I decided to design an onboard piezo/Mic blender for my Roland AC-60 Acoustic Amp,since none of the onboard preamps seemed to work properly on it.All the piezo preamps both UST's & Piezos,I've tried on this amp were exhibiting severe loading or overload effect, with a very unpleasent mid boost!
No clear specs. are given or available form Roland,apart from the -10dBu fig.given for the piezo/guitar input.
Am I then correct in assuming that this -10dBu means,the input will only accept around 330mV @10K!
Well,my preamp is driving line level signals,so how can I possibly use my preamp on AC-60?
After spending a good part of 9 months developing /constructing this "Blender pre,it just dawned on me that the SIGNAL level is the PROBLEM,& nothing was wrong with my preamp!
Has anyone else encountered a similar problem with an AC-60?
No clear specs. are given or available form Roland,apart from the -10dBu fig.given for the piezo/guitar input.
Am I then correct in assuming that this -10dBu means,the input will only accept around 330mV @10K!
Well,my preamp is driving line level signals,so how can I possibly use my preamp on AC-60?
After spending a good part of 9 months developing /constructing this "Blender pre,it just dawned on me that the SIGNAL level is the PROBLEM,& nothing was wrong with my preamp!
Has anyone else encountered a similar problem with an AC-60?
Trouble with roland ac-60
The AC-60 is designed to handle inputs from on-board preamps in guitars, etc. The input gain (channel volume) should be at roughly mid point, otherwise, you're overdriving the front end. If this is the case, try a T-pad between your preamp and the AC-60. Have you tried the less sensitive 'magnetic pickup' input setting?
The AC-60 is designed to handle inputs from on-board preamps in guitars, etc. The input gain (channel volume) should be at roughly mid point, otherwise, you're overdriving the front end. If this is the case, try a T-pad between your preamp and the AC-60. Have you tried the less sensitive 'magnetic pickup' input setting?
Thank you Albertg,
You're absolutely right..however,the AC60 has line/mic inputs as well.The line i/p too exhibited the same problem.I then guessed that this perhaps had to do with the buffer/tone circuit, since the problem still persisted even at very low volume levels.
Btw,the input buffer is modified to a non invert.charge amp by just adding a 10nF cap in parallel with a 10M res in the feedback loop.
Since I had a 100k gain pot across the feedback loop in the second stage preceding the tone circuit,I then assumed that this would be loading the tone circuit,so I replaced it with a 100k resistor instead & wired a 10k lin pot in series after the buffer o/p cap.Yep,it worked! NO MORE LOADING EFFECT!
The remaining problem was that the tone circuit had far too much gain,so I've now scaled it down..& it's working as it should.
I'm a bit confused about adding a balanced o/p to this mixer circuit-pl.refer to 2nd on the right- 'cause of the master vol.pot!
Q:Can I just connect this 'pot' in the feedback loop instead?
Q:Have you any suggestions for a simple & effective balanced out-put schematic?
Thanks!
You're absolutely right..however,the AC60 has line/mic inputs as well.The line i/p too exhibited the same problem.I then guessed that this perhaps had to do with the buffer/tone circuit, since the problem still persisted even at very low volume levels.
Btw,the input buffer is modified to a non invert.charge amp by just adding a 10nF cap in parallel with a 10M res in the feedback loop.
Since I had a 100k gain pot across the feedback loop in the second stage preceding the tone circuit,I then assumed that this would be loading the tone circuit,so I replaced it with a 100k resistor instead & wired a 10k lin pot in series after the buffer o/p cap.Yep,it worked! NO MORE LOADING EFFECT!
The remaining problem was that the tone circuit had far too much gain,so I've now scaled it down..& it's working as it should.
I'm a bit confused about adding a balanced o/p to this mixer circuit-pl.refer to 2nd on the right- 'cause of the master vol.pot!
Q:Can I just connect this 'pot' in the feedback loop instead?
Q:Have you any suggestions for a simple & effective balanced out-put schematic?
Thanks!
Attachments
Circuit design such as you're suggesting is beyond my capability.. Could you explain your setup? What is the signal chain? What are the piezos used for?
Assuming a guitar is the source device, it seems to me:
1. A simple 'impedance match' preamp with necessary gain to drive the piezo input would be all that's required.
2. Most simple tone control circuits have broad ranges; relatively useless for most situations. Ex. The fundamentals generated by a 24-fret guitar in standard tuning are: ~82Hz - 1318Hz. The partials extend to about 8kHz for steel strings and 4kHz for nylon (my instruments).
3. I'd like shelving low and high ranges with variable corner freq, and a notch midrange, with var freq. (like on a good mixer)
4. Have you listened to the Bose line source systems? They are very clean, open, and smooth. If you have a bad sounding instrument, they will make it sound worse! They really let you hear the true sound of the instrument. Bose uses HEAVY EQ in their systems.
If you're interested, I'll tell you about my latest projects...
Albert
Assuming a guitar is the source device, it seems to me:
1. A simple 'impedance match' preamp with necessary gain to drive the piezo input would be all that's required.
2. Most simple tone control circuits have broad ranges; relatively useless for most situations. Ex. The fundamentals generated by a 24-fret guitar in standard tuning are: ~82Hz - 1318Hz. The partials extend to about 8kHz for steel strings and 4kHz for nylon (my instruments).
3. I'd like shelving low and high ranges with variable corner freq, and a notch midrange, with var freq. (like on a good mixer)
4. Have you listened to the Bose line source systems? They are very clean, open, and smooth. If you have a bad sounding instrument, they will make it sound worse! They really let you hear the true sound of the instrument. Bose uses HEAVY EQ in their systems.
If you're interested, I'll tell you about my latest projects...
Albert
Well, my preamp consists of a Piezo disc preamp as shown + a mic preamp.The piezo disc is fitted under the 'top' left of the the bridge/saddle as opposed to UST. These are then phase corrected and then summed by the mixer shown above in fig.2/2.Both these work properly, separately & mixed as unbalanced signals.
Going back to my original query,...
What I'd like to do is,to take is a balanced output from the mixer as well.but rather confused,since the master volume on the mixer is feeding directly from the center pin on the volume control.
Would it be ok then to connect vol.pot in the feedback loop instead & then wire a balanced o/p to a XLR or a TRS connector?[/B]
Both tone controls on these are now behaving properly,once I modified & scaled down t.cont on the piezo preamp.I'm quite restricted by space too,since this is intended as an on-board preamp,hence keeping it simple with basic tone circuits & these work quite adequately for my purpose for the time being.However,I will make a full blown floor model once I finish this.
No,I've not tried the Bose line source systems,but if it's heavily EQ'ed, as you've mentioned,then I can't imagine these being very transparent IMHO!
Why have they used so much 'eq'ing? bad design perhaps? he..he..he
Yes,you're spot on with regard to bad sounding guitars,sounding badly through preamps/amps.....well,I too discovered this fact a long time ago!Although I am using a cheapo guitar,it sounds almost like a Taylor!After I changed the saddle,nut, & lowered the action & fitted Custom gauge strings to it.Amazing what these small changes can do to a guitar!
Yes please,please let me know about all your projects.
Going back to my original query,...
What I'd like to do is,to take is a balanced output from the mixer as well.but rather confused,since the master volume on the mixer is feeding directly from the center pin on the volume control.
Would it be ok then to connect vol.pot in the feedback loop instead & then wire a balanced o/p to a XLR or a TRS connector?[/B]
Both tone controls on these are now behaving properly,once I modified & scaled down t.cont on the piezo preamp.I'm quite restricted by space too,since this is intended as an on-board preamp,hence keeping it simple with basic tone circuits & these work quite adequately for my purpose for the time being.However,I will make a full blown floor model once I finish this.
No,I've not tried the Bose line source systems,but if it's heavily EQ'ed, as you've mentioned,then I can't imagine these being very transparent IMHO!
Why have they used so much 'eq'ing? bad design perhaps? he..he..he
Yes,you're spot on with regard to bad sounding guitars,sounding badly through preamps/amps.....well,I too discovered this fact a long time ago!Although I am using a cheapo guitar,it sounds almost like a Taylor!After I changed the saddle,nut, & lowered the action & fitted Custom gauge strings to it.Amazing what these small changes can do to a guitar!
Yes please,please let me know about all your projects.
Well, you could try the circuit under the heading "Hey!, That's Cheating" at Balanced Transmitter and Receiver II. If you have 1/2 TL072 available, you won't need to mess with the tone circuit.
If you have a steel-string guitar, be sure to connect the strings to the shield of the system, if you have hum problems, and be careful when using a mike!
Is this a dual-battery setup? If so, variations in battery voltage balance can cause asymmetrical output. You may consider using one of those charge pump devices to produce the -9V from a single battery.
The original Bose L1 (not the newer ones) has good bass response down to the guitar's low E (~82Hz). This from 2 inch drivers. What they are doing is exactly what we do when we adjust our tone controls. There is some substantial bass boost going on. That's why the L1 sounds good with guitar/voice input without a subwoofer. I have tested this. The later models REQUIRE a subwoofer. (More $ for Bose). Bose made its fortune on the idea of compensating for speaker limitations with EQ in the amp.
My idea for guitar amplification is similar. Pre-equalize everything the way you want it, then 'fix' the design. I just need flat response from 80Hz to 2500Hz. That's it. I don't need feedback comp, because my Parker is a solid body. For hollow bodies, it's different. Nothing is more annoying than have to hear body resonance during a performance. Room resonances are a different issue, however.
Since I love the Roland stereo chorus, I'm building two speaker columns, each with 6 - 4 inch drivers ($0.89 each from Parts Express). I will test them on my Roland JC-55 amp initially, then I'll wire speaker jacks into the AC-60. I want the sound to surround the audience. I love the AC-60, but it sounds boxy.
If you have a steel-string guitar, be sure to connect the strings to the shield of the system, if you have hum problems, and be careful when using a mike!
Is this a dual-battery setup? If so, variations in battery voltage balance can cause asymmetrical output. You may consider using one of those charge pump devices to produce the -9V from a single battery.
The original Bose L1 (not the newer ones) has good bass response down to the guitar's low E (~82Hz). This from 2 inch drivers. What they are doing is exactly what we do when we adjust our tone controls. There is some substantial bass boost going on. That's why the L1 sounds good with guitar/voice input without a subwoofer. I have tested this. The later models REQUIRE a subwoofer. (More $ for Bose). Bose made its fortune on the idea of compensating for speaker limitations with EQ in the amp.
My idea for guitar amplification is similar. Pre-equalize everything the way you want it, then 'fix' the design. I just need flat response from 80Hz to 2500Hz. That's it. I don't need feedback comp, because my Parker is a solid body. For hollow bodies, it's different. Nothing is more annoying than have to hear body resonance during a performance. Room resonances are a different issue, however.
Since I love the Roland stereo chorus, I'm building two speaker columns, each with 6 - 4 inch drivers ($0.89 each from Parts Express). I will test them on my Roland JC-55 amp initially, then I'll wire speaker jacks into the AC-60. I want the sound to surround the audience. I love the AC-60, but it sounds boxy.
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