Hi,
I would like some advice on setting up my Classe Audio DR4 phono pre amp to match my Linn Troika cartridge.
The Classe Pre amp has changeable gain resistors in the MC phono circuit so I can adjust the gain to suit my cartridge. I can't really figure out what it should be set at and I thought some of you smart beans could have a think about it for me. I am quite a noob with it although I have had the system for some time I have never really known if it is set to optimum as the pre amp was bought 2nd hand and not matched to the cartridge previous.
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Here are the specs on the cartridge:
Specifications: Low-output moving-coil cartridge with unique three-point fixing arrangement. Recommended tracking force: 1.5–1.7gm. Stylus type: Nude Vital super-elliptical.
Output is about normal for a low-output 'coil (around 0.2mV at 5cm/s), and the tubed SP-10 had no noise problems. With the down force set at 1.7gm, the Troika just failed the 70µm lateral modulation cut on the Ortofon Test Record at 78°F (it was a hot day); with the down force increased to 1.8gm, it managed to clear the 70µm cut, but 2.1gm was needed for the maximum 80µm cut. It cleared the 50µm vertical cut at 1.7gm down force. While not quite as surefooted as the Shure V15 V MR (others report that the Troika is less secure at lower temperatures), this is pretty good tracking for a moving-coil design.
Channel balance at 1kHz was spot on at around 0.05dB difference, while crosstalk was both superbly low and symmetrical, measuring -34dB at 1kHz, left-on-right, and -35dB, right-on-left. Obviously, the motor geometry is very well-aligned, both with the stylus orientation and the groove (as should be expected at this price level). The cartridge designers' ability to optimize the compliance for a dedicated tonearm design was shown by the positioning of LF tonearm resonance: ideally placed laterally around 10Hz in the Ittok, and vertically a little lower, around 9Hz, both with only a moderate Q and a moderate amplitude rise. The measured frequency response, using the third-octave noise bands on Denon XL-7007, showed the ubiquitous upper-midrange depression to be 2–3dB or so deep, with a 2dB rise at 20kHz.—John Atkinson
-source: Stereopile magazine review.
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Here are the specs and instructions from the Classe DR4 Pre Amp Owners Manual:
Schematic here:
The Phono input can accommodate both magnetic or moving coil cartridges of varying output. In the MC Position, additional gain is factory set to 22dB. The gain can be adjusted from 20 to 40dB, in order to optimize system gain and low noise. (Note: The MC gain is in addition to the standard MM gain of 35dB.)
Changing the value of R6 and R48 (Left / Right) according to this chart:
Resistor Gain
1000F - 20dB
1270F - 22dB - Standard
1650F - 24dB
2150F - 26dB
2870F - 28dB
3830F - 30dB
5110F - 32dB
7680F - 43dB
1151F - 36dB
1961F - 38dB
4221F - 40dB
-------------------------------
I do not know what it is set to at the moment as I have not taken the lid off to see.
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My System:
Linn Sondek LP12 - Ittok II - Valhalla - Troika cartridge
Classe Audio Pre Amp
Krell KSA150 Pure Class A amp
Duntech Princess speakers with newly rebuilt crossovers.
---------------
How this question came about:
I've had the above system foe about 10 years and always found the turntable to be somewhat noisy and very detailed, every pop and crackle and sometimes a bit of interference could come in with some buzzing etc. It just never really sounded Hi End to match the system. Just a bit too much background noise to sound great.
The Krell amp has been rebuilt completely and may have been the source of some of the above problems. I have never been really happy with the setup but I have no audio mates to nut out the problem so I just lived with it.
The Krell amp is in the shop again currently and I am using a cheap Yamaha integrated (RX-350) to get by. It has a MM phono pre and IT SOUNDS WONDERFUL! It sounds just like a CD but with a few tiny pop and crackles here and there. Totally listenable and enjoyable. Not much gain - I can run it full wick without clipping and it is at an easy level.
I was quite shocked at the difference in the two systems given my speakers are notorious for exposing the weakest link.
So this has led me to pose the potential mismatch level question.
I would like some advice on setting up my Classe Audio DR4 phono pre amp to match my Linn Troika cartridge.
The Classe Pre amp has changeable gain resistors in the MC phono circuit so I can adjust the gain to suit my cartridge. I can't really figure out what it should be set at and I thought some of you smart beans could have a think about it for me. I am quite a noob with it although I have had the system for some time I have never really known if it is set to optimum as the pre amp was bought 2nd hand and not matched to the cartridge previous.
-------------------------------------------
Here are the specs on the cartridge:
Specifications: Low-output moving-coil cartridge with unique three-point fixing arrangement. Recommended tracking force: 1.5–1.7gm. Stylus type: Nude Vital super-elliptical.
Output is about normal for a low-output 'coil (around 0.2mV at 5cm/s), and the tubed SP-10 had no noise problems. With the down force set at 1.7gm, the Troika just failed the 70µm lateral modulation cut on the Ortofon Test Record at 78°F (it was a hot day); with the down force increased to 1.8gm, it managed to clear the 70µm cut, but 2.1gm was needed for the maximum 80µm cut. It cleared the 50µm vertical cut at 1.7gm down force. While not quite as surefooted as the Shure V15 V MR (others report that the Troika is less secure at lower temperatures), this is pretty good tracking for a moving-coil design.
Channel balance at 1kHz was spot on at around 0.05dB difference, while crosstalk was both superbly low and symmetrical, measuring -34dB at 1kHz, left-on-right, and -35dB, right-on-left. Obviously, the motor geometry is very well-aligned, both with the stylus orientation and the groove (as should be expected at this price level). The cartridge designers' ability to optimize the compliance for a dedicated tonearm design was shown by the positioning of LF tonearm resonance: ideally placed laterally around 10Hz in the Ittok, and vertically a little lower, around 9Hz, both with only a moderate Q and a moderate amplitude rise. The measured frequency response, using the third-octave noise bands on Denon XL-7007, showed the ubiquitous upper-midrange depression to be 2–3dB or so deep, with a 2dB rise at 20kHz.—John Atkinson
-source: Stereopile magazine review.
---------------------------------------------------
Here are the specs and instructions from the Classe DR4 Pre Amp Owners Manual:
Schematic here:
An externally hosted image should be here but it was not working when we last tested it.
The Phono input can accommodate both magnetic or moving coil cartridges of varying output. In the MC Position, additional gain is factory set to 22dB. The gain can be adjusted from 20 to 40dB, in order to optimize system gain and low noise. (Note: The MC gain is in addition to the standard MM gain of 35dB.)
Changing the value of R6 and R48 (Left / Right) according to this chart:
Resistor Gain
1000F - 20dB
1270F - 22dB - Standard
1650F - 24dB
2150F - 26dB
2870F - 28dB
3830F - 30dB
5110F - 32dB
7680F - 43dB
1151F - 36dB
1961F - 38dB
4221F - 40dB
-------------------------------
I do not know what it is set to at the moment as I have not taken the lid off to see.
-----------------------
My System:
Linn Sondek LP12 - Ittok II - Valhalla - Troika cartridge
Classe Audio Pre Amp
Krell KSA150 Pure Class A amp
Duntech Princess speakers with newly rebuilt crossovers.
---------------
How this question came about:
I've had the above system foe about 10 years and always found the turntable to be somewhat noisy and very detailed, every pop and crackle and sometimes a bit of interference could come in with some buzzing etc. It just never really sounded Hi End to match the system. Just a bit too much background noise to sound great.
The Krell amp has been rebuilt completely and may have been the source of some of the above problems. I have never been really happy with the setup but I have no audio mates to nut out the problem so I just lived with it.
The Krell amp is in the shop again currently and I am using a cheap Yamaha integrated (RX-350) to get by. It has a MM phono pre and IT SOUNDS WONDERFUL! It sounds just like a CD but with a few tiny pop and crackles here and there. Totally listenable and enjoyable. Not much gain - I can run it full wick without clipping and it is at an easy level.
I was quite shocked at the difference in the two systems given my speakers are notorious for exposing the weakest link.
So this has led me to pose the potential mismatch level question.
To me this seems to be the most likely culprit. One thing you may consider is to create a nice little aux board using dip switches and a bank of resistors. The leads could be soldered to the spots on the board where the resistors sit.
Why not email Classé ?
As for not really enjoying or thinking your system lacks, using top tier products should give, good results, but there are no guarantees.
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Hello,
Please note that any RLC system can potentially present a high frequency peak given the appropriate component values. Not all MC heads are the same. The internal inductance varies from a few uH to several hundred uH and the loading of the system includes the large capacitance of the shielded cables of the turntable arm plus that of the interconnecting cables between the turntable and the preamp. A low preamp input resistance can usually avoid peaking but the optimum response is achieved by taking into account the whole chain from the MC head through cables and connectors to the RC of the preamp. The manufacturer of the cartridge usually suggests the recommended load in most cases that matter.
Please note that any RLC system can potentially present a high frequency peak given the appropriate component values. Not all MC heads are the same. The internal inductance varies from a few uH to several hundred uH and the loading of the system includes the large capacitance of the shielded cables of the turntable arm plus that of the interconnecting cables between the turntable and the preamp. A low preamp input resistance can usually avoid peaking but the optimum response is achieved by taking into account the whole chain from the MC head through cables and connectors to the RC of the preamp. The manufacturer of the cartridge usually suggests the recommended load in most cases that matter.
Hi demeterart,
What further information would one need in order to solve the problem you have suggested giving the info I have already supplied?
I will email the manufactures and return their response.
Hello,
Well, what is inside the black box named Z1 at the front end? Or you could simple ask the manufacturer what is the equivalent input impedance ( R in parallel to a C) of the preamp and if that is configurable. You could also ask, the manufacturer of the cartridge this time, about the recommended load for their MC and see if you can match the two answers.
Well, what is inside the black box named Z1 at the front end? Or you could simple ask the manufacturer what is the equivalent input impedance ( R in parallel to a C) of the preamp and if that is configurable. You could also ask, the manufacturer of the cartridge this time, about the recommended load for their MC and see if you can match the two answers.
Hi Null changing my gain calc as handbook says mc sensitivity is 0.3mV and your cartridge gives 0.2mV so only need 3.5dB gain over factory setting giving a total of 25.5dB . None of the quoted sens are referenced to an o/p level but have roughly calc the o/p as 1V rms unbal and correspondingly 2V rms bal . If you wouldnt mind replying what is the i/p sens of the Krell at max o/p into 8 ohms bal and/or unbal i/p.
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I opened it up today and snapped some pics.
I find all this awfully complicated as I am not trained in electronics. I have some self taught skills though.
My first post I quoted from the manual a series of values in order to get a certain dB change: That list again here -
Resistor Gain
1000F - 20dB
1270F - 22dB - Standard
1650F - 24dB
2150F - 26dB
2870F - 28dB
3830F - 30dB
5110F - 32dB
7680F - 43dB
1151F - 36dB
1961F - 38dB
4221F - 40dB
I do not know what the "F" designates?
Mine is marked 4120F and is not on the above list. What is this component?
In the schematic it is a resistor. I've never seen a resistor looking like this.
The other marking on this component reads RN60D
Here is a rather small image of the whole Pre amp:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I find all this awfully complicated as I am not trained in electronics. I have some self taught skills though.
My first post I quoted from the manual a series of values in order to get a certain dB change: That list again here -
Resistor Gain
1000F - 20dB
1270F - 22dB - Standard
1650F - 24dB
2150F - 26dB
2870F - 28dB
3830F - 30dB
5110F - 32dB
7680F - 43dB
1151F - 36dB
1961F - 38dB
4221F - 40dB
I do not know what the "F" designates?
Mine is marked 4120F and is not on the above list. What is this component?
In the schematic it is a resistor. I've never seen a resistor looking like this.
The other marking on this component reads RN60D
Here is a rather small image of the whole Pre amp:
An externally hosted image should be here but it was not working when we last tested it.
Hi Null thanks for the pics ,but what you have highlighted is R47 which is the equivalent right hand channel of R7 (412 ohms) on the schematic .If you look at R48 it is 127 ohms (the factory setting).I can see why you have done this because its in the same location as R6 on the left hand channel . We appear to have a case of the schematic numbering not quite agreeing with the actual. Could you take another pic of the left hand channel (to confirm this) with bottom left of new pic showing LEFT MC OUT and top of pic going to top of board , this might enable us to also decipher Z1.
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Hi Null , anticipating you dont have a gain problem , maybe you have an earthing one . Are the RCA connectors insulated from chassis .The schematic shows the chassis connection to the RCAs is via a 4.7uF capacitor . Whilst the DR4 is electrically safe the Krell might be supplying the signal earth which if this is over long interconnects would exaberate the problem.
Ok some more pics
I'll chat some more but I have to run now.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I'll chat some more but I have to run now.
Hi Null great pics again .Confirmed both mc chs are on the factory gain settings. The handbook and schematic should refer to adjusting R7 and R48 not R6 and R48 . Cant see any sign of Z1 just a large dc blocking capacitor C1 on the i/p .
Conclusion excessive mc gain is not the problem so dont adjust . 3.5dB is the last 1/4 turn before full volume and we were looking to reduce the gain and not increase it . The RX-350 will be quieter 22dB quieter as your putting a mc into a mm i/p
Back to the drawing board . The pops and crackles you refered to earlier are we talking about vinyl surface noise or are you picking up electrical interference ie lights being switched on and off etc and do you have a mains hum problem.
Conclusion excessive mc gain is not the problem so dont adjust . 3.5dB is the last 1/4 turn before full volume and we were looking to reduce the gain and not increase it . The RX-350 will be quieter 22dB quieter as your putting a mc into a mm i/p
Back to the drawing board . The pops and crackles you refered to earlier are we talking about vinyl surface noise or are you picking up electrical interference ie lights being switched on and off etc and do you have a mains hum problem.
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Thanks for your time and effort.
Agreed I don't think it is a gain problem now as it always had a healthy volume.
Perhaps the problem is interfearence from the LP12 power supply. It has a buzzing sound a bit like a fridge but quite a low volume. You have to put your ear quite close to hear it.
One other thing that has been a problem in the past with the pre amp is the input and output pins on the Bal XLR sockets are a bit loose. In the past the male interconnect has pushed the female socket pin through the body of the socket. I noticed the middle pin of one of the output sockets had this fault. I believe it must have still been making contact though.
My Krell amp is currently in the shop with it's own problems and I hear it might make an expenseive boat anchor in the future.
Perhaps I will go DC motor on the LP12 and wait for the Krell to be fixed up.
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