Orange 86 Build Thread

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ElSmurf

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As I'm getting ready to start building this thing, I'd like to know what value to use for the bypass cap on C5. And if I should even use one. From the little I've learned about tube circuits while researching for this build, it seems to me the bypass cap adds gain but also raises THD.
I see most builds ommitting the BP caps, but Guavatone's build as per the pic in the first post seems to have what looks like a .018uf cap parallel to C5, nothing on C3.
I would love to know what my options are.
 

guavatone

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ElSmurf said:
As I'm getting ready to start building this thing, I'd like to know what value to use for the bypass cap on C5. And if I should even use one. From the little I've learned about tube circuits while researching for this build, it seems to me the bypass cap adds gain but also raises THD.
I see most builds ommitting the BP caps, but Guavatone's build as per the pic in the first post seems to have what looks like a .018uf cap parallel to C5, nothing on C3.
I would love to know what my options are.

I'd rather not add to the over abundance of babble on Caps.  It's just an option and I would not go higher than 100 nF and PIO if you like that "sound".  Be careful using BP as a descriptor w caps. BP preceding the word capacitor generally mean BiPolar.

PS

excuse my cromugeon-ness ;-)
 

ron_swanson

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guavatone said:
first. Are you doing one or 2 channels in the 2 RU?

For AC heaters you should only use one winding or connect in parallel

Hello guavatone,

Thanks for the reply ... I've had other commitments to attend to lately so have been unable to address this build, but hoping to get back on track now... admittedly still a bit lost here with this particular build...

Yes, I am building a 2Ch unit in a 2RU enclosure. 

Cheers, Greg
 

guavatone

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ron_swanson said:
Hello guavatone,

Thanks for the reply ... I've had other commitments to attend to lately so have been unable to address this build, but hoping to get back on track now... admittedly still a bit lost here with this particular build...

Yes, I am building a 2Ch unit in a 2RU enclosure. 

Cheers, Greg

Would it be easier to talk on the phone to get you kickstarted?

I just looked at your last posts. For THE 275v I would do parallel wiring - tie 0V together for center tap ground and the other ends go to 2 diodes for the rectification- 2 diode bridge. And for 6.3V you could use series wiring - tie 0V to 0V and 6.3 to 6.3 each going to the balancing resistors on the aux PSU

-actually just check with John at  antek for 275V in series. It may be right the way you have it. Their data sheet is throwing me off today for some reason
 

timgoldsmith

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Orange 86 Meter Requirents.

Im sourcing bits fo build and talking to meter vendors who have some interesting stuff.

I'm looking at a vertically mounted edgewise panel meter on the face
One thing they asked but I don't yet know:

True VU (with rectifier) or 200uA (you drive the meter)???

Thanks all! Hi Guavatone!

Tim
 

guavatone

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Hi Tim. I’m sorry. I don’t provide support for meters at this point. I may sound like an asshole here, but I just don’t understand the point. i Imagine just using ideas from other preamps with meters will be fine
 

ElSmurf

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As I'm starting the wiring of my unit, can someone please confirm or correct my current understanding of the filament section of the PSU board.

Whether in basic mode or elevated mode, the LT AC from the power supply is connected to pin 1&2 of the LT supply connectors. In basic mode, with C1 jumpered, R1 and R2 form the artificial center tap, going to ground, for the LT AC. In elevated mode, the regulated HT from the preamp board ads DC to the LT AC. In both modes I would either connect pin 3&4 to the HTR connectors on the preamp board, or connect pin 3&4 to HTR and pin 5&6 to V1 LT - making sure phase is identical on both heaters.

If this is correct, is there any advantage (hum or sound wise) to having two twisted pairs coming from the PSU board to each tube as opposed to a single pair which is then bridged on the preamp board? Also, what would be a good value for the DC elevating the AC? Reading the tubewizard page it says anywhere between 30-60V is ok.

Doing my best to wrap my head around this whole tube thing! 😅
 

guavatone

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I wouldn’t bother with elevated in the basic build. It’s just an option for tinkering or other circuits where it’s technically more sound. I prefer running 2 separate twisted pairs from the Aux PS board. It makes it easier to keep the AC lines away from the signal lines.
 

ElSmurf

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Hopefully my last question before I can start testing my unit. What would be the best grounding/shielding strategy for the input chain (XLR in -> Pad PCB -> Sowter 9970 -> Preamp PCB IN)? The three ground connections on those two PCBs got me confused. Any clarification would be greatly appreciated.
 

guavatone

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Do you mean the extra ground connections on the PAD/mic PCB? i think I went a bit ground crazy on my PCBs bc I always find myself wanting/needing another ground solder point. Just shielded 2 conductor cables will do it.
 

ElSmurf

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I spent a few days looking up what I could find on the subject and ended up using the ideas from the Grounding 101 pdf by Ian/ruffrecords. I've been testing my unit and it seems the preamp section is working like it should and all my voltages are ok. I just need to figure out why the two relays switch on on powerup and don't respond to the switches. Also, why my gain knob is working in reverse, with the highest setting going silent. I'm sure it's something silly in both cases but any hints are of course welcome.
 

guavatone

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are using the new constant impedance gain switch?

does your ground on aux psu have continuity with ground on the relays? Eg, beeping with the multimeter. Other counties used the term buzzing. IIRC

i have a hunch that the gain switch wires are backwards, which is easy to do bc the only Mislabeled parts is the main PREAMP PCB switch VT1 and VT2 are reversed
 
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ElSmurf

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The ground has continuity between the relay and the aux ground on the psu pcb.

Today I separated the output pcb from everything else, just to check the relay switch circuit. With 24V coming in, I get 17V on the base of Q2-O with the switch open, 15.3V with the switch to ground. It seems as if the relay is getting either 16V or 15V, depending on the switch. I desoldered and checked the BC560 and it measures ok AFAIK. The resistor and capacitor values are correct as well. The only thing I can think of right now is that I used a BC560B instead of a BC560C as stated in the BOM. Luckily I can see the humor in being stumped by a 5 component circuit.

*edit* I checked the polarity of the BC560 on the output board today and it reads as an NPN transistor, which I think would explain the weird behavior of both relay switching circuits. I ordered a pair of BC557s from Mouser which should be here in a few days and then I'll know for sure if that was the problem.

As for the switch, I'm using the new version. I tried reversing the wiring from the gain pcb but then I could only change gain in very small increments, down from full gain. One thing I'm not sure of is whether to connect the shield of that cable to ground or not. Right now it's connected on both ends like on the first diagram in the Directions pdf.

Since the switch goes to silence in full clockwise position and R-FB12 is connected to the ground plane, I'm guessing I shouldn't connect the shield to the switch pcb's ground. Once I have the relay problem sorted out I will it a try.
 
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