Setup suggestion between DAC-AH and ST-70

rklosinski · 30th January 2007, 07:28 PM

I would like to minimize stuff im the signal path of my current setup. I have a DAC-AH (modified) and would like to connect it my ST-70 (again, modified). The problem is volume control. How to do it w/o adding a pre-amp of some type. The ST-70 is driving a pair of Epos M5's. Should I use a step attenuator in between the two? Currently I just reduce the amplitued digitally, which really sucks.

Thanks
Rich

SY · 30th January 2007, 08:34 PM

Why not just substitute a volume control potentiometer for the ST-70 grid leaks?

rklosinski · 30th January 2007, 08:54 PM

I guess that would be better than modifying the output of the dac-ah, since it will not effect impedence. I also thought about a passive linestage (step attenuator), but they can get costly.

SY · 30th January 2007, 09:07 PM

And since you've already got a chassis, why pay for the redundancy? In any case, a 100k pot should do the job. What does your input stage look like? If it's still the pentode of a 7199, you've got an easy job doing this.

rklosinski · 31st January 2007, 12:47 AM

I have the VTA70 driver pcb.

JandG · 31st January 2007, 02:47 AM

I use a by-passed output stage DAC-AH into a 100k input tube amp using 10k mono PEC pots mounted in very small, these pots sound excellent. I use very small RS project boxes with 4" pig tails attatched at rear of amp. I also run the DAC-AH with a TVC from time to time, but the PEC pots, I could live with just as easy as the TVC. since you amp is modded just mount the PEC's in that.If your DAC_AH still has the output stage, ..by-pass that & listen...................good stuff

rklosinski · 31st January 2007, 06:42 AM

If you are bypassing the DAC-AH output, I assume you bypassed the output op amps. The problem is that either you present a diferent impedence to the output of the DAC-AH, or to the input of the tube amp.

The best would be the DAC-AH drives the top of the pot, with the bottom going to ground. Then the wiper goes out to the tube amp. Even thought the ac impedenece is changing (from 100k to 110k) I dont think it enough to cause a problem, especially since the input of the st-70 does not have any caps.

30th January 2007, 07:28 PM	#1
rklosinski diyAudio Member Join Date: Jan 2007 Location: Sacramento	Setup suggestion between DAC-AH and ST-70 I would like to minimize stuff im the signal path of my current setup. I have a DAC-AH (modified) and would like to connect it my ST-70 (again, modified). The problem is volume control. How to do it w/o adding a pre-amp of some type. The ST-70 is driving a pair of Epos M5's. Should I use a step attenuator in between the two? Currently I just reduce the amplitued digitally, which really sucks. Thanks Rich

30th January 2007, 08:34 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Why not just substitute a volume control potentiometer for the ST-70 grid leaks? __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

30th January 2007, 09:07 PM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	And since you've already got a chassis, why pay for the redundancy? In any case, a 100k pot should do the job. What does your input stage look like? If it's still the pentode of a 7199, you've got an easy job doing this. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

31st January 2007, 02:47 AM	#6
JandG diyAudio Member Join Date: Jan 2005 Location: Washington State	What mods are in the DAC-AH..? I use a by-passed output stage DAC-AH into a 100k input tube amp using 10k mono PEC pots mounted in very small, these pots sound excellent. I use very small RS project boxes with 4" pig tails attatched at rear of amp. I also run the DAC-AH with a TVC from time to time, but the PEC pots, I could live with just as easy as the TVC. since you amp is modded just mount the PEC's in that.If your DAC_AH still has the output stage, ..by-pass that & listen...................good stuff

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30th January 2007, 08:54 PM	#3
rklosinski diyAudio Member Join Date: Jan 2007 Location: Sacramento	I guess that would be better than modifying the output of the dac-ah, since it will not effect impedence. I also thought about a passive linestage (step attenuator), but they can get costly.

31st January 2007, 12:47 AM	#5
rklosinski diyAudio Member Join Date: Jan 2007 Location: Sacramento	I have the VTA70 driver pcb.

31st January 2007, 06:42 AM	#7
rklosinski diyAudio Member Join Date: Jan 2007 Location: Sacramento	If you are bypassing the DAC-AH output, I assume you bypassed the output op amps. The problem is that either you present a diferent impedence to the output of the DAC-AH, or to the input of the tube amp. The best would be the DAC-AH drives the top of the pot, with the bottom going to ground. Then the wiper goes out to the tube amp. Even thought the ac impedenece is changing (from 100k to 110k) I dont think it enough to cause a problem, especially since the input of the st-70 does not have any caps.

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