yaesu ft-707 bad audio - Page 1
Forum section: electronics / rf-microwave

author: ME
author_rank: Frequent Contributor
timestamp: February 21, 2025, 08:51:48 am
content: I have a new to me yaesu ft 707, I have reports of the audio having too much bottom ie bass, Is there any way to fix this?, I have tried 2 different dynamic mics with the same result, So far only tested on 80m lsb.

author: A.Z.
author_rank: Super Contributor
timestamp: February 21, 2025, 12:38:33 pm
content: pick a copy of the user manual in pdf format and take the time to carefully read it

author: CaptDon
author_rank: Super Contributor
timestamp: February 21, 2025, 02:19:45 pm
content: Funny thing mentioning bad transmit equalization, There have been two flakes on 20m around 14.239 / 14.240 USB and about 3 nights every week for the past 3 weeks have been dinking with the one guys transmit EQ curve. He is constantly making changes. I have dialed in sound systems in unfamiliar venues in less time than the 20M guy has spent on one mic. Anyway, to the O.P., I am not sure if the 707 has an adjustable EQ? I had a 747 (may have been 727?) and never messed with any kind of EQ. Always got good reports and it was a nice rig. I had it while still on Iceland in 94. I am guessing your 707 must be at least that old? If there are no mic EQ adjustments perhaps a component has shifted value by a wide margin? I am thinking capacitor BUT capacitors usually lose value and if it were a coupling cap you would lose the bottom end not gain and if they were a high frequency shunt to ground you would gain more highs and mid range. The problem you have encountered kind of bucks the norm.

author: ftg
author_rank: Frequent Contributor
timestamp: February 21, 2025, 04:01:52 pm
content: If there is no mic EQ adjustment or any internal mic tone adjustments, how does it sound on receive?If the BFO has drifted in frequency the SSB filter might be cutting out the highs and letting more of the lower frequencies pass.

author: ME
author_rank: Frequent Contributor
timestamp: February 21, 2025, 06:29:23 pm
content: The rx is fine,Any ideas how i can change the lsb tx bfo?, I see no mention of it in the manual, Thanks.

author: CaptDon
author_rank: Super Contributor
timestamp: February 22, 2025, 02:02:19 pm
content: There is no equivalent to a BFO shift of the transmit signal passing through the crystal or mechanical filter section. The frequency that goes through the filter is usually generated by a fixed crystal or PLL frequency generator and is unlikely to have drifted enough to cause your problem. The generated carrier is above the filter bandpass to generate the lower sideband and is below the filter bandpass to generate the upper sideband. Although the receiver can have various bandwidths selected by filters in the I.F. the transmit bandwidth is fixed by the non-switchable filter in the transmit section. If you have a XIT (Transmit Incremental Tuning) it shifts the transmit frequency BUT NOT the bandpass. By the way, if the internal frequency reference going through the transmit SSB filter section did actually shift off of the design frequency and was giving you excess low frequency or lack of high frequency transmit audio on LSB then the exact opposite would be true on USB, You would lack low frequency response. I do feel the audio section is to blame. What happened to the original mic? It may have had very poor low frequency response to begin with since amateur radio audio bandpass is generally noted as 300 to 3000Hz and your replacement mic has better low frequency response which the transmit section of the 707 is not expecting. Maybe the original mic had a bit of audio shaping built in?