G-PULTEC problems, please help!

[PeteC]

Jakob,

I downloaded a 100Hz sine wave test tone and normalised it in Mixbus

the send is measuring 2.27v AC on both the hot and cold legs of the balanced out.

seems well within the ac signal voltage.
maybe something else going on then ?

Rgds
Pete
 

 

[PeteC]

more....
with an incoming signal at c. 2.27v when the bass boost is up I'm getting an output signal over 4v ac from the EQ - this seems to be overdriving the return input of my audio interface.

maybe my HT is too high and I'm getting too much gain from the tube stage ?

Rgds
PeteC

 

[gyraf]

..balanced AC voltage is measured between hot and cold (XLR pins 2&3) - is that how you measured it?

Also, remember that the unit will boost selected frequencies up to some 20dB at full-boost.

If it sounds right with no low-boost, but sounds ugly when boosting, it'll be a result of levels exceeding the working range of the unit (as the filters can't and won't add distortion).

Try measuring output level of the unit when it sounds bad?

Alter your operating levels till it sounds right?

Jakob E.

edit/ps: higher HT voltage won't affect unit gain, only potentially shorten tube life.

 

[PeteC]

Hi Jakob,  thanks for your help and advice so far...

I have unbalanced input at present - input voltage at 2.2v ac

measuring across the hot and cold of balanced output I'm seeing following voltages.

with low boost down and Low freq control down I see 1.73vac
with low boost full up and low freq still down i see 2.37vac

but when i turn up the low freq switch we quickly get gain .....

with low boost control fully on here are the voltages at the different low freq switch positions

1 : 2.37vac
2 : 3.94 vac
3 : 5.26 vac
4 : 6.39 vac
5 : 8.31vac
6 : 9.86vac

is this what you'd expect from a properly working unit ?

many thanks
PeteC

 

[gyraf]

figures seem to be in the right area

try setting up your system to lower output levels

Jakob E.

 

[PeteC]

thank Jakob,

I just ran pink noise test out from mixbus at just under 1vac  and swept everything - sounds very good

i think it is a levels problem as you said right at the start
this is configurable in Harrison MIxbus so no problem to adjust send levels
thanks for helping me get there in the end, and getting confidence that my build is OK.

now to finish the other channel EQ !

Rgds
PeteC

 

[PeteC]

added a 4.7K 2watt resistor to the 3k3 dropper to get under 250v to prolong tube life

Rgds
PeteC

 

[MicDaddy]

hey PeteC, sounds like you're about to be rocking with your pair of eqp-1a.  Don't relish too much  8)

Something maybe worth noting, I've found my G-pultec does not like to drive certain other pieces in the chain specifically the 1176 shown in the photo.  If I stack them the other way around it sounds beautiful.  I've read of dropping a 600 across the output, but have not tried that or if that is even appropriate in this application.

Ended up commissioning Dan of collective cases for one of his 2RU chassis, and ever so glad I did.

Thanks again Dan,

Just waiting on the Jewel and the on/off switch

 

[spase]

where i can find that edcor adapter pcbs for this project?

 

[PeteC]

thanks MicDaddy

where do i find more info about strapping a 600 across the output ?  - I'm guessing you mean 600ohms ? sorry to be a bith thick as we say here in Yorkshire  ;D

cheers
PeteC

 

[PeteC]

one last question ( honest , .....at least for now )

embarrassingly I drilled an extra hole in my Gpultec faceplate when I was using the Gyraf template - to the left of the on/off switch

now I'm wondering whether I can use this to advantage - say for a phase switch or something - anyone care to make a suggestion ( apart from drill it right next time you fool.......) ?

cheers
Petec

 

[sonicwarrior]

where i can find that edcor adapter pcbs for this project?

I have 8 as I'm using the Lundahls now instead of the XS1100. But I'm from Germany so if you are not from Europe this wouldn't make much sense.

 

[spase]

where i can find that edcor adapter pcbs for this project?

I have 8 as I'm using the Lundahls now instead of the XS1100. But I'm from Germany so if you are not from Europe this wouldn't make much sense.

Im from Macedonia.In Europe

 

[Celf]

I have two questions

1: The heater doesn't seem to be elevated. Odd?

2: Can I get a 185vac (40mA) & 6.3vac transformer to work? For example, lowering the b+ RC resistor from 3k3 to 1k, and a voltage doubler for the 6.3vac before the LM317?

 

[MicDaddy]

Looking for a USA source for a suitable power on/off switch.  :'(

Majestic12 helped me with the Lorlin RMS1016 which Allied carries but has no stock.

Nothing suitable at radioshack  : or my local hardware      any pointers would be appreciated.

Thanks!! 

 

[sonicwarrior]

@MicDaddy:
I have a similar problem and found this today:
http://www.groupdiy.com/index.php?topic=23458.msg279568#msg279568

I'll try the RMS1035 as Mouser has them in stock now (the linked thread is from 2007).

 

[Celf]

Anyone knows why the heater isn't elevated?

 

[gyraf]

The design does not elevate the heater - reason is to keep things simple.

You can easily try to lift the FF voltage if you like, but I haven't found it giving any significant benefit in real-life.

Jakob E.

 

[schrobbelbop]

Hi All!

Please help!!!

Im building a stereo pultec in a purusha case. But when i hook up 2 srpp board we have a hum! 50 hz and harmonics...
when i cut off 1 heater supply from 1 board it dissapears!

 

[gyraf]

We do not recommend multiple G-Pultecs sharing the same case.

It's hard to tell what might be wrong without knowing details of your construction: Do you have individual supplies for the two amplifiers, or are you sharing one - and in that case, how? Is it a known-working solution, used by someone else also?

Jakob E.