All things G1176 - the new "repost" thread.

[Autophase]

Hi guys, having.built and loving my gssl I've decided to add fet to my arsenal.
I intend to build 2x stereo units of the 1176, I was Hoping anyone the UK, could give me an.idea of cost and best place to source parts in the UK (I got most of the stuff for the gssl from rapid last time)
I would also appreciate any advice from those who have made stereo units.
Thanks

If by 'stereo' units you mean to operate them together on a stereo signal (as opposed to two compressors in the same box) then you need to make sure you have the time and facilities to perform a lot of matching of components for the two boards. Otherwise the compression curves will not be the same for both channels.

Yes I mean actual stereo fet compressor. Surely it's only the main fets used for compression and the ones for the meter that.need to be critically matched?
Are you advising.me that going down the stereo rout isn't a good idea?

 

[gswan]

The main FETs in each channel are a start, however you will also need to match the GR amp characteristics as well.

 

[Autophase]

The main FETs in each channel are a start, however you will also need to match the GR amp characteristics as well.

Is this the best way to.make a stereo 1176? I can't be the only person who has wanted to have a stereo fet compressor with both boards In one box with a single set of controls?

 

[gswan]

The main FETs in each channel are a start, however you will also need to match the GR amp characteristics as well.

Is this the best way to.make a stereo 1176? I can't be the only person who has wanted to have a stereo fet compressor with both boards In one box with a single set of controls?

Probably not. If you want to have a single set of controls then you will need to work out the modifications. You will also need to work out the most effective way to generate the GR signal to the FETs so that both channels compress and track accurately together, or you will get stereo image smearing problems.

 

[Autophase]

Right I see, thanks.
I think I'll talk to mnats before ordering up 4 sets of boards.
Out of interest are you aware of any stereo fet projects?

 

[gswan]

It is possible, but requires a modified GR section and well matched GR fets. There should be a single GR amp fed with a mono signal created from the sum of the stereo inputs. This is then used to feed both fets so that they both attenuate by exactly the same amount.
Also, with a single set of input and output controls, the gains of the amplifier stages will need to be accurately matched.

 

[Autophase]

It is possible, but requires a modified GR section and well matched GR fets. There should be a single GR amp fed with a mono signal created from the sum of the stereo inputs. This is then used to feed both fets so that they both attenuate by exactly the same amount.
Also, with a single set of input and output controls, the gains of the amplifier stages will need to be accurately matched.

Thanks for the advice mate, I've taken my questions to the 1176 stereo link thread as it seems to be more specific for this.

 

[Autophase]

Hi Guys, This is a revision of a prevous post.
I'm going to build 2x  Stereo 1176's. I have settled on Revision G, I just have a couple of questions.

1: is this thread the main support thread for rev f/g builds?
2: I have access to a Transistor curve tracer so I have decided to pair all the FET's my self, what characteristics should I be looking for, are there specific settings common to most curve tracers that I should use?


Thanks

 

[gswan]

Hi Guys, This is a revision of a prevous post.
I'm going to build 2x  Stereo 1176's. I have settled on Revision G, I just have a couple of questions.

1: is this thread the main support thread for rev f/g builds?
2: I have access to a Transistor curve tracer so I have decided to pair all the FET's my self, what characteristics should I be looking for, are there specific settings common to most curve tracers that I should use?

Id vs Vgs should be exactly the same curve to correctly match the GR fets.

 

[clorax hurd]

Hi,

I'm just buying parts so I can finish my gyraf 1776, but I'm very confused by the switches in all the part lists I could find.

When I look on the schematics or the front panel, I see 4 positions on the RATIO switch, but still, in the BOM, there is written that I should buy 2 pole 6 position. Why 6 position? I see 2 pole 4 position in the schematics.

Regarding the METER switch. I see 2 pole 2 positions in the schematics. If the "Bypass" on front panel is the 3rd position, then 3 position switch makes sense. But I see 2 poles on the schematics, and 4 poles in the BOM.

Can someone please help me understand this?
thanks!

 

[dgoszillai]

about the oep 2:1
what is the difference between 1:2 or 2:1 for the sound ? (i'm noob)
let's say i want 2:1 on both in & out (dunno why)
i understand how to do the input. but for output i only have to reverse the OEP on the board with pin in 2:1 hole. i mean i don't have to cut trace behind output OEP right ? (still noob) thx for help you may save my day + my1176 from burning.

 

[gswan]

A simple transformer has a ratio of the number of turns on the primary (the side that the signal is fed into) to the number of turns on the secondary (the side where signal comes out). This is called the turns ratio, or N.

The turns ratio affects the voltage ratio by the factor N. So for a 1:2 ratio transformer, a 1Vrms signal on the primary is transformed by N to a 2Vrms signal on the secondary.

But you don't get anything for nothing. Some people wrongly think that transformers have 'gain'. They do not. The simply transform. The consequence of a transformer stepping up the voltage by N is that the current is stepped down by N.

Consequently the impedance of the circuit is transformed by N squared. This means that if you have the 1:2 transformer stepping up your output voltage by 2, it also steps up the output impedance (as seen by whatever it is connected to) by a factor of 4. This impedance transformation is very often used to couple high impedance sources (guitar pickups, some microphones) to a low impedance input, which is important for frequency response over a long cable which may have significant capacitance.

How it affects the sound will depend on what you are connecting it to and from.

 

[dgoszillai]

thx very much for this explanation !
ok so mostly i will send tempest drum machine to my 1176 and back to a culture vulture or direct soundcard with short cables
what setting shold i try ?  :-\

 

[spase]

i have a mnats Rev J (03.11.06) board so which bom should i need?

 

[Ted]

I'm having some troubles with my G1176

All voltages are good, both rail and transistors.

BUT

With q1 Fet in, i got a very low level. It's compressing but not the way it should. Even with both input and output fully open i am losing 10db gain in the box.
With q1 out, the level is normal!
Also then the GR meter works, and is compressing normal. (only the metering off course)

The VU function isn't working neither. Not with or without q1

I already double checked every resistor, connection, soldering bulbs etc. but can't find the mistake...
Also switched q1 for another BF245A.

Any help is much appreciated!



Ted

 

[gswan]

Did it calibrate correctly (qbias calibration)? It sounds like the FET is turned on. Check Vgs and see where it sits against your FET test curve. Retry the Qbias calibration.

 

[spacecho]

Hello All,

I have built a couple 1176 rev H (Mnats) boards (21.3.05 boards) they both work and compress as normal

but seem to have ac voltage on the xlr hot / cold and it seems the ground..

I'm measuring 17-20vac on the metal parts (using a multimeter) - i have checked the layout and all capacitors and diodes are polarized correctly as far as i can tell.

Is this normal? I'm assuming it is not - i can't seem to find the component overlay for the rev H board - have searched for the last hour.. if anyone could point me to it it would be appreciate it. Also if anyone could confirm that they are not reading ac voltage on the xlr hot and cold it would be appreciated.

I've built many devices and never had an error - this has me confused..

 

[s2udio]

Where are you referencing your meter negative probe too ?
The metal case should be at ground potential !?
What does the PIN 2 read on DC ?

 

[spacecho]

Hello S2udio,

Thanks for your reply - i finally got to do more checking:

I didn't have the pin 1 xlr input connected to chassis earth, also xlr was mis wired.

Fixed these issues.

The unit compresses and all functions seem to operate normally - the vu needle is even centered, all controls work as expected.

there is no voltage difference between center tap and chassis ground, however i am reading 13-14vdc between the hot or cold pins on the xlr input and the chassis earth (or center tap 0v) There is no voltage between the xlr output hot or cold pins..

I've checked and re- checked - i'm assuming this is not right although none of the equipmnent i connected it to has been damaged or behaved strangely.

Could anyone check for voltage between hot and chassis ground or cold and chassis ground on the xlr input?

 

[gswan]

There should be no DC voltage between any of the outputs and chassis ground. The output is transformer coupled and the only way you will get DC on the output is if your metering is miswired.