... the trany's $4+ shipping. I guess not too bad if it goes wrong? 


              Brad     

[shooter]

Yup, that's the board I was thinking of n ya, I have not had much long-term success bending things that are semi rigid.
thanks

[shooter]

I got most of the pieces parts, drew up a schematic and got a question on the XLR out.  The transformer is 2 wire in, 2 wire out.  the examples I've found show a ground reference for the output side of the XLR.  Is that ground my internal ground provided to whatever the XLR goes to, or is it "their" ground?  I'm thinking of all the posts that talk about; "it's clean, till I plug it into......."

thanks for the help

[HotBluePlates]

... a question on the XLR out.  The transformer is 2 wire in, 2 wire out.  the examples I've found show a ground reference for the output side of the XLR.  Is that ground ...

That ground is the chassis of your amp/preamp/device.

But if you want it to not hum, you also need to understand how to make your amp safely incorporate a ground-lift:

Throughout your amp, there should be no place where ground is connected to the chassis; the circuit ground should be a ground buss isolated from the chassis (which means using plastic jacks, or metal jacks with insulaters to prevent contact to the chassis). The 3rd wire of the power cord should be firmly bolted to the chassis, for safety and to allow tripping a circuit breaker if there is a short to the chassis. You should have a SPST ground lift switch which connects to the chassis ground bolt on 1 terminal, and to your circuit ground buss (probably at the main filter cap and/or PT high voltage center-tap) on the other terminal. Place a 0.01uF 1kV cap and a 51Ω 1/2-1w resistor between the 2 terminals of the SPST switch.

What happens is if you flip the ground-lift switch such that the terminals are connected, your circuit ground is connected to chassis and to the power cord 3rd wire; this kills noise when no other devices are connected. When the ground-lift switch is flipped so the terminals are not shorted, the resistor and cap are between circuit ground and chassis ground; if you have your amp connected to other amps/devices with their own 3-wire power cord, this arrangement prevents ground current from circulating through the connecting cables, and defeats ground-loop buzz/hum when there would otherwise be circulating ground currents.

With all of the above, you would still allow the XLR output jack to contact the chassis, and connect its ground pin to the XLR shell/chassis ground. This keeps the jackplate (and metal-shell XLR connectors) at ground potential.

You will find a proper ground-lift results in the least noise when circuit ground is connected to chassis ground when you play through the device on its own, but the least noise usually in ground-lift when connected to other devices with their own 3-wire power cords.

[shooter]

thanks HBP, I typically use a lifted grd I got from a fender schematic, 100ohm with 2 diodes back to back.  I'll try the lift switch on this build.

[shooter]

Finally got the hybrid up and runnin.  Initial tests sound pretty good!  I played for 2 minutes movin all the knobs, the range on the tone stack might be to narrow for the customer, we'll see.  She is the loudest one yet.  There is very little Solid state sound till you hit about 10 gain n 9 volume, then it starts sounding transistor harsh otherwise it's nice and tight sound with just the edges smoothed instead of ground off!

still need to get the XLR limited and wired, the tube pre puts out about 7ish vac p-p.

Thanks to all that helped me on this endeavor.

[shooter]

The amp I’m working on (schematic attached) works fine but the tone stack is pretty odd to me, which might be normal to everyone else.  If bass is around 7, mid and treble don’t have any real effect.  I took signal amplitude measurements at 100hz, 2khz, and 4khz and here’s the numbers;

100hz  T=0 M=0 B = 1-10      1.9vacp-p – 5.5vacp-p     (viewed @ .022 leaving preamp)
            T=0 M=0-10 B = 0      2.2vacp-p – 5.1vacp-p     
            T=0-10 M=0 B = 0      2.1vacp-p – 2.5vacp-p     


2kz      T=0 M=0 B = 1-10      2.2vacp-p – 5.5vacp-p     (viewed @ .022 leaving preamp)
            T=0 M=0-10 B = 0      2.1vacp-p – 5.2vacp-p     
            T=0-10 M=0 B = 0      2.1vacp-p – 2.8vacp-p


4khz   T=0 M=0 B = 1-10      1.6vacp-p – 5.8vacp-p     (viewed @ .022 leaving preamp)
           T=0 M=0-10 B = 0      1.6vacp-p – 5.4vacp-p     
           T=0-10 M=0 B = 0      1.6vacp-p – 2.9vacp-p

If these seem normal for the TS, I was gonna try and re-learn the freq base(FFT?) on my scope n see if there are frequency effects I’m not seeing in time base mode.

I’ve only had 1 qualified musician so far and overall was well liked but said the “low end was kinda muted, muddied, didn’t have the same sparkle as the higher notes”.  Pretty sure scoping it that is coming from the SS pwramp section, I get no compression or clipping in vs out of the preamp section.  There is about a 5degree phase shift though. 
Any ideas, thoughts would be greatly welcome.

 

[SILVERGUN]

Here's a simple tone stack layout pic that has helped me in the past with the std. TMB hookup

[shooter]

Thanks SG, I'm wired like your layout except I don't have the leads grounded to the pot case, just grounded back to the input jacks ground. there's no noise issues so I'm thinkin that's not a problem.  I normally use linear pots but used audio taper because that's what I could get in dual ganged at 1 vendor.