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Topping D50s insufficient gain

Nathan_A

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#21
I briefly ran my Topping D50s direct into an Adcom 5500 before deciding to stick with my Yamaha MX-1, and it was able to drive the amp without issue.

I suspect some kind of input gain control on the amp that's lowering its sensitivity or some kind of software volume control oddity. On the latter point I've had problems (at least in Linux) when connecting over USB to some external DACs where setting it to PCM IEC856 output that it'll default to some oddly low volume level despite showing max. volume. I had to toggle the device back to USB Stereo Output (or whatever it was called), then max out the volume in that mode, and switch it back to PCM IEC856, and then the volume was properly set to max. I have no idea if something along these lines is happening in your setup, but it's just to point out that PC-based USB audio to outboard DACs can get a little wonky, so it can be helpful to remove that variable by trying an alternate source like a CD/DVD/BR player with a digital out and no internal volume control just to get a baseline and sanity check for yourself.
 
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Thread Starter #22
Tomorrow i will try a cd in my dvd player and also test voltage to rule out a defective unit. I will also dig into the the settings in my laptops. I don't recall ever coming across settings that allow for toggling between usb stereo output and pcm on a window 10 machine but i will definitely check it out.

Thank you
 
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Thread Starter #26
Thanks for that file. I think the fuse in my meter is blown so i can't get a reading. Could someone please tell me if this makes sense? I found this thread on another forum. "The old war horse 555 is very low gain at only 130mV for a 1volt output. Which is: with a 2v source and a passive at full level, the 555, can only reach 16v!!! to the speakersYou either need a very high gain preamp, or seeing the Adcom is very old now you may want to get another amp, which most will have much higher gain than this old 555 more like 1.5v for full output (not 1v) and your source and passive will be fine then"
 

sejarzo

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#27
Thanks for that file. I think the fuse in my meter is blown so i can't get a reading. Could someone please tell me if this makes sense? I found this thread on another forum. "The old war horse 555 is very low gain at only 130mV for a 1volt output. Which is: with a 2v source and a passive at full level, the 555, can only reach 16v!!! to the speakersYou either need a very high gain preamp, or seeing the Adcom is very old now you may want to get another amp, which most will have much higher gain than this old 555 more like 1.5v for full output (not 1v) and your source and passive will be fine then"
Makes no sense to me. 130mV input generating a 1.00 V output is 17 dB gain, not 27 dB gain.

This page shows 27 dB gain for both the GFA-555 and GFA-555 II.

https://www.hifiengine.com/manual_library/adcom/gfa-555.shtml
 

sejarzo

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#30
That's my point. The gain is indeed 27 db, and the person who posted that info is wrong. I thought it was just someone misreading 27 as 17 and doing the calculation wrong, but I just found this tidbit on the spec page for the "new" GFA-555se:

1587090062074.png


Big difference between saying 130mV input generates 1 Vrms output rather than 130mV input generates 1 Watt output.
 

sejarzo

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#31
1 watt at 8 ohms requires 0.354 amp current. 0.354 amps across 8 ohms is 2.83 Vrms. 2.83 Vrms output versus 130 mV input is 27 dB gain, just as the spec say. Thus that post you quoted is a pile of crap because someone didn't read the spec correctly, or didn't know how to interpret it.
 
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Thread Starter #32
I will fully admit that i can't spot somebody's lack of electronics knowledge because i have none myself. I'm just trying to figure out if this Topping should in fact be able to drive the Adcom to it's full potential.
 

sejarzo

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#33
I will fully admit that i can't spot somebody's lack of electronics knowledge because i have none myself. I'm just trying to figure out if this Topping should in fact be able to drive the Adcom to it's full potential.
As long as the true input sensitivity of a power amp is equal to or less than 2Vrms for full rated output, any modern DAC with a 2Vrms output will drive it adequately. Many older power amps from the pre-digital era have lower input sensitivities, some as low as 0.775 Vrms. That made sense as the output from a moving magnet phono cartridge was only 5 mV or so, or only 1/400 that of a DAC or CD player. Less gain (which always generates noise) was required between the cartridge output and power amp input.
 
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Thread Starter #34
That makes sense to me. Is there anything that would cause this amplifier to have less than the 1.7V than it's supposed to have? With the exception of one of the caps and a bridge rectifier going bad it has behaved the same for the last 25 years.
 

Blumlein 88

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#36
Try this. Using audiocheck send a -10 dbFS tone of a few hundred hertz. Most meters work until 400 hz because some power systems operate at that level. So 400 hz or even 200hz would be a good choice.

Check the output of the D50 by putting the meter across the RCA center pin and the shield. You should get a reading of about .63 volts AC. If it is much lower than this then you've found your problem.

Let us assume you did get .63 volts. Hook things up and feed that to the amp. At the output of the amp you should see a touch over 14 volts on the meter. If it is much less you've found the problem is with the amp. If you have speakers connected this could be pretty loud as it is nearly 25 watts at 8 ohms. At this frequency (400 hz or less) that shouldn't hurt the speaker to do this for a few seconds while you get a voltage reading.

If you do this you'll find out if the D50 is outputting the right signal and whether or not the amp is providing the gain it was designed to provide.
 

solderdude

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#37
Do note that if you use a multimeter it must be either autoranging or have at least a 2VAC meter range.
The cheap multimeters that have a 200VAC meter range can not be used for these measurements.

-3dB should give 1.41V by the way, from the DAC with PC and DAC volume control at 0dB setting.
 
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Thread Starter #38
It's never been modded. I bought it from someone that i know who is the original owner and did nothing but use it. I'm going to pick up my friend meter which has auto ranging and a setting for 2v ac. Hopefully I'll have answers sometime this weekend.
 
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Thread Starter #39
i picked up a meter that has auto range. depending on which 0 db file i use i get anywhere between 2.1 and 2.5v. does it seem right that it would actually put out more than 2v/
 
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Thread Starter #40
please disregard my last post. i was trying to do it by just touching the leads to the jacks on the back of the dac. i finally decided to use an actual rca cable and touch the meter leads to that and now i'm getting more like 1.9v.

with a 0-10db 400hz tone i get .63v at the rca's and 13.65 at the banana plugs that are at the opposite end of the speaker wire from the amp. it seems like all test results are as they should be.
 
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