| Nuuk |
I have asked this question in the loudspeakers section but will more likely find an answer here.
I am currently using a VBIGC, full details of which can be found HERE
I am sure that when I first used this amp, I could only use the first few positons on the volume control but now I need to have the volume control at nearly maximum for normal listening.
Yesterday, I put in some EQ for my open baffle speakers and found that I could hardly get any volume at all.
Has anybody any ideas what has happened. The mystery is all the more puzzling as both channels are exactly the same! |
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| peranders |
| Can you tell me how you have calculated these cap values, because these seems totally wrong. What is your goal with them? |
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| carlosfm |
Nuuk, what are you trying to do?
EQ?:confused:
It seams that those resistors and caps are making a heavy attenuatiion on the signal... |
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| sonnya |
| quote: | Originally posted by Nuuk
I have asked this question in the loudspeakers section but will more likely find an answer here.
I am currently using a VBIGC, full details of which can be found HERE
I am sure that when I first used this amp, I could only use the first few positons on the volume control but now I need to have the volume control at nearly maximum for normal listening.
Yesterday, I put in some EQ for my open baffle speakers and found that I could hardly get any volume at all.
Has anybody any ideas what has happened. The mystery is all the more puzzling as both channels are exactly the same! |
first of all. Your 220nF across 9.1K make a lowpass filter. Wich starts to attenuates the signal 6dB/octave from 80Hz up to 13KHz where the attenuating start to flatten out at -47dB |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Nuuk
Yesterday, I put in some EQ for my open baffle speakers and found that I could hardly get any volume at all.
Has anybody any ideas what has happened. |
You MESSED UP my instructions. The 220nF Cap and 9k1 Resistor are siupposed to be in SERIES, not parallel.
Sayonara |
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| Nuuk |
| quote: | | You MESSED UP my instructions. The 220nF Cap and 9k1 Resistor are siupposed to be in SERIES, not parallel. |
Oops, sorry KYW, we English are not taught the language so well as our overseas friends ;)
I'll move that 0.22uF cap in series and try again. I still have the strange thing about the overall gain of the VBIGC though. |
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| carlosfm |
| quote: | Originally posted by Nuuk
I'll move that 0.22uF cap in series and try again. |
The cap AND the resistor.:bawling: |
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| carlosfm |
Nuuk,
I've looked to your VBIGC schematic, as posted on your site, and now I'm confused.
Don't you have a gain of 68 on your amp?:confused: :eek: |
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| Nuuk |
| quote: | | The cap AND the resistor. |
I'm confused now (what's new;) ) This is what T said:
| quote: | Resistor in series with signal = 12k
Resistor in series with capacitor to ground = 9K1 & 0.22uF
For a little treble lift try a 1nF Capacitor (or larger/smaller to taste) in parallel with the 12k Resistor. |
The 9K1 resistor is already going to ground so I only need to move the 0.22uF cap in series with it rather than parallel - don't I?
Or is the 9K1 in series with the 12K? |
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| Nuuk |
Could somebody please confirm that this is the correct arrangement?
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Nuuk
Could somebody please confirm that this is the correct arrangement?
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I can. This is as originally suggested.
Sayonara |
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| Nuuk |
| Thanks again, I'll try that this afternoon. |
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| Nuuk |
OK - I now have a bit more bass BUT to me it seems as though the timing has been affected in the process!
Could this be a correct observation or a trick caused by the bass being a bit more prominent. The music just seems to have lost the speed it had before. |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Nuuk
OK - I now have a bit more bass BUT to me it seems as though the timing has been affected in the process!
Could this be a correct observation or a trick caused by the bass being a bit more prominent. The music just seems to have lost the speed it had before. |
I would think the observation correct. The so called "speed" with certain speakers is almst allways an overly prominent midrange. Bring the bass in line and things get "slow" (I'd say normal). The little filter I suggested was just a quick test to show you a certain degree of what you can expect from equalising the system.
BTW, adding a suitable subwoofer will "slow down" the sytem as well, even a "horn" or "URPS" one....
Sayonara |
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| Nuuk |
| quote: | | The so called "speed" with certain speakers is almst allways an overly prominent midrange. Bring the bass in line and things get "slow" (I'd say normal) |
And so the old 'compromise' issue rears its ugly head again!
I have noticed that 'speed' effect has decreased as I get more used to it. I mention this as it is not a good thing to pass final judgement on one or two hours listening.
And another point, some CD's sound better and others worse. I suppose that being single, I could have two or three systems in different rooms for the various types of music I listen to! ;)
BTW T, is it OK to play around with the values in that EQ circuit (within limits of course!)? |
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| Christer |
| quote: | Originally posted by Kuei Yang Wang
I would think the observation correct. The so called "speed" with certain speakers is almst allways an overly prominent midrange. Bring the bass in line and things get "slow" (I'd say normal). The little filter I suggested was just a quick test to show you a certain degree of what you can expect from equalising the system.
BTW, adding a suitable subwoofer will "slow down" the sytem as well, even a "horn" or "URPS" one....
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The term speed seems strange, but you put it within quotes
so I suppose you don't find it quite appropriate. I think I get
what you mean, but just to check if I do. Are you saying that
"high speed" is when the fundamental of a bass tone is too
attenauted wrt. to the harmonics, so we get an exaggerated
spectrum of high harmonics, giving too sharp transients??
That would make a lot of sense to why those smallish toy
speakers everybody buys nowadays seem to have bass
but yet sound so hard and wrong. |
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| Nuuk |
Christer, I think that T and I are talking of the same thing when we talk of 'speed' so let me answer. It is the timing of the music overall rather than just the 'speed' of the bass.
With more bass, the impression of timing (of the music) is that it slows down. With less the music seems to speed up.
An example. Many people liked the Linn Kann loudspeaker because it appeared to give a very 'fast' foot-tapping presentation which it did at the expense of deeper bass reproduction. |
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| Christer |
OK Nuuk, so you really mean an impression of a change in tempo?
Well, it is known that the perception of a frequency is somewhat
dependant on level, so there are probably many other such
perceptional "errors" going on in the brain. |
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| ronc |
I like "fast sound". I guess to each his own? I like horns with fast drivers but lets face it, horns are complicated, BIG,and sometimes very room dependant.At one time i was into OBs and may go back just because of the simplicity and totally un colored
sound.
ron |
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| theChris |
| i of course like both sounds in the applicable ways. i feel that long, deep notes should be produced as such, and short, impactful notes as well. it is ashame a dynamic EQ of some kind, or music format cannot be made such that we can truely have both. |
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| Kuei Yang Wang |
Konnichiwa,
| quote: | Originally posted by Nuuk
And so the old 'compromise' issue rears its ugly head again!
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You could add the old dreaded "tonecontrols" to your system....
;-)
| quote: | Originally posted by Nuuk
And another point, some CD's sound better and others worse. I suppose that being single, I could have two or three systems in different rooms for the various types of music I listen to! ;)
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Or use something like a Behringer EQ to change the sound according to taste....
| quote: | Originally posted by Nuuk
BTW T, is it OK to play around with the values in that EQ circuit (within limits of course!)?
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Sure. The capacitors determine the turnover frequencies, the one to ground becomes large in value to make the "lift" start at lower frequencies and smaller to start at higher frequencies. The Capacitor in parallel to the 12k Resistor becomes larger to make the HF lift start at lower frequencies and smaller to make it start at higher frequencies. The ratio between the resistors determines the amount of LF/HF lift, currently set to be around 6db maximum.
I'd suggest keeping the resistors fixed and experimenting and making the resistor switchable in steps of 0.5/1/2 (can be done using center neutral toggles).
Sayonara |
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| Nuuk |
| quote: | | Sure. The capacitors determine the turnover frequencies, the one to ground becomes large in value to make the "lift" start at lower frequencies and smaller to start at higher frequencies. The Capacitor in parallel to the 12k Resistor becomes larger to make the HF lift start at lower frequencies and smaller to make it start at higher frequencies. The ratio between the resistors determines the amount of LF/HF lift, currently set to be around 6db maximum. |
And thank you once again T. That will save me a bit of research ;) |
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| carlosfm |
Uncontrolled or slow bass usually means the amp is not man enough to drive the speakers, badly positioned speakers (near walls) or badly designed:eek: speakers.
In your case Nuuk, you just added a small bass lift.
Reposition your speakers or close the bass reflex port.:clown: |
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| Nuuk |
| quote: | | Reposition your speakers or close the bass reflex port. |
Thanks Carlos - where do I find the port?
;) |
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| ronc |
Well you could cut a port near the bottom, advantages are, the OB is lighter by the amount of material removed, it gives something for the cat to crawl in and out of, you can look thru the hole for things you have dropped on the floor on the opposite side................uuuuuu i cant think of any more!!!!!!
ron |
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| carlosfm |
| quote: | Originally posted by Nuuk
Thanks Carlos - where do I find the port?
;) |
:D
Is that a Motorola piezo tweeter?
I love those, with a good crossover.
Nuuk, why are you using that filter?
Did you feel lack of bass?
Isn't that woofer too big for a two way speaker?
Those tweeters shoud be crossed at around 5 to 6khz, they are very sensitive in the midband, it becomes nasty.
With that woofer and tweeter, it sould be a 3-way speaker.
I'm talking generically, of course, as I don't know your speakers.
:angel: |
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| Nuuk |
Hi Carlos,
The Goodmans 201's are very good 'full-range' units and I was using them with the Motorola tweeters crossed over at 16K.
The beauty of the big drivers is that you can keep any crossover out of the 75-4Khz range.
I did find that on some types of music I could do with a bit more at the bottom end, hence I am trying the EQ kindly suggested by T.
Ron, would I need one cat or two if I cut holes in the baffles? If I found that I had more bass with the cats blocking the holes would I be in trouble for nailing them in there? :D
And does one breed of cat sound better than the others? I have a feline that you may be able to help me here! |
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| ronc |
While doing a scientific study on the aperodic loading of bass ports with cats i happened to notice that long hair cats had a much more profound effect on the impedance loading of the driver. Using SWAG (scientific wild *** guess) the theory is the longer hair causes a greater diffusion of the exiting pressure and a greater partical density.
NOTE! No cats were harmed during this study, however i did use up a large box of band-aids on myself.
ron |
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| GregGC |
| quote: | Originally posted by ron clarke
While doing a scientific study on the aperodic loading of bass ports with cats i happened to notice that long hair cats had a much more profound effect on the impedance loading of the driver. Using SWAG (scientific wild *** guess) the theory is the longer hair causes a greater diffusion of the exiting pressure and a greater partical density.
NOTE! No cats were harmed during this study, however i did use up a large box of band-aids on myself.
ron |
:) :D :bawling: |
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| Nuuk |
| Ron, you make me feel so inadequate, not having an engineering background like your good self! :bawling: |
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| ronc |
I did go to Texas A&M, i am proud to be an aggee,sorry,agie,sorry,agye,sorry..............proud to have gone to Texas A&M.
ron
In other news,i have gone to dual mono blocks with the pre in the middle. All using hammond alum cabs and am mounting all 3 cabs on a 1.5" thick (thats 35mm to yall euro dudes) wooden base and beveling the
edges at a 45 deg. angle then mounting 1.5"l x 1" dia. hard Cr. brass spikes to the bottom. I am painting all the cabs with heat resistant flat black paint and baking them to harden the coating (have to use the oven for something). Will post pics when finished. Gotta finish a set of mono blocks first as well as a set of monster horns for the Fostex Fe-168e sigmas.
ron |
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| carlosfm |
Nuuk,
Well... full-range drivers usually have difficculty on the frequency extremes.
For a sealed box, it seams to me that your big driver needs more volume, a bigger box.
You can try to add a bass reflex port.
Bass may become a little slower, but then Ron can send you some cats.:D
BTW why not use an old driver as a passive radiator?:eek:
Ah, forget it.:D |
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| Nuuk |
| Carlos - it's an open baffle! ;) |
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| carlosfm |
| quote: | Originally posted by Nuuk
Carlos - it's an open baffle! ;) |
:clown:
Then WHY DIDN'T YOU SHOW THE BACK?:D
Close the back door, man.:clown: |
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| Nuuk |
| quote: | | Then WHY DIDN'T YOU SHOW THE BACK? |
Because I only had a picture of the front and side :D :D |
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| Nuuk |
OK chaps, I replaced VBIGC with OPA627BIGC so I could take a look inside the former.
And what did I find? The transformer for the valve circuit (not heaters) is putting out 27 volts on one side but only 5 volts on the other. No wonder it didn't sound right!
So can anybody tell me what is happening here. I have measured the voltages with and without the valve circuit connected. And the transformer was putting out the correct voltages when I put it in!
Suggestions/advice please. :whazzat: |
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| ofb |
| that couldn't be anything other than a short in the winding, could it? |
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| Nuuk |
| quote: | | that couldn't be anything other than a short in the winding, could it? |
Not unless they are putting things in transformers that I don't know about! ;)
BUT the big question is what would have caused it? The transformer in question was not clamped down in the usual way so there should be no question that the windings could have been damaged. |
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| Ropie |
| So are you saying that the problem has mysteriously righted itself? How are the V levels this morning? |
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| Nuuk |
Well, I was taking the transformer out for a closer physical examination when I noticed that one of the secondary wires going in to a connecting terminal block was loose.
I have put it back in the terminal block and now have 27-0-27 AC as expected.
I am surprised that the buffer worked at all!
Lesson - the biggest electronics mysteries are often down to something very simple. :o |
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| Ropie |
| quote: | Originally posted by Nuuk
Lesson - the biggest electronics mysteries are often down to something very simple. :o |
Yes, and these are usually just as hard to find! Glad to hear it's back to normal - does it sound even better now it's had an 'overhaul'?;) |
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| Nuuk |
| quote: | | does it sound even better now it's had an 'overhaul'? |
I have not put it back into service yet as I want to listen to the OPA627BIGC for a couple of days to better judge the differences between the two.
This is necessary for my degree in Gaincloning! ;) |
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| carlosfm |
| quote: | Originally posted by Nuuk
Well, I was taking the transformer out for a closer physical examination when I noticed that one of the secondary wires going in to a connecting terminal block was loose.
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What terminal block, Nuuk?
I've learned long time ago that there's nothing like solder.:bawling: |
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| carlosfm |
| quote: | Originally posted by Nuuk
I have not put it back into service yet as I want to listen to the OPA627BIGC for a couple of days to better judge the differences between the two.
This is necessary for my degree in Gaincloning! ;) |
Can we bet?:D |
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| Nuuk |
| quote: | | What terminal block, Nuuk? |
I agree Carlos but when I am putting something together for the first time, I use terminal blocks so that I can easily change things around. Removing them later on and soldering the connections is on the agenda! ;) |
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| carlosfm |
| quote: | Originally posted by Nuuk
I agree Carlos but when I am putting something together for the first time, I use terminal blocks so that I can easily change things around. Removing them later on and soldering the connections is on the agenda! ;) |
Oh...
I though that you had finished that amp long ago.:D |
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| Nuuk |
| quote: | | I though that you had finished that amp long ago. |
Question: 'Is a DIY hi-fi project ever finished?' ;) |
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| Nuuk |
Seems that I spoke to soon.
When I put my VBIGC back in the main system today I found that I still have a lack of gain such that I can run it at full volume and it is not too loud.
I have taken it back to the 'test' room and run it with my test speakers and another CD player but the result is just the same.
I just can't see what would be affecting both channels in exactly the same way as the channel balance is spot on!
BTW - the test speakers are also very efficient and I can't use them with a standard (unbuffered) IGC at full volume! :xeye: |
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| Ropie |
| Just a thought, Nick - is the stepped attenuator wired in correctly? |
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| Nuuk |
| quote: | | Just a thought, Nick - is the stepped attenuator wired in correctly? |
In a word - YES ;)
Thank goodness I have a reserve stack of Gainclones in the house :D |
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| ronc |
Hate to bring up the obvious Nuuk ole bud but have you tested the tube?
ron |
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| sandro600 |
ron , how do you test the 6922 tubes?
Nuuk do you still have the Velleman speaker protection circuits in ? |
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| ronc |
Well in my pre GC days i would use a signal generator on input posts and monitor the output with a scope as measured across a resistor.
However since i got knocked out adjusting the bias on my PP 6BQ5 amp i have kinda sorta gotten away from tubes.
ron
Yep, keep your other hand in your pocket around high voltages!!!!!!Its a shocking experience. |
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| Nuuk |
| quote: | | Hate to bring up the obvious Nuuk ole bud but have you tested the tube? |
I have not tested them so far Ron as it seemed very improbable that they had both deteriorated by the same amount.
However, anything is possible in this game and I will swap the tubes over (I'm using one per channel but different pins) to see what that does.
One observation I have made is that when powering up, the DC offset indication LED on the protection module (yes they are still there) comes on as before but now stays on for several seconds before going out again. |
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| ronc |
Just an off the head thing, but the DC offset thing sounds like some sort of a CR (cap discharging thru a resistor) response)?Like it has more to discharge?
ron |
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| Nuuk |
| I tried swapping the valves over but then I had nothing out of the left channel again! I think there may be a loose connection so will have the valve buffers out of the case and go over them thoroughly. |
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