phono amp question - adding input tx

wicked1 · 30th July 2010, 03:31 PM

Hello,
I built an aikido phono amp about a year ago. I've made a few changes and replaced my input tubes with some that sound a bit better but have lower gain.
I still get enough volume, but before I'd turn it up about 1/2 way, and the music was much louder than any buzz/hum. Now, I need to turn it up almost all the way (for relatively loud listening) and the background noise is much more noticeable.
This was my first p2p project, and I just can't get this last bit of noise out of it.
Then on to the needle.. It's a high output moving coil.. so relatively low output. (1.6mv)

SO, my question..
Would adding input tx's be a good idea to boost the clean signal from the TT, so I wouldn't need to turn up the volume and amplify the background noise so much?

thanks!!

kevinkr · 30th July 2010, 03:48 PM

1.6mV is a bit high for use with most moving coil SUTs (step up transformer) and the commonly employed alternative vintage mic SUTs. your HOMC cartridge may well be happiest loaded into 47K (the several I had all performed best into 47K) which is what they are usually designed for.. A better idea would probably be to find some good sounding, low noise, and higher mu triodes for the input stage of your Aikido.

I use SUTs with my Zu/Denon DL-103 (370uV out) and tried quite a few pairs before I found something I actually liked.

wicked1 · 30th July 2010, 04:10 PM

I've got the dl-110. I played around w/ the input load when I built it. I ended up going way lower than the recommended 47k. It's been a year, but if I remember correctly, it was was a bit slanted towards the high end. I believe I settled on 4.7k for the input which sounded more balanced to my system/ears.

Maybe I'll play with that some more now that's it's had a year to break in. I just read something saying the lower input imp., the lower the output from the cartridge. (specifically said once you put it on a MC input at about 600ohm's, the output of the cartridge drops to about .8mv)

wicked1 · 3rd August 2010, 04:20 PM

Ok, put the resistor back to 47k, and I do believe it sounds better this way.. It's a bit louder, so covers up more of the background noise. Also, now that things have broken in, it does sound better w/ the recommended 47k. The tone is still even, and everything is a bit tighter/punchier. I know that's about as non technical as I can get, but I think u know what I mean.

Since I'm the only one who even noticed the noise, this will probably hold me over till the next time I get hyper critical..

Eli Duttman · 3rd August 2010, 11:50 PM

Quote:

SO, my question..
Would adding input tx's be a good idea to boost the clean signal from the TT, so I wouldn't need to turn up the volume and amplify the background noise so much?

Kevin made an important point about the 1:10 SUTs commonly used with LOMC cartridges. You can use trafos to step the voltage up, but you have to use microphone trafos whose ratio is 1:2 or thereabouts. CineMag offers a couple of models that appear useful here. The CMMI-2C has a 1:2 ratio, while the CMMI-3.5C has a 1:3.5 ratio. Please notice that mic trafos need to be driven by a 150 Ω or lower source impedance. The way to deal with that fact and the proper loading of the HOMC cart. is to use a low noise, high transconductance, JFET source follower between the cart. and the trafo. A bipolar PSU holds the cap. count in the signal path to 1, which "sits" between the FET and the trafo.

You will have to experiment with the load presented to the trafo's secondary, in order to maximize performance. Send Steve Eddy a PM or EMail if this method is of interest, as he is expert in the use of mic trafos as means of obtaining voltage gain.

Sheldon · 01:19 AM

Quote:

Originally Posted by wicked1

Since I'm the only one who even noticed the noise, this will probably hold me over till the next time I get hyper critical..

You should not notice any background noise at normal listening levels, unless you are right next to the speaker - certainly not at the listening position. Another way of putting it, is that the surface noise from empty grooves should swamp any noise from the amp. If it doesn't, the system needs work - that's not being hyper critical.

Sheldon

wicked1 · 4th August 2010, 01:52 AM

it's only slightly worse than that (ear next to speaker). I don't hear it in my listening position, but in a few spots as I walk around the room.
The reason I brought up the topic is that when I had higher gain input tubes, noise was not an issue. You'd have to turn up the volume far louder than any listening level to hear the hum. With the lower gain inputs, I hear the hum more.. still, just barely.

But, I agree with you. I'd rather not hear it at all with the input tubes I want to use.

wicked1 · 21st September 2010, 06:01 PM

Well, I want to close this thread out by mentioning....
I basically moved some things and rewired all of my equipment (interconnects.. not under the hood) and the noise is gone!! I have no idea where a signal was running next to mains or whatever was going on, because I did look for that sort of thing while trying to chase down the buzz.
Anyway.. happy days..

30th July 2010, 03:31 PM	#1
wicked1 diyAudio Member Join Date: Jan 2008	phono amp question - adding input tx Hello, I built an aikido phono amp about a year ago. I've made a few changes and replaced my input tubes with some that sound a bit better but have lower gain. I still get enough volume, but before I'd turn it up about 1/2 way, and the music was much louder than any buzz/hum. Now, I need to turn it up almost all the way (for relatively loud listening) and the background noise is much more noticeable. This was my first p2p project, and I just can't get this last bit of noise out of it. Then on to the needle.. It's a high output moving coil.. so relatively low output. (1.6mv) SO, my question.. Would adding input tx's be a good idea to boost the clean signal from the TT, so I wouldn't need to turn up the volume and amplify the background noise so much? thanks!!

30th July 2010, 03:48 PM	#2
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	1.6mV is a bit high for use with most moving coil SUTs (step up transformer) and the commonly employed alternative vintage mic SUTs. your HOMC cartridge may well be happiest loaded into 47K (the several I had all performed best into 47K) which is what they are usually designed for.. A better idea would probably be to find some good sounding, low noise, and higher mu triodes for the input stage of your Aikido. I use SUTs with my Zu/Denon DL-103 (370uV out) and tried quite a few pairs before I found something I actually liked. __________________ www.kta-hifi.net

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30th July 2010, 04:10 PM	#3
wicked1 diyAudio Member Join Date: Jan 2008	I've got the dl-110. I played around w/ the input load when I built it. I ended up going way lower than the recommended 47k. It's been a year, but if I remember correctly, it was was a bit slanted towards the high end. I believe I settled on 4.7k for the input which sounded more balanced to my system/ears. Maybe I'll play with that some more now that's it's had a year to break in. I just read something saying the lower input imp., the lower the output from the cartridge. (specifically said once you put it on a MC input at about 600ohm's, the output of the cartridge drops to about .8mv)

3rd August 2010, 04:20 PM	#4
wicked1 diyAudio Member Join Date: Jan 2008	Ok, put the resistor back to 47k, and I do believe it sounds better this way.. It's a bit louder, so covers up more of the background noise. Also, now that things have broken in, it does sound better w/ the recommended 47k. The tone is still even, and everything is a bit tighter/punchier. I know that's about as non technical as I can get, but I think u know what I mean. Since I'm the only one who even noticed the noise, this will probably hold me over till the next time I get hyper critical..

4th August 2010, 01:52 AM	#7
wicked1 diyAudio Member Join Date: Jan 2008	it's only slightly worse than that (ear next to speaker). I don't hear it in my listening position, but in a few spots as I walk around the room. The reason I brought up the topic is that when I had higher gain input tubes, noise was not an issue. You'd have to turn up the volume far louder than any listening level to hear the hum. With the lower gain inputs, I hear the hum more.. still, just barely. But, I agree with you. I'd rather not hear it at all with the input tubes I want to use.

21st September 2010, 06:01 PM	#8
wicked1 diyAudio Member Join Date: Jan 2008	Well, I want to close this thread out by mentioning.... I basically moved some things and rewired all of my equipment (interconnects.. not under the hood) and the noise is gone!! I have no idea where a signal was running next to mains or whatever was going on, because I did look for that sort of thing while trying to chase down the buzz. Anyway.. happy days..

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