Welcome, Guest. Please Login.
Linuxslate.com Forums

<=== Back to the Linuxslate.com Homepage

Newest Forum Posts

Sep 21st, 2023, 9:46pm
News: Welcome to the linuxslate.com forums. May 2020: Forum registration has been disabled due to recent advancements in bypassing captcha's and the resulting increase in spam on the forums. Registration may be re-enabled at a later date. In the meantime, if you would like to register, please email "john" at this domain, and I will manually create an account for you. Registration is for legitimate and relevant discussion only. Misused accounts will be deleted without warning.

Pages: 1 2 
7591 Amp Build (from Rowe/AMI R-4359) (Read 7735 times)
Forum Administrator


Posts: 119
Re: 7591 Amp Build (from Rowe/AMI R-4359)
Reply #15 - May 29th, 2023, 8:57am
In my last post, I stated that this project was "essentially" complete.  Now I will demonstrate why I didn't just say "compete".
After some use, and testing, I decided that I was not happy with the VFD (Vacuum Fluorescent Display) Spectrum analyzer that I had purchase and installed in this amplifier.  Here are some specific complaints I had about the VFD SA:
  • It put significant noise back onto the audio lines.
  • It defaulted to a Clock mode. I was not trying to make an overpriced clock radio.
  • Testing showed that the spectrum analyzer was highly inaccurate, and did not respond at all over significant parts of the audio spectrum.
  • The display was "OK" , but again, for what is supposed be a "high-end" piece of audio equipment, I wanted better.

After some research of available bare VFD SA boards available on AliExpress, I found out the board I had bought was essentially "counterfeit", or a poor quality version of a board known as "AK2515".
On big hint is that the knock-off, or poor quality VFD's do not even specify a frequency range in the AliExpress advertising.
But even "real" AK2515 boards still have the clock mode.
A little more research lead me to this unit from Douk Audio:

This unit does have a full set of advertised specifications.  It does not have a clock mode, and while there is no question that Douk Audio is still a "Chi-Fi" company, I at least trust them to have a little better quality than most of the other Chinese vendors.
The board still needed some connector modifications, and I had to drill a new hole in one of the support brackets, I was able to install the Douk Audio VFD into the amplifier without too much difficulty.
The new display is slightly larger, and noticeably brighter and "bolder" than the previous one.
I will point out that I still consider all of these to be highly inaccurate for actually measuring audio frequency -- especially in stereo display mode.
First, there are 25 bars, and there is no "blank spot" or skipped bar in stereo mode.  This means that the left channel has 12 bands and the right channel has 13 bands.
Furthermore, these displays don't actually have an analog filter for each band.  They use a microprocessor to do DSP and scan the display.  The result of all of the above is that even if the same pure sine wave signal is fed into both channels, the left and right channels will not display the same levels at the same band anyplace in the audio spectrum.
That said they still provide a visually interesting visualization of the music, and they have to the bright, and attractive color that only VFD's can provide.
Back to top

Mobile Linux ?
Got That!
WWW   IP Logged
Pages: 1 2