letterbeacon
Well-known member
Bravo Dave -what a text book build!
GroupDIY Bridge compressor.
- Thread starter DaveP
- Start date
Help Support GroupDIY Audio Forum:
The metalwork is all finished now.
The top cover is done and the front panel drilled for 19" rack attachment.
The DC heater supply is finished and the HT runs without smoke!
I'm in the process of checking voltages and tidying up now, full testing will start next week.
best
DaveP
The top cover is done and the front panel drilled for 19" rack attachment.
The DC heater supply is finished and the HT runs without smoke!
I'm in the process of checking voltages and tidying up now, full testing will start next week.
best
DaveP
Thanks Matt and Doug,
All the voltages are correct and the HT comes up after 12~15 seconds and by that time the tubes are hot enough. The meter zeros nicely too.
Next week I test the S:N ratio and frequency response and plot the compression chart. I hope to also post some with and without samples on soundcloud.
If everything is ok I will type up a pdf manual and parts list.
Then its off to two UK studios where some forum members have been kind enough to offer to test it in action.
This has been a long project and I'm glad it has all come together at last.
Big Thank you to all who have contributed and encouraged.
best
DaveP
All the voltages are correct and the HT comes up after 12~15 seconds and by that time the tubes are hot enough. The meter zeros nicely too.
Next week I test the S:N ratio and frequency response and plot the compression chart. I hope to also post some with and without samples on soundcloud.
If everything is ok I will type up a pdf manual and parts list.
Then its off to two UK studios where some forum members have been kind enough to offer to test it in action.
This has been a long project and I'm glad it has all come together at last.
Big Thank you to all who have contributed and encouraged.
best
DaveP
rafafredd
Well-known member
sick one!
skal1
Well-known member
Yes Dave p British engineering @ its best....
dustbro
Well-known member
dude... great job! Can't wait to build one of these up
Neither can I Dustbro!
I was going through the frequency response and discovered there was a nasty resonance peak at 37kHz. It has taken me two days to find it.
Although these interstages are cheap and work very well in compression ( I got -36dB on one setting!). They do complain when in this circuit, but I've fitted a 220pF across the bridge between the two and that seems to have tamed it a little. I still have some more tweaking to do but the end is now in sight.
What I can report is that it's got 2.6W into 600 ohms which is +35dBm
Happy Independence day to all in the US of A, just think, if you hadn't got so uppity back in 76 you might have still had a Queen now........ on second thoughts maybe not ;D
best
DaveP
I was going through the frequency response and discovered there was a nasty resonance peak at 37kHz. It has taken me two days to find it.
Although these interstages are cheap and work very well in compression ( I got -36dB on one setting!). They do complain when in this circuit, but I've fitted a 220pF across the bridge between the two and that seems to have tamed it a little. I still have some more tweaking to do but the end is now in sight.
What I can report is that it's got 2.6W into 600 ohms which is +35dBm
Happy Independence day to all in the US of A, just think, if you hadn't got so uppity back in 76 you might have still had a Queen now........ on second thoughts maybe not ;D
best
DaveP
I'm still tweaking this comp to get the best out of it.
Finding the resonance and dealing with it helped, but it is quite powerful, unlike that on a mic TX.
However I have found that a modified Fender tone stack has a frequency profile that is the inverse of the output of T2, so using a low impedance version of that (scaled 10 fold: Resistors are x0.1, Caps are 10x) allows me to adjust the frequency response in some detail.
The object is to deal with the 36kHz resonance without spoiling the frequency response above 10kHz, not an easy task.
best
DaveP
I am due to go into the studio at Dubrek's at Derby UK in just over a week and it will be ready by then.
Finding the resonance and dealing with it helped, but it is quite powerful, unlike that on a mic TX.
However I have found that a modified Fender tone stack has a frequency profile that is the inverse of the output of T2, so using a low impedance version of that (scaled 10 fold: Resistors are x0.1, Caps are 10x) allows me to adjust the frequency response in some detail.
The object is to deal with the 36kHz resonance without spoiling the frequency response above 10kHz, not an easy task.
best
DaveP
I am due to go into the studio at Dubrek's at Derby UK in just over a week and it will be ready by then.
I've got the response virtually flat from 30hz to 20kHz then there is a +6dB peak at 36kHz with the ringing on square waves that you might expect goes with that.
I think I will be able to get it down to +2dB which I will be happy with. I'm having to revise a lot on filters and traps which is what has taken the time.
I'm worried about possible intermodulation, thats why I'm spending time on this.
best
DaveP
I think I will be able to get it down to +2dB which I will be happy with. I'm having to revise a lot on filters and traps which is what has taken the time.
I'm worried about possible intermodulation, thats why I'm spending time on this.
best
DaveP
rafafredd
Well-known member
There was a very good PRR post about getting zobels right. But I can't find the info.
OK, its finally sorted!
The frequency response is now flat from 30Hz to 35kHz plus or minus 1dB (attached).
The square wave response is now much better too, I'll have to try and take a picture of that if I can.
I'll post the correction network in the following post.
best
Davep
The frequency response is now flat from 30Hz to 35kHz plus or minus 1dB (attached).
The square wave response is now much better too, I'll have to try and take a picture of that if I can.
I'll post the correction network in the following post.
best
Davep
emrr said:
Doug,
I'm not up to date with some American phrases, wild to me would be what it was, not what it is now! The bump at 30 Hz does not really exist, it is an artifact caused by excel's attempt to smooth curves.
Anyway, I've done my best but it could be tweaked a bit more in the middle if I went to non-standard resistor values. The final schematic is attached.
The correction network deserves some comment. The 3.9k is the terminating resistance. The next section is part of a scaled tonestack to correct the mid peak. The last section is a damped bandstop filter centred on 32kHz, there is also a 220pF across T2 primary which does much the same thing. From what I understand, this has a much flatter response than the original 26C?
I'm supposed to be going into Jay's studio next weekend which I'm really looking forward to, I've asked him to post a frank report.
best
DaveP
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